CBSE Class 11

Here we are providing Class 11 Biology Important Extra Questions and Answers Chapter 15 Plant Growth and Development. Important Questions for Class 11 Biology are the best resource for students which helps in Class 11 board exams.

Class 11 Biology Chapter 15 Important Extra Questions Plant Growth and Development

Plant Growth and Development Important Extra Questions Very Short Answer Type

Question 1.
In which phase of the growth curve the growth is maximum?
Answer:
Exponential phase

Question 2.
Write the full form of IAA?
Answer:
Indole acetic acid

Question 3.
Which plant hormone controls the process of apical dominance?
Answer:
Auxin

Question 4.
Which hormone acts as a “stress hormone”?
Answer:
Abscisic acid (ABA)

Question 5.
Name the only gaseous natural plant growth regulator.
Answer:
Ethylene.

Question 6.
What are photo plastic seeds?
Answer:
Photo plastic seeds require light for germination.

Question 7.
What is the exponential period of growth?
Answer:
It is the second phase of maximum growth.

Question 8.
What is vernalization?
Answer:
Vernalization is a promoter of flowering by previous cold treatment.

Question 9.
What is senescence?
Answer:
It is the period between reproductive maturity and the death of a plant.

Question 10.
What will happen if short-day plants are exposed in day lengths in excess of their certain critical photoperiod?
Answer:
These will remain only vegetative.

Question 11.
Name the three stages of cellular growth
Answer:

1. Cell division
2. Cell enlargement
3. Cell maturation

Question 12.
Name the plant hormones concerned with the following:
(i) Elongation of cell
Answer:
Auxins

(ii) Shedding of leaves
Answer:
Abscisic acid

(iii) Breaking of seed dormancy
Answer:
Gibberellins

Question 13.
List four growth regulators of plants
Answer:

1. Auxins
2. Gibberellins
3. Cytokinins
4. Abscisic acid

Question 14.
Mention two functions of auxins
Answer:

1. Promote cell elongation
2. Bring about rooting on stem cutting

Question 15.
Does far-red light help in growth?
Answer:
Far-red light brings about flowering in short-day plants.

Question 16.
Name the chemical which carries stimulus for flowering from leaves.
Answer:
Florigen

Question 17.
Where is auxin synthesized in the plants
Answer:
Meristems, enlarging tissues and young leaves.

Question 18.
Which hormone can be used to prevent abscission?
Answer:
Auxin (growth hormone)

Question 19.
Define photoperiodism.
Answer:
The response of plants in terms of flowering to the relative length of day and night is called photoperiodism.

Question 20.
Define development.
Answer:
When the cells change their shapes and take up specialized functions, it is called development.

Plant Growth and Development Important Extra Questions Short Answer Type

Question 1.
Draw a diagram to show the sigmoid growth curve and write the names of the three phases in it.
Answer:
The rate of growth whether measured as length, area, volume or weight is not uniform. Under ideal conditions when the rate of growth is plotted against time, an S-shaped curve called the sigmoid curve.

1. Lag-phase: Growth is slow in the initial stage.
2. Exponential period: It is the second period of maximum growth.
3. Stationary phase: When the nutrients become limiting growth slows down.

S-shaped or sigmoid population growth curve characteristic of many species when introduced into a variable new environment.

Question 2.
What is vernalization? Give its importance in flowering plants.
Answer:
The term vernalizations are the promotor of flowering by previous cold treatment. In flowering plants, plants that require cold treatment usually behave as biennials. They germinate and grow vegetatively in the first season and produce flowers in the second season. It is now definitely known that by various grafting experiments the growing point is the site that receives the cold stimulus. It is responsible for the productions of a hormone-like substance called remain.

The effect of vernalization can be removed if plants are again treated with high temperatures.

Question 3.
Explain the biological meaning of growth. In what essential ways does plant growth differ from animal growth?
Answer:
Growth is the sum total of various processes that combine to cause an irreversible increase in mass, weight, or volume. The growth is invariably accompanied by differentiation, which is explained by quantitative changes in terms of the structure and functions of the cell. Plant growth differs from animal growth in its unlimited and undefined pattern of growth.

Question 4.
Explain how the method of science operated in the discovery of auxins?
Answer:
The discovery of auxin was the result of an investigation by Darwin (1880) while studying the bending of the coleoptile of phalaris sp (grass) towards the light. He established that the tip of coleoptiles was able to perceive the light stimulus.

The light stimulus was transmitted to the sub-apical region where differential growth caused bending. A hypothesis was formulated that there is a transmitter. Boysen-Jensen (1913) demonstrated experimentally. In (1928) it was finally proved the existence of a chemical transmitter and called the substance Auxin.

Question 5.
Discuss the role of growth regulators in agriculture.
Answer:
Growth regulators play important role in agriculture:

1. Dorminy of seed is broken within a few time
2. The miniature of the plait body is improved.
3. Time of germination becomes less.
4. Some plant growth regulators are IBA, IAA
5. Initiation and promotion of cell division are very useful in tissue culture by growth regulators.

Question 6.
Explain Bolting.
Answer:
Just prior to the reproductive phase in ‘rosette’ plants like cabbage, the internodes elongate enormously causing a marked increase in stem height. This is called Bolting. In natural conditions, bolting requires either long days or cold nights.

Question 7.
Write the functions of Auxin (IAA).
Answer:

1. Auxin promotes elongation and growth of stems and roots and the enlargement of fruits by stimulating cell walls to stretch in more than one direction.
2. Auxin promotes cell division in vascular cambium.
3. Auxin promotes root initiation.
4. It causes the development of callus in tissue cultures.
5. Auxin is also involved in apical dominance and abscission.

Question 8.
What part of the plant perceives the light response?
Answer:
It has been demonstrated that a plant from which all leaves have been removed fails to flower even under the inductive light regime. This has been confirmed from experiments with Xanthium, a short-day plant. Even if one eight of a leaf was exposed to short days, flowering occurred. Even a single leaf exposed to a short day was able to induce flowering when it was grafted onto a plant kept under non-inductive conditions.

Question 9.
Distinguish between phototropism and photoperiodism.
Answer:

Question 10.
Distinguish between Long day plants and Short-day plants.
Answer:

Question 11.
What do you understand by photoperiodism and vernalization? Describe their significance.
Answer:
Some plants require the exposure of light for a longer period and some requirements for a shorter period than the critical period for flowering.

The plants requiring a longer exposure to light in than critical period are called long-day plants, whereas those requiring light for a shorter period are called short-day plants and the remaining come under the class or neutral or intermediate day plants.

The ability of the plant to detect and respond to the length of the daily period of light or more precisely, the relative length of day and night to which the plant is exposed, is called photoperiodism.

Significance: Photoperiodism plays a decisive role in the flowering process.

Vernalization: The method of inducing early flowering by pretreatment of seeds with a certain low temperature is known as vernalization.

The effect of temperature on the growth of plants, especially for flowering. The plants from the temperate regions require a period of low temperature before flowering takes place.

Significance: Significance of temperature between 1 – 10° C to certain varieties of wheat, rice, millets, and cotton accelerates the growth of seedlings and results in early flowering.

Question 12.
Write an essay on growth regulators in plants.
Answer:
The analysis or growth curves provide evidence of physiological control on growth. Plants produce some specific chemical substances, which are capable of moving from one organ to the other so as to produce their effect on growth. These substances which are active in very small amounts are called plant hormones. They are organic compounds and are capable of influencing physiological activities leading to promotion, inhibition, and modification of growth.

The growth regulatory substances are grouped under five major classes, namely auxins, gibberellins, cytokinins, ethylene, and abscisic acid. The other related growth regulators are jasmonic acid, salicylic acid, and brassinosteroids. Some vitamins also regulate the growth of plants.

Organic substances, other than nutrients, which in low concentration regulate growth, development, and differentiation, are termed, growth regulators. These may either promote or inhibit growth. The growth regulators synthesized are not produced naturally within the plants.

Growth hormones or phytohormones are organic substances, which are synthesized in one part of the plant and transported to another part where these affect a specific physiological process to regulate growth. Growth hormones play a very important role in the growth and development of animals.

Question 13.
How will you measure the rate of growth? Describe an instrument used to measure the increase in height of an angiosperm plant.
Answer:
The growth in length can easily be measured with the help of an ordinary measuring scale at an interval of time. For precise measurement, the equipment named auxanometer or autograph can be used. An auxanometer is used to measure the rate of growth of a plant in terms of shoot length.

A thread is tied to the growing tip of a potted plant and at the other end, weight is tied after passing the thread over a pulley. The needle attached in the center of the pulley will show the deflection, which can be read on the graduated arc to find out the increase in length of the plant.

Measurement of growth by Arc-Aux. nanometer

The growth can also be measured by an increase in weight, both fresh and dry volume of the plant. The increase in the number of cells especially in algae, yeast, and bacteria also gives an idea about the rate of growth.

The measurement of the area of the volume of an organ of the plant will also provide information about the rate of growth.

Question 14.
“Growth is an important phenomenon of living.” Justify this statement with reasons.
Answer:
Growth is one of the most important phenomena of all living organisms. Growth in plants occurs by cell division and cell enlargement, invariably followed by cell differentiation. It is the result of coordination of biophysical increase in size, weight, and volume of an organism or its part. In plants, it is associated with both anabolic and catabolic activities, involve an increase in size.

Thus, growth is a quantitative phenomenon and can be measured in relation to time. Growth in living organisms is intrinsic and differs from extrinsic growth in non-living objects. Plants also show movement due to growth. Hence growth is an important phenomenon in living organisms.

Question 15.
What are the important characteristics of growth? Describe in brief.
Answer:
Growth in plants occurs by cell division and cell differentiation. The cell division generally occurs in apical regions of shoot and root. The meristematic cells present at shoot and root apices are responsible for growth in plants. These cells are also present in vascular bundles of roots and stems of dicot plants. They help in increasing the thickness of stem and root due to secondary growth.

The rate of plant growth is slow in the initial stages and increases rapidly later op. The growth slows down due to the limitation of nutrients. The rate of growth is also called the efficiency index.

Question 16.
What are the different phases of growth? Explain with the help of well-labeled diagrams.
Answer:
Growth in plants is localized in the meristematic region only, i.e., apical, lateral and even, intercalary regions. The growth in length is due to the enlargement and elongation of cells at the apical regions and in thickness due to the activity of lateral and intercalary meristems.

The period of growth is generally divided into three phases, namely, formative, elongation, and maturation.

The formative phase: This phase has constantly dividing cells and restricted to the apical meristem both at the root and shoot tips. The cells of this region are rich in protoplasm with a large nucleus and thin cellulose wall.

Growth regions in a root by parallel line (Different phases of growth)

The phase of elongation: It lies just behind the formative phase and is aimed at the enlargement of cells.

The phase of maturation: Is further behind and here the cells start maturing to obtain a permanent size. These phases are also known as regions. The time interval from the formative phase to the maturation phase is called the grand period of growth.

Plant Growth and Development Important Extra Questions Long Answer Type

Question 1.
What do you understand by senescence? What are the various types of senescence observed in plants? Can growth regulators restart senescence?
Answer:
1. Senescence: Senescence may be defined as the period between reproductive maturity and death of a plant or a plant part. Senescence is accompanied by a reduction in functional capacity and an increase in cellular breakdown and metabolic failures. This process ultimately leads to the complete loss of organisms or plant parts.

2. Types of senescence: In plants, it is of four types:
1. Whole plant senescence: It occurs in plants in which the whole plant dies after seed production e.g., wheat, gram, etc. These plants are annuals and die after seed production. This phenomenon also occurs in some monocarpic plants, which live for several years but flower once. For example, certain bamboos and sago palms.

2. Sequential senescence: In some perennial plants, the tips of the main shoot and branches remain in the meristematic stage. They continue to produce new buds and leaves. The older leaves and lateral organs senescence and die. This type of senescence is called sequential senescence. Example: Mango and Eucalyptus.

Types of plant senescence

3. Shoot senescence: In certain perennial plants, the aerial shoot dies each year after flowering and fruiting. But the underground modified stem and roots survive under unfavorable conditions. These parts give rise to new shoots again next year under favorable conditions. Example: Banana and gladiolus.

4. Simultaneous or synchronous senescence: This occurs in temperate deciduous trees which shed their leaves annually in autumn. Example: Maple and elm.

5. Reduction of senescence: Cytokinins, the growth regulators retard senescence. They prevent the breakdown of proteins and other biomolecules. Instead, they stimulate the rate of synthesis of proteins and their mobilization. Auxins also retard senescence.

Question 2.
Mention any two causes of seed dormancy. Give its significance.
Answer:
Many seeds fail to germinate even when they are provided with favorable conditions. This phase when the seed remains in action is called seed dormancy. This natural barrier for development is gradually overcome with time. Sometimes this dormancy is due to the conditions in the seed itself then it is known as innate dormancy.

It may be due to the following reasons:

1. Impermeability of seed coat: In some plants, the embryo is undifferentiated and unorganized when the seed is shed. It takes time to attain full development before it germinates.
2. Due to immature embryo: In some plants, the embryo is un-differentiated and unorganized when the seed is shed. It takes time to attain full development before it germinates.

Significance of seed dormancy:

1. It enables the seed to be disseminated in time and space.
2. It helps them to germinate when environmental conditions are more favorable.

Advantages of reproduction by seed:

1. The plant is independent of water for sexual reproduction and therefore, better adapted for a land environment.
2. The seed protects the embryo.
3. The seed contains food for the embryo (either or cotyledons or in the endosperm).
4. The seed is usually adapted for dispersal.
5. The seed can remain dormant and survive adverse conditions.
6. The seed is physiologically sensitive to favorable conditions and sometimes must undergo a period of after-ripening so that it will not germinate immediately.
7. The seed is a product of sexual reproduction and, therefore, has the attendant advantages of genetic variation.

Question 3.
What is the difference between:
(a) Nastic and tropic movements.
Answer:
Difference between Nastic and tropic movements:

(b) Phototropism and geotropism.
Answer:
Difference between Phototropism and geotropism:

Question 4.
What do you understand by the spontaneous and induced movements in plants? Illustrate your answer with suitable diagrams.
Answer:
Spontaneous movements: Plastids in cells may show movements in response to light, the stem of a plant grows upwards against the force of gravity or bends towards light. Spontaneous movement may be at protoplasm or organ or even at the whole plant level. The protoplasmic movements, accomplished by naked protoplasm in unicellular plants, are generally divided into ciliary, amoeboid, cyclosis, and gliding. Spontaneous movement is self-controlled.


Induced movement: The induced (paratonic) movement is the movement of a complete cell or organelle and is influenced by external stimuli. This is also called tactic (taxes or taxis) movement and is common among lower plants. The movement may be due to chemical substances, such as sucrose and malic acid, present in archegonium of ferns and moss, which attract spermatozoids; and mobile bacteria are attached by peptone.

Different types of movement.

Question 5.
Describe the various steps involved in seed germination?
Answer:
Awakening of inactive embryos present inside the seed into a seedling, capable of independent existence, is termed germination.

Two conditions affect the germination of seed:
(a) External conditions: External conditions necessary for germi¬nation are water, oxygen, temperature, and light.
(b) Internal conditions: Sometimes the seeds fail to germinate even if various external conditions are favorable.

Germination is also controlled by certain internal factors which are discussed as:

1. Maturity of the embryo: In certain, plants, the embryo is immature in fully developed seeds.
2. After ripening: In certain, plants, even if the embryo is mature but they do not possess the necessary growth hormones. These germinate only when necessary growth hormones are synthesized.
3. Dormancy period: Certain seeds remain dormant after their shedding.
4. Viability period: The period for which the embryo in seed remains living is termed as viability period. The seeds germinate only within the viability period.
5. Reserve food material: The availability of sufficient reserve food material is essential for germination.
6. Enzymes and growth hormones: Digestive and respiratory enzymes play an essential role in germination. In the absence of activation of certain enzymes, seeds will not germinate. Hormones like auxins, gibberellins, and cytokinins also play important role in germination.

Seed germination includes all the physical and physiological changes that occur in the seed.
(a) Absorption of water: The water enters the seed mainly through the micropyle and imbibed by the reserve food and cell wall material, resulting in swelling of the seed. It causes the rupture of seed coats, allowing the radical to grow into the primary root. Aerobic respiration is essential for seed germination as it makes available the energy needed for the growth of the embryo.

(b) Mobilization of reserve food materials: The food is stored in the endosperm, or in cotyledons. The various enzymes convent this food into soluble substances, which serve as a respiratory substrate, and the energy released during aerobic respiration is used in various metabolic and physiological changes dining embryo growth. The digested food passed towards the embryo through cotyledon.

(c) Development of embryo into seedling: The embryonic cells become metabolically very active. The radicle starts growing and is first to emerge out through ruptured seed coats. It develops into a root that grows downwards into the soil. The root developing from the radicle is termed as the primary root.

After the development of the primary root from the radicle, either the epicotyl or the hypocotyl starts elongation, forming dicotyledonous seeds.

Different stages of germination of seed.

Here we are providing Class 11 Biology Important Extra Questions and Answers Chapter 14 Respiration in Plants. Important Questions for Class 11 Biology are the best resource for students which helps in Class 11 board exams.

Class 11 Biology Chapter 14 Important Extra Questions Respiration in Plants

Respiration in Plants Important Extra Questions Very Short Answer Type

Question 1.
Whether respiration is a catabolic or anabolic process?
Answer:
Catabolic (destructive)

Question 2.
Name the cell organelle where cellular respiration takes place.
Answer:
Mitochondria

Question 3.
Give the chemical equation for aerobic respiration.
Answer:
C₆H₁₂O₆ + 6O₂ → 6H₂O + 6CO₂ + 686 kcal.

Question 4.
Name the substance that is oxidized during respiration.
Answer:
Glucose

Question 5.
What is fermentation?
Answer:
Respiration by microorganisms without the utilization of oxygen is called fermentation.

Question 6.
What is the main source of energy?
Answer:
Carbohydrates, lipids, and proteins.

Question 7.
In what form the energy released by oxidation is stored in the body?
Answer:
In the high-energy bonds of ATP molecules.

Question 8.
Name two respiratory, mediums for living beings.
Answer:
Air and water.

Question 9.
What is cell respiration?
Answer:
Enzymatic oxidation of food in body cells is known as cell respiration.

Question 10.
What holds the energy in the body?
Answer:
Molecules of food hold energy in their chemical bonds.

Question 11.
Name some industrial products of fermentation.
Answer:
Wine, Alcohol, Vinegar, Bread, etc.

Question 12.
Define anaerobic respiration.
Answer:
Respiration carried out in the absence of oxygen is called anaerobic respiration.

Question 13.
Define RQ is words
Answer:
RQ is the ratio between the amount of CO₂ evolved to the amount of oxygen used.

Question 14.
How is oxygen distributed in the plant body?
Answer:
By diffusion from a cell of the cell.

Question 15.
Name the parts of the plant body that allow the exchange of gases.
Answer:
Lenticels, stomata, and general body surface.

Question 16.
How many ATP molecules are produced in aerobic respira¬tion?
Answer:
36

Question 17.
When a molecule like that of C₆H₁₂O₆ is oxidized completely, what are its end products?
Answer:
CO₂ and water,

Question 18.
Name two Anti-transpirants.
Answer:
Abscisic acid, Phenyl mercuric acetate.

Question 19.
What metal element is involved in the movement of stomata?
Answer:
Potassium

Question 20.
Why is respiration necessary for the plant?
Answer:
Respiration is necessary as it releases the energy which is used for daily activities.

Question 21.
Why is less energy released during anaerobic respiration?
Answer:
During anaerobic respiration, food is incompletely oxidized and so less energy is released.

Question 22.
What is fermentation?
Answer:
Anaerobic respiration by some microbes is called fermentation.

Respiration in Plants Important Extra Questions Short Answer Type

Question 1.
What is respiration?
Answer:
A process of physiochemical change by which environmental oxygen is taken in to oxidize the stored food or release CO₂, water, and energy. The energy released is used for doing various life activities, whereas CO₂ being is used by the plants for their growth and development.

Question 2.
Define aerobic respiration.
Answer:
The process of release of energy through intake of molecular oxygen and release of CO₂ is known as Aerobic respiration.

Question 3.
Define the process of fermentation showing chemical equation.
Answer:
In this process, the carbohydrate is incompletely oxidized into some carbonic compounds such as ethyl alcohol, acetic acid, lactic acid, and CO₂. This process of oxygen being carried out in microbes is known as fermentation.
C₆H₁₂O₆ → 2 C₂H₅OH + Energy (247 kJ).

Question 4.
On what factor the respiratory quotient depends?
Answer:
The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called the respiratory quotient

RQ (the respiratory quotient) depends upon the type of respiratory substrate used during respiration. This is different for different substrates.

Question 5.
What is a citric acid cycle?
Answer:
This is also known as the Tricarboxylic acid cycle. When acetyl CO- A enters into a reaction to form citric acid and how pyruvate is broken down during metabolism is highlighted by the concept of cycles. This series of reactions is known as the citric acid cycle.

Question 6.
What will be the value of RQ when organic acids are used as respiratory substrate?

Answer:
Organic acids contain more oxygen than carbohydrates; therefore the RQ is more than one. Less amount of oxygen is required for their oxidation.

Question 7.
How many types of respiration occur in plants?
Answer:
Depending upon the availability of oxygen, respiration is of two types.

1. Aerobic respiration
2. Anaerobic respiration.

Aerobic respiration: Complete oxidation of organic substances in presence of oxygen takes place.
Anaerobic respiration: This type of respiration takes place in the complete absence of oxygen.

Question 8.
Describe the process of glycolysis and where it occurs.
Answer:
Glycolysis is the first stage of breakdown of glucose and common in all organisms. In anaerobic organisms, it is only the process of respiration. In this process, glucose undergoes partial oxidation. This process occurs in the cytoplasm of the cell.

Question 9.
What is the role of the citric acid cycle?
Answer:

1. Carbon skeletons are obtained for the growth and maintenance of the cell during this cycle.
2. Many intermediate compounds are formed which are used in the synthesis of biomolecules like amino acids, fats, etc.
3. ATP molecules having high energy are generated during this pathway.

Question 10.
What is a compensation point?
Answer:
At a low concentration of CO₂ and non-limiting light intensity, the photosynthetic rate of a given plant will be equal to the total amount of respiration. The atmospheric concentration of CO₂ at which photosynthesis just compensates for respiration is referred to as the CO₂ compensation point.

Question 11.
Write the significance of the citric acid cycle.
Answer:
During this pathway, carbon skeletons are obtained for use in the growth and maintenance of the cell. Many intermediate compounds are formed, which are used in the synthesis of other biomolecules like amino acids, nucleotides, chlorophyll cytochromes, and fats.

Question 12.
Why does anaerobic respiration produce less energy than aerobic respiration?
Answer:
Because it does not involve the use of molecular oxygen. Food is not completely oxidized to CO₂ and waste. So a lot of energy is still retained with the food. Less energy is produced on anaerobic respiration. It yields only about 5% of the energy available in glucose. Then it is a wasteful process or respiration. In anaerobic respiration, yeast metabolizes glucose to ethanol and CO₂ without any use of molecular oxygen.

Question 13.
What is oxidative phosphorylation?
Answer:
Glucose is completely oxidized by the end of the citric acid cycle but the energy is not released unless NADH and FADH are oxidized. Oxygen acts as the final hydrogen acceptor. The whole process by which oxygen effectively allows the formation of ATP molecule by phosphorylation of ADP is called oxidative phosphorylation.

Question 14.
Fill in the blanks with suitable words.
Answer:
(a) Pyruvic acid oxidized into CO₃ and H₂O before entering the citric acid cycle.
(b) The RQ is more than one if the respiratory substrate is oxalic acid.
(c) Glycolysis takes place in crystal.
(d) The acetyl —COA is accepted by Coenzyme A (a sulfur-containing compound).

Question 15.
Explain the effects of temperature on the rate of respiration.
Answer:
Respiration is reduced at very high (above 50°c) and very low (near freezing temp.) temperatures. This is because enzymes can work best between 30°c – 40°c and get inactivated at very high and very’ low tempera¬tures.

Question 16.
How does the exchange of respiratory gases occur in plants?
Answer:
The gaseous exchange takes place through

1. General body surface
2. Lenticels.
3. Stomata present in leaves and young stems. Oxygen becomes transported from cell to cell by diffusion.

Question 17.
Explain RQ significance.
Answer:
RQ value for carbohydrates is 1. It is less than one if proteins are being burnt and more than one if fats are being burnt. So RQ values are important in identifying the kind of substrate used in respiration.

Question 18.
Describe in detail the aerobic oxidation of pyruvic acid.
Answer:
Pyruvic acid generated in the crystal is transported to mitochondria and initiates the second phase of respiration. Before pyruvic acid enters the Kreb’s cycle, one of its three carbon atoms is oxidized to carbon dioxide in the reaction called oxidative decarboxylation.

Pyruvate is first decarboxylated and then oxidized by the enzyme pyruvate dehydrogenase. The combination of the remaining two-carbon acetate unit is readily accepted by a sulfur-containing compound coenzyme A to form acetyl COA. During the process, NAD is reduced to NADH. This process is represented as.

During this process, two molecules of NADH are produced, and thus, it results in a net gain of 6ATP molecules.

(2 NADH + 3 = 6 ATP). 2 molecules of pyruvic acid produced during glycolysis,

Question 19.
Describe the net gain of ATP during respiration.
Answer:
There is a gain of 36 ATP molecules during aerobic respiration of one molecule of glucose. The detail is given in the table.

In most eukaryotic cells, 2 molecules of ATP are required for transporting the NADH produced in glycolysis into mitochondrial for further oxidation. Hence, the net gain of ATP is 36 molecules.

Table ATP molecules produced during respiration.

Question 20.
Define the following:
(a) Respiration
Answer:
Respiration: It is defined as the phenomenon of the release of energy by oxidation of various organic molecules, for cellular use is known as respiration.

(b) Respiratory substrate
Answer:
Respiratory substrate: The compounds that are oxidized during the process of respiration are called respiratory substrates.

(c) Respiratory quotient
Answer:
Respiratory quotient: During respiration oxygen is used and CO₂ is released. The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called respiratory quotient (RQ).

(d) Anaerobic respiration
Answer:
Anaerobic respiration: The type of respiration, in which the carbohydrate is incompletely oxidized into some carbonic compounds in absence of oxygen, is called Anaerobic respiration.

(e) Aerobic respiration
Answer:
Aerobic respiration: It is that process of respiration which leads to complete oxidation of organic compound in the presence of oxygen.

This type of respiration is common in higher organisms.

(f) Fermentation.
Answer:
Fermentation: In anaerobic respiration yeasts metabolize glucose to ethanol and CO₂ without any use of molecular oxygen. This process is called fermentation in yeasts.

Question 21.
Describe the pentose phosphate pathway.
Answer:
Sometimes oxidation of glucose takes place by another pathway, which is called the pentose phosphate pathway (PPP). In the pentose pathway, glucose-6 phosphate (6C) produced during the early stages of glycolysis or the photosynthates produced during photosynthesis are oxidized to give rise to 6-phosphogluconate. This reaction takes place in the enzyme glucose 6phosphale dehydrogenase and generates NAD PH.

The 6-phosphoglucose molecules are further oxidized by the enzyme 6-phosphogluconate dehydrogenase. As a result of this, one molecule of each ribose-5 phosphate, carbon dioxide, and NADPH is produced, which in turn undergoes many changes to produce glycolytic intermediate. These reactions take place in the cytoplasm.
(From glycolysis)

Question 22.
Calculate the efficiency of respiration in the living system.
Answer:
During aerobic respiration, O₂ is consumed and CO₂ is released. The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called respiratory quotient (RQ) or respiratory ratio.

The RQ (respiratory quotient) depends upon the respiratory substrate. When a carbohydrate is used as a substrate.

C₆H₁₂O₆ – 2C₂H₅OH + 2CO + Energy (247 K.J) on complete oxidation. RQ will be

The total energy yield from 38 ATP molecules comes to 1298 kJ. The energy released by one molecule of glucose on complete oxidation is 2870 kJ. Thus, the efficiency is 45%. Much of the energy generated during respiration is released in the form of heat.

Respiration in Plants Important Extra Questions Long Answer Type

Question 1.
Illustrate the mechanism of the electron transport system.
Answer:
The glucose molecule is completely oxidized by the end of the citric acid cycle. But the energy is not released unless NADH and FADH are oxidized through the electron transport system. Here oxidation means the removal of electrons from it.

The metabolic pathway through which the electron passes from one carrier to another is called the electron transport system (ETS) and it is operative in the inner mitochondrial membrane. Electrons from NADH produced in the mitochondrial matrix are oxidized by an NADH dehydrogenase (Complex I) and electrons are then transferred to ubiquinone.

The ubiquinone located within the inner membrane also receives reducing equivalents via FADH, which is generated during the oxidation of succinate, through the activity of the enzyme, succinate dehydrogenase (complex II). The reduced ubiquinone is then oxidized with the transfer of electrons to the cytochrome complex (Complex III).

Cytochrome is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for the transfer of electrons between complex III and complex IV.

(Complex IV) is cytochrome.

When the electrons pass from one carrier to another via complex 1 to IV in the electron transfer chain, they are coupled to ATP synthase (Complex V) for the production of ATP from ADP and inorganic phosphate. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of FADH, produces 2 molecules of ATP.

The electrons are earned by the cytochromes and recombine with their protons before the final stage when the hydrogen atom is accepted by oxygen to form water. Oxygen acts as the final hydrogen acceptor. The whole process by which oxygen allows the production of ATP by phosphorylation of ADP is called oxidative phosphorylation.

Note: There are two routes by which hydrogen from the substrate molecule passes. In route 1.3 ATP molecules are formed for every pair of hydrogen atoms. In route 2, only 2ATP molecules are formed from one pair of hydrogen atoms.

Oxygen acts as the final hydrogen acceptor and forms water.
NAD = nicotinamide adenine dinucleotide.
MN = flavin mononucleotide,
FAD = flavin adenine dinucleotide.

ETC produces 32 ATP molecules per glucose molecule and is the major source of cell energy.

Electron Transport Chain.

Question 2.
Describe the process and role of the citric acid cycle in living organisms.
Answer:
In the process of respiration, the carbohydrates are converted into pyruvic acid through a series of enzymatic reactions. These reactions are known as glycolysis and take place in the cytosol. The pyruvic acid thus formed enters in mitochondria where O₂ and necessary enzymes are available; the pyruvic acid is finally converted into CO₂ and H₂O. This reaction series is known as Krebs Cycle or Citric acid cycle or Tricarboxylic acid (TCA) cycle.

During this cycle, 3 molecules of NAD and one molecule of FAD (Flavin Adenine Dinucleotide) are reduced to produce NADH and FADH respectively. NADH and FADH, so produced during the citric acid cycle are linked with the electron transport system and produce ATP by oxidative phosphorylation, The summary equation for this phase of respiration may therefore be written as follows:


Kreb’s cycle. It follows glycolytic reactions shown in and pyruvate oxidation.

It involves two processes

1. removal of hydrogen and
2. the breaking off of carbon dioxide units one by one.

Here we are providing Class 11 Biology Important Extra Questions and Answers Chapter 13 Photosynthesis in Higher Plants. Important Questions for Class 11 Biology are the best resource for students which helps in Class 11 board exams.

Class 11 Biology Chapter 13 Important Extra Questions Photosynthesis in Higher Plants

Photosynthesis in Higher Plants Important Extra Questions Very Short Answer Type

Question 1.
What is the full form of NADP?
Answer:
Nicotinamide Adenine Dinucleotide phosphate.

Question 2.
What are the complete photosynthetic units of plants?
Answer:
Chloroplasts.

Question 3.
Give one difference between chlorophyll ‘a’ and chlorophyll ‘b’.
Answer:
Chlorophyll (a) has a methyl group (CH₃) whereas chlorophyll (b) has an aldehyde group (CHO).

Question 4.
How many ATP molecules are required for the synthesis of one molecule of glucose in the C₃ pathway?
Answer:
18 ATP molecules are required for the synthesis of one molecule of glucose.

Question 5.
In which part of the leaves chlorophyll is found?
Answer:
In the thylakoid membrane of the chloroplast.

Question 6.
What is the primary acceptor of C02 in the C₃ plant? ,
Answer:
RiBulose 1.5 biphosphate (RuBP).

Question 7.
In which part of chloroplast light reaction takes place?
Answer:
Grana.

Question 8.
What is the relation between photosynthetic units and reaction centers?
Answer:
A photosynthetic unit consists of P6g0 and P700 reaction centers of photosystems.

Question 9.
What is the compensation point?
Answer:
The point at which the rate of photosynthesis is equal to the rate of respiration.

Question 10.
What is Kranz’s anatomy?
Answer:
It is a type of leaf structure in which the vascular bundle is surrounded by bundle sheath and mesophyll cells.

Question 11.
Which kinds of reactions of photosynthesis occur in the grana and stroma of chloroplasts?
Answer:

• Grana light reaction
• Stroma dark reaction

Question 12.
Give the overall general chemical equation of photosynthesis?
Answer:

Question 13.
Expand the abbreviation RuBP, NADP
Answer:
RuBP: Ribulose biphosphate
NADP: Nicotinamide Adenine Dinucleotide Phosphate

Question 14.
Give two points of difference between sun plants and shade plants.
Answer:
Sun plants need relatively high light intensity to saturate their photosynthetic rates while shade plants reach saturation at low intensities.

Question 15.
Name the process which is responsible for converting solar energy into chemical energy.
Answer:
Photosynthesis

Question 16.
Wherefrom does oxygen come out during photosynthesis?
Answer:
From water

Photosynthesis in Higher Plants Important Extra Questions Short Answer Type

Question 1.
Expand the abbreviation RuBP. What is its role in photosynthesis?
Answer:
The full form of RuBP is ribulose 1,5 biphosphate; RuBP is the first acceptor of atmospheric CO₂ during the dark reaction of photosynthesis. The reaction is called carboxylation.

RuBP is regenerated during the final formation of sugar molecules.

Question 2.
What is the porphyrin system?
Answer:
The porphyrin system consists of

1. A complex ring structure of alternating single and double bonds called a porphyrin ring having four pyrrole rings containing a magnesium atom in the center.
2. A lengthy hydrocarbon tail attached to the porphyrin group called phytol.

Question 3.
What are the two main functions of pigments other than chlorophyll in green leaves?
Answer:
The functions of pigments other than chlorophyll are:

1. to absorb light energy and transfer it to chlorophyll for photosynthesis.
2. to protect the chlorophyll molecule from photooxidation.

Question 4.
What is the significance of chlorophyll-a in photosynthesis carried out by higher plants?
Answer:
In higher plants, all the pigments carotenes, xanthophylls, and chlorophyll-b transfer the absorbed solar energy to chlorophyll-a. It is the chlorophyll-a molecule, which initiates the process of photosynthesis.

Question 5.
Write two differences between cyclic and non-cyclic photophosphorylation?
Answer:
Differences between cyclic and non-cyclic photophosphorylation:

Question 6.
What are the steps that are common to C₃ and C₄ photosynthesis?
Answer:
The following steps are common in both C₃ and C₄ photosynthesis.

1. Photolysis of H₂O and photophosphorylation in the light reaction.
2. The dark reaction occurs in the stroma in both cases.
3. Carboxylation-but in C₃ plants CO₂ acceptor is RuBP whereas in C₄ it is phosphoenolpyruvic acid.
4. The Calvin cycle resulting in the formation of starch occurs in both C₃ and C₄ photosynthesis.

Question 7.
What is the coupling factor in photosynthesis?
Answer:
These are similar to the F₀– F₁ complex of mitochondria present in appressed and non-appressed regions, granular and stromal thylakoids. These participate in the photophosphorylation process.

Question 8.
What is 3 – PGA?
Answer:
It is a protein molecule located on the outer surface of the thylakoid membrane. It is the first stable intermediate product of photosynthesis. It comprises 16% of the chloroplast protein, which is the most abundant protein of the biological world on earth.

Question 9.
What is the Emerson effect or photosynthetic enhancement?
Answer:
Emerson in 1957 showed that the rate of photosynthesis can be increased if monochromatic beams of two different wavelengths i.e. long and short are used simultaneously around a trap center in a photosynthetic unit. This phenomenon is known as the Emerson effect or photosynthetic enhancement.

Question 10.
What is translocation in plants?
Answer:
The process of long-distance movement of organic substances synthesized during photosynthesis from chlorophyll-containing cells or leaf which serve as regions of supply or source to different plant organs as regions of their utilization of sink is known as translocation. The term translocation is generally restricted to movements of solutes in the tissues of the phloem and xylem of plants.

Question 11.
Describe the process of photorespiration.
Answer:
It is a process of loss of photosynthetically fixed carbons, occurring in some plants during intense heat and low carbon dioxide concentrations. Under these conditions the enzyme RuBP oxygenase and converts Ribulose Bisphosphate (5 carbon), into phospho-glyceric acid (3 carbon) and phosphoglycolate (2 carbon). Soon glycolate is formed of phosphoglycolate. In peroxisomes, glycolate soon changes into glycine and glycine into serine and CO₂ without the production of assimilatory powers (ADT and NADPH₂). All the changes taking place as follows.

Photorespiration is also called the C₂ cycle because 2 carbon compounds are formed during the process. This process does not field any unstable or free energy in the form of ATP.

Question 12.
Explain the following:
(i) There will be no life without photosynthesis.
Answer:
For the existence of life, food and O₂ are very essential. Photosynthesis is the only process that can trap solar energy and can synthesis food for own and all other organisms. During photosynthesis, O₂ is given out and CO₂ is taken. So, it keeps the balance of O₂ and CO₂ in nature. Thus, photosynthesis is essential for the existence of life.

(ii) There is no oxygen evolution in bacterial photosynthesis.
Answer:
In bacterial photosynthesis, the raw material for the supply of proton (H⁺) is H₂S than H₂O. Thus, there are productions of S than O₃ during splitting in light reaction.
2 H₃S → 2 HS + 2H+
HS + HS → H₂S + S

(iii) Chlorophyll is an essential photosynthetic pigment.
Answer:
Chlorophyll-b and other pigments of a reaction center of photosystem absorb solar energy and transfer it to chlorophyll-a. Ultimately it is the chlorophyll-a that initiates the photosynthesis process. Solar energy enters into the ecosystem only through photosynthesis.

Question 13.
What is the role of NADP in photosynthesis?
Answer:
NADP is a co-enzyme useful in photosynthesis when non-cyclic photophosphorylation occurs, water is split. [n such a situation NADP acts as an acceptor of electrons and protons to form NADPH. This NADPH is used as reducing power for the fixation of CO₂ in the dark reaction. If the dark reaction is slow, then oxidized NADP will not be available and the non-cyclic cycle will then cease to operate.

Question 14.
Give four important differences between photosynthesis and respiration.
Answer:

Question 15.
Explain the principle of limiting factor with a suitable graph.
Answer:
Law of limiting factor: When a chemical reaction is conditioned as to its rapidity by a number of separate factors then the rate of reaction is as rapid as the slowest factor permits.

As is clear that as the light intensity is increased the rate of photosynthesis increases proportionately until some other factor like CO, becomes limiting. Ultimately the plant becomes light-saturated indicating that light is no more the limiting factor. If now the cone, of CO, is increased the rate of photosynthesis increases until the light becomes a limiting factor.

Question 16.
(i) List the three categories of photosynthetic pigments.
Answers:
Chlorophylls, Carotenoids, Phycobilins.

(ii) Which pigments are known as accessory pigments and why?
Answer:
Carotenoids and phycobilins.
They absorb light in the wavelength range not absorbed by chlorophyll and transfer it to chlorophyll.

Question 17.
(i) What does chlorophyll do to the light falling on it?
Answer:
Chlorophyll molecule becomes excited as soon as light falls on it. It was given out an electron acceptor which returns to release gradually energy in the form of ATP.

(ii) Which pigment system absorbs the red wavelength of light?
Answer:
Photosystem I.

Question 18.
Name the two main sets of reactions in photosynthesis in which light energy is required write down the reaction.
Answer:
(i) Photolysis for breaking down of water molecule.
energy

(ii) Photophosphorylation for the conversion of light energy into chemical energy.
ADP + iP → ATP

Photosynthesis in Higher Plants Important Extra Questions Long Answer Type

Question 1.
What is photorespiration? Describe the process in detail and link it with the Calvin cycle.
Answer:
Enzyme Rubisco catalyzes the carboxylation reaction where CO₂ combines with RuBP. This enzyme catalyzes the combination of O₂ with RuBP called oxygenation. Respiration that is initiated in chloroplasts and occurs in light only is called photorespiration.

The oxygenation of RuBP in presence of O₂ is the first of photorespiration, which leads to the formation of one molecule of phosphoglycolate, a two-carbon compound, and one molecule of PGA. While PGA is used up in the Calvin cycle, the phosphoglycolate is dephosphorylated to form glycolate in the chloroplast and in turn diffused to peroxide, where it is oxidized to glyoxylate.

In the peroxide, the glyoxylate is used to form amino acid and glycine-calycine enters mitochondria where two glycine molecules (4 carbon) give rise to one molecule of serine (3 carbon) and one CO₂ (one carbon). The serine is taken up by peroxisome and converted into glycerate. The glycerate enters the chloroplast where it is phosphorylated to form PGA. PGA molecules enter the Calvin cycle to make carbohydrates releasing one molecule of CO₂ In mitochondria photorespiration is also called the photosynthetic carbon oxidation cycle.

Increased O₂ level increases photorespiration whereas increased CO₂ level increases photorespiration ( and increases C₂ photosynthesis).

In C₃ plants photosynthesis occurs only in one cell type i.e. mesophyll cells. Both light reactions and carbon reactions occur in mesophyll cells in C₃ plants. In C₄ plant photosynthesis requires the presence of two types of photosynthesis cells that is mesophyll cells and bundle sheath cells. The C₄ plants contain dimorphic chloroplasts, which means chloroplasts in mesophyll cells are granular. Therefore C₂ pathway does not operate in the C₄ pathway.

All the important changes can be summarised as

Question 2.
Describe carbon reactions of the C₃ pathway. Does this pathway operate also in C₄ plants?
Answer:
The reactions catalyzing the assimilation of CO₂ to carbohydrates take place in the stroma where all the necessary enzymes are localized. These reactions are referred to as ‘carbon reactions’ (also called dark reactions) leading to the photosynthetic reduction of carbon to carbohydrates.

In the first phase of carbon reaction, C02 enters the leaf through the stroma. This CO₂ is accepted by a 5-carbon molecule, ribulose-1-5 bisphosphate (RuBP) already present in the leaf. It forms two molecules of 3-carbon, compound, 3- phosphoglycerate (PGA). This 3-carbon molecule is the first stable product of this pathway and hence it is called C, PATHWAY.

The formation of (PGA) with CO₂ combining with RuBP is called carboxylation. This reaction is catalyzed by an enzyme called ribulose bisphosphate carboxylase (Rubisco). This enzyme also possesses oxygenase activity and hence abbreviated as Rubisco. This activity allows O, to compete with C02 for combining with RuBP.

After the carboxylation reduction of PGA occurs and ATP and NADPH, formed during photochemical reactions with the reduction of PGA, glyceraldehyde-3 phosphate-a carbohydrate is formed. These 3-carbon molecules, also called triose phosphates act as precursors for the synthesis of sucrose and starch. To complete the cycle, and to continue it, regeneration of the 5-carbon acceptor molecule, that is RuBP takes place.

The C₃ type of carbon reaction occurs in the stroma of the chloroplast. This pathway is called the Calvin cycle.

The CO₂concentrating mechanism is called the C₄  pathway. Operation of the C₄ pathway requires the cooperation of both cell-type mesophyll and bundle sheath cells. The objective of the C. pathway is to build up a high concentration of CO₂ which suppresses photorespiration. This C. pathway is more efficient than the C₃ pathway. Hence C? pathway does not operate C₄ plants. (See the table)

Schematic representation of C₃ pathway Calvin cycle.

Question 3.
Describe briefly the experiment conducted by the scientist, T.W. Englemann.
Answer:
T.W. Englemann plotted the action spectrum of photosynthesis.

Photosynthesis can occur in visible light of wavelength varying between 390 to 763 nm. The rate of photosynthesis is not uniform in light of all wavelengths.

It varies depending upon their relative absorption by chlorophyll pigments. The graph showing the relative yield or rate of photosynthesis in plants exposed to monochromic light of different wavelengths is termed as ACTION SPECTRUM. The rate of photosynthesis, as shown in the action spectrum is maximum in the blue region of light.

Curves showing a comparison of absorption and action spectra of chlorophyll pigments during photosynthesis

Question 4.
What is a photosystem? Which is the pigment that acts as a reaction center? Describe the interaction of photosystem 1 and photosystem II.
Answer:
The light is entrapped by a group of chlorophyll molecules which together constitute a photosystem. Each pigment system has a trap or reaction center, which is either P₇₀₀ or P₆₈₀ ao. In this ‘P’ stands for pigment and figures 680 and 700 for the wavelength of light. Chlorophyll molecule acts as a trap center with the transfer of high energy electron to electron transport system (ETS).

The high-energy electrons return rapidly to their normal low energy orbitals in the absence of light and the excited chlorophyll molecule reverts to its original stable condition. These two photosystems: photosystem-I and photosystem-11 exist with different forms of chlorophyll ‘a’ as the reaction center. The PS-II is located in the appressed regions of grana thylakoids and the PS-I in the stroma thylakoids and non-appressed regions of grana.

The function of two photosystems that interact with each other is to trap light energy and convert it to chemical energy (ATP). This chemical energy stored in the form of ATP is used by living cells.

Distribution of pigment in photosystem I and Photosystem II.

Question 5.
What led to the evolution of the C₄ pathway of photosynthesis? Describe in detail.
Answer:
Kortschak (1965) observed that in sugarcane, the compound in which CO, got incorporated was oxaloacetic acid or oxaloacetate (OAA), a 4-carbon compound instead of phosphoglyceric acid, a 3-carbon com¬pound.

Hatch and Slack (1965-1967) found it a regular mode of CO₂ fIxation in a number of monocots such as sugar cane, maize, sorghum, and Pennisetum. They found that the initial acceptor of CO₂ in such plants is Phosphoenalpymvic acid instead of RuBP and the first stable compound is oxaloacetate acid, a 4-carbon compound. These plants are termed C₄ plants as the first stable compound is a 4-carbon compound and other plants are termed C₃ plants.

Hatch and Slack observed that these plants have another pathway of CO₂ a fixation that precedes the Calvin cycle occurring in C₃ plants. This cycle is known as the C₄ pathway.

Question 6.
Describe in detail how ATP and NADPH2 are formed during photochemical reactions?
Answer:
Photosynthesis at present is thus considered basically an oxidation-reduction process during which water is oxidized to release oxygen and CO₂ is reduced to carbohydrates. Photosynthesis involves two steps- the first step is light-dependent called Light reaction or Hill reaction or photochemical phase. The second step is the Dark reaction or Blankman’s reaction or the Biosynthetic phase, which does require light.

Light Reaction or Hill Reaction: During this process, solar energy is converted into chemical energy, light is trapped by chlorophyll and carotenoid pigments and is converted into chemical energy which is stored in the form of ATP energy-rich molecule.

Photolysis of water occurs that leads to the evolution of oxygen and formation of H⁺ ions, the latter combining with NADP to form NADPH₂ often termed as reducing power. ATP and NADPH together termed assimilatory power as CO₂ fixation during the dark reaction.

Photolysis of water takes place in presence of light and water oxidizing enzyme as follow:

The unstable OH” combines to form water and molecular oxygen after losing the electrons which are accepted by oxidized chlorophyll molecule. (P₆₈₀ of PS₁₁) through an unknown electron acceptor compound “Z”. This step requires the presence of Mn⁺⁺ and Cl’ ions.

Here we are providing Class 11 Biology Important Extra Questions and Answers Chapter 12 Mineral Nutrition. Important Questions for Class 11 Biology are the best resource for students which helps in Class 11 board exams.

Class 11 Biology Chapter 12 Important Extra Questions Mineral Nutrition

Mineral Nutrition Important Extra Questions Very Short Answer Type

Question 1.
What is tank farming?
Answer:
It is growing plants in water or solution culture.

Question 2.
Name any nitrogen-fixing symbiotic bacteria.
Answer:
Rhizobium.

Question 3.
What is necrosis?
Answer:
The death of tissues and cells and usually results in holes in the leaves is called necrosis.

Question 4.
Name the bacteria which convert ammonia into nitrite.
Answer:
Nitrosomonas.

Question 5.
What is the major role of calcium?
Answer:
It is a constituent of calcium pectate of the middle lamella of a cell wall.

Question 6.
What is chlorosis?
Answer:
Yellowing of leaves in a distinctive pattern due to lack of one or two other elements is called chlorosis.

Question 7.
From where do the plants get hydrogen?
Answer:
From the water absorbed by the plants.

Question 8.
What are hunger signs?
Answer:
Morphological abnormalities caused due to the deficiency of one or- the other essential elements.

Question 9.
What is premature abscission?
Answer:
Fall of leaves, flowers, or fruits before their maturation is called premature abscission.

Question 10.
Name two micronutrients.
Answer:
Boron, Copper,

Question 11.
Define hydroponics.
Answer:
The technique of growing plants in a nutrient solution is known as hydroponics.

Question 12.
What is the toxicity of micronutrients?
Answer:
Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 percent is considered toxic.

Question 13.
What is nitrogen?
Answer:
Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls, and many vitamins.

Question 14.
Define nitrogen fixation.
Answer:
The process of conversion of nitrogen (N ) to ammonia is termed nitrogen fixation.

Question 15.
Define the biological nitrogen fixation.
Answer:
The reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation.

Question 16.
Write the two deficiency symptoms of molybdenum.
Answer:

1. Premature falling of flowers.
2. Low levels of as carbic acid arid reduced organic nitrogen content.

Mineral Nutrition Important Extra Questions Short Answer Type

Question 1.
What are chelators or chelating agents?
Answer:
These are usually organic chemicals that hold or bind iron in the form of soluble complexes to make available iron to the plant. The chelator itself is not taken up by the plant. EDAA (Ethylene Diaminotetra Acetic Acid) is a commonly used chelator in water culture experiments.

Question 2.
What type of condition is created by leghaemoglobin in the root nodules of the legume?
Answer:
Leghaemolobin is an oxygen scavenger, it creates anaerobic conditions in the cells of root nodules and protects the nitrogen-fixing enzyme nitrogenase of the bacteroids.

Question 3.
What are micronutrients? Give examples.
Answer:
The elements that are required by the plants in fewer amounts or traces are called micronutrients e.g. B(Boron). Mo (Molybdenum). Mn (Manganese). Cl (chlorine). These elements are present in plant tissues. They mostly act as cofactor or activator of enzymes.

Question 4.
Some bags of fertilizers are labeled 15 – 15 – 15. What does it mean?
Answer:
The number 15 – 15 – 15 on the bags indicates the percentage by weight of nitrogen, phosphorus, and potassium in the chemical fertilizer. The majority of the fertilizers contain these elements in bulk such fertilizers are called complete fertilizers. Common fertilizers consist of chemicals either singly or in various compositions like urea, nitrate of soda, ammonium sulfate, etc.

Question 5.
What do you mean by mineral nutrition?
Answer:
The utilization of minerals by plants for growth and development is called mineral nutrition. The minerals are obtained from the soil for their growth. Plant analysis reveals the presence of a large number of minerals and nutrients in the soil. The number and amount of the mineral elements present varies from plants to plant/

Question 6.
Differentiate between micronutrients and macronutrients:
Answer:
Difference between micronutrients and macronutrients:

Question 7.
Mention symptoms of any four mineral deficiencies in plants.
Answer:

1. Chlorosis: Nondevelopment or loss of chlorophyll that leads to yellowing the entire leaf or part of it is termed chlorosis.
2. Mottling: It is the appearance of patches of green and non-green areas on leaves.
3. Necrosis: It is the localized death of tissue of the leaf.
4. Curling: It is caused due to unequal growth of the leaf.

Question 8.
Write a short note on Industrial Apological Nitrogen fixation.
Answer:
Ammonia is produced industrially by a direct combination of nitrogen and hydrogen (obtained from H₂O) at high temperatures and pressure. Subsequently, NH₃ is converted into various types of fertilizers such as urea, potash, etc which are used for plant growth and protein synthesis. ’

Question 9.
What is ion-exchange absorption?
Answer:
Ions, both cations and anions, have a tendency to get absorbed on the surfaces of the cell walls and exchange with ions present in the soil solution. The process of exchange between absorbed ions and ions in solution is known as ion exchange.

Mode of Iron- absorption carbonic acid exchange

Question 10.
What are the deficiency symptoms of calcium?
Answer:

1. Termination of meristematic activity due to the disintegration of meristematic tissues.
2. Chlorosis on margins of leaves followed by curling and necrosis.
3. Thickening of roots.
4. Premature fall of flowers reduced seed formation.
5. Blossom end rot disease in tomato.

Question 11.
Give three criteria of essentiality of an element.
Answer:
The elements which are required for plant growth and to complete their life cycle, are known as essential elements.

The criteria for the essentiality of an element are given below:

1. The element is necessary for growth and reproduction.
2. The element is required specifically and not replaced by another element.
3. The element must be involved in the metabolism of the plant.

Out of 105 elements only 20 or so have been found essential for plant growth and metabolism.

Question 12.
Write an explanatory note on the Biological fixation of nitrogen.
Answer:
Biological nitrogen fixation is the conversion of molecular nitrogen into nitrogenous compounds through living organisms.

Nitrogen-fixing organisms are of two types:

1. Symbiotic and
2. Non-Symbiotic.

Symbiotic nitrogen-fixing bacteria or Rhizobium Leguminaris occurs in the roots of leguminous plants such as gram. lea. soybean, groundnut, and various pules. It grows to form root nodules containing a pigment leghaemoglobin. It contains enzymes that catalyze biological nitrogen fixation.

Molecular nitrogen is converted into an ammonia molecule in 3 steps. Each step of reduction requires 5 ATP molecules. Ammonia is not liberated but combines with the keto group to form amino acids.

Representation of Biological Nitrogen Fixation

Question 13.
Write short notes on reductive amination and transmutation.
Answer:
Reductive amination: In this process, ammonia reacts with a ketoglutaric acid and forms glutamic acid as indicated below a ketoglutaric acid+.
NH₄⁺ + NAD (P) H — Glutamata + H₂O + NAD (P)

Transmination: It involves the transfer of amino groups from one amino acid. Glutamic acid is the main amino acid from which other 17 amino acids are formed through transamination. The enzyme responsible for such a reaction is termed transaminase.

Question 14.
Complete the following table.

Answer:

Question 15.
Write two different micronutrients and Macronutrient.
Answer:

Question 16.
What is active mineral uptake?
Answer:
The absorption of minerals by the roots at the expense of metabolic energy against the concentration gradient is called active uptake. Certain carriers are active in the cell membrane that takes the minerals from the outside to the inside of the cell.

Question 17.
What is the role of endodermis in roots?
Answer:
In roots, the endodermis is well marked due to the presence of Casparian strips on its anticlinal wall. It prevents the plasmolysis of cells of endodermis and allows the soil water to pass through.

Question 18.
Write a brief note on mineral nutrition in plants.
Answer:
Plants have an autotrophic mode of nutrition. There synthesize organic matter by utilizing raw materials from outside. All inorganic materials except carbon, hydrogen, and oxygen are obtained from the soil. The source of these inorganic materials is the minerals present in the soil.

The process of absorption, distribution, and utilization of these mineral substances by the plants for their growth and development is termed mineral nutrition. Woodward (1699) was the first person to show that plants obtain minerals from the soil for their growth and development.

These findings were confirmed by De Saussure (1804). Plant analysis reveals the presence of a large number of mineral nutrients in the soil. The number and amount of mineral elements present vary from plant to plant. In the same plant, these parameters differ from place to place. Plants absorb all mineral elements present in the soil whether required for their growth or not.

Mineral Nutrition Important Extra Questions Long Answer Type

Question 1.
What is water culture? How will you determine the essentiality of mineral elements experimentally?
Answer:
The technique of growing the plants by placing their roots in different nutrient solutions instead of growing in soil is termed hydroponics or water culture. For determining the essence of the mineral element, seedlings are grown in a balanced nutrient solution, are taken as control solution, lacking one or another element.

The growth of the plants grown in containers containing nutrient solution deficient in one or the other mineral element is compared to that of seedling grown in the balanced nutrient solution. If the plant shows some deficiency symptoms, it implies that the mineral element which was lacking in that culture set is an essential element.

However, the mineral element is a non-essential element if by eliminating that element from the nutrient solution, the growth is comparable to that of the control set.

An experiment set up to determine the essentiality of minerals by water-culture technique.

Question 2.
What is the role of micronutrients in the plant’s life? What are the deficiencies symptoms of iron?
Answer:

Deficiency symptoms of iron (Fe):

1. The appearance of interveinal chlorosis, symptoms appearing first in younger leaves. Veins remain green.
2. Chlorosis is followed by necrosis.
3. Reduction in meristematic activity.
4. Retardation of growth.

Question 3.
Make a list of macronutrients and mention their major function.
Answer:
The macronutrients are carbon, hydrogen. oxygen, nitrogen. phosphorus. sulfur, potassium. calcium, magnesium, and silicon.
Carbon: It regulates the metabolic activities required by meristematic and differentiatiñg tissues.

Carbon, hydrogen, and oxygen: These elements are absolutely essential for plant growth. These enter into all chemical compositions of all types of organic compounds like carbohydrates, proteins, lipids, organic acids, amino acids. enzymes, nucleic acids, hormones, etc. These are protoplasmic and formwork elements.

Nitrogen: Nitrogen is essential for all metabolic activities as various biochemical reactions occur in presence of enzymes, It plays an important role in cell division, vegetative, and reproduction growth.

Phosphorus: It is the structural component of nucleic acids. Phospho-lipids, nucleoproteins, ATP, NADP+, sugar phosphates, and a number of co-enzymes. Phosphorus plays an indispensable role in energy, metabolism. It plays an active role in metabolic processes like photosynthesis, respiration, and protein synthesis.

Potassium: It is essential for the functioning of a large number of enzymes taking part in different metabolic activities like photosynthesis, respiration, starch synthesis, synthesis of nucleic acids. It controls the closing and opening of stomata.

Calcium: It is essential for the control of carbohydrate metabolism. It plays some role in binding nucleic acids and proteins in chromosomes.

Magnesium: It is essential for binding together two subunits of ribosomes. It is essential for fat metabolism, carbohydrate metabolism. It is also an activator of enzymes involved in the synthesis of nucleic acids.

Silicon: It plays an important role in the Biological activities of the plants.

Question 4.
Define the following:
(i) Nutrients,
Answer:
Nutrients: The chemical substances used by living organisms as raw materials for metabolic activities are termed nutrients.

(ii) Nutrition,
Answer:
Nutrition: The uptake and utilization of both inorganic and organic raw materials by a living organism for their growth, various metabolic activities, and development is called nutrition.

(iii) Micronutrients
Answer:
Micronutrients: Micronutrients are the essential elements present in plant tissues in relatively lesser amounts i.e. less than 1 mg per gram of dry matter. These mostly act as cofactor or activator of enzymes. These are iron, copper, zinc, manganese, molybdenum, boron, and chlorine.

(iv) Macronutrients,
Answer:
Macronutrients: Macronutrients are the essential elements present in plant tissues in relatively larger concentrations, i.e. at least 1 mg per gram of dry matter. These are carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, calcium, magnesium, and potassium.

(v) Active absorption,
Answer:
Active absorption: It is observed that the concentration of K’ions in vacuolar sap was found to be 1000 times more than the pond water. This can occur by utilization of metabolic energy only. The absorption of minerals by the plant against the concentration gradient involving the expenditure of energy is termed active absorption. Inactive absorption, the minerals move from the soil water from low concentration to higher concentration within the cell.

(vi) Passive absorption,
Answer:
Passive absorption: Passive absorption is the absorption of minerals by physical processes not involving the direct expenditure of metabolic energy. A substance moves passively from higher concentration to lower concentration. Ions can also be absorbed and accumulated against an F.CP (Electro Chemical Potential) gradient without the use of metabolic activities. Several theories have been proposed to explain the movement of ions such as ion exchange. Donnan equilibrium and mass flow of ions.

(vii) Symplastic movement and
Answer:
Symplastic Movement: It is the type of movement in which, ions entering the cell wall of the epidermis move across the cell wall of the cortex, cytoplasm of endodermis, the cell wall of the pericycle, and finally in the xylem vessels.

(viii) Apoplastic movement.
Answer:
In apoplastic transport, water and minerals flow in an upward direction via the apoplast to the xylem in the root. The concentration of solutes transported in aboveground organs is established through a combination of import from the xylem, absorption by cells, and export by the phloem

Question 5.
What do you understand by heterotrophic mode of nutrition? Elaborate your answer with suitable examples.
Answer:
This is the type of nutrition, in which organisms obtain readymade organic food materials from some other source and are not capable of synthesizing these from inorganic raw materials of their own. The organ¬isms, which show this type of mode is known as Heterotrophs.

The heterotrophs are divided into two main types:

1. parasites
2. saprophytes.

Parasites obtain readymade organic food material from other living plants or animals. The plant or animal which provides food to the parasite is termed the host. Many bacteria and fungi are parasites. They cause various diseases in their hosts.

Total Stemparasite

Some flowering plants also show parasitic modes of nutrition. These plants send haustorial or parasitic roots into the host to draw nutrients from it. Depending upon the organ of the host on which parasite is attached, it may be a stem parasite or root parasite.

Saprophytic plants such as Morotropa, bacteria, fungi grow on decaying animal and vegetable matter and absorb the organic food from it.

Heterotrophic plants could be symbiotic and insectivorous also.

Here we are providing Class 11 Biology Important Extra Questions and Answers Chapter 11 Transport in Plants. Important Questions for Class 11 Biology are the best resource for students which helps in Class 11 board exams.

Class 11 Biology Chapter 11 Important Extra Questions Transport in Plants

Transport in Plants Important Extra Questions Very Short Answer Type

Question 1.
Define heat of wetting or hydration.
Answer:
Imbibition of water is always associated with heat generation is called wetting or hydration.

Question 2.
What phenomenon is always associated with imbibition?
Answer:
Heating of wetting or hydration.

Question 3.
Which solution de-plasmolyse the plasmolyse solution?
Answer:
Hypotonic solution.

Question 4.
What is the full form of D.P.D.?
Answer:
Diffusion pressure deficit.

Question 5.
Name the element that regulates turgidity in guard cells.
Answer:
Potassium.

Question 6.
Which type of guard cells are found in grasses?
Answer:
Dumb bell-shaped.

Question 7.
Which is the important factor that affects water potential?
Answer:
Solute concentration.

Question 8.
Why do plants growing in arid regions bear small leaves with sunken stomata?
Answer:
To reduce transpiration.

Question 9.
Name two antitranspirants.
Answer:
Abscisic acid (ABA), Phenyl Mercuric Acetate (PMA).

Question 10.
When does wilting occur?
Answer:
When the rate of evaporation of water exceeds the rate of uptake of water by roots.

Question 11.
What is water potential?
Answer:
The capacity of a solution to hold the maximum amount of water is called water potential.

Question 12.
What will be the water potential of distilled water at normal pressure and temperature?
Answer:
Zero.

Question 13.
What are the porins?
Answer:
The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through.

Question 14.
Define the water potential.
Answer:
Water potential is a concept fundamental to understanding water movement.

Question 15.
What is antiport?
Answer:
In an antiport, both molecules move in opposite directions.

Question 16.
What is flaccid?
Answer:
When the water flows into the cell and out of the cell are in equilibrium the cells are said to be flaccid.

Question 17.
Define isotonic.
Answer:
If the external solution balances tire osmotic pressure cytoplasm it is said to be isotonic.

Question 18.
Define translocation.
Answer:
The bulk movement of substances through the conducting or vascular tissues of plants is called translocation.

Question 19.
Define Casparian strip.
Answer:
The inner boundary of the cortex, the endodermis, is impervious to water because of a bond of suberised matrix called the Casparian strip.

Question 20.
Define cohesion.
Answer:
The mutual attraction between water molecules.

Question 21.
What is transpiration?
Answer:
Transpiration is the evaporative loss of water by the plants. It occurs mainly through the stomata in the leaves.

Transport in Plants Important Extra Questions Short Answer Type

Question 1.
What is osmosis?
Answer:
It is the movement of water molecules from a region of its higher concentration to low concentration through the plasma membrane. It is a vital process. Various physiological process in plants takes through osmosis.

Question 2.
What is the active transport of water?
Answer:
It is the transport of water molecules against the concentration gradient with the utilization of energy (ATP). The molecules from low to high concentration move through the active transport of water.

Question 3.
How does transpiration differ from guttation?
Answer:

Question 4.
Define permanent wilting co-efficient or permanent wilting percentage.
Answer:
The percentage of water on a dry weight basis of the soil that still remains at the time when the plant shows permanent wilting is termed as permanent wilting co-efficient. It various between 1-1.5% depending upon the texture of the soil. It is higher in clayey soil than sandy soil.

Question 5.
What are the conditions for imbibition to take place?
Answer:
There are two conditions necessary for imbibition to take place:

1. Water potential gradient between the surface of the adsorbent and the liquid imbibed.
2. The affinity between the adsorbent and the imbibed liquid. It is a type of diffusion by which the movement of water takes place.

Question 6.
Give an account of the water relations of a plant cell when it is placed in
(a) Hypertonic solution,
Answer:
When the cell is placed in hypertonic solution exosmosis occurs, the protoplast contracts and the cell membrane detaches from the cell wall and contracted protoplast. This contraction of the protoplast by ex¬osmosis is termed plasmolysis.

(b) Hypotonic solution.
Answer:
When a plasmolysed cell is placed in water or hypotonic solution, endosmosis occurs and the protoplast regains the original position. This phenomenon is termed de-plasmolysis.

Question 7.
What is the ascent of sap?
Answer:
Water and minerals absorbed by the plants through roots from the soil are transported to different parts of the plant as these play a vital role in their growth. Water along with various dissolved inorganic substances in it are termed sap. The upward translocation of sap (water and dissolved inorganic substances) from the roots to the aerial parts of the plant is termed ascent of sap.

Question 8.
What are the advantages of transpiration?
Answer:

1. Ascent of sap: Transpiration pull created in leaves is responsible for ascent of sap.
2. Absorption of water: Transpiration pull is also responsible for passive absorption of water.
3. The distribution of minerals in different parts of the plant is done by transpiration.
4. Cooling effect: Transpiration lowers the temperature of the leaf and causes a cooling effect.
5. The increased rate of transpiration favours the development of tissue, which provides strength to the plant.
6. Excessive transpiration induces hardness which imparts resistance of plants to drought.

Question 9.
What is the diffusion pressure? What are the factors which affect the rate of diffusion?
Answer:
The pressure exerted by the particles due to their tendency to diffuse from the region of higher concentration to the region of lower concentration.

Various factors affect the rate of diffusion:

• Diffusion pressure gradient
• Temperature
• The density of diffusing substance
• The density of the medium.

Question 10.
Define water holding capacity or field capacity of the soil.
Answer:
After heavy rainfall or irrigation, the amount of water actually retained by soil even against the force of gravity is termed as water holding capacity or field capacity of the soil. It is expressed in terms of the percentage of water present per unit dry weight of soil.

Question 11.
Describe osmosis as a special case of diffusion.
Answer:
Uptake and distribution of water, solutes, and gases occur in a plant as a result of diffusion. The diffusion of water through a semipermeable membrane is known as osmosis. The diffusion of water molecules continues across the membrane until an equilibrium is attained. Osmosis can be demonstrated by a simple experiment as follows:

A thistle funnel is taken and tied with a semipermeable membrane (parchment paper) to the wide mouth of the thistle funnel and made tight.

The thistle funnel is filled with concentrated sugar solution and its wide mouth is dipped into water contained in a beaker. The membrane allows water molecules to pass through and not the sugar molecules. The level of sugar solution will rise in the funnel from ‘A’ to ‘B’. This demonstrates osmosis.

A demonstration of osmosis. A thistle funnel is filled with sucrose solution and kept inverted in a beaker containing water,
(a) Water will diffuse across the membrane (as shown by arrows) to raise the level of the solution in the funnel
(b) Pressure can be applied as shown to stop the water movement into the funnel.

Question 12.
What is the factor which affects the rate of transpiration?
Answer:
There are two factors.
A. External (Environmental) factors.
B. Internal (Living factors).

A. External factors:

1. Light: Causes stomatal opening
2. Temperature: High temperature decreases relative humidity increasing transpiration.
3. Humidity: It directly affects the rate of transpiration that is related to the vapour pressure of the atmosphere.
4. Wind: High velocity of wind causes closure of stomata.
5. Soil moisture: The rate of transpiration is directly proportional to the quantity of available moisture in the soil.

B. Internal factor:

1. Root Shoot Ratio: Roots absorbs water, should transpire water, hence their ratio affects transpiration.
2. Leaf area: Smaller plants tend to transpire more rapidly per unit area than larger plants.
3. Leaf Anatomy: Modification of leaves affects transpiration.

Question 13.
In what way does the concept of water potential help in explaining water movement?
Answer:
The additional pressure (more than osmotic pressure) is applied so that water can be made to flow out of the solution.
There are two factors

1. The concentration of dissolved solutes in a solution,
2. Pressure difference determines the chemical potential of water, which is the driving force for water movement in plants.

This chemical potential is the water potential. It is the difference in the free energy of water molecules in solution and in the pure state at the same temperature and pressure.

Question 14.
Of what importance is potassium in the opening and closing of stomata?
Answer:
The opening and closing of stomata are controlled by the accumulation of solutes in the guard cells. In the guard cell solutes are taken from neighbouring epidermal and mesophyll cells. The major solute which is taken in by the guard cells is potassium.

The rise in potassium level causes the stomatal opening and a decrease in level causes stomatal closing. The uptake of potassium controls the water potential. The extent of K⁺ accumulation in guard cells determines the size of the stomatal opening.

Question 15.
Does transpiration serve any useful function in the plants?
Answer:
Transpiration helps in the movement of xylem sap. It increases the absorption of mineral nutrients by the roots from the soil. Solar radiation absorbed by the leaves is used in photosynthesis but some radiations will cause heating of leaves. Transpiration, however, reduces the heating of the leaves.

Question 16.
Describe the role of osmotic potential in regulating the water potential of plant cells.
Answer:
Osmotic potential is the amount by which the water potential of pure water is reduced by the presence of the solute. The osmotic potential has a negative value.

If we apply additional pressure, the water can be flown out of the solution.

Osmosis is driven by two factors:

1. The concentration of dissolved solutes in solution,
2. Pressure difference.

Water potential is the driving force for water movement in plants. Water potential represents the free energy associated with water. Osmotic potential regulates the flow of water molecules through the membrane.

Question 17.
Explain the facilitated diffusion.
Answer:
In facilitated diffusion special proteins help move substances across membranes without the expenditure of ATP energy. Facilitated diffusion cannot cause net transport of molecules from a low to high concentration-this would require the input of energy.

The transport rate reaches a maximum when all of the protein transporters are being used (saturation). Facilitated diffusion is very specific: it allows the cell to select substances for uptake. It is sensitive to inhibitors that react with protein side chains.

Question 18.
What is active transport? Explain with an appropriate example.
Answer:
Active transport is carried out by membrane proteins. Hence different proteins in the membrane play a major role in both active as well as passive transport. Pumps are proteins that use energy to carry substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration.

The transport rate reaches a maximum when all the protein transporters are being used or are saturated. Like enzymes, the carrier protein is very specific in what it carries across the membrane. These proteins are sensitive to inhibitors that react with protein side chains.

Question 19.
What is imbibition?
Answer:
Imbibition is a special type of diffusion when water is absorbed by solids-colloids-causing them to enormously increase in volume. The classical examples of imbibition are absorption of water by seeds and by dry wood. The pressure that is produced by the swelling of wood has been used by prehistoric man to split rocks and boulders.

If it were not for the pressure due to imbibition, seedlings would not have been able to emerge out of the soil into the open; they probably would not have been able to establish.

Question 20.
What is turgor pressure? Give its two roles in plants.
Answer:
The pressure exerted by the cell sap on its wall when it has absorbed the maximum amount of water is called turgor pressure.

1. Leaves stand erect and look fresh due to turgor pressure.
2. The movement of soluble food in phloem is due to turgor pressure.

Question 21.
What is guttation?
Answer:
Oozing of droplets along the leaf margin on the vein endings at night is called guttation. In the morning when water evaporates, a layer of salts remains on the leaf which may cause burning.

Guttation occurs through the hydathodes. Education occurs when absorption exceeds transpiration and water pressure builds up in the xylem vessels. It forces the water outward through the hydathode.

Transport in Plants Important Extra Questions Long Answer Type

Question 1.
Describe the theories related to the translocation of water.
Answer:
There are three most important theories related to the translocation of water.

1. Root pressure theory
2. Capillarity
3. Cohesion theory.

1. Root pressure theory: Water flows from higher water potential to low water potential. Water from the soil is absorbed by root hairs and conducted through xylem vessels. Mineral ions from the soil are taken up by roots and get deposited in the xylem vessels.

When the stem of a plant is cut transversely above the soil surface, a drop of the xylem sap will exude from the cut surface. This indicates the presence of positive pressure in the xylem. This pressure is known as Root Pressure.

2. Capillarity: Capillarity means a rise in water in tubes of small diameter kept in a water vessel. The uptake of water through xylem vessel is possible in small size plants through capillarity. This is due to the forces of adhesion and cohesion.

Adhesive forces attract molecules of different kinds whereas cohesive forces attract molecules of the same kind to each other. According to this theory, water is taken due to the force of adhesion and flows upward due to the force of cohesion.

3. Cohesion: This is the most important theory of water movement through plants. It is based on the force of cohesion between water molecules. This sets up a continuous water column from the top to the root tip of the plant. According to this theory water evaporates from the leaf to the atmosphere, results in a decrease in the water potential of epidermal cells.

This loss of water is balanced by water moving from adjacent cells along a water potential gradient. The movement of the water occurs from the soil to the root. Uptake of water is termed as cohesion theory and also known as transpirational pull.

Question 2.
Is there a general mechanism to explain the opening and closing of stomata? Justify your answer.
Answer:
There is no general mechanism to explain the opening and closing of stomata. Because opening and closing of stomata are regulated by the accumulation of solute in the guard cells. Solutes are taken in the guard cells, as a result, osmotic potential and water potential of guard cells are lowered, the guard cells become turgid and swell size, resulting in the stomatal opening. With a decline in guard cell solutes, water moves out, resulting in the stomatal opening.

There are two theories to explain the mechanism of opening and closing of stomata.

1. Classical starch sugar conversion theory: According to this theory, the change in osmotic concentration is brought about due to the conversion of starch into glucose and vice-versa.
2. K+ Influx and Efflux theory: According to this theory when the leaf is exposed to light, the pH of the guard ceils rises due to the active transfer of H+ ions from the cytoplasm into chloroplast’s utilization of CO. in photosynthesis. In the majority of plants, stomata remain open during the day and close at night.

Hence, there is no general mechanism to explain the stomatal opening and closing.

Question 3.
Mention some factors that influence stomatal opening and closing. How are these factors involved in regulating stomatal behaviour?
Answer:
Factors affecting stomatal movements:

1. Light: In most of the plant’s stomata open during the day. The effect of light causes the opening of stomata or it may be either due to the hydrolysis of starch into glucose.
2. The water content of leaves: A decrease of water content in stomatal cells results in an increase in their D.P.D. Water from guard cells moves into these cells and stomata close.
3. CO₂ concentration: Low CO₂ concentration in guard cells causes the opening of stomata.
4. pH: High pH stimulates the opening of stomata and low pH causes closure of stomata and high concentration of CO₂ causes closure of stomata.
5. Temperature: High temperature stimulates the opening of the stomata.
6. Atmospheric Humidity: Humid environment favours opening and dryness causes closure of stomata.
7. Minerals: Minerals like P, Mg, Ca etc. affect the stomatal opening. A high concentration of K+ ions causes the opening of stomata.
8. Growth Hormones: Cytokinins stimulates the opening of stomata. Abscisic acid induces the closure of stomata.

Question 4.
Write short notes on:
(i) Cohesion-Tension and Transpiration pull theory.
Answer:
Transpiration pull theory: Ascent of sap has been explained satisfactorily by Dixon with the help of a theory called Transpiration pull theory. According to this theory water continuously evaporates from the turgid and moist cell walls of mesophyll cells in the leaves.

It makes the mesophyll air saturated. The air outside the leaf is dry. So a gradient is set up which allows the water vapours to go out from the interior of the leaf to the outside through the stomata. The mesophyll cells draw water from the deeper tissue, which in turn take water from the xylem of the leaf. It creates a kind of pull in the leaf called transpiration pull.

The xylem of the leaf is connected to the xylem of the stem and further to the xylem of the roots. Since there is a continuous column of water in the plant, water is virtually lifted up due to transpiration pull a situation similar to one like drawing a bucket of water from a well. The column of water does not break because of the great force of cohesion among the water molecules. This theory is also called the cohesion of water molecules theory.

(ii) Mass flow hypothesis.
Answer:
Mass flow hypothesis: The carbohydrates prepared in the leaves are translocated to other parts of the plant in the form of sucrose through phloem at the expense of metabolic energy. Munch’s mass flow hypothesis is the most accepted theory for the translocation of organic food.

According to this hypothesis, organic substances move from the region of high osmotic pressure to the region of low osmotic pressure due to the development of a gradient of turgor pressure. This can be proved by taking two interconnected osmometers. One of the osmometers has a high solute cone than the other. The whole apparatus is placed in water.

Water enters the osmometer with a high solute cone. It creates high turgor pressure in it. High turgor pressure forces the solution to move through the tube to the other osmometer. It is called mass flow. If somehow, the solute is continuously added to the donor osmometer and converted into the osmotically inactive compound in the other osmometer, this system can work indefinitely.

Munch’s mass flow apparatus.