Biology

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Definition – Significance and Site of Photosynthesis

Photosynthesis is referred as photochemical oxidation and reduction reactions carried out with the help of light, converting solar energy into chemical energy. It is the most important anabolic process. Plants and photosynthetic bacteria use simple raw materials like carbon dioxide water and with the help of light energy synthesize carbohydrates and evolve oxygen. The overall chemical equation for photosynthesis is:

Ruben and Kamen (1941) demonstrated six molecules of water as insufficient for the evolution of 6 molecules of O₂ and modified the equation as:

Photosynthesis is a collection of oxidation and reduction reactions (Redox reaction).

Oxidation:
Water is oxidised into oxygen (loss of electrons).

Reduction:
CO₂ is reduced into Carbohydrates (gain of electrons).

In some bacteria, oxygen is not evolved and is called as non-oxygenic and anaerobic photosynthesis. Examples: Green sulphur, Purple sulphur and green fiamentous bacteria.

Significance of Photosynthesis

1. Photosynthetic organisms provide food for all living organisms on earth either directly or indirectly.
2. It is the only natural process that liberates oxygen in the atmosphere and balances the oxygen level.
3. Photosynthesis balances the oxygen and carbon cycle in nature.
4. Fuels such as coal, petroleum and other fossil fuels are from preserved photosynthetic plants.
5. Photosynthetic organisms are the primary producers on which all consumers depend for energy.
6. Plants provide fodder, fire, fie wood, timber, useful medicinal products and these sources come by the act of photosynthesis.

Site of Photosynthesis

Chloroplasts are the main site of photosynthesis and both energy yielding process (Light reaction) and fixation of carbon di oxide (Dark reaction) that takes place in chloroplast. It is a double wall membrane bounded organelle, discoid or lens shaped, 4-10 µm in diameter and 1-33 µm in thickness. The membrane is a unit membrane and space between them is 100 to 200 A °. A colloidal and proteinaceous matrix called stroma is present inside.

A sac like membranous system called thylakoid or lamellae is present in stroma and they are arranged one above the other forming a stack of coin like structure called granum (plural grana). Each chloroplast contains 40 to 80 grana and each granum consists of 5 to 30 thylakoids.

Thlakoids found in granum are called grana lamellae and in stroma are called stroma lamellae. Thlakoid disc size is 0.25 to 0.8 micron in diameter. A thinner lamella called Fret membrane connects grana. Pigment system I is located on outer thylakoid membrane facing stroma and Pigment system II is located on inner membrane facing lumen of thylakoid.

Grana lamellae have both PS I and PS II whereas stroma lamellae have only PS I. Chloroplast contains 30-35 Proteins, 20-30% phospholipids, 5-10% chlorophyll, 4-5% Carotenoids, 70S ribosomes, circular DNA and starch grains.

Inner surface of lamellar membrane consists of small spherical structure called as Quantasomes. Presence of 70S ribosome and DNA gives them status of semi-autonomy and proves endosymbiotic hypothesis which says chloroplast evolved from bacteria. Thlakoid contains pigment systems which produces ATP and NADPH + H⁺ using solar energy. Stroma contains enzyme which reduces carbondioxide into carbohydrates. In Cyanobacteria thylakoid lies freely in cytoplasm without envelope (Figure 13.1).

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Special Modes of Nutrition

Nutrition is the process of uptake and utilization of nutrients by living organisms. There are two main types such as autotrophic and heterotrophic nutrition. Autotrophic nutrition is further divided intophotosynthetic and chemosynthetic nutrition. Heterotrophic nutrition is further divided into saprophytic, parasitic, symbiotic and insectivorous type. In this topic you are going to learn about special mode of nutrition.

Saprophytic Mode of Nutrition in Angiosperms

Saprophytes derive nutrients from dead and decaying matter. Bacteria and fungus are main saprophytic organisms. Some angiosperms also follow saprophytic mode of nutrition. Example: Neottia. Roots of Neottia (Bird’s Nest Orchid) associate with mycorrhizae and absorb nutrients as a saprophyte. Monotropa (Indian Pipe) grow on humus rich soil found in thick forests. It absorbs nutrient through mycorrhizal association (Figure 12.9).

Parasitic Mode of Nutrition in Angiosperms

Organisms deriving their nutrient from another organism (host) and causing disease to the host are called parasites.

a. Obligate or Total parasite:
Completely depends on host for their survival and produces haustoria.

(i) Total Stem Parasite:
The leafless stem twine around the host and produce haustoria. Example: Cuscuta (Dodder), a rootless plant growing on Zizyphus, Citrus and so on.

(ii) Total Root Parasite:
They do not have stem axis and grow in the roots of host plants produce haustoria. Example: Rafflesia, Orobanche and Balanophora.

b. Partial Parasite:
Plants of this group contain chlorophyll and synthesize carbohydrates. Water and mineral requirements are dependent on host plant.

(i) Partial Stem Parasite:
Example: Loranthus and Viscum (Mistletoe) Loranthus grows on fig and mango trees and absorb water and minerals from xylem.

(ii) Partial Root Parasite:
Example: Santalum album (Sandal wood tree) in its juvenile stage produces haustoria which grows on roots of many plants (Figure 12.10).

Symbiotic Mode of Nutrition

a. Lichens:
It is a mutual association of Algae and Fungi. Algae prepares food and fungi absorbs water and provides thallus structure.

b. Mycorrhizae:
Fungi associated with roots of higher plants including Gymnosperms. Example: Pinus.

c. Rhizobium and Legumes:
This symbiotic association fixes atmospheric nitrogen.

d. Cyanobacteria and Coralloid Roots:
This association is found in Cycas where Nostoc associates with its coralloid roots. (Figure 12.11).

Insectivorous Mode of Nutrition

Plants which are growing in nitrogen deficient areas develop insectivorous habit to resolve nitrogen deficiency. These plants obtain nitrogen from the insects.

a. Nepenthes (Pitcher plant):
Pitcher is a modified leaf and contains digestive enzymes. Rim of the pitcher is provided with nectar glands and acts as an attractive lid. When insect is trapped, proteolytic enzymes will digest the insect.

b. Drosera (Sundew):
It consists of long club shaped leaves with tentacles that secrete sticky digestive fluid which looks like a sundew and attracts insects.

c. Utricularia (Bladder Wort):
Submerged plant in which leaf is modified into a bladder to collect insect in water.

d. Dionaea (Venus Fly Trap):
Leaf of this plant modified into a colourful trap. Two folds of lamina consist of sensitive trigger hairs and when insects touch the hairs it will close and traps the insects.(Figure 12.12).

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Nitrogen Cycle and Nitrogen Metabolism

Nitrogen Cycle

This cycle consists of following stages:

1. Fixation of Atmospheric Nitrogen

Di-nitrogen molecule from the atmosphere progressively gets reduced by addition of a pair of hydrogen atoms. Triple bond between two nitrogen atoms (N≡N) are cleaved to produce ammonia (Figure 12.7).

Nitrogen fixation process requires Nitrogenase enzyme complex, Minerals (Mo, Fe and S), anaerobic condition, ATP, electron and glucose 6 phosphate as H⁺ donor. Nitrogenase enzyme is active only in anaerobic condition.

To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen. Nitrogen fixing bacteria in root nodules appears pinkish due to the presence of this leghaemoglobin pigment.

Overall Equation:
N₂ + 8e^– + 8H⁺ + 16ATP → 2NH₃⁺ + H₂ + 16ADP + 16Pi

2. Nitrification

Ammonia (NH₃⁺) is converted into Nitrite (NO₂^–) by Nitrosomonas bacterium. Nitrite is then converted into Nitrate (NO₃^–) by Nitrobacter bacterium. Plants are more adapted to absorb nitrate (NO₃^–) than ammonium ions from the soil.

3. Nitrate Assimilation

The process by which nitrate is reduced to ammonia is called nitrate assimilation and occurs during nitrogen cycle.

4. Ammonification

Decomposition of organic nitrogen (proteins and amino acids) from dead plants and animals into ammonia is called ammonification. Organism involved in this process are Bacillus ramosus and Bacillus vulgaris.

5. Denitrification

Nitrates in the soil are converted back into atmospheric nitrogen by a process called denitrification. Bacteria involved in this process are Pseudomonas, Thiobacillus and Bacillus subtilis. The overall process of nitrogen cycle is given in Figure 12.8.

Nitrogen Metabolism Ammonium Assimilation (Fate of Ammonia)

Ammonia is converted into amino acids by the following processes:

1. Reductive Amination

Glutamic acid or glutamate is formed by reaction of ammonia with α-ketoglutaric acid.

2. Transamination

Transfer of amino group (NH₃⁺) from glutamic acid (glutamate) to keto group of keto acid. Glutamic acid is
the main amino acid from which other amino acids are synthesised by transamination. Transamination requires the enzyme transaminase and co enzyme pyridoxal phosphate (derivative of vitamin B6 – pyridoxine)

3. Catalytic Amination: (GS/GOGAT Pathway)

Glutamate amino acid combines with ammonia to form the amide glutamine.

(GOGAT – Glutamine – 2 – Oxoglutarate aminotransferase)

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Nitrogen Fixation – Definition, Types, Examples

Inspiring act of nature is self-regulation. As all living organisms act as tools for biogeochemical cycles, nitrogen cycle is highly regulated. Life on earth depends on nitrogen cycle. Nitrogen occurs in atmosphere in the form of N₂ (N≡N), two nitrogen atoms joined together by strong triple covalent bonds. The process of converting atmospheric nitrogen (N₂) into ammonia is termed as nitrogen fixation. Nitrogen fixation can occur by two methods:

1. Biological
2. Non-Biological (Figure 12.5).

Non – Biological Nitrogen Fixation

• Nitrogen fixation by chemical process in industry.
• Natural electrical discharge during lightening fixes atmospheric nitrogen.

Biological Nitrogen Fixation

Symbiotic bacterium like Rhizobium fixes atmospheric nitrogen. Cyanobacteria found in Lichens, Anthoceros, Azolla and coralloid roots of Cycas also fix nitrogen. Non-symbiotic (free living bacteria) like Clostridium also fix nitrogen.

a. Symbiotic Nitrogen Fixation

(i) Nitrogen Fixation with Nodulation

Rhizobium bacterium is found in leguminous plants and fix atmospheric nitrogen. This kind of symbiotic association is beneficial for both the bacterium and plant. Root nodules are formed due to bacterial infection. Rhizobium enters into the host cell and proliferates, it remains separated from the host cytoplasm by a membrane (Figure 12.6).

Stages of Root Nodule Formation:

1. Legume plants secretes phenolics which attracts Rhizobium.
2. Rhizobium reaches the rhizosphere and enters into the root hair, infects the root hair and leads to curling of root hairs.
3. Infection thread grows inwards and separates the infected tissue from normal tissue.
4. A membrane bound bacterium is formed inside the nodule and is called bacteroid.
5. Cytokinin from bacteria and auxin from host plant promotes cell division and leads to nodule formation

Non-Legume:
Alnus and Casuarina contain the bacterium Frankia. Psychotria contains the bacterium Klebsiella.

(ii) Nitrogen Fixation Without Nodulation

The following plants and prokaryotes are involved in nitrogen fixation.

• Lichens – Anabaena and Nostoc
• Anthoceros – Nostoc
• Azolla – Anabaena azollae
• Cycas – Anabaena and Nostoc

b. Non-Symbiotic Nitrogen Fixation

Free living bacteria and fungi also fix atmospheric nitrogen.

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Difference Between Hydroponics and Aeroponics

1. Hydroponics or Soilless culture:

Von Sachs developed a method of growing plants in nutrient solution. The commonly used nutrient solutions are Knop solution (1865) and Arnon and Hoagland Solution (1940). Later the term Hydroponics was coined by Goerick (1940) and he also introduced commercial techniques for hydroponics. In hydroponics roots are immersed in the solution containing nutrients and air is supplied with help of tube (Figure 12.3).

Aeroponics:

This technique was developed by Soifer Hillel and David Durger. It is a system where roots are suspended in air and nutrients are sprayed over the roots by a motor driven rotor (Figure 12.4).

Hydroponics and aeroponics are both methods of growing plants. The latter, aeroponics, is a method used to grow plants in the air – without the use of soil. Hydroponics is also a method that does not use soil, but instead, uses only a nutrient solution in a water solvent.

An advanced form of hydroponics, aeroponics is the process of growing plants with only water and nutrients. This innovative method results in faster growth, healthier plants, and bigger yields, all while using fewer resources. Plants grow in a soilless medium called rockwool.

In hydroponics we provide a solution in which plants can feed the amount they need when they want to. Because of this, we have more control over the speed and growth of our plants. Although this is a relatively new method of growing cannabis, it is cheaper than aeroponics.

Hydroponics offers the advantage of no energy wasted searching for nutrients. Aeroponic systems are a specialized version of hydroponics where the roots of the plant extend only in air and the roots are directly sprayed with a nutrient water mix (the recipe).

There are two main types of aeroponic systems: high pressure aeroponics and low pressure aeroponics. The main difference being the droplet size of the mist used in each case. Low-pressure aeroponics uses low-pressure, high-flow pumps, whereas high-pressure aeroponics uses high-pressure, low-flow pumps.

There are six main types of hydroponic systems to consider for your garden: wicking, deep water culture (DWC), nutrient film technique (NFT), ebb and flow, aeroponics, and drip systems.

The major disadvantage of aeroponics is the cost. Aeroponic systems are more expensive than most hydroponic systems and are completely dependent on a power source to run the air and nutrient pumps and the timer. Even a short interruption in power can result in the roots drying out and killing your plants.

One of the best advantages of Aeroponics is that plants grow quickly in such systems. They thrive and are able to produce great harvests. The plants grown are also much stronger and healthier due to this oxygen richness too.

In Aeroponic farming, the plantations can be vertical in the structure which helps the farmers to save a lot of space which in turn produces more food. There would be a great reduction in the disease and the infestation of pests. The Aeroponic farming can also be automated which reduces the cost of labour.

Fruits and Vegetables can also be grown comfortably in Aeroponics systems. Lot of vegetables and fruits can be grown like Beets, Broccoli, Cabbage, Carrots, Cauliflower, Corn, Cucumber, Eggplant, Grapes, Melons, Onions, Peas, Peppers, Potatoes, Radish, Raspberry, Strawberry, Sweet Potato, Tomatoes, and Watermelon.

Both hydroponics and aquaponics have clear benefits over soil-based gardening: lessened, adverse environmental impacts, reduced consumption of resources, faster plant growth, and higher yields. Many believe that aquaponics is a better option over hydroponics when choosing a soilless growing system.

Is hydroponics really good for the environment? Yes, hydroponics is good not just for the environment, but for several other reasons such as higher yield, water conservation and the removal of pesticides and herbicides.

You will have to mix up advanced nutrients for aeroponics of the proper strength consisting all of the required nutrients in the proper proportions (depending upon what your plant needs for its growth). You should not miss the Growing Exotic Hydroponic Plants.

Plants grown through hydroponics and aeroponics have the advantage natural and unrestricted growth. This system has enabled the cultivation of numerous plants that were previously considered difficult or impossible to grow from cuttings, as it becomes possible to propagate them from a single stem cutting.

There are vast numbers of people who have heard of hydroponics, and the majority of those know that systems can be set up indoors. In hydroponics, we can now provide all the light we need to plants to help them grow, so in this case, no they don’t need sunlight.