CBSE Notes

By going through these CBSE Class 11 Biology Notes Chapter 16 Digestion and Absorption, students can recall all the concepts quickly.

Digestion and Absorption Notes Class 11 Biology Chapter 16

→ The digestive system of humans consists of an alimentary canal and associated digestive glands.

→ The alimentary canal consists of the mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.

→ The accessory digestive glands include the salivary glands, the liver (with gall bladder) and the pancreas.

→ Inside the mouth, the teeth masticate the food, the tongue tastes the food and manipulates it for proper mastication by mixing with the saliva.

→ Saliva contains a starch digestive enzyme, salivary amylase that digests the starch and converts it into maltose (disaccharide).

→ The food then passes into the pharynx and enters the oesophagus in the form of a bolus, which is further carried down through the oesophagus by peristalsis into the stomach.

→ In the stomach mainly protein digestion takes place.

→ Absorption of simple sugars, alcohol and medicines also takes place in the stomach.

→ The chyme food enters into the duodenum portion of the small intestine and is acted on by the pancreatic juice, bile and finally by the enzymes in the succus entericus so that the digestion of carbohydrates, proteins and fats is completed.

→ The food then enters into the jejunum and ileum portions of the small intestine.

→ Carbohydrates are digested and converted into monosaccharides like glucose. Proteins are finally broken down into amino acids.

→ The fats are converted to fatty acids and glycerol.

→ The digested end products are absorbed into the body through the epithelial lining of the intestinal villi. The undigested food (faeces) enters into the caecum of the large intestine through the ileocaecal valve, which prevents the backflow of the faecal matter.

→ Most of the water is absorbed in the large intestine.

→ The undigested food becomes semi-solid in nature and then enters into the rectum, anal canal and is finally egested out through the anus.

→ Digestion: Digestive system process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods.

→ Thecodont: The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of the jaw bone. This type of attachment is called thecodont.

→ Diphyodont: A set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This type of dentition is called diphyodont.

→ Papillae: The upper surface of the tongue has small projections called papillae, some of which bear taste buds.

→ Epiglottis: A cartilaginous flap called epiglottis prevents the entry of food into the glottis-opening of the wind pipe-during swallowing.

→ Stomach: The oesophagus is a thin long tube that extends posteriorly passing through the neck, thorax and diaphragm and enlarges into a T shaped bag-like structure called the stomach.

→ Villi: The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer form irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine.

→ Microvilli: The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance.

→ Lacteal: Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal.

→ Glisson’s capsule: The hepatic lobules are the structural and functional units of the liver containing hepatic cells arranged in the form of cords. Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule.

→ Chyme: The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and called the chyme.

→ Faeces: The undigested, unabsorbed substances called faeces are temporarily stored in the rectum till defaecation.

→ Micelles: Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into small droplets called micelles which move into the intestinal mucosa.

→ Chylomicrons: Micelles are re-formed into very small protein-coated fat globules called the chylomicrons which are transported into the lymph vessels (lacteals) in the villi.

By going through these CBSE Class 11 Biology Notes Chapter 15 Plant Growth and Development, students can recall all the concepts quickly.

Plant Growth and Development Notes Class 11 Biology Chapter 15

→ Growth is one of the most conspicuous events in any living organism. It is an irreversible increase expressed in parameters such as sizes, area, length, height, volume, cell number, etc. It conspicuously involves increased protoplasmic materials.

→ In plants, meristems are the sites of growth. Root and shoot apical meristems sometimes along with intercalary meristem, contribute to the elongation growth of the plant axis.

→ Growth is indeterminate in higher plants. Following cell division in root and shoot apical meristem cells, the growth could be arithmetic or geometrical.

→ Growth may not be and generally is not sustained at a high rate throughout the life of cell/tissue/organ/organism.

→ One can define three principal phases of growth- the lag, log, and senescent phase.

→ When a cell loses the capacity to divide it leads to differentiation. Differentiation results in the development of structures that are commensurate with the function the cells finally have to perform.

→ General principles for differentiation for cells, tissues, and organs are similar.

→ A differentiated cell may differentiate and then redifferentiate.

→ Since differentiation in plants is open, the development could also be flexible, i.e, the development is the sum of growth and differentiation. Plant exhibit plasticity in development.

→ Plant growth and development are under the control of both intrinsic and extrinsic factors.

→ Intercellular intrinsic factors are the chemical substances, called plant growth regulators (PGR).

→ There are diverse groups of PGRs in plants, principally belonging to five groups: auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These PGR’s are synthesized in various parts of the plant; they control different differentiation and developmental events.

→ Any PGR has diverse physiological effects on plants. Diverse PGRs also manifest similar effects. PGRs may act synergistically or antagonistically.

→ Plant growth and development are also affected by light, temperature, nutrition, oxygen status, gravity, and such external factors.

→ Flowering in some plants is induced only when exposed to a certain duration of photoperiod. Depending on the nature of photoperiod requirements, the plants are called short-day plants, long-day plants, and day-neutral plants.

→ Certain plants also need to be exposed to low temperatures so as to hasten to flower later in life. This treatment is known as vernalization

→ Vernalisation: Vernalisation is the low-temperature requirement of some plants for flowering. The cold treatment given to shoot tips or seeds is called vernalization.

→ Photoperiodism: Flowering in certain plants depends not only on a combination of light and dark exposures but also on their relative durations. This is termed photoperiodism.

→ Short-day plants/Long-day plants: The former group of plants is called short-day plants while the later ones are termed long-day plants.

→ Stress hormone: ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

→ Apical dominance: In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.

→ Dedifferentiation: Plants show another interesting phenomenon. The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed dedifferentiation.

→ Differentiation: The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed differentiation.

→ Absolute growth rate: Measurement and the comparison of total growth per unit time is called the absolute growth rate.

→ Relative growth rate: The growth of the given system per unit time expressed on a common basis e.g. per unit initial parameter is called the relative growth rate.

→ The open form of growth: The cell(s) of such meristems have the capacity to divide and self-perpetuate. The product, however, soon loses the capacity to divide and such cells make up the plant body. This form of growth wherein new cells are always being added to the plant body by the activity of the meristem is called the open form of growth.

By going through these CBSE Class 11 Biology Notes Chapter 14 Respiration in Plants, students can recall all the concepts quickly.

Respiration in Plants Notes Class 11 Biology Chapter 14

→ Plants unlike animals have no special systems for breathing or gaseous exchange.

→ Stomata and lenticels allow gaseous exchange by diffusion. Almost all living cells in a plant have their surfaces exposed to air.

→ The breaking of C-C bonds of complex organic molecules by oxidation cells leading to the release of a lot of energy is called cellular respiration.

→ Glucose is the favored substrate for respiration. Fats and proteins can also be broken down to yield energy.

→ The initial stage of cellular respiration takes place in the cytoplasm.

→ Each glucose molecule is broken through a series of enzyme-catalyzed reactions into two molecules of pyruvic acid. This process is called glycolysis.

→ The fate of the pyruvate depends on the availability of oxygen and the organism.

→ Under anaerobic conditions, either lactic acid fermentation or alcohol fermentation occurs.

→ Fermentation takes place under anaerobic conditions in prokaryotes, unicellular eukaryotes, and germinating seeds.

→ In eukaryotic organisms in the presence of oxygen aerobic respiration occurs.

→ Pyruvic acid is transported into the mitochondria where it is converted into acetyl CoA with the release of CO₂.

→ Acetyl CoA then enters the tricarboxylic acid pathway or Krebs cycle operating in the matrix of the mitochondria.

→ NADH⁺+ H⁺ and FADH, are generated in the Krebs’ cycle.

→ The energy in these molecules as well as that in the NADH⁺+H⁺ synthesized during glycolysis are used to synthesis ATP. This is accomplished through a system of electron carriers called the electron transport system (ETS) located on the inner membrane of the mitochondria.

→ The electrons as they move through the system release enough energy that is trapped to synthesize ATP. This is called oxidative phosphorylation. In this process 02 is the ultimate acceptor of electrons and it gets reduced water.

→ The respiratory pathway is an amphibolic pathway as it involves both anabolism and catabolism.

→ The respiratory quotient depends upon the type of respiratory substance used during respiration.

→ Respiration: The breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to the release of a considerable amount of energy is called respiration.

→ Respiratory substrates: The compounds that are oxidized during this process are known as respiratory substrates.

→ Glycolysis: In any case, all living organisms retain the enzymatic machinery to partially oxidize glucose without the help of oxygen. This breakdown of glucose to pyruvic acid is called glycolysis

→ Aerobic respiration: Aerobic respiration is the process that leads to a complete oxid&tion of organic substances in the presence of oxygen, and releases CO₂, water, and a large amount of energy present in the substrate.

→ Electron transport system (ETS): The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system.

→ Oxidative phosphorylation: Unlike photophosphorylation where it is the light energy that is utilized for the production of proton gradient required for phosphorylation, in respiration it is the energy of oxidation-reduction utilized for the same process. It is for this reason that the process is called oxidative phosphorylation.

→ Respiratory quotient: 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 the respiratory quotient (RQ) or respiratory ratio.

By going through these CBSE Class 11 Biology Notes Chapter 13 Photosynthesis in Higher Plants, students can recall all the concepts quickly.

Photosynthesis in Higher Plants Notes Class 11 Biology Chapter 13

→ Green plants make their own food by photosynthesis. During this process, carbon dioxide from the atmosphere is taken in by leaves through stomata and used for making carbohydrates, principally glucose and starch.

→ Photosynthesis takes place only in the green parts of the plants, mainly the leaves. Within the leaves, the mesophyll cells have a large number of chloroplasts that are responsible for CO₂ fixation.

→ Within the chloroplasts, the membranes are sites, for the light reaction, while the chemosynthetic pathway occurs in the stroma.

→ Photosynthesis has two stages: the light reaction and the carbon fixing reactions.

→ In the light reaction, the light energy is absorbed by the pigments present in the antenna and funneled to special chlorophyll a molecule called reaction center chlorophylls.

→ There are two photosystems, PSI and PSII. PSI has a 700nm absorbing chlorophyll-a P₇₀₀ molecule at its reaction center, while PSII has a P₆₈₀ reaction center that absorbs red light at 680 nm.

→ After absorbing light, electrons are excited and transferred through PSII and PSI and finally to NAD forming NADH.

→ During this process, a proton gradient is created across the membrane of the thylakoid. The breakdown of the gradient due to the protons being moved through the F₀ part of the ATP as the enzyme releases enough energy for the synthesis of ATP.

→ Splitting of water molecules is associated with PSII resulting in the release of O₂, protons, and transfer of electrons to PSII.

→ In the carbon fixation cycle, CO₂ is added by the enzyme Rubisco, which also catalyzes a wasteful oxygenation reaction in C₃ plants: photorespiration.

→ Some tropical plants show a special type of photosynthesis called the C₄ pathway. In these plants, the first product of CO₂, a fixation that takes place in the mesophyll, is a 4 Carbon compound. In the bundle sheath cells, the Calvin pathway is carried out for the synthesis of carbohydrates.

→ The rate of photosynthesis is affected by light intensity, carbon dioxide concentration, temperature, availability of water, and plant factors

→ Action spectrum: A first action spectrum of photosynthesis was thus described. It resembles roughly the absorption spectra of chlorophyll (a) and (b).

→ Light reactions: The former set of reactions since they are light-dependent are called light reactions.

→ Dark reactions: The latter, though they are dependent on products of light reaction, that is ATP and NADPH, can theoretically take place in the dark and are called dark reactions.

→ Chlorophyll a: Chlorophyll a is the chief pigment associated with photosynthesis.

→ Accessory pigments: Other thylakoid pigments like chlorophyll b, xanthophylls, and carotenoids, are called accessory pigments.

→ Photosystem I (PSI) and photosystem II (PSII): The pigments are organized into two discrete photochemical light-harvesting complexes (LHC) called Photosystem I (PSI) and photosystem II (PSII).

→ Antennae: Each photosystem has all pigments (except one molecule of chlorophyll a) forming a light-harvesting system also called antennae.

→ P₇₀₀ and P₆₈₀: In PSI the reaction center chlorophyll a has an absorption peak at P₇₀₀ nm hence is called P₇₀₀ while in PSII it has absorption maxima at 680 nm, and is called P₆₈₀.

→ Z scheme: The whole scheme of transfer of electrons, starting from the PSII, Uphill to the acceptor down to the electron transport chain to PSI excitation of electrons, transfer to another acceptor, and finally downhill to NADP causing it to be reduced to NADPH⁺ H⁺. This is called the Z scheme, due to its characteristic shape.

→ Photorespiration: C₄ plants have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to highlight intensities, they lack a process called photorespiration, and have greater productivity
of biomass.

→ Bundle sheath cells: The particularly large cells around the vascular bundles of the C₄, pathway plants are called bundle sheath cells.

By going through these CBSE Class 11 Biology Notes Chapter 12 Mineral Nutrition, students can recall all the concepts quickly.

Mineral Nutrition Notes Class 11 Biology Chapter 12

→ Plants obtain their inorganic nutrients from the air, water, and soil. Plants absorb a wide variety of mineral elements.

→ Not all the mineral elements that they absorb are required by plants. Out of the more than 105 elements discovered so far, less than 21 are essential and beneficial for normal plant growth and development.

→ The elements required in large quantities are called micronutrients while those required in fewer quantities or in the trace are termed as micro¬nutrients.

→ These elements are either essential constituents of proteins, carbohydrates. fats, nucleic acid, etc., and/or take part in various metabolic processes.

→ Deficiency of each of these essential elements may lead to symptoms called deficiency symptoms.

→ Chlorosis, necrosis, stunted growth, impaired cell division, etc. are some prominent deficiency symptoms.

→ Plants absorb minerals through roots by either passive or active processes. They are carried to all parts of the organism through xylem along with water transport.

→ Nitrogen is very essential for the sustenance of life.

→ Plants cannot use atmospheric nitrogen directly. But some of the plants, especially roots of legumes, can fix this atmospheric nitrogen into biologically usable forms.

→ Nitrogen fixation requires a strong reducing agent and energy in the form of ATP. N, fixation is accomplished with the help of nitrogen-fixing microbes, mainly Rhizobium.

→ The enzyme dinitrogenase which plays an important role in bio-logical N, fixation is very sensitive to oxygen.

→ Most of the processes take place in an anaerobic environment.

→ The energy, ATP. required is provided by the aerobic respiration of the host cells.

→ Ammonia produced following N. fixation is incorporated into amino acid as the amino group.

→ Transamination: It involves the transfer of an amino group from one amino acid to the keto group of a keto acid. Glutamic acid is the main amino acid from which the transfer of H₂ the amino group takes place and other amino acids are formed through transamination. The enzyme transaminase catalyzes all such reactions.

→ Leghaemoglobin: The nodules have adaptations that ensure that the enzyme is protected from oxygen. To protect these enzymes, the nodule contains an oxygen scavenger called leghaemoglobin.

→ Nitrification: Ammonia is first oxidized to nitrite by the bacteria Nitrosomonas and/or Enterococcus. The nitrite is further oxidized to nitrate with the help of the bacterium Nitrobacter. These steps are called nitri¬fication.

→ Critical concentration: The concentration of the essential element below which plant growth is retarded is termed as critical concentration.