Biochemical - Class 9 West Bengal Board Life Science

Biochemical Processes in Plants and Animals

Photosynthesis: Site and Structure

Photosynthesis primarily occurs in the mesophyll tissue of plant leaves, which contains two types of parenchyma cells: palisade and spongy parenchyma. Palisade parenchyma cells are elongated and contain more chlorophyll, while spongy parenchyma cells are smaller and contain less chlorophyll. In dorsiventral (bifacial) leaves, both cell types are present, but in isobilateral leaves, only spongy parenchyma is found.

• Other sites: Young green stems, flower stalks, and certain lower organisms (e.g., Euglena, Chlamydomonas) can also perform photosynthesis due to the presence of chlorophyll.
• Chloroplast structure: Chloroplasts have…

Biochemical Processes in Plants and Animals

Photosynthesis: Site and Structure

Photosynthesis primarily occurs in the mesophyll tissue of plant leaves, which contains two types of parenchyma cells: palisade and spongy parenchyma. Palisade parenchyma cells are elongated and contain more chlorophyll, while spongy parenchyma cells are smaller and contain less chlorophyll. In dorsiventral (bifacial) leaves, both cell types are present, but in isobilateral leaves, only spongy parenchyma is found.

• Other sites: Young green stems, flower stalks, and certain lower organisms (e.g., Euglena, Chlamydomonas) can also perform photosynthesis due to the presence of chlorophyll.
• Chloroplast structure: Chloroplasts have two main parts—grana (site of light reaction) and stroma (site of dark reaction).

Photosynthesis: Raw Materials and Pigments

Photosynthesis requires water, carbon dioxide, sunlight, and chlorophyll. The process involves both oxidation and reduction reactions, with water providing hydrogen and releasing oxygen, and carbon dioxide being reduced to glucose.

• Main raw materials: Water ($H_2O$), carbon dioxide ($CO_2$), sunlight, chlorophyll.
• Photosynthetic equation: $6CO_2 + 12H_2O \xrightarrow{\text{sunlight, chlorophyll}} C_6H_{12}O_6 + 6O_2 + 6H_2O$
• Pigments: Chlorophyll (green), carotenoids (carotene—orange, xanthophyll—yellow).
• Accessory molecules: ADP, NADP, RuBP are essential for the process.

Absorption and Action Spectrum

Different pigments absorb different wavelengths of visible light, which affects the rate of photosynthesis. The absorption spectrum shows which wavelengths are absorbed, while the action spectrum shows which wavelengths are most effective for photosynthesis.

• Chlorophyll a: Absorbs mainly in blue-violet and red regions.
• Carotenoids: Absorb in blue and green regions.
• Key point: Maximum photosynthetic activity occurs at wavelengths where chlorophyll a absorbs most.

Light and Dark Reactions of Photosynthesis

Photosynthesis occurs in two main stages: the light-dependent (light reaction) and light-independent (dark reaction) phases. The light reaction takes place in the grana and involves two photosystems (PS II and PS I), leading to the production of ATP and NADPH.

• Light reaction: Involves photolysis of water, electron transport, and formation of ATP (photophosphorylation) and NADPH.
• Non-cyclic photophosphorylation: Both PS II and PS I are involved, producing ATP, NADPH, and $O_2$.
• Cyclic photophosphorylation: Only PS I is involved, producing ATP but not NADPH or $O_2$.
• Dark reaction (Calvin cycle): Occurs in the stroma, does not require light, and is enzyme-dependent. It involves carbon fixation, reduction, and regeneration of RuBP, ultimately producing glucose.

Mineral Nutrition in Plants

Plants require various mineral elements for growth, classified as macronutrients and micronutrients based on their required quantities. Macronutrients are needed in larger amounts, while micronutrients are required in trace amounts.

• Macronutrients: N, P, K, Ca, Mg, S.
• Micronutrients: Fe, Mn, Zn, B, Mo, Cu, Ni, Co, Cl.
• Functions: Formation of protoplasm, enzyme activity, chlorophyll synthesis, redox reactions, water balance, and buffer action.

Transpiration and Its Regulation

Transpiration is the physiological process by which excess water vapor is lost from plant surfaces, mainly through stomata, cuticle, and lenticels. It is regulated by both external and internal factors.

• Stomatal transpiration: 80–90% of water loss, regulated by guard cells.
• Cuticular transpiration: About 10%, through the waxy cuticle.
• Lenticular transpiration: About 0.1%, through small openings in woody stems.
• Regulating factors: Sunlight, temperature, humidity (inverse relation), wind speed, $CO_2$ concentration (inverse relation), leaf area, stomatal number and position, protoplasm density, plant hormones.

Transport of Water, Minerals, Food, and Gases

Plants transport water and minerals via xylem (upward movement—Ascent of Sap) and food via phloem (downward and multidirectional movement). Theories explaining ascent of sap include root pressure and transpiration pull (cohesion-tension theory).

• Root pressure: Effective in small plants, not in tall trees.
• Transpiration pull (Dixon and Joly): Universally accepted, explains water movement in tall trees.
• Phloem transport: Sieve tubes, companion cells, phloem parenchyma, and fibers are involved in distributing food substances.

Respiration in Plants and Animals

Respiration is a biochemical process involving the breakdown of glucose to release energy. It can be aerobic (with oxygen), anaerobic (without oxygen), or fermentation (e.g., alcoholic or lactic acid).

• Aerobic respiration: Complete oxidation of glucose, produces $CO_2$, $H_2O$, and 686 kcal energy.
• Anaerobic respiration: Partial oxidation, produces less energy (about 50 kcal), and byproducts like ethanol or lactic acid.
• Glycolysis: Occurs in cytoplasm, converts one glucose to two pyruvate molecules, common to all types of respiration.
• Krebs cycle: Occurs in mitochondrial matrix, cyclic process producing NADH, FADH2, and $CO_2$.
• Respiratory organs: Stomata, lenticels, pneumatophores in plants; skin, trachea, gills, lungs in animals.

Nutrition and Digestion

Nutrition in plants is mainly autotrophic (holophytic), but exceptions include saprophytic, parasitic, symbiotic, and insectivorous nutrition. Animals show holozoic nutrition, involving ingestion, digestion, absorption, assimilation, and egestion.

• Types in plants: Saprophytic (Penicillium), parasitic (Cuscuta), symbiotic (Lichen), insectivorous (Drosera).
• Types in animals: Parasitic (Ascaris), symbiotic (E. coli), coprophagy (housefly), sanguinivory (leech, mosquito).
• Digestive enzymes: Amylase, maltase, sucrase, lactase, pepsin, trypsin, lipase.
• Balanced diet: Contains carbohydrates, proteins, fats, minerals, vitamins, and water in proper proportions.
• Metabolic disorders: Hypothyroidism, hyperthyroidism, diabetes mellitus, obesity, hypertension, atherosclerosis, liver cirrhosis, arthritis.

Circulatory System and Blood

The circulatory system includes arteries, veins, and capillaries. Arteries carry blood away from the heart under high pressure, veins return blood under low pressure, and capillaries connect the two.

• Arteries: Thick walls, high pressure, no valves, mostly oxygenated blood (except pulmonary artery).
• Veins: Thin walls, low pressure, valves present, mostly deoxygenated blood (except pulmonary vein).
• Open circulation: Seen in cockroach, with 13-chambered heart and hemolymph (colorless blood).
• Double circulation in humans: Systemic and pulmonary circuits, ensuring separation of oxygenated and deoxygenated blood.
• Blood cells: RBCs (no nucleus when mature, contain hemoglobin), WBCs (nucleated, five types), platelets (no nucleus, clotting).
• Blood groups: Determined by antigens (A, B, AB, O) and antibodies (alpha, beta).
• Erythroblastosis fetalis: Occurs when Rh-negative mother carries Rh-positive fetus; maternal antibodies attack fetal RBCs in subsequent pregnancies.
• Blood clotting: Involves thromboplastin, prothrombin, thrombin, fibrinogen, and fibrin, with calcium ions as cofactors.

Excretion in Plants and Animals

Excretion removes metabolic wastes. In plants, excretion is less complex and involves leaf fall, bark shedding, and fruit drop. Excretory products may be nitrogenous or non-nitrogenous.

• Plant excretion: Leaf fall (Shimol, Amra), bark shedding (Arjun, Guava), fruit drop (Lemon, Tamarind, Apple).
• Nitrogenous wastes: Quinine, reserpine (alkaloids).
• Non-nitrogenous wastes: Gums, resins.
• Excretory organs in animals: Contractile vacuole (Amoeba), flame cell (Planaria), nephridia (earthworm), Malpighian tubules (cockroach), kidneys (human).
• Nephron structure: Malpighian corpuscle (Bowman's capsule + glomerulus), tubules (PCT, loop of Henle, DCT), collecting duct.
• Other excretory organs: Liver (converts ammonia to urea via ornithine cycle), lungs (removes $CO_2$), skin (sweat, sebum, cerumen).
• ADH hormone: Promotes water reabsorption in kidney tubules; deficiency leads to diabetes insipidus.

Key Exam Takeaways

• Photosynthesis occurs mainly in leaf mesophyll; palisade cells have more chlorophyll.
• Light reaction produces ATP and NADPH; dark reaction (Calvin cycle) produces glucose.
• Transpiration is highest through stomata, regulated by guard cells and environmental factors.
• Water and minerals move upward via xylem (transpiration pull), food moves via phloem.
• Respiration includes glycolysis (cytoplasm) and Krebs cycle (mitochondria); both enzyme-dependent.
• Nutrition types: autotrophic in plants, holozoic in animals; exceptions exist.
• Circulatory system: arteries vs. veins, double circulation in humans, open system in cockroach.
• Blood groups depend on antigens and antibodies; Rh incompatibility can cause erythroblastosis fetalis.
• Excretion in plants is less complex; in animals, kidneys are main excretory organs, supported by liver, lungs, and skin.
• ADH regulates water reabsorption in kidneys; its deficiency causes diabetes insipidus.