Biochemistry & Plant Physiology BBO5T09

Syllabus topics (RTMNU)

• Lipids: Definition, Properties and role of fatty acids, oils and waxes
• Degradation of fats (β-Oxidation and Glyoxylic acid cycle)
• Enzymology: Definition, Characteristics (Properties), and classification of enzymes
• Basic concepts of enzymology: Holoenzyme, Apoenzyme, Prosthetic group, Co-enzyme, Co-factor, Active site and Isoenzyme
• Mechanism of enzyme action: Enzyme-substrate complex theory, Lock and key model, Induced fit model
• Enzyme inhibitors: Definition, Competitive and non-competitive inhibition

Lipids: Definition, Properties and Role of Fatty Acids, Oils and Waxes

Definition: Lipids are a group of organic compounds that are insoluble in water but soluble in organic solvents such as ether, chloroform and benzene. They are esters of fatty acids with alcohols (mainly glycerol).

Fatty acids are long-chain carboxylic acids (R–COOH), usually with an even number of carbon atoms (C₁₂–C₂₄).

• Saturated — no double bond, e.g. palmitic acid (C₁₆), stearic acid (C₁₈); solid at room temperature.
• Unsaturated — one or more C=C double bonds, e.g. oleic (1), linoleic (2), linolenic acid (3); liquid at room temperature.

Oils and fats are triglycerides (triacylglycerols): one glycerol + three fatty acids joined by ester bonds. Oils (liquid, rich in unsaturated fatty acids) are common in seeds — groundnut, sunflower, mustard, castor.

Waxes are esters of long-chain fatty acids with long-chain monohydric alcohols, e.g. cutin and suberin-associated waxes, carnauba wax on palm leaves.

Properties: insoluble in water; lower density than water; saponification (hydrolysis with alkali gives soap + glycerol); hydrogenation of unsaturated oils gives solid fat (vanaspati); rancidity on oxidation; high energy content (about 9 kcal/g).

Role in plants:

1. Stored food in seeds (energy reserve) — used during germination.
2. Structural part of membranes (phospholipids, glycolipids).
3. Waxes form the cuticle and reduce water loss (transpiration) and protect from pathogens.
4. Source of hormones and pigments (carotenoids are lipid-derived).

Degradation of Fats: β-Oxidation and Glyoxylate (Glyoxylic Acid) Cycle

First, lipase hydrolyses a triglyceride → glycerol + 3 fatty acids. Glycerol enters glycolysis (as dihydroxyacetone phosphate).

β-Oxidation (in glyoxysomes in germinating oily seeds, also mitochondria): the fatty acid is broken down two carbons at a time from the carboxyl end; oxidation happens at the β-carbon (C-3).

1. Activation: fatty acid + CoA + ATP → fatty acyl-CoA (acyl-CoA synthetase).
2. Oxidation (dehydrogenation): acyl-CoA → trans-Δ²-enoyl-CoA; FAD → FADH₂.
3. Hydration: + H₂O → L-3-hydroxyacyl-CoA.
4. Oxidation: → 3-ketoacyl-CoA; NAD⁺ → NADH.
5. Thiolysis: + CoA → acetyl-CoA + acyl-CoA shorter by 2 C.

The cycle repeats. Palmitic acid (C₁₆) gives 8 acetyl-CoA after 7 rounds.

Glyoxylate cycle (in glyoxysomes of germinating fatty seeds like castor and groundnut): converts acetyl-CoA into succinate and then sugar. It bypasses the two CO₂-releasing steps of Krebs cycle using two special enzymes — isocitrate lyase (isocitrate → succinate + glyoxylate) and malate synthase (glyoxylate + acetyl-CoA → malate).

Net: 2 acetyl-CoA → succinate. Succinate → mitochondria → oxaloacetate → phosphoenolpyruvate → glucose (gluconeogenesis) → sucrose transported to the growing seedling.

Enzymology: Definition, Characteristics and Classification of Enzymes

Definition: Enzymes are biological catalysts, mostly proteins, that speed up biochemical reactions without being used up. (Ribozymes are RNA enzymes.)

Characteristics: (1) protein in nature; (2) high catalytic efficiency — small amount needed; (3) specificity for substrate; (4) lower activation energy; (5) do not change equilibrium; (6) sensitive to temperature (optimum around 25–40 °C, denatured by heat); (7) sensitive to pH; (8) can be inhibited; (9) reversible action in many cases.

IUB classification (6 classes):

Basic Concepts: Holoenzyme, Apoenzyme, Prosthetic Group, Co-enzyme, Co-factor, Active Site and Isoenzyme

• Apoenzyme: protein part of an enzyme; inactive alone.
• Co-factor: non-protein part needed for activity. It may be a metal ion (Mg²⁺, Zn²⁺, Fe²⁺) or an organic molecule.
• Holoenzyme = apoenzyme + co-factor (complete active enzyme).
• Prosthetic group: co-factor tightly (often covalently) bound, e.g. haem in catalase, FAD in succinate dehydrogenase.
• Co-enzyme: organic co-factor loosely bound, often a vitamin derivative, e.g. NAD⁺, NADP⁺, CoA.
• Active site: small pocket on the enzyme where the substrate binds and the reaction takes place.
• Isoenzymes (isozymes): different molecular forms of an enzyme that catalyse the same reaction, e.g. lactate dehydrogenase (5 forms), peroxidase isozymes in plants.

Mechanism of Enzyme Action: E–S Complex, Lock and Key, Induced Fit

Enzyme–substrate complex theory (Michaelis and Menten): E + S ⇌ ES → E + P. The enzyme binds the substrate to form a temporary ES complex, lowers the activation energy, and releases the product; the enzyme is free again.

Lock and key model (Emil Fischer, 1894): the active site is rigid and exactly fits the substrate, like a key in a lock. Explains specificity, but not flexibility.

Induced fit model (Koshland, 1958): the active site is flexible; binding of substrate changes the shape of the enzyme so that it fits closely, like a glove on a hand. Explains broad specificity and inhibition better.

Enzyme Inhibitors: Competitive and Non-competitive Inhibition

Inhibitor: a substance that reduces or stops enzyme activity.

Likely exam questions

1. (Long, 8 marks) Describe β-oxidation of fatty acids and the glyoxylate cycle in germinating oily seeds.
2. (Long, 8 marks) Define enzymes. Give their characteristics and IUB classification, and explain the mechanism of enzyme action.
3. (Short, 4 marks) Distinguish between competitive and non-competitive inhibition.
4. (Short, 4 marks) Explain apoenzyme, co-enzyme and prosthetic group.
5. (Short, 4 marks) Write the role of waxes in plants.

Syllabus topics (RTMNU)

• Water relation: Concept and significance of Imbibition, Diffusion, Osmosis, Osmotic pressure
• Cell as osmotic system
• DPD
• Plasmolysis
• Active and passive absorption of water
• Ascent of sap: Definition, Cohesion-adhesion theory
• Transpiration: Definition, Types, Mechanism (K+ Malate Hypothesis)
• Phloem transport: Source and sink concept, Munch Hypothesis
• Mineral uptake: Passive (Donnan's Equilibrium), and Active (Carrier Concept) uptake of minerals

Water Relations: Imbibition, Diffusion and Osmosis

Imbibition: absorption of water by solid hydrophilic colloids (cellulose, starch, proteins) causing them to swell, e.g. swelling of dry seeds, wooden doors swelling in rainy season. Significance: first step of seed germination; produces imbibition pressure that can break the seed coat; helps seedlings come out of soil.

Diffusion: movement of molecules of a substance from a region of higher concentration to lower concentration until evenly spread. Significance: exchange of O₂ and CO₂ through stomata, loss of water vapour in transpiration, movement of ions.

Osmosis: movement of water (solvent) molecules from a dilute solution (higher water potential) to a concentrated solution (lower water potential) through a semi-permeable membrane.

• Endosmosis: water enters the cell (cell placed in hypotonic solution) — cell becomes turgid.
• Exosmosis: water leaves the cell (hypertonic solution) — cell shrinks.

Significance: absorption of water by root hairs, cell-to-cell movement of water, turgidity for support, opening and closing of stomata.

Osmotic Pressure, Cell as an Osmotic System and DPD

Osmotic pressure (OP): the pressure that must be applied to a solution to stop the entry of water into it through a semi-permeable membrane. It depends on solute concentration.

Turgor pressure (TP): pressure exerted by cell contents on the cell wall. Wall pressure (WP) is the equal and opposite pressure of the wall on the contents.

Cell as an osmotic system: the plasma membrane and tonoplast act as semi-permeable (differentially permeable) membranes; the cell sap in the vacuole is the solution; the cell wall is fully permeable. So a plant cell behaves like an osmometer.

Diffusion Pressure Deficit (DPD) or suction pressure: the amount by which the diffusion pressure of water in a solution is less than that of pure water. It shows the cell's ability to absorb water.

Plasmolysis

Definition: shrinkage of the protoplast away from the cell wall when a cell is kept in a hypertonic solution, due to exosmosis.

Stages: incipient plasmolysis (protoplast just begins to leave the wall at corners) → evident plasmolysis → final plasmolysis (protoplast becomes a round mass). If the cell is put back in water, it regains turgidity — deplasmolysis.

Significance: proves the cell membrane is semi-permeable; used to find OP of cell sap; explains why salting pickles and adding sugar to jams preserves them (microbes get plasmolysed); explains wilting of plants when excess fertiliser is applied.

Active and Passive Absorption of Water

Ascent of Sap: Definition and Cohesion–Adhesion Theory

Definition: upward movement of water with dissolved minerals from roots to the aerial parts through the xylem.

Cohesion–adhesion–tension theory (Dixon and Joly, 1894) — most accepted:

1. Continuous water column: xylem vessels and tracheids form a continuous water column from root to leaf.
2. Cohesion: water molecules attract each other strongly by hydrogen bonds, so the column does not break (cohesive force is very high).
3. Adhesion: water molecules stick to the walls of xylem, preventing the column from slipping down.
4. Transpiration pull: evaporation of water from leaf mesophyll cells lowers their water potential; they draw water from neighbouring cells and finally from xylem, creating tension (negative pressure).
5. This tension is passed down the whole column and water is pulled up like a rope.

Evidence: negative pressure in xylem, decrease in stem diameter during heavy transpiration. Limitation: air bubbles (cavitation) can break the column, but water bypasses through other vessels.

Transpiration: Definition, Types and Mechanism (K⁺ Malate Hypothesis)

Definition: loss of water in the form of vapour from aerial parts of the plant.

Types: (1) Stomatal — through stomata, 80–90%; (2) Cuticular — through cuticle, 3–10%; (3) Lenticular — through lenticels on bark, very small.

Mechanism of stomatal opening — K⁺ malate (K⁺ ion) hypothesis (Levitt; Fischer and Hsiao):

1. In light, guard cells take up CO₂; pH rises; starch is converted to phosphoenolpyruvate (PEP).
2. PEP + CO₂ → oxaloacetate → malic acid.
3. Malic acid gives H⁺ and malate²⁻. A proton pump (ATP-driven) sends H⁺ out and K⁺ enters guard cells from neighbouring cells; Cl⁻ also enters.
4. K⁺ malate accumulates in the vacuole, OP rises, water enters by osmosis → guard cells become turgid and bend → stoma opens.
5. In dark (or under ABA during water stress) K⁺ leaves, guard cells lose water → stoma closes.

Significance: ascent of sap, cooling of leaves, mineral distribution; but excess causes wilting — a "necessary evil".

Phloem Transport: Source–Sink Concept and Münch Hypothesis

Source: part where food is made or released (mature leaves, storage organs in spring). Sink: part where food is used or stored (roots, fruits, growing tips). Transport is from source to sink, so it can be up or down (bidirectional).

Münch's pressure-flow (mass flow) hypothesis (1930): sugar is actively loaded into sieve tubes at the source → OP rises → water enters from xylem → high turgor pressure. At the sink, sugar is unloaded → water leaves → low pressure. The pressure difference pushes sap from source to sink.

Mineral Uptake: Passive (Donnan's Equilibrium) and Active (Carrier Concept)

Passive uptake (no energy, along gradient): diffusion, ion exchange, and Donnan equilibrium — the cell has fixed (non-diffusible) negative ions on the inner side of the membrane; to balance them, extra cations from outside move in, so ions accumulate inside even against apparent concentration gradient, without energy.

Active uptake (uses ATP, against gradient) — carrier concept: a carrier molecule (protein) in the membrane binds a specific ion on the outer surface forming a carrier–ion complex, moves it across, releases it inside using energy, and returns. Evidence: uptake stops when respiration is inhibited; carriers are specific and can be saturated.

Likely exam questions

1. (Long, 8 marks) Define ascent of sap and explain the cohesion–adhesion (transpiration pull) theory.
2. (Long, 8 marks) What is transpiration? Describe its types and explain the K+ malate hypothesis of stomatal movement.
3. (Short, 4 marks) Define DPD and give its relation with OP and TP.
4. (Short, 4 marks) Explain Münch's mass flow hypothesis.
5. (Short, 4 marks) What is plasmolysis? Give its significance.

Syllabus topics (RTMNU)

• Photosynthesis: Definition, Significance, Photosynthetic pigments, Photosystems
• Mechanism of photosynthesis: Light reaction: Cyclic and non-cyclic photophosphorylation
• Carbon Fixation (Dark Reaction): Calvin Cycle (C3), HSK pathway (C4), CAM pathway
• Photoperiodism: Definition, Classification (SDP, LDP & DNP), Photoperiodic induction, Florigen concept
• Circadian rhythms and Biological clock

Photosynthesis: Definition and Significance

Definition: Photosynthesis is the process by which green plants make carbohydrates from CO₂ and water using light energy trapped by chlorophyll, releasing O₂.

Significance: (1) source of all food on earth; (2) converts light energy into chemical energy; (3) releases O₂ and maintains the O₂–CO₂ balance; (4) fossil fuels (coal, petroleum) are products of past photosynthesis; (5) provides fibres, timber, medicines.

Photosynthetic Pigments

Chlorophyll absorbs mainly blue (about 430–450 nm) and red (about 640–680 nm) light and reflects green. A chlorophyll molecule has a porphyrin head with a central Mg atom and a long phytol tail.

Photosystems

A photosystem is a group of pigment molecules (light-harvesting complex/antenna) with a reaction centre, located in the thylakoid membrane.

• PS I: reaction centre P₇₀₀; mainly on stroma lamellae; involved in cyclic and non-cyclic flow.
• PS II: reaction centre P₆₈₀; mainly in grana; linked with photolysis of water (oxygen-evolving complex with Mn).

Light Reaction: Cyclic and Non-cyclic Photophosphorylation

Photophosphorylation: formation of ATP from ADP + Pi using light energy.

Non-cyclic (Z-scheme):

1. PS II absorbs light; P₆₈₀ loses electrons to pheophytin → plastoquinone → cytochrome b₆f → plastocyanin → PS I.
2. The electron gap in P₆₈₀ is filled by photolysis of water: 2H₂O → 4H⁺ + 4e⁻ + O₂.
3. PS I absorbs light; P₇₀₀ sends electrons via ferredoxin to NADP⁺ reductase → NADPH.
4. Proton gradient across thylakoid drives ATP synthase → ATP.

Cyclic: only PS I works; electrons from P₇₀₀ go to ferredoxin → cytochrome b₆f → plastocyanin → back to P₇₀₀. Only ATP is formed.

Carbon Fixation (Dark Reaction): Calvin Cycle (C₃)

Occurs in the stroma; uses ATP and NADPH. Worked out by Melvin Calvin using ¹⁴C.

1. Carboxylation: CO₂ + RuBP (5C) → 2 molecules of 3-phosphoglyceric acid (3-PGA, 3C), catalysed by RuBisCO. First stable product is 3C, hence C₃.
2. Reduction: 3-PGA → 1,3-bisphosphoglycerate → glyceraldehyde-3-phosphate (G3P) using ATP and NADPH.
3. Regeneration: most G3P regenerates RuBP using ATP; some forms glucose/sucrose/starch.

For one glucose: 6 CO₂, 18 ATP and 12 NADPH are used. Examples: wheat, rice, sunflower.

HSK Pathway (C₄)

Hatch–Slack–Kortschak pathway in maize, sugarcane, sorghum. Leaves show Kranz anatomy (bundle-sheath cells around veins with many chloroplasts).

1. In mesophyll cells: CO₂ + PEP → oxaloacetic acid (OAA, 4C) by PEP carboxylase. OAA → malate.
2. Malate moves to bundle-sheath cells, releases CO₂ (→ pyruvate).
3. CO₂ enters Calvin cycle with RuBisCO in bundle sheath.
4. Pyruvate returns to mesophyll and regenerates PEP using ATP.

Advantages: almost no photorespiration, high efficiency at high light and temperature, better water use.

CAM Pathway

Crassulacean Acid Metabolism in succulents (Bryophyllum, Opuntia, pineapple). Stomata open at night: CO₂ + PEP → OAA → malic acid stored in vacuole (leaf becomes acidic). By day stomata close; malic acid releases CO₂ for the Calvin cycle. This saves water in deserts — separation in time (C₄ is separation in space).

Photoperiodism: Definition, Classification, Photoperiodic Induction and Florigen

Definition: the response of plants (especially flowering) to the relative length of day and night. Discovered by Garner and Allard (1920) in Maryland Mammoth tobacco.

• Short-day plants (SDP): flower when day is shorter than a critical length (really need a long uninterrupted night) — e.g. Xanthium, soybean, chrysanthemum.
• Long-day plants (LDP): flower when day is longer than critical — e.g. wheat, radish, spinach.
• Day-neutral plants (DNP): flowering not affected — e.g. tomato, cotton, sunflower.

Photoperiodic induction: a plant needs exposure to the right photoperiod for a certain number of cycles; after that it flowers even in unfavourable conditions. The stimulus is perceived by leaves (pigment phytochrome).

Florigen concept (Chailakhyan, 1936): leaves produce a flowering hormone, florigen, which moves to the shoot apex and causes flowering. Grafting experiments support it; today the FT protein is regarded as a major part of florigen.

Circadian Rhythms and Biological Clock

Circadian rhythms are daily cycles of about 24 hours in plant activities that continue even in constant conditions — e.g. leaf movements of beans, opening of flowers at fixed times, stomatal opening. They are controlled by an internal biological clock that is reset by light (phytochrome, cryptochrome) and temperature. The clock helps plants measure day length in photoperiodism.

Likely exam questions

1. (Long, 8 marks) Describe cyclic and non-cyclic photophosphorylation with the help of a Z-scheme.
2. (Long, 8 marks) Explain the Calvin cycle and the HSK (C4) pathway. Add a note on the CAM pathway.
3. (Short, 4 marks) Distinguish between short-day and long-day plants with examples.
4. (Short, 4 marks) What is the florigen concept?
5. (Short, 4 marks) Write a note on photosynthetic pigments.

Syllabus topics (RTMNU)

• Respiration: Definition, Types, significance and Respiratory Quotient (RQ)
• Aerobic Respiration: Glycolysis, Kreb's Cycle, Oxidative phosphorylation (ETS)
• Anaerobic Respiration: Concept, Lactic acid fermentation and Alcoholic fermentation
• Plant Movements: Definition, Outline of classification
• Tropic Movement (Geotropism, Phototropism, Thigmotropism)
• Nastic movement (Seismonasty)

Respiration: Definition, Types and Significance

Definition: Respiration is the biochemical oxidation of food (mainly glucose) in living cells to release energy, which is stored as ATP.

Types: (1) Aerobic — uses O₂, complete oxidation to CO₂ and H₂O; (2) Anaerobic — without O₂, incomplete oxidation, little energy (e.g. in yeast, in roots in waterlogged soil).

Significance: provides ATP for all life activities (growth, absorption, synthesis); intermediates of Krebs cycle are used to make amino acids, fats and pigments; CO₂ released is used in photosynthesis; fermentation is used in industry (alcohol, bread, curd).

Respiratory Quotient (RQ)

Definition: RQ is the ratio of the volume of CO₂ released to the volume of O₂ consumed in respiration. RQ = Volume of CO₂ evolved ÷ Volume of O₂ absorbed.

RQ is measured with Ganong's respirometer.

Aerobic Respiration: Glycolysis

Glycolysis (EMP pathway) — Embden, Meyerhof and Parnas; occurs in the cytoplasm; no O₂ needed; glucose (6C) → 2 pyruvate (3C).

1. Glucose → glucose-6-phosphate (hexokinase; 1 ATP used).
2. → fructose-6-phosphate (isomerase).
3. → fructose-1,6-bisphosphate (phosphofructokinase; 1 ATP used).
4. Split by aldolase → glyceraldehyde-3-phosphate (G3P) + dihydroxyacetone phosphate (interconvertible) → 2 G3P.
5. 2 G3P → 2 1,3-bisphosphoglycerate (2 NADH formed).
6. → 2 3-phosphoglycerate (2 ATP formed, substrate-level).
7. → 2 2-phosphoglycerate → 2 phosphoenolpyruvate (enolase, water removed).
8. → 2 pyruvate (pyruvate kinase; 2 ATP formed).

Net gain: 2 ATP + 2 NADH + 2 pyruvate per glucose.

Krebs Cycle (TCA / Citric Acid Cycle)

Occurs in the mitochondrial matrix. First, link reaction: pyruvate + CoA + NAD⁺ → acetyl-CoA + CO₂ + NADH (pyruvate dehydrogenase).

1. Acetyl-CoA (2C) + oxaloacetate (4C) → citrate (6C) (citrate synthase).
2. Citrate → isocitrate (aconitase).
3. Isocitrate → α-ketoglutarate (5C) + CO₂; NADH formed.
4. α-ketoglutarate → succinyl-CoA (4C) + CO₂; NADH formed.
5. Succinyl-CoA → succinate; GTP/ATP formed (substrate-level).
6. Succinate → fumarate; FADH₂ formed (succinate dehydrogenase).
7. Fumarate → malate (fumarase, + H₂O).
8. Malate → oxaloacetate; NADH formed. Cycle repeats.

Per acetyl-CoA: 2 CO₂, 3 NADH, 1 FADH₂, 1 ATP (GTP). One glucose → 2 turns.

Oxidative Phosphorylation (Electron Transport System)

On the inner mitochondrial membrane. NADH and FADH₂ pass electrons through Complex I (NADH dehydrogenase) → ubiquinone → Complex III (cytochrome bc₁) → cytochrome c → Complex IV (cytochrome oxidase) → O₂, the final acceptor, which forms water. Energy released pumps H⁺ into the intermembrane space; H⁺ flows back through ATP synthase (Complex V), making ATP — Mitchell's chemiosmotic theory. Textbook yield: 1 NADH → 3 ATP, 1 FADH₂ → 2 ATP (newer values 2.5 and 1.5).

Anaerobic Respiration: Concept, Lactic Acid and Alcoholic Fermentation

Concept: breakdown of glucose without O₂. Glycolysis is the same; pyruvate is then reduced using NADH, so NAD⁺ is regenerated and glycolysis continues. Net gain only 2 ATP.

• Alcoholic fermentation (yeast, some plant tissues): pyruvate → acetaldehyde + CO₂ (pyruvate decarboxylase); acetaldehyde + NADH → ethanol (alcohol dehydrogenase). C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Uses: bread, beer, ethanol.
• Lactic acid fermentation (Lactobacillus, muscle cells): pyruvate + NADH → lactic acid (lactate dehydrogenase). No CO₂. Uses: curd, cheese.

Plant Movements: Definition and Outline of Classification

Definition: a change in the position or orientation of a plant or its part in response to a stimulus or due to internal causes.

• Movement of locomotion (whole organism): e.g. Chlamydomonas (tactic movements).
• Movement of curvature (fixed plants): (a) autonomic/spontaneous — growth movements like nutation, and turgor movements like leaflets of Desmodium; (b) paratonic/induced — tropic (direction of stimulus decides direction) and nastic (direction not decided by stimulus).

Tropic Movements: Geotropism, Phototropism, Thigmotropism

• Geotropism (gravitropism): response to gravity. Roots are positively geotropic (grow down), shoots negatively geotropic. Explained by statoliths (starch grains) settling in root cap cells and unequal auxin distribution (Cholodny–Went theory).
• Phototropism: response to unilateral light. Shoots bend towards light (positive) because auxin moves to the shaded side and causes more elongation there; roots are negatively phototropic.
• Thigmotropism: response to touch/contact, e.g. tendrils of pea and cucurbits coil around a support because the side away from contact grows faster.

Nastic Movement: Seismonasty

Seismonasty: a non-directional movement in response to shock, touch or vibration. Best example: Mimosa pudica (touch-me-not) — leaflets fold and the petiole droops within seconds. Mechanism: the stimulus travels as an electrical signal to the pulvinus (swollen leaf base); K⁺ and Cl⁻ ions leave the lower pulvinus cells, water follows by exosmosis, they lose turgor and the leaf droops. Turgor is regained in a few minutes and the leaf reopens. It is a turgor movement, not a growth movement.

Likely exam questions

1. (Long, 8 marks) Describe glycolysis and the Krebs cycle. Calculate the net ATP gain in aerobic respiration of one glucose molecule.
2. (Long, 8 marks) Define plant movements, give an outline of their classification, and explain tropic movements and seismonasty.
3. (Short, 4 marks) What is respiratory quotient? Give its values for different substrates.
4. (Short, 4 marks) Distinguish between alcoholic and lactic acid fermentation.
5. (Short, 4 marks) Explain the electron transport system briefly.