Plant Anatomy and Physiology — Practice

Question 1

Which tissue is dead at maturity and provides mechanical strength?
(a) sclerenchyma (b) collenchyma (c) parenchyma (d) meristem

Accepted Answer

(a) sclerenchyma.

Sclerenchyma cells have thick lignified walls and are dead at maturity, giving rigid mechanical support (fibres, sclereids). Collenchyma and parenchyma are living.

Question 2

Secondary growth is usually absent in monocots because their vascular bundles are:
(a) closed (lack cambium) (b) open (c) scattered only (d) radial

Accepted Answer

(a) closed (lack cambium).

Monocot vascular bundles are closed — they have no cambium between xylem and phloem — so there is no lateral meristem to produce secondary tissues and increase girth.

Question 3

The main force responsible for the ascent of sap in tall trees is:
(a) transpiration pull (b) root pressure (c) capillarity (d) active transport

Accepted Answer

(a) transpiration pull.

Water rises by the cohesion–tension theory: transpiration at the leaves creates tension that pulls up an unbroken, cohesive water column. Root pressure is too weak to raise water in tall trees.

Question 4

Stomata open when the guard cells:
(a) become turgid (b) become flaccid (c) lose potassium ions (d) die

Accepted Answer

(a) become turgid.

When guard cells take up K⁺ and water, they swell and bow apart, opening the stomatal pore. Loss of turgor (flaccidity) closes the stomata.

Question 5

The translocation of sugars in the phloem is explained by the:
(a) pressure-flow (mass-flow) hypothesis (b) cohesion–tension theory (c) root pressure (d) transpiration pull

Accepted Answer

(a) pressure-flow (mass-flow) hypothesis.

Sugar loaded at the source raises osmotic pressure, water enters, and the resulting pressure pushes phloem sap toward the sink, where sugar is unloaded — the pressure-flow hypothesis.

Question 6

The oxygen released during photosynthesis comes from:
(a) water (b) carbon dioxide (c) glucose (d) chlorophyll

Accepted Answer

(a) water.

The photolysis of water at photosystem II releases the O₂, as shown by isotope experiments. CO₂ is reduced to sugar and is not the source of the oxygen.

Question 7

The enzyme that fixes CO₂ in the Calvin cycle is:
(a) RuBisCO (b) PEP carboxylase (c) ATP synthase (d) nitrogenase

Accepted Answer

(a) RuBisCO.

RuBisCO (ribulose bisphosphate carboxylase-oxygenase) fixes CO₂ onto RuBP in the Calvin cycle. It also acts as an oxygenase, causing photorespiration in C₃ plants.

Question 8

The first stable product of the Calvin cycle (C₃ pathway) is:
(a) 3-phosphoglyceric acid (3-PGA) (b) oxaloacetic acid (c) glucose (d) pyruvate

Accepted Answer

(a) 3-phosphoglyceric acid (3-PGA).

CO₂ combines with RuBP to form two molecules of the 3-carbon 3-PGA — the first stable product, giving the pathway its 'C₃' name.

Question 9

The specialised leaf anatomy of C₄ plants with prominent bundle-sheath cells is called:
(a) Kranz anatomy (b) dorsiventral anatomy (c) isobilateral anatomy (d) reticulate anatomy

Accepted Answer

(a) Kranz anatomy.

C₄ plants (maize, sugarcane) show Kranz anatomy — bundle-sheath cells surround the vascular bundles, concentrating CO₂ for the Calvin cycle and suppressing photorespiration.

Question 10

Glycolysis occurs in the ______ and yields a net of ______ ATP:
(a) cytoplasm; 2 (b) mitochondrial matrix; 2 (c) cytoplasm; 36 (d) inner membrane; 4

Accepted Answer

(a) cytoplasm; 2.

Glycolysis takes place in the cytoplasm, converting glucose to two pyruvate molecules with a net gain of 2 ATP and 2 NADH.

Question 11

The Krebs (citric acid) cycle occurs in the:
(a) mitochondrial matrix (b) cytoplasm (c) inner mitochondrial membrane (d) chloroplast stroma

Accepted Answer

(a) mitochondrial matrix.

The Krebs cycle runs in the mitochondrial matrix, producing CO₂, NADH, FADH₂ and GTP. The electron transport chain that follows is on the inner membrane.

Question 12

The respiratory quotient (RQ) for the oxidation of carbohydrates is:
(a) 1.0 (b) 0.7 (c) 1.3 (d) 0

Accepted Answer

(a) 1.0.

RQ = CO₂ released / O₂ consumed. For carbohydrates it is 1.0; for fats it is about 0.7; for organic acids it exceeds 1.

Question 13

Which plant hormone is a gas and promotes fruit ripening?
(a) ethylene (b) auxin (c) cytokinin (d) abscisic acid

Accepted Answer

(a) ethylene.

Ethylene is the only gaseous plant hormone; it promotes fruit ripening, senescence and abscission and breaks dormancy.

Question 14

The 'stress hormone' that closes stomata during water shortage is:
(a) abscisic acid (b) gibberellin (c) auxin (d) cytokinin

Accepted Answer

(a) abscisic acid.

Abscisic acid (ABA) is the stress/dormancy hormone: it triggers stomatal closure under water stress and enforces seed and bud dormancy.

Question 15

Vernalisation is the promotion of flowering by exposure to:
(a) low temperature (b) short days (c) high light (d) drought

Accepted Answer

(a) low temperature.

Vernalisation is the promotion of flowering by a period of cold treatment, as in winter varieties of wheat, preventing premature flowering before winter.

Practice — Plant Anatomy and Physiology

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