Free Forms and Functions of Plants MCQs with Answers

231. In chlorophyll 'a', the group attached to prophyrine ring is

• A. hydroxyl group
• B. methyl group
• C. carboxyl group
• D. aldehyde group

Explanation: Chlorophyll 'a' is an essential pigment in photosynthesis, and its structure includes a porphyrin ring. Attached to this porphyrin ring is a methyl group (CH3). This is a distinguishing feature of chlorophyll 'a' as opposed to chlorophyll 'b', which has a formyl group instead. The hydroxyl, carboxyl, and aldehyde groups are not part of chlorophyll 'a's core structure.

232. Sunken stomata are present in:

• A. Hydrophytes
• B. Xerophytes
• C. Mesophytes
• D. All of the above

Explanation: Sunken stomata are a characteristic adaptation found in xerophytes, which are plants adapted to dry, arid environments. This adaptation helps reduce water loss by protecting the stomata from direct exposure to the air, thereby minimizing transpiration. Hydrophytes, on the other hand, have adaptations suitable for water-rich environments and do not need to conserve water in the same way. Mesophytes live in environments with moderate water supply and do not have sunken stomata. Therefore, the correct answer is xerophytes.

233. Chlorophyll a and b chiefly absorb:

• A. Violet blue light
• B. Orange light
• C. Blue-red light
• D. Red, orange light

Explanation: Chlorophyll a and b primarily absorb blue and red light. Blue light, being high in energy, excites electrons to a higher energy level, while red light boosts electrons to a lower energy level compared to blue light. Green light is not absorbed but rather reflected, giving plants their green color.

234. A set of xylem tissues are:

• A. Vessels, tracheids, parenchyma
• B. Sieve tubes, companion cells, fibers
• C. Parenchyma, sieve tube, vessels
• D. Fibers, companion cells, tracheids

Explanation: Xylem tissue is primarily responsible for water transport in plants and consists of four main components: tracheids, vessels, parenchyma, and fibers. Option A correctly lists these components. The other options include elements that belong to phloem tissue, such as sieve tubes and companion cells, which are involved in the transport of nutrients.

235. Carotenoid contains:

• A. Carotenes
• B. Xanthophylls
• C. Chlorophyll - C
• D. Both (A) and (B)

Explanation: The carotenoids are divided into two main classes: carotenes and xanthophylls. Carotenes are pure hydrocarbons, meaning they consist only of carbon and hydrogen. Xanthophylls are similar to carotenes but have one or more oxygen atoms in their structure. Although both are types of carotenoids, chlorophylls, such as chlorophyll - C, are not related to carotenoids but are rather a different group of pigments involved in photosynthesis. Therefore, the correct answer is that carotenoids contain both carotenes and xanthophylls.

236. The attraction of water molecules to the xylem vessels is called:

• A. Adhesion
• B. Cohesion
• C. Collision
• D. Corrosion

Explanation: The correct answer is Adhesion. Adhesion describes the attraction between unlike molecules. In the context of xylem vessels, it refers to the attraction between water molecules and the molecules in the walls of the xylem. This interaction helps water move upwards through the plant. Cohesion, on the other hand, describes the attraction between similar molecules, such as water molecules themselves, which assists in maintaining a column of water inside the xylem. Collision involves physical interactions that lead to changes in motion, which is not applicable here. Corrosion is a chemical process affecting metals, not relevant to plant physiology.

237. The concentration of water molecules is inversely proportional to the:

• A. Water potential
• B. Pressure potential
• C. Solute potential
• D. Osmotic potential

Explanation: The correct answer is Solute potential. The concentration of water molecules is inversely proportional to solute potential because when solute concentration increases, it lowers the water potential, thus decreasing the concentration of free water molecules. Water moves from areas of higher water potential (lower solute concentration) to areas of lower water potential (higher solute concentration), which is the principle of osmosis. Water potential encompasses solute potential, but it also includes pressure potential, which is not directly related to solute concentration. Therefore, the direct inverse relationship is with solute or osmotic potential.

238. Bulliform cells are present in:

• A. Grasses
• B. Under ground stems
• C. Fruit-nuts
• D. Cabbage leaves

Explanation: Bulliform cells or motor cells are large, bubble-shaped epidermal cells that occur in grps on the upper surface of the leaves of many monocots. Grass is monocot and contains bulliform cells.

239. Stroma of chloroplasts carries the fixation of

• A. N2
• B. O2
• C. CO2
• D. NH3

Explanation: The stroma of chloroplasts is where the Calvin cycle occurs, which is responsible for fixing carbon dioxide (CO2) into organic molecules like glucose. This process uses ATP and NADPH generated during the light-dependent reactions. In contrast, nitrogen fixation, crucial for converting atmospheric nitrogen (N2) into a form usable by plants, is performed by certain bacteria. Oxygen (O2) is a byproduct, not a fixed compound in photosynthesis, and ammonia (NH3) is involved in processes outside the chloroplast.

240. In chlorophyII-b, the porphyrine ring is attached to the:

• A. Methyl group
• B. Carboxyl group
• C. Aldehyde group
• D. Hydroxyl group

Explanation: The porphyrin ring in chlorophyll-b is specifically attached to an aldehyde group, which includes a carbonyl group (C=O) bonded to a hydrogen atom. This distinguishes it from chlorophyll-a, where the attachment is a methyl group. Methyl groups (CH3) are simple carbon groups not present in chlorophyll-b's structure. Carboxyl groups (COOH) and hydroxyl groups (OH) are not involved in the attachment of the porphyrin ring in chlorophyll-b.