Free Forms and Functions of Plants MCQs with Answers

101. Why do some vegetables lose water when salt is applied to them?

• A. Due to the less negative water potential of the external environment than the cell
• B. Due to the more negative water potential of the external environment than the cell
• C. Due to the less positive water potential of the external environment than the cell
• D. Due to more positive water potential of the external environment than the cell

Explanation: When salt is applied to vegetables, it dissolves and creates a solution with a more negative water potential. This results in a water potential gradient where the internal water potential of the vegetable cells, being less negative, causes water to move out of the cells into the external environment to reach equilibrium. In simpler words due to the presence of salt the solute potential on the surface of the vegetable increases while the water potential decreases as compared to the inside, due to watch water moves out of the cell to the surface.

102. Who proposed the starch-sugar hypothesis?

• A. Ernst munch
• B. Robert Hooke
• C. Mohl
• D. Darwin

Explanation: The starch-sugar hypothesis is one hypothesis that explains the opening and closing of stomata. It was proposed by German botanist H. Mohl.

103. Pressure flow theory was formulated by

• A. Ernst Munch
• B. Charles Darwin
• C. Robert Brown
• D. Robert Hooke

Explanation: The pressure-flow hypothesis was formulated by Ernst Münch in 1930.The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem. Glucose generated by photosynthesis at the source is converted to sucrose which is moved to the phloem sieve tube cells through the companion cell by active transport. The remaining transport in the phloem is carried out by the differences in the osmotic pressure, which facilitates the transport from higher pressure to lower pressure regions of the sink. Again by active transport, the sucrose is transported from phloem to the cells of the sink where it will be stored for a long.

104. Which of these cells is not present in phloem?

• A. Companion cells
• B. Sieve tube members
• C. Vessels
• D. Parenchyma

Explanation: Phloem components are sieve tubes, companion cells, phloem fibres, and phloem parenchyma cells.The main components of the xylem are the xylem tracheid, vessels, and xylem parenchyma.

105. In roots the apoplast pathway of water is disrupted when water reaches:

• A. Plasmodcsmala
• B. Cortex
• C. Endodermis
• D. Pith

Explanation: In roots, the apoplast pathway of water is disrupted when water reaches the endodermis. The endodermis is a specialized layer of cells in the root that is characterized by the presence of the Casparian strip, a waxy barrier made of suberin. The Casparian strip blocks the apoplastic movement of water and minerals, forcing substances to enter the symplast pathway by crossing the cell membranes of the endodermal cells.

106. Opening and closing of stomata is due to the:

• A. Hormonal signals affecting guard cells
• B. Change in turgor pressure of guard cells
• C. Role in gaseous exchange
• D. Impact of plant respiration

Explanation: The correct answer is that the opening and closing of stomata are driven by changes in the turgor pressure of guard cells (Option B). When guard cells absorb water, they become turgid, causing the stomatal pores to open. Conversely, when they lose water, they become flaccid, leading to the closure of the pores. Option A, concerning hormonal signals, does play a regulatory role but does not directly cause the movement. Options C and D, which mention gaseous exchange and plant respiration, describe processes facilitated by stomata but do not influence their opening and closing directly.

107. In guard cells when sugar is converted into starch, the stomatal pore

• A. Opens partially
• B. Closes completely
• C. Opens completely
• D. Remains unchanged

Explanation: The correct answer is that the stomatal pore closes completely when sugar is converted into starch in guard cells. This conversion decreases the osmotic potential, causing water to exit the cells and leading to a loss of turgor pressure. As a result, the guard cells become flaccid and the stomatal pore closes, preventing gas exchange and water loss. The other options are incorrect because they fail to account for the osmotic changes and resulting turgor pressure reduction that cause the stomatal closure.

108. A rye plant less than _ tall has branch roots about:

• A. Two meters
• B. Five meters
• C. One meter
• D. Half meter

Explanation: The correct answer is "One meter". A rye plant less than one meter tall can develop branch roots with a combined length of over 600 kilometers, allowing it to access a large volume of soil for nutrients and water. The other options describe unrealistic sizes for rye plants and their root systems when they are less than one meter tall.

109. Most of mycorrhizae are present in:

• A. 50% of vascular plants
• B. 70% of angiosperms
• C. 70% of gymnosperms
• D. 90% of angiosperms

Explanation: Answer is "90% of angiosperms"Explanation: Mycorrhizal fungi get sugar and shelter from the plant, and in exchange increase the plant's mineral nutrient uptake efficiency. Mycorrhizae are present in 90% families of flowering plants.

110. The xylem water tension is strong enough to pull water to:

• A. 200 meters
• B. 400 feet
• C. 300 meters
• D. 500 feet

Explanation: The correct answer is "200 meters." Xylem water tension, a result of transpiration and the cohesive and adhesive properties of water, can pull water to great heights in plants, up to around 200 meters. This limit is determined by the physical properties of water and the structure of the xylem. The other options represent heights that are either within a typical range but not the maximum (400 feet, 500 feet) or exceed the maximum observed in nature (300 meters).