All Free Biology MCQs with Answers

1241. Water potential of pure water is__________?

• A. zero
• B. one
• C. negative
• D. two

Explanation: Water potential is defined relative to pure water, which is assigned a value of 0 MPa under standard reference conditions. Solutions have lower, usually negative, water potential, so students may incorrectly choose negative by applying the rule for a solution to pure water.

1242. Shrinkage of protoplast due to exosmosis of water is__________?

• A. imbibition
• B. plasmolysis
• C. deplasmolysis
• D. adhesion

Explanation: Plasmolysis occurs when a plant cell loses water by exosmosis, causing the protoplast to shrink away from the cell wall. Deplasmolysis is the reverse process after water re-enters the cell, so it is the likely distractor for students who confuse water loss with water gain.

1243. The following vegetable have 90% of water?

• A. Cabbage
• B. Lady finger(okra)
• C. Cassava
• D. Non of these

Explanation: Lady finger, or okra, contains approximately 90% water, although the exact value varies with variety and measurement method. Cabbage also has a high water content, but it is commonly reported as slightly above 90%, while cassava contains much less water. Students may choose cabbage because it is a watery vegetable, but the question is referring to the approximate value for okra.

1244. Thick, waxy & leathery cuticle around leaves is present in___________?

• A. Hydrophytes
• B. Mesophytes
• C. Xerophytes
• D. Halophytes

Explanation: Xerophytes are plants adapted to dry habitats and commonly have a thick, waxy cuticle that reduces evaporation from leaf surfaces. Hydrophytes usually have reduced cuticles because water is abundant, so choosing hydrophytes reverses the relationship between habitat and water conservation.

1245. Rose is an example of____________?

• A. Hydrophytes
• B. Mesophytes
• C. Xerophytes
• D. Halophytes

Explanation: Rose grows best where water is reasonably available but not continuously abundant, so it is classified as a mesophyte. Students may choose xerophyte because roses can tolerate some dry conditions, but xerophytes are specially adapted to very arid habitats.

1246. Stomata open due to _________ of K+ into the guard cells from the surrounding epidermis

• A. Diffusion
• B. Active transport
• C. Osmosis
• D. All of these

Explanation: Light activates ion transport mechanisms in guard cells, and K+ is accumulated from surrounding cells by active transport. The increased solute concentration lowers the guard cells' water potential, so water enters by osmosis and the stomata open. Students may choose osmosis because water movement follows K+ uptake, but osmosis moves water, not K+ into the guard cells.

1247. Addition of salts and other solutes from other cells into xylem sap, __________ the water potential of the xylem sap

• A. Increases.
• B. Lowers.
• C. Doesn't effect.
• D. Maintains.

Explanation: Adding salts and other solutes makes the xylem sap more concentrated, which lowers its water potential. Water therefore has a greater tendency to move toward that solution by osmosis or along a water-potential gradient. Students may choose increases because more dissolved material means a larger numerical solute concentration, but water potential becomes more negative as solute concentration rises.

1248. Symbionts which help plants in uptake of phosphorous and trace metals such as zinc and copper.

• A. Bacteria
• B. Viruses
• C. Fungi
• D. Cyanobacteria

Explanation: Mycorrhizal fungi form symbiotic associations with plant roots and extend fungal hyphae through the soil, increasing the area from which phosphorus and trace metals such as zinc and copper can be absorbed. The plant supplies carbohydrates to the fungus in return. Students may choose bacteria because some bacteria are plant symbionts, but the classic symbionts responsible for this mineral uptake are fungi.

1249. Low level of CO2 favours _________ of the stomata.

• A. Opening
• B. Closure
• C. Both of these
• D. None of these

Explanation: Low carbon dioxide concentration, especially inside the leaf, promotes stomatal opening so that more CO2 can enter for photosynthesis. High internal CO2 generally signals that sufficient carbon dioxide is available and favours closure. Students may choose closure by confusing low CO2 with drought stress, which causes closure through water conservation.

1250. There are _________ hypothesis which may explain opening and closing of stomata?

• A. One
• B. Two
• C. Three
• D. Four

Explanation: The two commonly taught explanations for stomatal movement are the starch-sugar hypothesis and the potassium-ion hypothesis. Both explain how changes in guard-cell solutes alter water entry and turgor, producing opening or closing. Students may choose three by counting light, CO2 and water stress as separate hypotheses, but these are factors or signals rather than the main hypotheses.