Plant Physiology

Bending of shoot of a plant towards light can be referred to as

[amp_mcq option1=”photonasty” option2=”positive phototropism” option3=”negative phototropism” option4=”photoperiodism” correct=”option2″]

The correct answer is B, positive phototropism.

Phototropism is the growth of a plant in response to a light stimulus. When a plant shoot bends and grows towards the light source, it is exhibiting positive phototropism.

Photonasty is a non-directional plant movement in response to light intensity (e.g., opening and closing of flowers). Negative phototropism is growth away from a light source (e.g., roots). Photoperiodism is the physiological response of an organism to the length of day or night.

The increase in length of stems and roots in plants is due to

[amp_mcq option1=”lateral meristem” option2=”intercalary meristem” option3=”apical meristem” option4=”secondary growth” correct=”option3″]

The increase in length of stems and roots in plants is primarily due to the activity of apical meristems, located at the tips of shoots and roots. This growth is known as primary growth.

– Meristems are regions of actively dividing cells in plants responsible for growth.
– Apical meristems are located at the shoot apex and root apex and are responsible for primary growth (increase in length).
– Lateral meristems (vascular cambium and cork cambium) are responsible for secondary growth (increase in girth or diameter).
– Intercalary meristems are located between mature tissues (e.g., at nodes of grasses) and contribute to elongation in those specific regions.

Primary growth results in the formation of primary tissues (epidermis, ground tissues, primary xylem, and primary phloem). Secondary growth, mediated by lateral meristems, results in the formation of secondary tissues (e.g., wood and bark), leading to an increase in thickness, common in woody plants. While intercalary meristems cause elongation, the overall increase in length of the main axis of stems and roots is driven by apical meristems.

Which one of the following statements about transport mechanism in plants is correct?

[amp_mcq option1=”Diffusion of ions and small molecules across cell membrane requires energy.” option2=”Active transport of ions and small molecules across cell membrane against concentration gradient requires energy.” option3=”Cells conserve energy and no energy is required for transport of ions and small molecules against concentration gradient.” option4=”Cells do not transport ions across their membrane as these are charged molecules.” correct=”option2″]

The correct answer is B) Active transport of ions and small molecules across cell membrane against concentration gradient requires energy.

Statement A is incorrect: Diffusion (simple or facilitated) is a passive process driven by the concentration gradient; it does not require metabolic energy (ATP).
Statement B is correct: Active transport involves moving substances across a cell membrane against their concentration gradient (from a region of lower concentration to a region of higher concentration). This process requires the cell to expend metabolic energy, usually in the form of ATP, to power transport proteins (pumps).
Statement C is incorrect: Moving substances against a concentration gradient requires energy input. Cells use active transport precisely for this purpose, even though it consumes energy.
Statement D is incorrect: Cells regularly transport ions across their membranes using both passive mechanisms (ion channels) and active mechanisms (ion pumps) to maintain electrochemical gradients, osmotic balance, and for signalling. Ions are charged molecules, but their transport is essential for cell function.

Transport across cell membranes can be broadly classified into passive transport (diffusion, facilitated diffusion) and active transport. Passive transport does not require energy input and follows concentration gradients. Active transport requires energy and can move substances against gradients. Plants, like other organisms, use both types of transport for uptake of nutrients from the soil and for movement of substances within the plant.

How is the rate of transpiration affected by decreasing humidity and by decreasing light intensity ?

[amp_mcq option1=”Decreasing humidity: Decreases, Decreasing light intensity: Decreases” option2=”Decreasing humidity: Increases, Decreasing light intensity: Decreases” option3=”Decreasing humidity: Increases, Decreasing light intensity: Increases” option4=”Decreasing humidity: Decreases, Decreasing light intensity: Increases” correct=”option2″]

Decreasing humidity increases the rate of transpiration, while decreasing light intensity decreases the rate of transpiration.

– Transpiration is the loss of water vapor from plants, primarily through stomata on leaves.
– Humidity affects the water potential gradient: Lower humidity in the air increases the difference in water potential between the leaf’s interior and the surrounding air, driving water vapor out faster.
– Light intensity affects stomatal opening: Generally, stomata open in the light to allow CO2 intake for photosynthesis. Reduced light intensity causes stomata to close, reducing water loss through transpiration.

Other factors affecting transpiration rate include temperature (higher temperature increases evaporation), wind speed (moderate wind increases, strong wind can decrease by drying the leaf surface and causing stomatal closure), and soil water availability (low water availability leads to stomatal closure).

Leaves of lotus and water lily are not easily wet because the leaves

• 1. have surface uneven in micro-scale and water cannot come into contact with the depressed areas due to high surface tension
• 2. contain an oily substance
• 3. contain a greasy substance
• 4. have surface too smooth to attract water

Select the correct answer using the code given below.

[amp_mcq option1=”1 and 3 only” option2=”3 and 4″ option3=”1 and 2 only” option4=”1, 2 and 3″ correct=”option4″]

The correct option is D. Leaves of lotus and water lily are not easily wet because of the combined effect described in statements 1, 2, and 3.

The ‘lotus effect’ refers to the superhydrophobicity and self-cleaning property of lotus leaves. This is primarily due to the hierarchical microscopic and nanoscopic structure on the leaf surface (statement 1) combined with the presence of hydrophobic substances like epicuticular waxes (statements 2 and 3). The surface structure creates a rough texture where water droplets sit on the tips of micro-papillae, trapping air beneath them (Cassie-Baxter state). This minimizes contact area between water and the leaf surface, amplified by the low surface energy provided by the waxes (oily/greasy substances), resulting in high contact angles and low adhesion for water droplets. Statement 4 is incorrect as smoothness generally increases wetting.

Statement 1 describes the crucial structural aspect and its physical consequence (water cannot fully contact depressed areas, leading to high surface tension effects like droplet formation). Statements 2 and 3 describe the chemical composition of the coating (waxes), which are hydrophobic (water-repelling) and are typically described as oily or greasy. Both the structure and the hydrophobic coating are essential for the lotus effect.

Plants that behave as a Xerophyte in one season and as hydrophyte in another season is known as :

[amp_mcq option1=”Saprophytes” option2=”Tropophytes” option3=”Heliotrophytes” option4=”Virotophytes” correct=”option2″]

The correct option is B) Tropophytes.

Tropophytes are plants adapted to tropical climates with distinct alternating wet and dry seasons. They exhibit characteristics that allow them to survive during the dry period (e.g., shedding leaves) and thrive during the wet period, effectively behaving as xerophytes in one season and hydrophytes in another in terms of their physiological and morphological adaptations to water availability.

Saprophytes obtain nutrients from dead organic matter. Heliotropism is the growth or movement of a plant in response to sunlight. Xerophytes are plants adapted to very dry environments, and Hydrophytes are plants adapted to grow in water or very wet conditions.