Plant Physiology Archives

1. In plants, Xylems are responsible for transport of

In plants, Xylems are responsible for transport of

amino acids.

food.

oxygen.

water.

This question was previously asked in

UPSC CISF-AC-EXE – 2021

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Xylem is one of the two types of transport tissue in vascular plants (the other being phloem). The primary function of xylem is to transport water and some dissolved nutrients from the roots to the rest of the plant and also provides structural support.

Xylem tissue consists of tracheary elements (tracheids and vessel elements), which are dead cells that form continuous tubes for water transport, along with parenchyma cells, fibers, and sometimes sclereids. The movement of water in xylem is primarily driven by transpiration pull, evaporation of water from leaves.

Phloem is responsible for transporting sugars (food produced during photosynthesis, primarily sucrose) from the leaves to other parts of the plant where they are needed for growth or storage. Amino acids are also transported in the phloem. Oxygen is obtained by plants directly from the atmosphere through stomata and lenticels for cellular respiration.

2. Which of the following leaf modifications occur(s) in the desert areas

Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss ?

Hard and waxy leaves
Tiny leaves
Thorns instead of leaves

Select the correct answer using the code given below :

2 and 3 only

2 only

3 only

1, 2 and 3

This question was previously asked in

UPSC IAS – 2018

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All three listed leaf modifications are adaptations found in plants in desert areas to minimize water loss through transpiration.
1. Hard and waxy leaves: A thick, waxy cuticle on the leaf surface reduces evaporation of water.
2. Tiny leaves: Reducing the surface area of leaves directly reduces the total surface area available for transpiration.
3. Thorns instead of leaves: Thorns are often modified leaves or branches. If they are modified leaves (e.g., in cacti), they drastically reduce the surface area for transpiration. Thorns also deter herbivores, protecting the plant.

– Desert plants (xerophytes) have adaptations to conserve water.
– Adaptations include reducing leaf surface area and preventing water loss through barriers.
– Waxy cuticle, reduced leaf size, and modifications like thorns are common water-conserving adaptations.

Other adaptations in desert plants include sunken stomata, fleshy stems for water storage, and extensive root systems.

3. Which of the following leaf modifications occurs/occur in desert areas

Which of the following leaf modifications occurs/occur in desert areas to inhibit water loss?

1. Hard and waxy leaves
2. Tiny leaves or no leaves
3. Thorns instead of leaves

Select the correct answer using the codes given below.

1 and 2 only

2 only

1 and 3 only

1, 2 and 3

This question was previously asked in

UPSC IAS – 2013

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All the listed leaf modifications occur in desert areas to inhibit water loss: hard and waxy leaves, tiny leaves or no leaves, and thorns instead of leaves.

Desert plants (xerophytes) have evolved various adaptations to survive in arid environments with limited water availability. 1. Hard and waxy leaves (with thick cuticles) reduce cuticular transpiration. 2. Having tiny leaves or shedding leaves during dry periods minimizes the surface area for transpiration. Some plants have modified stems that photosynthesize instead of leaves. 3. Thorns are often modified leaves or stipules; they drastically reduce the surface area for transpiration and also deter herbivores, preventing tissue damage that could lead to water loss.

Other adaptations in desert plants include sunken stomata, fleshy stems or leaves for water storage (succulence), extensive root systems, and C4 or CAM photosynthesis pathways which are more water-efficient.

4. Many transplanted seedlings do not grow because

Many transplanted seedlings do not grow because

the new soil does not contain favourable minerals

most of the root hairs grip the new soil too hard

most of the root hairs are lost during transplantation

leaves get damaged during transplantation

This question was previously asked in

UPSC IAS – 2013

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Many transplanted seedlings do not grow because most of their root hairs are lost during the transplantation process.

Root hairs are fine, delicate extensions of root epidermal cells that greatly increase the surface area for absorption of water and mineral nutrients from the soil. When a seedling is dug up for transplantation, the soil around the roots is disturbed, and a large number of these fragile root hairs are broken or stripped off. The plant’s ability to absorb water is severely reduced until new root hairs can grow, leading to ‘transplant shock’, wilting, and potentially death if sufficient water uptake cannot be re-established quickly.

While factors like unfavorable soil conditions or leaf damage can also affect transplant success, the primary and most immediate challenge for a transplanted seedling is the drastic reduction in its water absorption capacity due to root hair loss. Proper watering and minimizing root disturbance during transplantation are crucial for survival.

5. Fruits stored in a cold chamber exhibit longer storage life because

Fruits stored in a cold chamber exhibit longer storage life because

exposure to sunlight is prevented

concentration of carbon dioxide in the environment is increased

rate of respiration is decreased

there is an increase in humidity

This question was previously asked in

UPSC IAS – 2013

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Fruits stored in a cold chamber exhibit longer storage life because the low temperature significantly reduces the rate of respiration in the fruits.

Respiration is a metabolic process in fruits that consumes stored sugars and leads to ripening and senescence. By lowering the temperature, this process is slowed down, thereby extending the time before the fruit spoils.

Other factors like preventing sunlight exposure and managing humidity are also important for fruit storage, but reducing the respiration rate through low temperature is the primary mechanism by which cold storage extends shelf life. Controlled atmosphere storage (modifying CO2 and Oxygen levels) is another technique used to further extend storage life by also impacting respiration and other metabolic processes.

6. Phloem tissues are mostly responsible for transport of

Phloem tissues are mostly responsible for transport of

water

oxygen

minerals

food

This question was previously asked in

UPSC CAPF – 2022

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The correct answer is D) food.

Plant vascular tissues consist of xylem and phloem. Xylem is primarily responsible for the transport of water and dissolved minerals from the roots to the rest of the plant. Phloem is primarily responsible for the transport of organic nutrients, mainly sugars (food) produced during photosynthesis in the leaves, to other parts of the plant where they are needed for growth or storage.

The transport of food in the phloem is called translocation and can occur in multiple directions (upwards, downwards, or sideways) depending on the source (where food is produced) and sink (where food is needed) areas. Oxygen is primarily exchanged through stomata on the leaves and lenticels on stems, not transported systemically through vascular tissue in this manner.

7. Which one of the following pairs is not correctly matched?

Which one of the following pairs is not correctly matched?

Positively phototropic : Shoot

Positively geotropic : Root

Chemotropic : Pollen tube

Hydrotropic : Flower

This question was previously asked in

UPSC CAPF – 2021

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Tropisms are directional growth responses of plants to external stimuli. They are named based on the type of stimulus and the direction of growth (positive if towards the stimulus, negative if away).

Positively phototropic growth means growth towards light (e.g., shoots). Positively geotropic growth means growth towards gravity (e.g., roots growing downwards). Chemotropic growth is a response to chemical stimuli (e.g., pollen tube growing towards the ovule guided by chemical signals). Hydrotropic growth is a response to water (e.g., roots growing towards water). Flowers are reproductive structures whose position and development are influenced by factors like light (photoperiodism for flowering) and hormones, but ‘hydrotropism’ is not a primary or characteristic tropic response of flowers themselves. Roots exhibit positive hydrotropism.

Other types of tropism include thigmotropism (response to touch) and thermotropism (response to temperature). The statement ‘Hydrotropic : Flower’ is the incorrectly matched pair as hydrotropism is characteristic of roots.

8. Which one of the following plant tissues has large air spaces?

Which one of the following plant tissues has large air spaces?

Sclerenchyma

Meristem

Collenchyma

Aerenchyma

This question was previously asked in

UPSC CAPF – 2021

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The question asks for a plant tissue characterized by large air spaces.
Let’s consider the options:
A) Sclerenchyma: This tissue provides mechanical support. It consists of cells with heavily thickened, often lignified walls, and the cells are usually dead at maturity. It does not contain large air spaces.
B) Meristem: Meristematic tissues consist of actively dividing cells involved in plant growth. The cells are small, thin-walled, and densely packed without significant intercellular spaces.
C) Collenchyma: This tissue provides mechanical support to growing parts of the plant. It consists of living cells with unevenly thickened primary cell walls. While there might be small intercellular spaces, they are not characterized by *large* air spaces.
D) Aerenchyma: This is a specialized type of parenchyma tissue that contains extensive intercellular air spaces. The word “aerenchyma” literally means “air tissue”. These air spaces facilitate gas exchange in plants growing in low-oxygen environments (like wetlands) and provide buoyancy to aquatic plants.
Therefore, Aerenchyma is the plant tissue with large air spaces.

– Understand the structure and function of different types of plant tissues.
– Recognize that aerenchyma is a specialized tissue adapted for gas exchange and buoyancy due to its large air spaces.
– Distinguish aerenchyma from other support tissues like sclerenchyma and collenchyma, and growth tissue like meristem.

Aerenchyma is often found in the stems and roots of aquatic plants (hydrophytes) and plants in marshy or waterlogged soils. It is a modification of parenchyma tissue, which is the most common type of ground tissue in plants.

9. Which one of the following statements about the Acacia tree is/are cor

Which one of the following statements about the Acacia tree is/are correct ?

1. It has a long shallow root system which enables it to find moisture
2. It has thorny leaves to prevent water loss
3. It has wide crown so the foliage can absorb the maximum Sunlight

Select the correct answer using the code given below :

1 only

2 and 3 only

1 and 2 only

1, 2 and 3

This question was previously asked in

UPSC CAPF – 2020

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All three statements about the Acacia tree are correct as adaptations for survival in arid/semi-arid and open environments.

1. A long shallow root system allows rapid absorption of infrequent surface rainfall common in dry areas.
2. Thorny stems/branches (often associated with leaves) deter herbivores, which is crucial for survival in environments where plant resources are scarce. While the phrasing “thorny leaves to prevent water loss” is botanically imprecise, thorns protect the plant, including its water-containing parts (leaves), indirectly contributing to survival in a water-limited environment. Also, reduced leaf size is a key adaptation for water loss prevention, often found in arid Acacias.
3. A wide crown maximizes light capture in open habitats like savannas, allowing for efficient photosynthesis when water is available.

Acacia species exhibit a range of adaptations depending on their specific environment, but the characteristics listed are common in many Acacias found in arid and semi-arid regions and savannas globally, helping them survive dry spells, intense sunlight, and herbivory.

10. Epidermal cells of plant roots increase their absorption surface by

Epidermal cells of plant roots increase their absorption surface by having

Scales

Root hairs

Endodermis

Stomata

This question was previously asked in

UPSC CAPF – 2019

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The correct answer is B, Root hairs.

Epidermal cells of plant roots often develop thin, hair-like extensions called root hairs. These significantly increase the surface area of the root epidermis, maximizing the absorption of water and dissolved mineral nutrients from the soil.

Scales are modified leaves. The endodermis is an inner layer of the root cortex that regulates the movement of water and minerals. Stomata are pores on leaves and stems used for gas exchange.