Plant Physiology

21. Damage to the apical meristem of a growing young plant will affect the

Damage to the apical meristem of a growing young plant will affect the

[amp_mcq option1=”length of the plant” option2=”colour of the flower” option3=”colour of the leaves” option4=”taste of the fruits” correct=”option1″]

This question was previously asked in
UPSC NDA-2 – 2018
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Damage to the apical meristem of a growing young plant will primarily affect its length.
– Apical meristems are located at the tips of shoots and roots.
– They are responsible for primary growth, which results in an increase in the length of the plant.
– Damage to these meristems inhibits or stops this primary growth.
Other types of meristems include lateral meristems (like cambium), responsible for secondary growth (increase in girth or diameter), and intercalary meristems (found at the base of leaves or internodes), responsible for increasing the length of internodes. The colour of flowers or leaves is related to pigments, and the taste of fruits is related to metabolic products, none of which are directly and immediately affected by damage to the apical meristem as significantly as the plant’s length.

22. Consider the following statements about cactus : 1. The leaves are r

Consider the following statements about cactus :

  • 1. The leaves are reduced to spines.
  • 2. The stem does the photosynthesis.

Which of the statements given above is/are correct ?

[amp_mcq option1=”1 only” option2=”2 only” option3=”Both 1 and 2″ option4=”Neither 1 nor 2″ correct=”option3″]

This question was previously asked in
UPSC NDA-2 – 2016
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Both statements about cactus adaptations are correct. Cacti are succulents adapted to arid environments. Their leaves are typically reduced to spines to minimize water loss through transpiration and provide defense. The fleshy green stems take over the function of photosynthesis, which is usually carried out by leaves in most plants.
– Statement 1 is correct: Reduction of leaves to spines is a key adaptation of cacti to reduce surface area and thus water loss through transpiration in hot, dry climates. Spines also deter herbivores.
– Statement 2 is correct: Cacti stems contain chlorophyll and are the primary sites of photosynthesis in the absence of significant leaf area. They are also succulent, storing water.
Cacti also have other adaptations for survival in arid environments, such as shallow but extensive root systems to absorb water quickly from rainfall, a waxy cuticle on the stem to reduce evaporation, and CAM photosynthesis, which allows them to keep their stomata closed during the day to conserve water.

23. During a laboratory experiment, a student immerses epidermal leaf peel

During a laboratory experiment, a student immerses epidermal leaf peel in a hypertonic solution. After some time, the student examined the cells under a microscope and observed that :

[amp_mcq option1=”the cells swelled.” option2=”the cells were plasmolysed.” option3=”the cells built up turgor pressure.” option4=”the cells size was unaffected.” correct=”option2″]

This question was previously asked in
UPSC NDA-1 – 2023
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A hypertonic solution is a solution that has a higher solute concentration (and thus a lower water potential) compared to the inside of the plant cell. When a plant cell is placed in a hypertonic solution, water moves out of the cell’s cytoplasm and vacuole into the surrounding solution by osmosis. This loss of water causes the protoplast (the cell membrane and its contents) to shrink and pull away from the rigid cell wall. This phenomenon is known as plasmolysis.
– A hypertonic solution has a higher solute concentration outside the cell.
– Water moves out of the cell by osmosis into the hypertonic solution.
– The protoplast shrinks and pulls away from the cell wall.
– This process is called plasmolysis.
In a hypotonic solution (lower solute concentration outside), water moves into the cell, causing it to swell and build up turgor pressure against the cell wall. In an isotonic solution (equal solute concentration), there is no net movement of water, and the cell size remains relatively unaffected, although turgor pressure is zero.

24. Browning of the chopped apple can be minimized by :

Browning of the chopped apple can be minimized by :

[amp_mcq option1=”using table sugar.” option2=”preserving in a container.” option3=”using lemon juice.” option4=”using milk of magnesia.” correct=”option3″]

This question was previously asked in
UPSC NDA-1 – 2023
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The correct answer is C) using lemon juice.
Browning of chopped apples is caused by enzymatic oxidation, specifically the action of the enzyme polyphenol oxidase when exposed to oxygen. Lemon juice contains citric acid and ascorbic acid (Vitamin C). The acidity lowers the pH, which inhibits the enzyme’s activity, and ascorbic acid is an antioxidant that preferentially reacts with oxygen, preventing the oxidation of phenolic compounds.
Other methods to minimize browning include using other acidic solutions (like pineapple juice or vinegar), covering the apple surface to reduce oxygen exposure, or blanching (briefly heating) to denature the enzyme, although blanching can alter texture. Using milk of magnesia (a base) would increase the pH and likely promote enzymatic activity, worsening browning. Sugar might help reduce water activity but is not effective against enzymatic browning.

25. In aquatic plants, large air sacs give them buoyancy effects. These sa

In aquatic plants, large air sacs give them buoyancy effects. These sacs are surrounded by which one of the following types of tissues?

[amp_mcq option1=”Parenchyma” option2=”Collenchyma” option3=”Sclerenchyma” option4=”Complex tissue” correct=”option1″]

This question was previously asked in
UPSC NDA-1 – 2022
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In aquatic plants, large air sacs or cavities that provide buoyancy are modifications of parenchyma tissue. This specialized parenchyma tissue with extensive intercellular air spaces is called aerenchyma. Aerenchyma facilitates gas exchange in submerged tissues and provides buoyancy, allowing the plant to float or remain upright in water.
Aerenchyma, a type of parenchyma tissue characterized by large air spaces, provides buoyancy and aids gas exchange in aquatic plants.
Collenchyma provides mechanical support to growing parts of the plant. Sclerenchyma provides rigid support and mechanical strength to mature parts of the plant. Complex tissues like xylem and phloem are responsible for transport of water, minerals, and food.

26. In a dicot pot herb, vaseline/vegetable oil was applied on the upper s

In a dicot pot herb, vaseline/vegetable oil was applied on the upper surface of one leaf (Experimental leaf 1) and on the lower surface of another leaf (Experimental leaf 2). Vaseline/Vegetable oil was not applied on the control leaf. The plant was deliberately not watered for several days. Which leaf will dry up last?

[amp_mcq option1=”Experimental leaf 1″ option2=”Experimental leaf 2″ option3=”Control leaf” option4=”All the leaves will dry up simultaneously” correct=”option2″]

This question was previously asked in
UPSC NDA-1 – 2021
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The correct answer is B) Experimental leaf 2. Applying vaseline/vegetable oil to the lower surface of the leaf blocks most of the stomata, significantly reducing water loss through transpiration.
– Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.
– Stomata are pores on the leaf surface, primarily on the lower surface in dicots, that regulate gas exchange and transpiration.
– Blocking stomata reduces the rate of transpiration and thus water loss.
– Experimental leaf 1 has vaseline on the upper surface, leaving most stomata on the lower surface open, so it will lose water almost as fast as the control leaf.
– The control leaf loses water normally from both surfaces (mainly lower).
– Since Experimental leaf 2 loses the least amount of water due to blocked stomata on the lower surface, it will dry up last among the three leaves when the plant is not watered.

27. Which one of the following is NOT a component of conducting tissue in

Which one of the following is NOT a component of conducting tissue in plants ?

[amp_mcq option1=”Fibres” option2=”Tracheids” option3=”Pericycle” option4=”Sieve tubes” correct=”option3″]

This question was previously asked in
UPSC NDA-1 – 2019
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The correct answer is C) Pericycle.
Conducting tissues in plants are xylem and phloem, which are responsible for the transport of water, minerals, and food. Components of xylem include tracheids, vessels, xylem parenchyma, and xylem fibres. Components of phloem include sieve tubes, companion cells, phloem parenchyma, and phloem fibres. Fibres (both xylem and phloem fibres), Tracheids (xylem), and Sieve tubes (phloem) are all components of the conducting tissues. The pericycle is a layer of parenchyma cells located just inside the endodermis in the root and stem, surrounding the vascular tissue. It is involved in the formation of lateral roots and secondary growth (vascular cambium and cork cambium) but is not considered a part of the vascular or conducting tissue itself.
Vascular tissues are complex tissues composed of different cell types working together for transport. Xylem transports water and minerals from roots to leaves, while phloem transports sugars (food) from leaves to other parts of the plant. The pericycle is meristematic in some cases and plays a crucial role in the development of lateral organs and thickening growth, but its primary function is not conduction.

28. Which one of the following statements about meristematic tissues in pl

Which one of the following statements about meristematic tissues in plants is correct ?

[amp_mcq option1=”These are dead tissues and form wood” option2=”They provide flexibility to plant due to their thickened walls” option3=”These are present in the bark of a tree only” option4=”Growth occurs in plants due to division of cells of these tissues” correct=”option4″]

This question was previously asked in
UPSC NDA-1 – 2018
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Statement D is correct. Meristematic tissues are composed of actively dividing cells responsible for plant growth, both in length (primary growth from apical meristems) and in girth (secondary growth from lateral meristems).
– Meristematic tissues are characterized by thin-walled, actively dividing cells.
– They are found in regions of active growth like root and shoot tips (apical meristems) and cambium layers (lateral meristems).
– Statement A is incorrect; meristematic tissues are living. Wood is primarily composed of secondary xylem, much of which consists of dead cells.
– Statement B is incorrect; meristematic cells have thin walls. Tissues like collenchyma provide flexibility due to thickened walls.
– Statement C is incorrect; meristematic tissues are found at various growing points, not just in the bark (though lateral meristems contribute to bark formation).

29. The accidental touch of Nettle leaves creates a burning sensation, whi

The accidental touch of Nettle leaves creates a burning sensation, which is due to inject of

[amp_mcq option1=”Hydrochloric acid” option2=”Methanoic acid” option3=”Citric acid” option4=”Sulphuric acid” correct=”option2″]

This question was previously asked in
UPSC NDA-1 – 2018
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The correct answer is B) Methanoic acid.
When you touch a nettle plant, the stinging hairs (trichomes) inject irritating chemicals into the skin. One of the primary compounds responsible for the burning sensation and rash is methanoic acid, also known as formic acid (HCOOH). Other irritants present include histamine, acetylcholine, and serotonin, which contribute to the inflammatory response.
Formic acid is a simple carboxylic acid found naturally in the venom of ants and bee stings, as well as in nettle stings. Its chemical formula is HCOOH. While other substances are involved in the nettle sting reaction, methanoic acid is a major contributor to the immediate burning pain.

30. Which one among the following is living and non-nucleated at maturity

Which one among the following is living and non-nucleated at maturity ?

[amp_mcq option1=”Sieve tubes” option2=”Companion cells” option3=”Collenchyma” option4=”Parenchyma” correct=”option1″]

This question was previously asked in
UPSC Geoscientist – 2024
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A
Sieve tubes are component cells of the phloem, responsible for the transport of sugars. At functional maturity, sieve tube elements are living cells but have lost their nucleus, vacuole, and other major organelles. They rely on associated companion cells for metabolic support. Companion cells, collenchyma, and parenchyma are all living and nucleated at maturity.
The absence of a nucleus and other organelles in mature sieve tube elements allows for efficient transport of phloem sap. Despite lacking a nucleus, they are considered living because they maintain a functioning plasma membrane and some cytoplasmic components, supported by the companion cells which are connected to them via plasmodesmata.
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