Plant Physiology

Which one among the following is not a feature of Xerophytes ?

[amp_mcq option1=”Smaller leaves” option2=”Large number of stomata” option3=”Waxy cuticle” option4=”Stomata in pits” correct=”option2″]

Xerophytes are plants adapted to arid conditions and have features that reduce water loss. A large number of stomata would lead to high transpiration and water loss, which is contrary to the adaptations of xerophytes.

Xerophytic adaptations aim at reducing water loss (e.g., reduced leaf surface area, thick cuticle, sunken stomata) or storing water.

Typical xerophytic features include smaller leaves (or modified into spines), thick waxy cuticles, sunken stomata or stomata located in pits, presence of trichomes (hairs) to trap moisture, and often succulent tissues for water storage. They tend to have fewer stomata per unit area or stomata that are effectively protected from dry air.

Xylem in the plants are responsible for the transport of :

[amp_mcq option1=”Water” option2=”Water and dissolved minerals” option3=”Gases” option4=”Food” correct=”option2″]

Xylem is the primary water-conducting tissue in vascular plants. It transports water and dissolved inorganic nutrients (minerals) absorbed by the roots upwards to the rest of the plant, especially the leaves.

Xylem and Phloem are the two main transport tissues in plants, forming the vascular system.

Phloem is responsible for the translocation of sugars (food produced during photosynthesis) from the leaves to other parts of the plant. Xylem also provides structural support to the plant body.

Water goes up through xylem vessels in tall trees. The process in plants and properties of water that help in upward movement are :

[amp_mcq option1=”Respiration and cohesion” option2=”Transpiration pull, cohesion and adhesion” option3=”Root pressure, cohesion and adhesion” option4=”Transpiration and adhesion” correct=”option2″]

Water movement upwards through xylem vessels in tall trees is primarily explained by the cohesion-tension theory, which relies on transpiration pull, cohesion, and adhesion.

Transpiration pull is the force generated by the evaporation of water from the leaves (transpiration). This pull creates tension in the water column within the xylem. Cohesion is the property of water molecules to stick together due to hydrogen bonding, maintaining an unbroken water column. Adhesion is the property of water molecules to stick to the hydrophilic walls of the xylem vessels, preventing the water column from breaking and helping it climb upwards against gravity.

Root pressure is another mechanism that can push water upwards, but its effect is generally limited and insufficient to raise water to the tops of tall trees, especially during the day when transpiration rates are high. Respiration is a metabolic process for energy release and is not directly involved in the upward movement of water.

The term Phyllotaxy refers to the pattern of :

[amp_mcq option1=”arrangement of leaves.” option2=”branching in stem.” option3=”flower formation on branch.” option4=”arrangement of flowers.” correct=”option1″]

Phyllotaxy is a botanical term that refers specifically to the pattern of arrangement of leaves on the stem of a plant. These patterns are often species-specific and can follow mathematical sequences like the Fibonacci sequence.

Common phyllotaxy patterns include alternate (one leaf per node, alternating sides), opposite (two leaves per node on opposite sides), and whorled (three or more leaves per node).

Branching in stem (option B) refers to the architecture of the stem system. Flower formation on a branch (option C) and arrangement of flowers (option D) relate to the inflorescence, which is the arrangement of flowers on a plant. Phyllotaxy is distinct from these terms.

What is the location of intercalary meristem in plants?

[amp_mcq option1=”Base of the leaves or internodes” option2=”Stems or roots” option3=”Tips of stems and leaves” option4=”Base of flower pedicel” correct=”option1″]

Intercalary meristem is a type of meristematic tissue found at the base of leaves and internodes in plants, particularly monocots like grasses. It is responsible for growth in length in the internodal regions, allowing parts that have already differentiated to elongate.

Apical meristems are found at shoot and root tips (C and parts of B), responsible for primary growth (increase in length). Lateral meristems (vascular cambium, cork cambium) are found in stems and roots (B), responsible for secondary growth (increase in girth). Intercalary meristems are located between mature tissues, enabling growth in regions away from the apical meristem.

The presence of intercalary meristems allows grasses to regrow quickly after being grazed or mowed, as growth can occur from the base of the leaves and stems rather than just from the tips.

Which one of the following acids is secreted by leaves of Nettle that causes painful stings?

[amp_mcq option1=”Methanoic acid” option2=”Citric acid” option3=”Tartaric acid” option4=”Acetic acid” correct=”option1″]

The stinging sensation caused by Nettle leaves (Urtica dioica) is primarily due to the injection of chemicals from specialized hairs (trichomes). One of the main chemicals responsible is formic acid, which is also known by its IUPAC name, methanoic acid (HCOOH).

Methanoic acid (formic acid) is a simple carboxylic acid found in natural sources like ant stings and nettle stings, causing irritation and pain.

Nettle stings also contain other irritating chemicals like histamine, acetylcholine, and serotonin, which contribute to the overall inflammatory response and sensation. Methanoic acid is the systematic name for the smallest carboxylic acid (one carbon atom).

Mature sclerenchyma cells have

[amp_mcq option1=”cellulose wall and are living” option2=”lignified wall and are living” option3=”suberized wall and are dead” option4=”lignified wall and are dead” correct=”option4″]

Mature sclerenchyma cells are characterized by having thick, lignified secondary cell walls and being dead at functional maturity.

Sclerenchyma provides mechanical support to the plant. The lignified walls make them rigid and strong. The two main types of sclerenchyma cells are fibres and sclereids.

Parenchyma and collenchyma cells are living at maturity and typically have cellulose walls. Collenchyma walls may be thickened but usually lack lignin. Suberized walls are found in cork cells (phellem).

Which one of the following statements about phloem is correct?

[amp_mcq option1=”Phloem transports water and minerals.” option2=”Phloem transports photosynthetic products.” option3=”Phloem is a simple tissue.” option4=”Phloem gives support to the plant.” correct=”option2″]

Phloem is the vascular tissue in plants responsible for transporting sugars (primarily sucrose), produced during photosynthesis, from the leaves (source) to other parts of the plant (sink) where they are needed for growth or storage.

Xylem transports water and minerals from the roots upwards. Phloem transports organic nutrients, mainly sugars, throughout the plant. Phloem is a complex tissue made of sieve elements, companion cells, phloem parenchyma, and phloem fibres.

Simple tissues are composed of only one type of cell (e.g., parenchyma, collenchyma, sclerenchyma). Phloem, like xylem, is a complex tissue. Support in plants is primarily provided by sclerenchyma and collenchyma tissues.

Which one of the following features is an indication for modification of stem of a plant?

[amp_mcq option1=”Presence of ‘eye’ on potato” option2=”‘Scale’ found in onion” option3=”‘Tendril’ found in pea” option4=”‘Hair’ present in carrot” correct=”option1″]

The presence of ‘eye’ on potato is an indication for modification of stem of a plant.

Modifications are adaptations of plant parts for specific functions. To identify a modification, we look for features characteristic of the original plant part.
A) ‘Eye’ on potato: An ‘eye’ on a potato is an axillary bud, located at a node. The presence of nodes and internodes is a characteristic feature of stems. Potato tubers are modified underground stems used for storage and vegetative propagation.
B) ‘Scale’ found in onion: Onion bulbs consist of a reduced stem base and fleshy modified leaves (scales) that store food. While the bulb includes a stem component, the ‘scales’ themselves are modified leaves.
C) ‘Tendril’ found in pea: Tendrils in peas are modified leaves or leaflets used for support.
D) ‘Hair’ present in carrot: Carrots are modified taproots. Root hairs are extensions of epidermal cells of roots, not stems.
Thus, the presence of buds (eyes) on a potato directly indicates its stem nature, even though it’s modified into a tuber.

Other examples of stem modifications include rhizomes (ginger), corms (colocasia), bulbs (onion, garlic), runners/stolons (grasses, strawberry), thorns (Bougainvillea, citrus), and cladodes (Opuntia). Root modifications include taproots for storage (carrot, radish), adventitious roots for support (banyan), and pneumatophores for respiration (mangroves).

If the xylem of a plant is mechanically blocked, which of the following functions of the plant will be affected?

[amp_mcq option1=”Transport of water only” option2=”Transport of water and solutes” option3=”Transport of solutes only” option4=”Transport of gases” correct=”option2″]

The correct answer is B) Transport of water and solutes.

Xylem is the primary tissue in vascular plants responsible for transporting water and dissolved mineral nutrients (solutes) from the roots upwards to the rest of the plant, including the leaves. If the xylem is mechanically blocked, this upward movement of both water and solutes will be significantly impaired.

Phloem is another vascular tissue responsible for transporting sugars (produced during photosynthesis) from the leaves to other parts of the plant. Gases are primarily exchanged through stomata on leaves and lenticels on stems, not transported through xylem or phloem in bulk flow. Therefore, blocking xylem specifically affects water and mineral transport.