Solution:

Photorespiration is a process that occurs in plants when the enzyme RuBisCO catalyzes the oxygenation of RuBP (Ribulose-1,5-bisphosphate) instead of carboxylation during the Calvin cycle. This process involves three different cellular organelles:

• Chloroplast: Where the initial oxygenation reaction occurs, producing 3-PGA and 2-phosphoglycolate
• Peroxisome: Where 2-phosphoglycolate is oxidized to glycolate and then to glyoxylate
• Mitochondria: Where glycine is converted to serine with the release of CO₂

This process requires the coordination of all three organelles, making it a unique pathway distributed across different cellular compartments.

Correct Answer: D. Chloroplast, peroxisome and mitochondria

Solution:

The mature female gametophyte in angiosperms (embryo sac) typically follows the Polygonum-type development, which results in a specific configuration:

• 3 cells at the micropylar end: 2 synergids + 1 egg cell
• 3 cells at the chalazal end: 3 antipodal cells
• 1 central cell with 2 polar nuclei (which later fuse to form the diploid secondary nucleus)

This configuration gives a total of 7 cells (3 antipodal cells + 1 central cell + 1 egg cell + 2 synergids) containing 8 nuclei (3 in antipodal cells + 2 polar nuclei in the central cell + 1 in egg cell + 2 in synergids).

Correct Answer: A. 7-celled and 8-nucleate

Solution:

Plant hormones play crucial roles in regulating various physiological processes, including seed dormancy. Among these hormones:

• Abscisic Acid (ABA): Promotes seed dormancy by inhibiting germination and promoting the synthesis of storage proteins during seed maturation
• Gibberellic Acid (GA): Antagonizes the effect of ABA and promotes seed germination by activating digestive enzymes like α-amylase
• Cytokinins: Promote cell division and stimulate germination
• Ethylene: Can promote seed germination and typically breaks dormancy rather than maintaining it

Abscisic acid (ABA) is the major hormone responsible for establishing and maintaining seed dormancy. It accumulates during seed maturation and prevents precocious germination. The ratio of ABA to GA is often what determines whether a seed remains dormant or germinates.

Correct Answer: B. Abscisic acid

Solution:

Let’s analyze each statement about C₄ plants:

• They have Kranz anatomy: CORRECT – C₄ plants have a specialized leaf anatomy called Kranz anatomy, characterized by bundle sheath cells arranged in a wreath-like manner around the vascular bundles
• The first stable product is oxaloacetic acid: CORRECT – In C₄ plants, PEP (phosphoenolpyruvate) carboxylase fixes CO₂ to form oxaloacetic acid (OAA) as the first stable product
• They show high rates of photorespiration: INCORRECT – C₄ plants have evolved a CO₂ concentrating mechanism that maintains high CO₂ levels around RuBisCO, minimizing photorespiration
• They can photosynthesize efficiently in high temperature and light intensity: CORRECT – C₄ plants are adapted to hot, dry environments and can photosynthesize efficiently under high temperature and light intensity

C₄ plants like maize, sugarcane, and sorghum are characterized by their ability to minimize photorespiration by separating the initial CO₂ fixation (in mesophyll cells) from the Calvin cycle (in bundle sheath cells). This spatial separation ensures high CO₂ concentration around RuBisCO, reducing its oxygenase activity and thus minimizing photorespiration.

Correct Answer: C. They show high rates of photorespiration

Solution:

In angiosperms, the development of the female gametophyte follows a defined sequence:

1. The megaspore mother cell (diploid) undergoes meiosis to form four haploid megaspores
2. Typically, three of these megaspores degenerate, leaving one functional megaspore
3. The functional megaspore undergoes three rounds of mitotic divisions to form an 8-nucleate structure
4. This 8-nucleate structure develops further and differentiates into the embryo sac (female gametophyte)

The embryo sac contains the egg cell, which after fertilization develops into the embryo. The central cell, after fertilization, develops into the endosperm. The entire structure develops within the ovule, which is already present before megasporogenesis begins.

Correct Answer: B. Embryo sac

Solution:

Wind-pollinated flowers (anemophilous) have evolved specific adaptations to facilitate pollen transfer by wind:

• Large, feathery stigma: Typical of wind-pollinated flowers, increasing the surface area to trap airborne pollen
• Bright colored petals: NOT a feature of wind-pollinated flowers; bright colors attract animal pollinators but are unnecessary for wind pollination
• Production of large quantities of pollen: Wind pollination is inefficient, so wind-pollinated plants produce enormous amounts of lightweight pollen to ensure some reaches compatible stigmas
• Well-exposed stamens and pistils: Wind-pollinated flowers typically have exposed reproductive organs to allow easy release and capture of wind-borne pollen

Wind-pollinated flowers generally have reduced or absent petals (as they don’t need to attract pollinators), whereas animal-pollinated flowers often have bright, showy petals to attract their pollinators.

Correct Answer: B. Bright colored petals

Solution:

Let’s analyze each tissue type:

• Collenchyma: Living cells with unevenly thickened primary cell walls due to deposition of pectin and cellulose (not lignin)
• Sclerenchyma: Cells with thick, lignified secondary walls, but they are typically dead at maturity
• Xylem parenchyma: Living parenchyma cells within xylem tissue that have lignified cell walls but maintain living protoplasts
• Xylem vessels: Conducting cells in xylem that are dead at maturity (lack protoplasts) with lignified walls

Xylem parenchyma cells are unique in that they have lignified cell walls (as they are part of the xylem tissue) but retain their living protoplasts. These cells are involved in lateral conduction of water, storage of food materials, and in some cases, heartwood formation.

Correct Answer: C. Xylem parenchyma