Plant Growth And Development

Scarification is a process that involves mechanically or chemically damaging or scratching the seed coat to allow water to penetrate and initiate germination. This action helps break the seed's dormancy by making it more permeable to water and gases.

So, the correct option is (A): Scarification

Carotenoids in higher plants primarily absorb violet and blue fractions of the visible spectrum of solar radiation. These pigments absorb light in the blue and violet regions and play a role in photosynthesis by capturing energy from these wavelengths and transferring it to chlorophyll for photosynthetic processes.

So, the correct option is (D): Violet and Blue

A high ratio of cytokinins to auxins promotes shoot differentiation. Cytokinins and auxins are plant hormones that play essential roles in regulating various aspects of plant growth and development, including the formation and differentiation of shoots and roots. A higher concentration of cytokinins relative to auxins encourages shoot formation and growth.

So, the correct option is (B): High cytokinin : auxin ratio

Zinc deficiency can lead to reduced auxin synthesis or impaired auxin transport within the plant, which can result in various growth abnormalities and symptoms such as stunted growth and leaf distortion. Zinc is essential for various enzymatic reactions and processes in plants, including those related to hormone biosynthesis and function.

So, the correct option is (A): Auxin

The primary reason for considering Nicotiana sylvestris and Nicotiana tabacum as separate species is indeed that they cannot interbreed in nature due to their different flowering responses to photoperiods.

So, the correct option is (A): They cannot interbreed in nature

T-lymphocytes, or T-cells, play a critical role in the immune system. Among T-cells, there are indeed three main types:

1. Cytotoxic T-cells (also known as killer T-cells) that are responsible for destroying infected or abnormal cells.
2. Helper T-cells that coordinate immune responses and activate other immune cells.
3. Suppressor T-cells (also known as regulatory T-cells) that help regulate and suppress excessive immune responses to prevent autoimmune reactions.

The other statements are not accurate:
- T-lymphocytes originate in the bone marrow, not lymphoid - tissues.
- They are involved in immune responses but do not scavenge damaged cells or cellular debris.
- They are not produced in the thyroid.

So, the correct option is (A): There are three main types-cytotoxic T-cells,helper T-cells and suppressor T-cells

Coconut milk factor is commonly associated with being a source of cytokinins, which are a type of plant hormone. Cytokinins are involved in various plant growth and development processes, including cell division and differentiation.

So, the correct option is (D): Cytokinin

When you prune a hedge, especially by cutting the main or apical shoot, it removes the dominant growth point and allows the dormant axillary buds along the branches to start growing. These axillary buds give rise to new shoots and branches, creating a denser and bushier hedge over time. This process is often referred to as "breaking apical dominance" and is a common technique used in hedge maintenance and shaping.

So, the correct option is (B): It frees axillary buds from apical dominance

Parthenocarpic fruits are those that develop without fertilization, and hormonal treatments like gibberellic acid and auxins can induce this phenomenon in plants like tomatoes. These treatments stimulate fruit development without the need for pollination and fertilization.

So, the correct option is (B): treating the plants with low concentrations of gibberellic acid and auxins

Premature yellowing of leaves is often associated with chlorophyll deficiency, which can be caused by a lack of essential nutrients like iron and magnesium. Chlorophyll is crucial for photosynthesis, and its synthesis depends on the availability of these nutrients. By applying iron and magnesium, you can potentially address the underlying issue of chlorophyll deficiency and promote healthy green leaves capable of photosynthesis, ultimately contributing to better seed yield. While the other options may have some benefits, addressing the nutrient deficiency is a more direct approach to combat leaf yellowing and improve overall plant health and seed yield.

So, the correct option is (D): Application of iron and magnesium to promote synthesis of chlorophyll

The production of cucumbers has significantly increased due to the application of phytohormones that promote the formation of female flowers. Among the options provided, the correct choice is Ethylene.

Explanation: Ethylene is a well-known plant hormone that influences the sexual differentiation in certain plants. It is specifically noted for its role in favoring the development of female flowers over male flowers in some species, including cucumbers. This shift in the flower sex ratio results in more fruit production because cucumber seeds develop from female flowers.

Let's look at the roles of each hormone:

• ABA (Abscisic Acid): Generally involved in stress responses and inhibition of growth. It does not stimulate the production of female flowers.
• Gibberellin: Primarily involved in promoting growth and elongation of cells, seed germination, and other processes, but not in the promotion of female flowers.
• Ethylene: Promotes the formation of female flowers in several plant species, including cucumbers, thereby increasing fruit production.
• Cytokinin: Concerned with cell division and growth, not specifically related to flower sex expression.

In plants, gaseous growth regulators, specifically ethylene, play various roles. One of its functions is to promote root growth and facilitate the formation of root hairs, which effectively increases the absorption surface of the plant. This allows the plant to uptake water and nutrients more efficiently, benefiting overall plant health and growth.

The given options present different responses linked to plant growth regulators:

• Seed up the malting process: This typically involves gibberellins, not gaseous regulators.
• Promote root growth and root hair formation to increase the absorption surface: This is a valid role of ethylene.
• Help overcome apical dominance: While auxins are mainly involved in apical dominance, ethylene can interact in this process too.
• Kill dicotyledonous weeds in the fields: This action is related to synthetic auxins used as herbicides, not gaseous ethylene.

Therefore, the correct answer aligns with ethylene's role by enhancing root growth and increasing the root absorption surface.