Plant Transport and Physiology

Deciduous plants shed leaves in autumn. The shedding of leaves is a controlled and orderly process preceded by the formation of abscission layer at the base of leaf or fruit.

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called as the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth. In most situations, ABA acts as an antagonist to gibberellins.

Diffusion of CO$ _2$ into the leaf is decreased due to the closure of stomata and reduces the transpiration, which is done by antitranspirants.

By the end of summer, the leaves may be damaged by insects, disease or general wear and tear and ready for renewal. They are equipped to self-destruct. At the point where the leaf stem meets twig or branch is an array of cells called the abscission layer. As autumn days shorten, this layer begins to choke off the veins that move water into the leaf and food into the tree. Once the leaf is completely choked off, the layer becomes dry and flakey and, through decomposition, detaches the leaf from the tree.

Plants with both submerged and floating or emerged leaves show heterophylly (Ranunculus), that is, occurrence of more than one type of leaves or dissected leaves (Hydrilla).This prevents the tearing of the leaves that are constantly exposed to water currents.

Plants that grow completely inside water and their roots are affixed to the soil under water with their leaves, stems and existing blooms of a plant are also submerged under normal water level.

The of tap roots is said to be towards gravity because the tap roots grow downward into the ground to absorb water and nutrients from deeper parts of the soil.

Fibrous roots are highly branched roots and have more root hairs as well as more surface area than a taproot system. Due to more surface area, fibrous root helps the plants of anchorage to soil very firmly. So, the correct answer is 'Anchorage of plant to soil'.

When the adventitious roots modified for aerial support is called as prop roots. Prop roots give mechanical support to the aerial branches. The lateral branches grow vertically downward into the soil and act as pillars. Prop or pillar or columnar roots are pillar-like roots which give extra mechanical support to heavy stem branches, e.g., banyan tree. 

Assimilatory roots (e.g., Tinospora) perform photosynthesis. Fasciculate roots (e.g., Dahlia) store food. Stilt roots (e.g., Maize) provide mechanical support. Sucking roots (e.g., Cuscuta) are haustoria for absorption from host plants, not moisture from air (that is velamen roots).

Growth of tap roots is towards gravity. Typically, a taproot is very thick. It is tapering in shape and grows directly downward into the soil towards the force of gravity. In plants with taproot systems, the taproot is the central root from which other roots sprout laterally.
Thus, the correct answer is option A.

To maintain osmotic balance in saline environments, mangroves accumulate compatible solutes like proline and sorbitol to lower their internal water potential without toxic salt accumulation.

Halophytes use multiple strategies to survive, including salt excretion through glands, accumulation of organic osmolytes like proline/sorbitol, and water storage in succulent tissues.

Utricularia are carnivorous plants which capture small prey with remarkable suction traps. These are rootless plants formed of very thin, forked leaves. Only the flower remain out of the water while the whole trap is underwater. When an aquatic animal touches its sensitive hairs, the traps suck it in, in just a few seconds, along with water, which is then drained through its walls.

• An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water or from debris accumulating around it.
• Most epiphytic orchids are found growing in tropical areas below the canopy of trees. Epiphytic orchids have adapted to obtain water and nutrients that grow with their roots which are located aerially.
  
• They have thick, spongy roots that absorb and store water and nutrients from the sporadic rainfall to be used over time.