Quiz 29: Plant Nutrition and Transport
As per the given conditions prevailing in different environmental conditions, the following types of flowering plants with the various adaptations will be able to survive: In a hot desert in New Mexico or Arizona: The plants growing in hot deserts usually have long and widespread roots, with large number of branches covered with a number of root hairs. These long roots extend upto huge distance to absorb as much water as possible in water scarce regions. The stem is reduced to minimize the surface area exposed to sunlight to prevent water loss. The leaf are usually spikes with reduced surface area, stomata are present in the lower regions of the leaf in depressions and are usually closed during the daytime to prevent water loss. The epidermis of the reduced leaves is coated with cutin or other waxy substance to prevent the loss of water. The plants growing in hot, arid regions also produce less flowers and fruits. The flowers if produced open at night time for pollination. These plants invest a lot amount of their energy in producing large, white and aromatic flowers with large number of reproductive parts. This kind of adaptation facilitates the process of pollination by attracting bats and other nocturnal insects and birds. Photosynthesis in these plants is usually carried out by CAM cycle. On the floor of a shady, moist forest in Georgia or Oregon: These plants have short roots and large leaves. The surface area of the large canopies is exposed to sunlight and the stomata are open in the broad daylight to facilitate the exchange for gases for photosynthesis. In the Arctic tundra in Alaska: The plants in this region possess reduced leaves and stems. The stomata and thickly coated epidermal hairs are found in depressions in the leaf surface to prevent the loss of water.
The top section of the diagram is more common among eudicots. In the stems of eudicots the vascular bundles are arranged in a ring like pattern. The vascular bundles basically consist of xylem and phloem; xylem transports water, ions and minerals throughout the plants whereas phloem transports plant nutrition. The vascular bundle in eudicots divides the parenchyma of the ground tissue into two parts known as cortex and pith. The cortex is the region which lies in between the vascular bundles and the epidermis. The pith is the inner most region of the plant which is surrounded by the vascular bundles. The bottom diagram represents the tissue arrangement of the monocots. The vascular bundles are scattered throughout the ground tissue. The region of parenchyma tissue in which the inner most region is known as pith. The ground tissue is guarded by the epidermis.
Redwood trees are huge trees and girdling is the best measure to kill these trees. By the process of girdling a strip of entire bark is removed along the circumference of the tree. The removal of the bark also strips down the cork cambium and the vascular cambium which comprises of the secondary phloem as well as the secondary xylem. In redwood species, older roots and stems thicken by activity at both vascular cambium and cork cambium. Lateral meristem is responsible for secondary growth of the plant. The tissue present here divides and thickens the plant stems and roots. The activity of lateral meristem results in the formation of vascular cambium and cork cambium. Vascular cambium is produced when the lateral meristem becomes active in older stems and roots and produces secondary xylem and secondary phloem. Secondary xylem is formed on the inner side of lateral meristem whereas secondary phloem is produced on the outer side of the lateral meristem. The inner region on the secondary xylem thickens and displaces the meristematic cells towards the outer surface of the stem forming a ring of vascular cambium. The expansion of the inner region of the secondary xylem puts pressure towards the stem and root surface. This in turn ruptures the cortex and outer part of secondary phloem. The parenchyma cells starts dividing forming cork cambium. Vascular cambium and cork cambium are also responsible for forming growth rings in plants which helps in determining the age of tress. With girdling, as the xylem and phloem are stripped off, the circulation of water and nutrients are interrupted. As these trees are very huge it takes months and months for these giant redwood trees to die.