Biology MCQs with answers Page - 50

BOD is amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period, for running rivers, it would be minimum and for Untreated Municipal waste water it would be maximum.

Secondary growth is the growth that results from cell division in the cambia (see below), or lateral meristem, and that causes the stems and roots to thicken. Primary growth is growth that occurs as a result of cell division at the tips of stems and roots, and that gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants. In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter. In woody plants, this process produces wood. Secondary growth results in an increase in diameter. Obstructions, both foreign objects such as this metal post, and parts of the plant, such as stubs of limbs, can be “swallowed” by continued growth. Because this growth usually ruptures the epidermis of the stem or roots, plants with secondary growth usually also develop a cork cambium. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. If this is kept up over many years, this process may produce a layer of cork. In the case of the cork oak it will yield harvestable cork. Secondary growth also occurs in many non-woody plants, e.g. tomato, potato tuber, carrot taproot and sweet potato tuberous root. A few long-lived leaves also have secondary growth.

Vitamin A improves our night vision and not the day vision. The sensory portion of the eyes (retina) contains rods and cones. The rods and cones are specialized cells responsible for the sense of vision. Rhodopsin is a pigment produced by the rods of the eyes. The rods are used for night vision, while the cones are used when ample light is available. Rhodopsin is made from Vitamin A. It is produced only when a small amount of light is available in the environment, so that we can see in the dark. Rhodopsin is not used when enough light is available in the surroundings (example, daylight). The cones of the eyes are responsible for vision when enough light is available. They do not produce rhodopsin for us to see clearly.

The first statement is partially correct. Sperm has a nucleus. RBC has no nucleus. Muscle cells have more than one nuclei. Skeletol Muscles have multiple cells because they can be able to generate more protein. But Cardiac and smooth muscle tissue only have one nucleus in their cell. The second statement is correct. The RBCs cannot divide and only sustain their numbers by stem cells dividing to make more such cells.

Various applications of the DNA sequencing include: identifying a particular individual, diagnosis of genetic and non-genetic diseases, improve quality of livestock and crops and confirm and establish species identity.