Biology Test - 52

\(\mathrm{A}+\mathrm{T} / \mathrm{C}+\mathrm{G}\) is not constant, is inconsistent regardingdouble helical structure of DNA. Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between \(\mathbf{G}-\mathrm{C}\) and \(A-T\) base pairs. Duplication of the genetic information occurs by the use of one DNA strand as a template for formation of a complementary strand.The density of DNA decreases on heating as hydrogen bonds breakdown. The amount of adenine is always equal to that of thymine, and the amount of guanine is always equal to that of cytosine i.e \(A=T\) and \(G=C\). The base ratio \(\mathrm{A}+\mathrm{T} / \mathrm{C}+\mathrm{G}\) may vary form species to species, but is constant for a given species.

The major reason behind some proteins having quaternary structure is to assemble the monomers to form a coordinated polymeric structure.

In proteins, Quarternary structure is present in the case of multimeric or oligomeric proteins. It is homogenous if the polypeptide is similar or heterogeneous if the polypeptides are different. Here (in the quarternary structure) the different polypeptide chains interact and get oriented with respect to each other in a specific manner. Some enzymes are multimeric proteins with different protein chains interacting in a particular fashion in three-dimensional space to give rise to active sites, crevices, pockets and other structures on the surface to form the functional protein molecule which can act as a catalyst.

Also in the multimeric proteins, the binding sites are derived by different protein chains. Only those proteins made of two or more polypeptide chains have a quaternary structure. Insulin (two chains), haemoglobin (four chains) and immunoglobulins (antibodies, four chains) are some examples of protein having a quaternary structure.

From inside to outside the correct order of the following cells in the retina would beGanglion cells - Bipolar cells - Photoreceptor cells.

Retina of the eye has three layers of cells:

Ganglion cells: These are in the outer layer and form the optic nerve that carries visual information to the brain. These cells take information from bipolar cells.

Bipolar cells: These cells are present next to ganglion cells and take information from photoreceptor cells.

Photoreceptor cells: These are present next to bipolar cells and detect the daylight vision and low light vision. There are two types of photoreceptor cells in the retina, cones (detect daylight vision and coloured vision) and rods (detect low light vision).

The residual volume of air in a normal human is \(1.1\) to \(1.2\) litre.

Residual volume is the amount of air that remains in a person's lungs after fully exhaling. Doctors use tests to measure a person's residual air volume to help check how well the lungs are functioning. It is normal to have some air remain after exhaling to keep the lungs from collapsing.

Under unfavorable conditions, many zooplankton species in lakes and ponds are known to enter a stage of suspended development called as diapause.

It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions, resulting in a delay in development.Diapause can be defined as the physiological state of dormancy or developmental arrest where most life processes are shut down.It is initiated during unfavorable conditions and is most commonly observed in insects, especially in arthropods.

The diapause stage can occur at any stage during an insect’s life cycle - from its pupae stage to the active, adult stage.When this phenomenon occurs during the egg or the pupil stage, the development slows down to a halt. In the adult stage, feeding habits or reproductive behavior is halted or slowed down.

The infective constituent of viruses is not the outer protein coat, but the genetic material inside the cell. Viruses can have either DNA or RNA as their genetic material. Viruses upon infecting the host cells start integrating into the host cell’s DNA or RNA, after incorporation the viral cells undergo the process of transcription and later translation, to produce the viral proteins, and the cells start replicating. The cells of the viruses thus produced compete with the normal host cells for nutrients and slowly deactivate the host’s normal defense and cell metabolism, thus making it over completely.

Viroids are the smallest infecting agents, they are made of only a strand of single-stranded circular RNA. They are devoid of the protein coating

Viruses are known as obligate parasites, since they are inactive outside the environment of a host cell, and become virulent only when it gains entry into the host. Thus it needs a host cell to complete its life cycle.

Prions are made of abnormally folded proteins and this can lead to the development of progressive neurodegenerative conditions.

Infective constituents of viruses are its genetic materials, which can either be RNA or DNA and not the protein coat.

Responsive growth movements toward or away from an external stimulus are called tropisms. If the plant movement is toward the stimulus, it is a positive tropism; away from the stimulus, a negative tropism.

Natality refers toBirth rate.

Natality is the rate of production of new individuals per unit area of population per unit time. Simply it is called birth rate.

Boron element is very essential for uptake and utilization of \(\mathrm{Ca}^{2+}\) and membrane function.

Boron is the mineral element required for uptake and utilization of calcium. Thus deficiency symptoms in plants should be interpreted with care. For example the deficiency symptoms of calcium and boron will be similar.

In most tuberculosis (TB) endemic countries, bacillus Calmette Guérin (BCG) is usually given around birth to prevent severe TB in infants. The neonatal immune system is immature. Our hypothesis was that delaying BCG vaccination from birth to 10 weeks of age would enhance the vaccine-induced immune response.