Biology (Part-2) (CDS-Solved Paper)

The mammalian heart is myogenic and is regulated by nerves. The heartbeat in this originates from sino-atrial (SA) node. The impulse starts in SA node, which is a small bundle of specialised cells located in the right atrium. The electrical activity spreads through the walls of the atria and causes them to contract. This forces blood into the ventricles. The SA node sets the rate and rhythm of the  heartbeat. It is also called natural pacemaker of heart.

The plant growth regulators are small, simple molecules of diverse chemical composition. They are indole compounds, adenine derivatives, carotenoids and terpenes. These are also known as plant exogenous hormones. These are synthetic substances that are similar to natural  plant  hormones. They are used to regulate the growth of plants and are important measures to ensure agricultural production.

Methane gas is released from land fills in urban areas. Landfill gas is a complex mixture of different gases created by the action of microorganisms within a landfill. This gas is approximately 40%-60% methane, with the remainder being mostly carbon dioxide.

HIV virus weakens the immunity of a person because it destroys lymphocytes. Human Immunodeficiency Virus (HIV) causes Acquired Immuno Deficiency Syndrome (AIDS). The virus attacks a specific type of immune system cell in the body, known as CD₄ helper lymphocyte cells. HIV destroys these cells, making it harder for the body to fight off other infections.

Carbon monoxide is the air pollutant which combines with the haemoglobin of human blood. It reduces the oxygen-carrying capacity of the blood, which leads to suffocation and may cause even death. Carbon monoxide is produced from incomplete burning of fuels, such as petrol and diesel. It is a poisonous gas.

Parthenogenesis It is a natural form of asexual reproduction in which growth and development of individual occur without fertilisation of eggs.
Apogamy It is the development of sporophytes without gametes and syngamy (fertilisation) from vegetative cells of the gametophyte.
Sporophytic Budding (Adventive embryony) In this, an embryo develops directly from a diploid cell other than egg (from nucellus and integument), e.g. Citrus, Opuntia.

Deficiency of fluoride or fluorine may cause dental caries or tooth decay, which means breaking down of dental tissues. Possibly, it may lead to osteoporosis (a bone disorder, which leads to a decrease in bone mass and an increase in bone fragility). However, due to a lack of fluoride in the diet, there are anti-osteoporotic functional food ingredients that can help in decrease the risk of osteoporosis fractures.

Excessive use of nitrogen fertiliser including manure may be responsible for the presence of toxic substance in groundwater. High application rates of nitrogen containing fertilisers combined with the water, leads to increased runoff of chemicals into surface water as well as their leaching into groundwater, thereby causing groundwater pollution.

Amphibians are most sensitive to environmental changes. It is because the egg shell of these animals does not have hard covering as it is found as reptiles and Aves. Their egg are covered with jelly-like substances. If any change occur in the environment like dryness dehydration, it affects the egg and thus their reproduction gets affected.

Insuline is the hormone which is essential for the uptake of glucose by cells in the human body.
The body manufactures insulin in the pancreas and the hormone is secreted by the beta (β) cells. The beta cells of the pancreas are perfectly designed as ‘fuel sensors’ stimulated by glucose.