Biology Test - 8

Insects count-2.5 million species
Plants species-50,000
Fishes- 3000
Birds −1300
Mammals −430

The natural methods of vegetative reproduction in stem include:

1. Offsets: Short horizontal branch producing a cluster of leaves above and the clusters of roots below.

e.g. Water hyacinth

2. Aerials shoot: Each segment of the stem having at least one node can form new plants

e.g. Opuntia

3. Rhizome: It is the main underground perennial stem buds present on the nodes take part for the formation of the new aerial shoot during the favourable season of growth.

e.g. Ginger

4. Bulbils: these are large size fleshy buds which are specialized for vegetative propagation

e.g. In agave bulbils are modified buds develop on the floral axis.

Bryophyllum has adventitious buds arise from notches present at the margin of leaves that help in vegetative reproduction.

The enzymes hexokinase which catalyses glucose to glucose-6-phosphate in glycolysis is inhibited by glucose-\(6\)-phosphate. This is an example of feedback allosteric inhibition.Hexokinase is a protein that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate. In many tissues and creatures, glucose is the most significant substrate of hexokinases, and glucose \(6\)-phosphate the most significant item.Hexokinase has a high proclivity for glucose, the hexokinase is allosterically hindered by its item which is glucose-6-phosphate. At the point when the centralization of glucose-6-phosphate expands, it ties with the compound at its allosteric site and achieves the conformational change in the protein.

The minimum number of meiotic divisions required to obtain 100 pollen grain of wheat is 25.

During sexual reproduction in angiosperms, meiosis occurs in microspore and megaspore mother cells. In one meiotic division, one microspore mother cell in the anther forms 4 microspores, each of which develops as a pollen grain. When there are 100 pollen grains, the meiotic divisions which will be required are \(\frac{100}{4}\) \(=25\). The number of meiotic divisions for 100 pollen grains is 25.

The nervous system of the cockroach is distributed very little in the head and most of the nervous system along the ventral part of the body of the cockroach. This is the reason cockroaches may live for few days even after removal of the head from the body.

The nervous system of the cockroach is spread throughout the body. The head holds a bit of nervous system while the rest is situated along the ventral (belly-side) part of its body.

\(\mathrm{O}_{2}\) dissociation curve of \(\mathrm{Hb}\) is Sigmoid.

A sigmoid curve is obtained when the percentage saturation of haemoglobin with \(\mathrm{O}_{2}\) is plotted against the \(\mathrm{pO}_{2}\). This curve is called the Oxygen dissociation curve. The binding of oxygen with haemoglobin is primarily related to the partial pressure of \(\mathrm{O}_{2}\), the partial pressure of \(\mathrm{CO}_{2}\), hydrogen ion concentration and temperature are the other factors that can interfere with this binding.

The cysts containing sticky gel-like substances in an ovary called Cystadenomas.

Cystadenomas can develop from cells on the outer surface of a woman's ovary. The cysts are many times filled with a thick and sticky gel or watery fluid. The cysts may become large, causing the woman pain.

Phosphorus is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides

Thiobacillus denitrificans is chemolithoautotrophic bacteria that denitrifies nitrate during oxidation of FeS_X compounds.

Denitrification is the process that converts nitrate to nitrogen gas, thus removing bioavailable nitrogen and returning it to the atmosphere. Dinitrogen gas (N₂) is the ultimate end product of denitrification, but other intermediate gaseous forms of nitrogen existed.

Expressed Sequence Tags (ESTs) are DNA sequences (genes) that are expressed as mRNA for protein synthesis. These are used in the human genome project for gene mapping.

Expressed sequence tags (ESTs) are fragments of mRNA sequences derived through single sequencing reactions performed on randomly selected clones from cDNA libraries. To date, over 45 million ESTs have been generated from over 1400 different species of eukaryotes.