BIOLOGY 5 Marks Questions

Chemically the plasma membrane consists of proteins (20-70%), lipids (20-79%), carbohydrates (1-5%) and water (20%). Nucleic acids (DNA and RNA) are absent in the plasma membrane. The lipids present in the plasma membrane are phospholipids, glycolipids (sugar lipids) and sterols.
Each lipid molecule consists of a three carbon glycerol poles (head) which is hydrophilic (water-loving) in nature and two long tails of fatty acids which are hydrophobic (water-fearing) in nature.
The hydrophilic glycerol poles of lipid are located towards the outside of the lipid bilayer whereas, the hydrophobic fatty acid tails are repelled by water and face towards the inner side of the membrane.
The hydrophilic and hydrophobic forces in lipid molecules cause the membrane to become a bilayer.

Plastids are both region or species-specific. These are as follows
i. Proplastids: These are colourless, rounded but amoeboid plastid precursors, found in meristematic and newly formed cells of plants. It has a double membrane envelope that surrounds a colourless matrix, containing DNA, ribosomes and reserve food. A few vesicles and lamellae also occur in the matrix.
ii. Leucoplasts: These are colourless plastids that occur in non-green plant cells commonly near the nucleus. They are as follows
a. Amyloplasts These leucoplasts store starch, e.g., the tuber of potato, grain of rice and wheat.
b. Elaioplasts These store fats, e.g., rose.
c. Aleuroplasts They are protein storing plastids, e.g., castor endosperm.
iii. Chromoplasts: These are non-photosynthetic coloured plastids which synthesise and store carotenoid pigments. They appear,
orange, red or yellow in colour. These mostly occur in ripe fruits (tomato and chillies) carrot roots, etc.
iv. Chloroplasts: These are photosynthetic plastids, which are green in colour and found in the leaves of all green plants. They have lamellae organised in the form of grana.

Two moles of triose phosphate are interconvertible. They are dihydroxyacetone phosphate and 3-bi phosphoglyceraldehyde. 3-phosphoglyceraldehyde is converted into 1, 3, bi phosphoglycerate and NAD+ is reduced to NADH. Phosphoglycerate kinase
catalyses the formation of 3-phosphoglycerate and ATP is produced. 3-phosphoglycerate is converted into 2-phosphoglycerate and PEP.
PEP makes pyruvate and releases ATP.

The statement of the biologist is correct. Because the life history of an organism can be summed up as gametic fusion, equational division, and reductional division. By the fusion of male and female gametes, the gametic zygote is formed and from the zygote develops the adult. The zygote is formed during sexual reproduction. Half of the chromosome comes from the mother and the other half chromosomes come from the father to bring the character from both the parents. The male and female gametes are formed as a result of meiosis. The body cell divides by mitosis. In prophase of meiosis I, the exchange of segments between the two adjacent non-sister chromatids of the homologous pair at different sites takes place which results in the genetic recombinations.

i. During zygotene of prophase I of meiosis homologous chromosomes pair together. This pairing is called synapsis.

ii. Bivalent: The complex formed by homologous chromosomes during zygotene is called a bivalent. They are also known as tetrad
iii. Chiasmata: During diplotene, the paired chromosomes make a X-shaped structure. This is called chiasmata. It is a site where two non-sister chromatids of homologous chromosomes have crossed over.