Biology:2017:CBSE:[Delhi]:Set-III

Biopiracy refers to the exploitation of plant and animal species by monopolisation, without any compensation to the indigenous countries. It can also be defined as the use of bio-resources by companies and organisations without proper authorisation from the countries and concerned people with no compensatory payment.

Immunisation is a method to ensure an anamnestic response in humans.

Homologous chromosomes synapse during meiosis and get separated to pass into different cells. As a result the gamete receives only 1 chromosome of each type and thus has only 1 gene for a trait.

To avoid illegal female foeticide in the country, our government has intentionally imposed strict conditions for M.T.P.

The correct order would be:

(ii) Prehistoric cave art

(iii) Agriculture

(i) Human settlement

(a) An algal bloom is the excessive growth of the planktonic forms in a nutrient rich water body. As the planktonic species multiply on the surface, they form a layer that covers the entire surface of the water body. This blocks the sunlight from reaching the submerged aquatic plants, that are necessary to supply nutrients to other aquatic life forms and keep the water clean. Blockage of sunlight leads to the death of these aquatic plants.

Due to the death of aquatic plants, the excretory substances released by the planktons gradually pollute the water and the toxic substances released by them are detrimental to other life forms in the water body.

To meet the high respiratory needs of a huge concentration of biomass of the planktons on the surface, the biological oxygen demand (BOD) of the water body increases. Due to the insufficient oxygen supply, many other aquatic forms die. Their carcasses further deteriorate the quality of water.

(b)We must take an approprite measure to prevent the over-enrichment of lakes and rivers with nutrients such as nitrogen and phosphorus. These nutrients drain into the water bodies due to the discharge of fertilisers and sewage into them. Presence of excessive nutrients leads to blooms, planktonic growth, etc. Hence, treating fertilisers and sewage before discharging into water bodies may act as a preventive measure.

Mycorrhizae are the associations between the fungi and the plants. The plant is benefitted by the soil nutrients that a fungus absorbs and transfers to the plant through its roots. The fungus in return derives carbohydrates from the plant.

• A single MMC (megaspore mother cell) is differentiated from the nucellus tissue of the ovule.
• MMC undergoes meiosis to form four megaspores.
• Three megaspores towards chalazal end degenerates, only a single megaspore towards micropylar end develops into functional megaspore.
• The nucleus of the functional megaspore undergoes three successive mitotic divisions (free nuclear) to form an eight nucleated embryo sac.
• At eight nucleated stage, cell walls are laid down.
• Three cells are grouped together at micropylar end, constitute egg apparatus.
• Three cells are arranged at chalazal end, called antipodal cells. Whereas two nuclei are present in the centre, called polar nuclei. Thus, a typical angiospermic embryo sac at maturity is eight nucleated and seven celled.

DNA is packed in the chromosome with the help of histone and non-histone proteins. There are four types of histone proteins associated with DNA packaging in cells. They are named as H1, H2, H3 and H4. Among these, H2 exists in two forms, H2A and H2B. Four histones, H2A, H2B, H3 and H4 make a cluster of two molecules each. This is the histone octamer consisting of eight molecules. The acidic DNA strand wraps around this octamer due to attraction to form a structure known as a nucleosome. The DNA strand wounds around histone octamer throughout its length such that it forms a beads-on-string structure. This is the chromatin fibre 10 nm in diameter. Each nucleosome has 147 base pairs of DNA along with eight molecules of histone. The ends of DNA are tucked with H1 histone. Along with these stretches of DNA entering and leaving the nucleosome, the total number of base pairs is 200 in a nucleosome.

Evolutionary significance:

1. Shrews– The first mammals that evolved in Jurassic period were like shrews.
2. Lobefins– Lobefins were the first amphibians and ancestors of modern day frogs.
3. Homo habilis – Human ancestors that existed 2 million years ago. These were the first human like beings.
4. Homo erectus -Human ancestors that existed 1.5 million years ago.