BIOLOGY 3 Marks Question

A.
→They are able to co-exist by mechanism of 'resource partitioning'.
→ If two species compete for the same resource, they could avoid competition by choosing different foraging patterns.
→ MacArthur showed that five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.
B.
→ Gause's 'Competitive Exclusion Principle' states that two closely related
species competing for the same resources cannot co-exist indefinitely
→ and the competitively inferior one will be eliminated eventually.
→ No

PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest are synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.
If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remains active during the high temperature induced denaturation of double stranded DNA. The amplified fragment if desired can now be used to ligate with a vector for further cloning.
Each cycle has three steps: (i) Denaturation, (ii) Annealing and (iii) Extensions.

The main sources of biofertilizers are bacteria, fungi and cyanobacteria.
→ The nodules on the roots of leguminous plants are formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as a nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
→ Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.
→ Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

→ isolation of DNA,
→ digestion of DNA by restriction endonucleases,
→ separation of DNA fragments by electrophoresis,
→ transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,
→ hybridisation using labelled VNTR probe, and
→ detection of hybridised DNA fragments by autoradiography.

A. During replication, Adenine pairs with thymine in DNA; during transcription, adenine pairs with uracil in RNA.
B. In retrovirus the nucleic acid is RNA and it is used to synthesize DNA; the process is called reverse transcription.
C. It is a highly energy-rich process/ or as per the need only the gene coding for a specific protein is transcribed.

→ The first meiotic division is completed in the primary oocyte during oogenesis.
→ Then primary oocyte undergoes first meiotic division to form a large haploid secondary oocyte and a tiny first polar body.
→ The primary oocyte comprises of 46 chromosomes, whereas secondary oocyte and first polar body have 23 chromosomes each.

A. Seed X-3 embryos; 1embryo sac; 1ovule;
B. The nucellar cells grow mitotically and develop into the embryos by asexual reproduction.
C. The plants growing from seed X will have to share the resources/endosperm so there is a possibility of some plant being undernourished/; only one plant in seed Y will use the entire endosperm for its growth or as the plants of seed X are clones they will not show variation and may succumb to environmental stress;/ plants from seed Y will have genetic variation and so can show greater adaptability.