CBSE Set Qa1 Biology Sample Test Papers For Class 12th for students online
You are on answers 1 to 19
Q9. In most
plants the terminal bud suppresses the development of lateral buds. What is this
phenomenon called? Name the phytohormone that can promote the phenomenon.
Ans9. The phenomenon in which the presence of the terminal bud suppresses the development of lateral buds is called the ‘Apical Dominance’. Auxins are responsible for this and can promote the phenomenon.
Q10. Sieve tubes
in angiosperms are associated with specialized parenchyma cells. Name those
cells. How do they help sieve tube members?
Ans10. Angiospermic sieve tubes are associated with specialised arenchymatous ‘Companion cells’. The companion cells help the sieve tube members in the translocation of food material.
Q11. How is the
digested fat absorbed?
Ans11. The digestion of fats produces water-insoluble glycerides and fatty acids, which need to be first incorporated into small, spherical, water-soluble droplets called ‘Micelles’ with the help of the bile salts and phospholipids in the intestinal lumen. From these micelles the digested fats are absorbed into the intestinal cells.
Q12. What are
antagonistic muscles? Give one example.
Ans12. The muscles which contract to produce opposite movements at the same joint, are called ‘Antagonistic muscles’. When a muscle contracts to produce a movement, its antagonist must relax to allow that movement to take place. The biceps is a flexor for the elbow joint, and the triceps is its antagonist and an extensor for that joint.
the methods of birth control by which fertilisation of ovum by sperm is
Ans13. The fertilisation of ovum by sperm can be prevented by any of the following methods :
Use of intra-uterine contraceptive devices (IUCD) like the copper T or loop, use of either vaginal diaphragms, condoms, or spermicidal creams, surgical techniques such as tubal ligation or vasectomy.
Q14. What is
artificial selection in terms of evolution? Name one plant that has been
produced as a result of artificial selection.
Ans14. Artificial selection over generations on specific criterion will lead to the evolution of a variety strikingly different from starting generation. Cabbage, cauliflower, and kohlrabi have been obtained through artificial selection from a common ancestor, colewort.
have evolved from reptiles’. How does palaentology provide evidence in support
of the above statement?
Ans15. The finding of the fossilised Archaeopteryx provides evidence in support of the evolution of Birds from reptiles. Archaeopteryx had the following birds like features :
However, it had the following reptiles like features as well :
(i) teeth in beak,
(ii) claws in wings,
(iii) vertebral column in tail.
Thus Archaeopteryx was a link between birds and reptiles.
discovered the coacervates? List the biological properties of co-acervates.
Ans16. Oparin and Sydney Fox discovered coacervates. The biological properties of coacervates are :
(i) they grow by absorbing molecules from their environment,
(ii) they can divide by budding,
(iii) important biochemical reactions occur into them.
Q17. What is mycorrhiza? How does it act as biofertiliser?
Ans17. Mycorrhiza is a symbiotic association of certain fungi with the roots of seed-bearing plants.
Mycorrhizae are of two types :
(i) Ectomycorriza, and
The Ectomycorrhiza forms a mantle on the outside of the root and functionally increases the surface of interaction between roots and soil. It enhances water and nutrient uptake and results in greater plant vigour, growth and yield as if it was a chemical fertiliser.
autoimmune diseases. Give two examples.
Ans18. The phenomenon of the immune system of body turning against ‘Self’ leads to ‘Autoimmune Diseases’. The actual disorder depends on which self-antigen is involved. When the body destroys its own RBC’s it leads to ‘Chronic Anaemia’; and when it destroys its own muscle cells, it leads to ‘myasthenia gravis’.
Q19. What is
transformation? Describe Griffith’s transformation experiment.
Ans19. The phenomenon by which the DNA isolated from one type of cell, when introduced into another type, is able to bestow some of the properties of the former to the latter, is referred to as ‘Transformation’.
In his experiment, Griffith used two
strains of Diplococcus pneumoniae :
(a) Pathogenic S-strain (smooth colonies, capsulated), and
(b) Non-pathogenic R-strain (rough colonies, non-capsulated)
When injected into mice, only S-strain produced the disease but the R-strain or heat killed S-cells did not produce disease. However, when heat killed S-cells were injected with live R-strain, the mice died due to the disease. From the blood of dead mice S type of capsulated bacteria were recovered which formed smooth colonies.
McCarty and MacLeod explained Griffith’s experiment. DNA leaked out from the heat-killed S-strain and was picked by non-pathogenic non-capsulated R-strain cells. This transformed the R-strain of bacteria to pathogenic capsulated S-strain.