Biology Class-Xll  
Sample Paper 1999 - (Part - 2)
(Solved)

Q1. Name the process in which bacteriophage picks-up a piece of DNA from one bacterial cell and transfers the same to another bacterial cell on infection.

Ans1. Transduction.

Q2. Which fraction of soil water is readily available to plants for absorption.

Ans2. Capillary water fraction .

Q3. What protects nitrogenase?

Ans3. ‘Leghemoglobin’ combines with oxygen and maintains anaerobic environment to protect nitrogenase.

Q4. Name two plants that produce rhizomes.

Ans4. Ginger, Turmeric.

Q5. Why is oxytocin called as ‘Birth Hormone’?

Ans5. Oxytocin helps in uterine contraction and the onset of labour at the time of child-birth.

Q6. From which germ layers do the following organs differentiate :
(i) Kidney
(ii) Urinary bladder

Ans6. Kidney and the urinary bladder differentiate from mesoderm.

Q7. What provided energy for abiotic synthesis on the primitive earth?

Ans7. ‘Lightning and solar radiation’ provided energy for abiotic synthesis on the primitive earth.

Q8. Name the two curable sexually transmitted diseases.

Ans8.
(i) Syphilis, and
(ii) gonorrhoea are curable sexually transmitted diseases.

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.

Q13. Describe the methods of birth control by which fertilisation of ovum by sperm is prevented.

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.

Q15. ‘Birds 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 :
(i) feathers,
(ii) wings,
(iii) beak,
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.

Q16. Who 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
(ii) Endomycorrhiza.
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.

Q18. Define 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’.

Q26. What is metastasis? List any four danger signals of cancer.

Ans26. A malignant tumour does not remain confined to the original tissue. Cancerous cells are carried by the blood and lymph to other parts of the body, where they multiply to produce secondary malignant growths. The spread of cancerous cells to distant sites is termed Metastasis.

Some danger signals of cancer are :
A lump or hard area in the breast.
A change in a wart or mole.                                                      
A persistent change in digestive and bowel habits.
A persistent cough or hoarseness.