Q 1. What is meant by trisomic condition? (1 mark)

Ans1. Trisomy is the presence of an extra chromosome i.e., so that a particular chromosome is present in three copies.

Q 2. State the presence or absence of sinus venous in a fish and a mammal. (1 mark)

Ans2. Fish and mammals do not have sinus venosus because a sufficiently high blood pressure cannot be maintained in the open spaces.

Q 3. Which type of cartilage is present between vertebrae to allow limited movement? (1 mark)

Ans3. White fibrocartilage

Q 4. Name any two breeds of wild rock pigeon that have been developed through artificial selection. (1 mark)

Ans4. (i) Pouter, and
(ii) Jacobin.

Q 5. Which chromosomes are called autosomes? (1 mark)

Ans5. Autosome is any chromosome other than a sex chromosome. In humans they are 22 pairs.

Q 6. When is a tumour referred to as malignant? (1 mark)

Ans6. A tumour is called malignant, if it has the capacity to undergo metastasis.

Q 7. What are the two factors that contribute for the dissociation of oxyhaemoglobin in the arterial blood to release molecular oxygen in an active tissue? (1 mark)

Ans7. PO₂ in the tissues lower than arterial blood, and PCO₂ in the tissues higher than arterial blood.

Q 8. Which one of the following is fatal unless oral rehydration therapy is administered :
(i) Whooping cough (ii) Cholera (iii) Tetanus (1 mark)

Ans8. Cholera

Q 9. What are the two functions of DNA polymerase? (2 marks)

Ans9. DNA Polymerase is responsible for :
(i) binding the deoxynucleotide bases after they have arranged on the DNA template,
(ii) proofreading the formed sequence for errors.

Q 10. Stanley Miller and Harold C. Urey performed an experiment by recreating in the laboratory the probable conditions of the atmosphere of the primitive earth.

(i) What was the purpose of the experiment?
(ii) In what forms was the energy supplied for the chemical reactions to occur?
(iii) For how long the experiment was run continuously? (2 marks)

Ans10.(i) The purpose of the experiment was to recreate the probable conditions prevalent on the primitive earth.
(ii) Energy was provided by heating the liquid-containing chamber as well as by electric sparks from electrodes in the gaseous chamber.
(iii) The experiment was run continuously for one week.

Q 12. Name the basic nitrogenous catabolite of proteins produced in birds. In what form is it eliminated from their body? What is the advantage of this type of excertion? (2 marks)

Ans12. Birds produce Uric acid as the basic nitrogenous catabolite. It is excreted in the form of water insoluble crystals. The advantage of excreting crystals of uric acid and urates is that no water is lost in removing them from the body. Thus the birds save a lot of precious water while managing the excretion of toxic end products of protein catabolism.

Q 13. Describe the theory of inheritance of acquired characters.
Who disproved it experimentally? (2 marks)

Ans13. ‘Theory of inheritance of acquired characters’ was given by Lamarck. According to this theory organisms undergo certain changes to adapt themselves to the environment. These characters acquired during the lifetime are passed on to progeny.
Weismann refuted Lamarckism by showing that even if tails of newborn mice were cut off generation after generation, no shortening of tails was observed in any subsequent generations.

Q 15. What is the biological significance of Azolla pinnate in agriculture? (2 marks)

Ans15. Azolla pinnata is a small, fast-growing fern that occurs floating on water. Anabaena azollae, a cyanobacterium lives in cavities of Azolla leaves. It fixes nitrogen from air and excretes the nitrogenous compounds into the leaf cavity of the fern. Thus Azolla pinnata serves as an excellent biofertilizer when grown in association with rice.

Q 16. Give any two reasons to justify that ginger is a modified stem. (2 marks)

Ans16.Ginger is a rhizome.
It is justified to say that ginger is a modified stem because:
(i) The 'Nodes' are marked as dry scars.
(ii) The nodes bear scale leaves, with buds of branches in their axils.

Q 17. Define biogeography. How do Darwin's Finches provide the biogeographical evidence in favour of evolution? (2 marks)

Ans17. The study of patterns of distribution of animals and plants in different parts of the earth is called ‘Biogeography’. On the Galapagos Island there are different species of Darwin's finches which have very different beak structures. The islands and their separation from each other by the ocean caused
different processes of natural selection to work on the the finches on each island and caused them to evolve into several distinct species, entirely dissimilar from each other.They however, resemble superficially with those of the South American mainland with which the Galapagos Islands were
once connected.

Q 18. Explain the structural and functional significance of fovea in the human eye. (2 marks)

Ans18.Fovea is a depressed area of the retina, which contains only cones and no rods. Ability for vision is highest in the fovea. When eyes are fixed on an object, its image is focussed on the fovea and is consequently seen most accurately.

Q 19. What is meant by R cells and S cells with which Frederick Griffith carried out his experiments on Diplococcus pneumoniae? What did he prove from these experiments? 3 marks

Ans19. R cells refer to that strain of Diplococcus pneumoniae, which formed Rough colonies. S cells refer to that strain which formed Smooth colonies.
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.
Griffith’s experiment proved that the substances, which provide the characters, are exchangeable and heat-stable. When transferred to an organism of different characters the character imparting-substances transform the host organism’s characters as per the characters of the donor organism.

Q 21. How does industrial melanism bring out the action of natural selection? (3 marks)

Ans21.The peppered moth, Biston betularia has two strains :
(i) a dull grey form, and
(ii) a black form: carbonaria
The occurrence of Carbonaria was rare before the Industrial Revolution because the dark form was more conspicuous on the tree trunks and was killed easily by the birds. However, a couple of centuries of Industrial Revolution offered better survivability to the dark form on the tree trunks
blackened with industrial soot due to its reduced conspicuousness. The grey form now stood out more conspicuously and was selectively predated by the birds. The frequency of dark form among moths increased manifolds. This phenomenon of 'Industrial Melanism' proves that the frequency of occurrence of a trait is dependent on its survivability and suitability against the factors of natural selection.

Q 22. How does intestinal juice contribute in the digestion of proteins? What provides alkaline pH in the small intestine? (3 marks)

Ans22. Intestinal juice contains the protease ‘Enteropeptidase’. Some of the inactive trypsinogen molecules of the pancreatic juice are first hydrolysed by enteropeptidase into an inactive peptide and active trypsin. Trypsin then hydrolyses the remaining trypsinogen molecules into trypsin. It also activates other pancreatic proteases, viz. chymotrypsin and carboxypeptidases. Trypsin hydrolyses basic proteins to peptides. Chymotrypsin hydrolyses casein and paracasein to peptides. Carboxypeptidases hydrolyse the terminal peptide bond of the peptide chain to release individual amino acids.
The bicarbonates of pancreatic and intestinal juices and bile from liver provide alkaline p_H.

Q 23. An mRNA strand has a series of codons out of which three are mentioned below.

(i) AUG, (ii) UUU and (iii) UAG
(a) What will these codons be translated into?

(b) What are the DNA codons that would have transcribed these RNA codons? (3 marks)

Ans23.
(a) (i) AUG and (ii) UUU will be translated. (iii) UAG is a stop codon which will not be translated.
(b)

Q 24. List any four symptoms shown by a Down's syndrome afflicted child. Explain the cause of this disorder. (3 marks)

Ans24. A child suffering with Down’s syndrome will have the following symptoms :
(i) A prominent forehead
(ii) A flattened nasal bridge
(iii) Habitually open mouth
(iv) Projecting lower lips
Down’s syndrome is caused by trisomy 21, i.e. an extra chromosome 21. Trisomy arises by non-disjunction during egg cell formation.

Q 25. Answer the following with reference to the anatomy of dicot stem :

(i) Where exactly are the cambial cells located in the vascular bundles?
(ii) What is the name given to such a bundle?
(iii) How are the xylem vessels arranged?
(iv) What type of cells constitute the pith? (3 marks)              

Q 29. Name the hormone that regulates each of the following and mention the source of it:

(i) Urinary elimination of water.

(ii) Storage of glucose as glycogen.

(iii) Sodium and potassium ion metabolism.

(iv) Basal metabolic rate.

(v) Descent of testes into the scrotum 5 marks.


Ans29.

Ans.25.
(i) The cambial cells are located in the vascular bundles of the young dicotyledonous stem, between xylem and phloem.
(ii) It is called Fascicular Cambium.
(iii) Xylem vessels are arranged towards the center, protoxylem innermost and metaxylem next.
(iv) Parenchymatous cells constitute the pith.

Q 26. Explain any three chemical barriers that offer non-specific defence mechanism. (3 marks)

Ans26. The non-specific chemical defence to the body is provided by :
(i) Lysozyme: Lysozyme is an enzyme, which destroys cell wall of many bacteria, and thus renders them non-pathogenic. It is found on skin, tears, and saliva.
(ii) Oil and sweat: Glands secrete oils and waxes, which make the surface acidic. This discourages many microorganisms from establishing themselves on the skin.
(iii) Acidic gastric juice: Some bacteria who survive the salivary secretion are killed by the highly acidic gastric juice in the stomach.