Q1. What induces parthenocarpy in grapes?

Ans1. Auxins.

Q2. What is the term used for the regions of a gene which become part of mRNA and code for the different regions of the proteins?

Ans2. Exons.

Q3. The venous blood in the lung has a PCO₂ of 46 mm Hg. Should the alveolar PCO₂ exceed or be less than 46 mm Hg to result in diffusion of CO₂ from the blood into the alveolus?

Ans3. It should be less than 46 mm Hg.

Q4. Which part of the plant leaf is modified to form spines of Acacia and the sheath covering the leaf of Ficus elastica.

Ans4. Stipules.

Q5. Name the enzyme that can break and reseal one strand of DNA.

Ans5. Topoisomerase.

Q6. What does J-shaped growth curve of a population indicate?

Ans6. The J-shaped curve indicates that the factors of environmental
resistance do not produce zero growth to contain the exponential growth.

Q7. What forms the cambial ring in a dicot stem during the secondary growth?

Ans7. The cambial rings are formed by alternately forming secondary xylem.

Q8. Name the principal mineral anion in the extracellular fluid.

Ans8. Ca^2+.

Q9. A mother with O type blood group has conceived. The expected blood group of the foetus is B. Will there be any problems to the mother or the foetus? If so, specify the problems?

Ans9. The connections between the mother and the foetus through placenta may cause some of the foetal B blood group RBCs to enter mother’s blood. This will cause production of antibodies against blood group B in the mother’s O-blood. These antibodies will then enter back into the foetal blood and may cause haemolysis there.

Q10.What are the two types of fibres of the connective tissue? Differentiate between the two.

Ans10. Connective tissue is made of two type of fibres :
(1) White fibrous, and
(2) Yellow elastic.
White fibrous fibres are longer, highly organized and made up of collagen;
they are strong, flexible with great strength.
Yellow elastic fibres are irregularly arranged and made up of elastin;they are elastic.

Q11.A farmer observed drops of water along the margins of leaves of tomato plants growing in his well-irrigated field on a winter morning. Give reasons for this occurrence. Why had the water drops appeared only along the leaf margins?

Ans11. Since it was cold season and the field was well irrigated, the water droplets were seen as a result of the process of guttation, which occurs in the herbaceous plants in nights. The water drops were seen only on the margins of leaf because the ‘Hydathodes’ from which guttational water loss occurs are found near the vein endings only.

Q12. Give the scientific name of the modern wheat. Why is it quoted as a typical example of rapid speciation?

Ans12. Modern wheat is Triticum aestivum. It is quoted as a typical example
of rapid speciation because it has originated by natural interspecific crossing and diploidisation of the hybrids. The final hexaploid Triticum aestivum is very different from any of its parents: T. monococcum, T. durum, Aegilops speltoides, or A. squarrosa.

Q13. Name any two of cyanobacteria and explain how they serve as main sources of bio-fertilizers.

Ans13. Nostoc and Anabaena are two of the cyanobacteria. Cyanobacteria are main sources of biofertilisers because they have the combination of photosynthetic and nitrogen fixing ability. They are present as free-living microorganisms in the soil and produce easily available nitrates and nitrites.

Q14. What are the two striking observations when different stages of embryos of different classes of vertebrates are studied comparatively? How does this study support evolution?

Ans14. Two striking observations are that gill clefts and notochord appear
in the embryonic development of all vertebrates from fish to mammals. The
notochord has been replaced by the vertebral column in all the adult
vertebrates. Similarly, gills are replaced by lungs in adult amphibians,
reptiles and mammals. Such similarities in embryonic development reinforce
the idea of evolution from common ancestors.

Q15. An animal should possess at least one out of the three possible characteristics to enable it to function as a ureotelic organism. List these characteristics.

Ans15. Ureotelism is the urinary elimination of nitrogen mainly as urea. An
animal can be ureotelic only if the animal can afford to :

(i) excrete sufficient volumes of water,
(ii) concentrate urea considerably in the urine,
(iii) retain considerable amounts of urea in the blood and body fluids.
Whale, camel, toad, and shark are all ureotelic.

Q16. Pick out the plant with whorled arrangement of leaves from the list given below and say why it is categorised so? Neem; Nerium; Nepenthes.

Ans16. Nerium has whorled leaves phyllotaxy. It is said to be of ‘whorled leaves’ type because 3-5 leaves occur at a node.

Q18. What category of pathogens causes poliomyelitis? How is crippling caused in the victim of this disease? How can this disease be prevented?

Ans18.Polio is caused by poliovirus. In CNS the virus destroys the dorsal
horn cells of the spinal cord, which control the activities of the muscles.
Without nerve impulses the muscles fail to work and shrink. Thus the limbs
become paralysed. This crippling disease can be prevented by avoiding the
ingestion of the virus via food or drink, and by vaccination of the kids in the target age group.

Q19. To which category of cells do B-cells and T-cells belong? How do they differ from each other with reference to their formation and response to antigens?

Ans19. B-cells and T-cells are ‘Lymphocytes’.
Both develop from stem cells of liver in foetus or bone-marrow cells in adults. But B-cells mature in bone marrow whereas the T-cells mature under the influence of thymus. T-cells are responsible for cellular immunity and B-cells produce antibodies.

Once an antigen-specific B-cell is triggered by its specific antigen, it gives rise to a clone of plasma cells by quick multiplication, which produce antibody for that antigen.

T-cells are also specific for antigens and when their destined antigen is
encountered a clone of T-cells is produced. However, T-cells are of three
different types :
(i) Killer T-cells directly attack and destroy antigens, by moving to the site of invasion and producing chemicals that attract phagocytes and stimulate them to feed more aggressively on antigens.
(ii) Helper T-cells act to stimulate antibody production by B-cells.
(iii) Supressor T-cells supress the total immune reaction keeping it from
attacking the body’s own cells.

Some of suppressor cells become memory cells.

Q21. Human skin colour is believed to be controlled by at least three separate genes :
What do you call this type of inheritance?

i) Suppose the genes are designated as A, B, and C and darkness is dominant over fairness, what shall be the genotypes of the darkest, fairest and intermediate skin colour?

ii) What will be the total number of allele combinations in the gametes of a person heterozygous,all the three genes.
Ans21.(i) This inheritance is called quantitative inheritance and individual genes show incomplete dominance.
(ii) The genotype of the darkest will be AABBCC, that of the intermediate
will be AaBbCc; and that of the fairest will be aabbcc.
(iii) The number of possible allele combinations in the gametes is eight for
such a three-gene combination (2³).

Q23. Expand PEP. Where is it produced in C₄ plants? What is its role in the biosynthetic process?

Ans23.Phosphoenolpyruvate.

It is produced in the mesophyll cells in C₄ plants.

Its function is to fix CO₂ by getting carboxylated. The carboxylation of PEP
produces Oxaloacetate, which gets converted to malate. Malate is transported
across to the Bundle sheath cells where malate is degraded to release CO₂ and Pyruvate. Pyruvate is returned to the mesophyll cells and CO₂ is fixed in
Calvin cycle. Its role is to fix CO₂ out of the Calvin cycle in the mesophyll
cell and thereby separate the fixation of CO₂ by Rubisco from uptake part.

Q24. What type of striated muscles constitutes the muscles of the eyeball? How is this specific type of muscle advantageous?

Ans24.Six striated ocular muscles attatch the sclera of the eye-ball to the
eye-socket. The ocular muscles move the eye ball for looking at different
directions.

Q25. The base sequence on one of the strands of DNA is TACTAGGAT.

(i) Write the base sequence of its complimentary strand.
(ii) What is the distance maintained between the two consecutive paired bases in the DNA molecule?
(iii) Who contributed the base complementarity rule?

Ans25.(i) The base sequence will be : ATGATCCTA.
(ii) The distance between two consecutive base pairs in DNA helix is 0.34 nm.
(iii) Chargaff proposed the base complementarity rule.

Q26. Name the parasympathetic nerve from the brain that innervates most of the visceral organs. List any four functions of this nerve.

Ans26.The Vagus nerve innervates most of the visceral organs.
Its major four functions are :
(i) Gastric and pancreatic secretion,
(ii) Cardiac slowing,
(iii) Gastrointestinal movements,
(iv) Respiratory reflexes.

Q27. Sometimes natural selection is not operative if the abnormal allele is somewhat advantageous to the individual. Explain this mechanism with a suitable example.

Ans27. Sometimes natural selection is not operative if the abnormal allele
is advantageous to the individual because the abnormality offers better
survivability due to its advantages over the normality.

Sickle cell anaemia is a good example of this phenomenon, where a defective
form of haemoglobin is found in the RBCs. Individual homozygous for this
trait die at an early age. Even those homozygous for this trait have
sickle-shaped RBCs, which are highly inefficient in binding oxygen. However,
natural selection has not eliminated this trait in those geographical locations in the world, where there is a prevalence of malaria. This has happened because a sickle shaped RBC effectively kills the malaria parasite, which harbours in it. Thus individuals homozygous for Sickle-cell trait have a better survivability in the event of malaria epidemics and are favoured during the natural selection despite of their abnormal trait.

Q29. What envelops the mammalian ovum preventing the entry of sperm into it easily? How does the sperm gain the entry eventually? What is the significance of the point of entry of the sperm?

Ans29. The cellular layer of follicle cells, called Corona Radiata; and non-cellular layer, called Zona Pellucida prevent the entry of sperm into the Ovum easily. In order for fertilisation to take place, the Corona Radiata must be penetrated or dissolved. This is accomplished by enzymatic hydrolysis of the material cementing the cells of Corona Radiata together. The sperm releases Sperm Lysin from the Acrosome, which consists of mainly Hyaluronidase enzyme that dissolves the follicle-cells away.

At the point of entry of sperm, the cortical granules below the Zona Pellucida forms a thick covering called fertilization membrane. The fertilisation membrane prevents Polyspermy.