CBSE Set Qa1 Biology Sample Test Papers For Class 12th for students online

Q1. At what stage the embryo is implanted in the uterus of the mother in case of a test tube baby? 
Ans1. 32-celled Morula.

Q2. Human heart is Myogenic yet a parasympathetic nerve can reduce the heart rate. Name the nerve.
Ans2. Vagus Nerve.

Q3. Which of the following diseases could be avoided by analysing the pedegree of parents – Klinefelter’s syndrome, Haemophilia, Amoebiasis.
Ans3. Haemophilia.

Q4. Name the functional contractile unit of the muscle.
Ans4. Sarcomere.

Q5. Name any two synthetic auxins used in agriculture.
Ans5. (i) NAA (naphthaleneacetic acid)

(ii) 2,4 D (2,4-dichlorophenoxyacetic acid)

Q6. What is pulvinus?
Ans6. Pulvinus is the swollen base of the leaf in many members of the bean family. It is responsible for sleep movements.

Q7. Name the fluid in which membranous labyrinth of the inner ear floats.
Ans7. Perilymph.

Q8. In a round worm the volume of the body increases due to the growth of the body cells without increase in their number. What do you call this type of growth?
Ans8. Auxetic growth.

Q9. Why is the cleavage in mammals referred to as simple holoblastic?
Ans9. Cleavage in mammals is referred to as Simple Holoblastic because in the absence of any Yolk in the mammalian egg, it divides completely. This means the cleavage furrow divides the egg or blastoderms completely.

Q10. Name the tissue that lines the urinary bladder. State any one advantage of this tissue being present there.
Ans10. The urinary bladder is lined by Transitional Epithelium. The advantage of having this stretchable tissue is that it may be considerably stretched without getting torn when the bladder is filled with urine.

Q11. Draw a labelled diagram of vertical section of an apple.
Ans11.

Q12. Why is human male referred to as heterogametic?
Ans12. Human male has an X and a Y chromosome in its karyotype. Thus to make a male zygote, gametes of two different karyotypes are required. Therefore human male is called heterogametic.

Q13. What are the events that take place at the point of stimulation of an axon?
Ans13. An unexcited axon has the Resting Membrane Potential on its membrane and is in the polarised State. In this state the inner side of the membrane is negative as compared to the outer membrane. A threshold stimulus causes the resting membrane potential to become the Action Potential, i.e. the inner side of the membrane becomes electropositive to its outside. This action potential propagates along the membrane of the nerve fibre as the nerve impulse. As the impulse has moved away, the membrane becomes Depolarised i.e., it becomes negatively charged on the inner side.

Q14. Write the transcribed m-RNA from the DNA strand with the base sequence of TAG TAC ACT. What is the specific term used for the last codon of the transcribed m-RNA in this case?
Ans14. The transcribed mRNA from the given sequence will be AUC AUG UGA. Last codon UGA is one of the nonsense Stop-codons and would terminate the translation of the polypeptide after it is encountered during the translation.

Q15. Why is blood group identification not required while transfusing serum?
Ans15. The serum is a cell-free fluid, which forms when the blood has clotted and the thrombus has separated from it. Since the blood group deciding antigens reside on the RBCs which are not present in the serum, hence it can be transfused to anyone without the customary requirement of the blood group identification.

Q16. The primitive earth had reducing atmosphere to enable abiotic origin of life. What put an end to it?
Ans16. The emergence of green bacteria and plants with the ability to produce photosynthetic oxygen caused heavy build up of oxygen in the earth’s atmosphere, which caused the reducing environment to be changed into an oxidising environment.

Q17. How a sickle-cell carrier has an advantage over the rest of the human population in a Malaria ridden area?
Ans17. A defective form of haemoglobin is found in the RBCs of the Sickle-cell carrier. They have sickle-shaped RBCs, which are highly inefficient in binding oxygen. However, a sickle shaped RBC effectively kills the malaria parasite too, which harbors in it. Thus individuals homozygous for Sickle-cell trait have a better survivability in the event of malaria epidemics and thus natural
selection has not eliminated this trait in those geographical locations in the world, where there is a prevalence of malaria.

Q18. What acts as an inducer in Lac Operon? How does it switch on the operon?
Ans18. Lactose acts as the inducer for Lac operon. When lactose is present, the repressor protein structure is modified such that the repressor cannot bind to the operator any more. This leads to the transcription of the operon and induction of b-galactosidase and the other two enzymes.

Q19. A Chrysanthemum plant with floral buds requires more than 12 hours of dark night time to flower. If the night is interrupted by white light for duration of an hour, will the flowers bloom the following morning? Name the pigment that perceives the light stimulus for flowering. Where is the pigment present in the plant and what are its two forms?
Ans19. Chrysanthemum is a short day plant if it needs a night longer than 12 hours. It will not bloom if the night of continuous 12 hours is not available, and is interrupted by any length of light. The pigment, which perceives the light response for flowering, is Phytochrome. Phytochrome is present in the leaves, and it exists in the red absorbing P_r form and the Far-Red absorbing P_fr forms.

Q20. Define Cancer. How are cancers broadly classified pathologically? Name one major cancer in women and one major cancer in men in India.
Ans20. Pathologically, cancers may be broadly classified into three major catagories :
(i) Carcinomas, which are malignant growths of the epithelial (ectodermal) tissues.
(ii) Sarcomas, which are malignant growths of the mesodermal tissues such as bone, muscle, lymph nodes and the likes.
(iii) Leukaemias, which are unchecked proliferation of blood cells, and there precursors in the bone marrow.
In India the major form of cancer in women is the uterine-cervical cancer and it is the cancer of the mouth and throat in men.

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