Subject

biology

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

1.

Name the respective pattern of inheritance where F1 phenotype

(a) does not resemble either of the two parents and is in between the two.

(b) resembles only one of the two parents.


(a) Incomplete Dominance is the condition in which the F1 phenotype does not resemble both the parents and is in between the two.

(b) Complete Dominance is the condition in which the F1 phenotype resembles the dominant parent i.e one of the two parents.

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2.

(a) Where do the signals for parturition originate from in humans?

(b) Why is it important to feed the newborn babies on colostrums? 

(a) The signals for parturition originate from the fully developed fetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin (birth hormone) from the maternal pituitary gland.

(b) The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) that protects the infant or new born babies and develops resistance in them.

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3.

Why is it desirable to use unleaded petrol in vehicles fitted with catalytic converters?


It is desirable to use unleaded petrol in the automobiles fitted with catalytic converter because lead in the petrol inactivates the catalyst.

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4.

Where is acrosome present in humans? Write its function


Acrosome is a cap-like structure present in the anterior part of the head of the sperm. It contains the enzyme hyaluronidase, which hydrolyses the outer membrane of the egg, thereby helping the sperm to penetrate the egg at the time of fertilization.

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5.

How do the pollen grains of Vallisneria protect themselves? 


Vallisneria being a water pollinated species protect their pollen grains by having a mucilaginous coat. The coat prevents the pollen grains from getting wet.
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6.

Given reasons for the following: 

(a) The human testes are located outside the abdominal cavity.

(b) Some organisms like honey-bees are called parthenogenetic animals.


(a) The human testes are located outside the abdominal cavity in a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2 -2.5o C lower than the normal internal body temperature) necessary for spermatogenesis.

(b) Honey bees are parthenogenetic organisms because in them an unfertilized egg develops into a new individual and there is no fertilization. This process of reproduction without fertilization is called parthenogenesis.

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7.

State the significance of Coelacanth in evolution. 


Coelacanths are considered to be the missing link between fishes and the first four-limbed animals (amphibians) and were the ancestors of modern day frogs and salamanders.

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8.

Mention the role of cyanobacteria as a biofertiliser. 


Cyanobacteria such as Anabaena and Nostoc are free-living and help fix atmospheric nitrogen and act as bio-fertilizers especially in paddy fields.

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9.

How is the entry of only one sperm and not many ensured into an ovum during fertilisation in humans? 


During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and with the help of acrosomal secretions induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilise an ovum

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10.

Write the name of the following: 

(a) The most common species of bees suitable for apiculture

(b) An improved breed of chicken


(a) Apis indica is the most common species of bee suitable for apiculture.

(b) Leghorn is an improved breed of chicken.

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