CBSE Class 12 Biology Answer Key 2025 (Available): Detailed Solutions PDF Download

4. Select the statements that are true for a typical monocotyledonous embryo from the given options.

(i) Scutellum is present towards the centre of the embryonal axis.

(ii)Embryonal axis of the lower end has radicle and root cap covered by coleoptile.

(іїї)The portion of embryonal axis above the level of attachment of scutellum is epicotyl.

(iv)Shoot apex and few leaf primordia of embryo are enclosed in a hollow foliar structure

5. Given below are a few statements with reference to the human sperm.

(i) Sperm head contains a large nucleus and a lot of cytoplasm.

(ii) Mitochondria in the middle piece of a sperm provides ATP for the sperm motility.

(iii) Posterior part of the sperm head is covered by acrosome.

(iv)Spermatids undergo maturation into spermatozoa by the process of spermiogenesis.

(v) Acrosomal secretions help in the entry of the sperm into the ovum at the time of fertilization.

Choose the option with all true statements from the given options

6. A normal couple produces half the sons as haemophilic and half the daughters as carriers.

Choose the option that correctly indicates the chromosom on which the gene for this trait is located.

1. X-chromosome of father
2. Y-chromosome of father
3. One X-chromosome of mother
4. Both the X-chromosomes of the mother

7. If the sequence of bases in DNA is ATICGATG, then the sequence of bases in the transcript will be :

8. In a translational unit UTRe are present at :

(d) 5' end (before start codon) and 3' end (after stop codon).

9. The lymphoid organ located within the lining of respiratory, digestive and urinogenital tract is :

(b) MALT

10. Land reptiles which went back into water about 200 mya to evolve into fish-like reptiles were :

(a) Ichthyosaurus

11. Certain viruses used as biological control agents belong to the genus

(a) Nucleopolyhedrovirus

12. The cloning site present in the ampicillin resistance gene of E. coli cloning vector pBR322 is:

(c) Pst 1

13. Assertion (A): An antibody is a protein molecule made by thelymphocytes.

Reason (R): An antibody binds to a specific foreign antigen and neutralizes its odd effects.

(a) Both assertion and reason are true and reason is the correct explanation

14. Assertion (A) : Male contraceptive Nirodh' works on the principle of avoiding chances of ovum and sperm meeting.

Reason (R) : It is made of thin rubber/latex sheath and is used to cover the penis before coitus.

(a) Both assertion and reason are true and reason is the correct explanation

15. Assertion (A): In dihybrid crosses involving sex-linked genes 1n Drosophila generation of non-parental gene combinations are observed.

Reason (R): Two genes present on different chromosomes show linkage and recombination in Drosophila.

(c) Assertion (A) is true, but Reason (R) is false.

16. Assertion (A) : Isolated single cells can be fused to produce somatic hybrids.

Reason (R): Cells selected for somatic hybridisation have desirable characters

(a) Both assertion and reason are true and reason is the correct explanation