CLASS XIIth biology previous year question paper solution

1. PYQ DISCUSION
MAYA RAM
PGT BIOLOGY
CPWS JODHPUR

2.  Normally one embryo develops in one seed but
when an orange seed is squeezed many embryos of
different shapes and sizes are seen. Mention how it
has happened.
 Ans: Some nucellar cells / diploid cells / integument
cells surrounding the embryo sac start dividing and
protrude into the embryo sac and develop into
embryos. (In such species each ovule contains many
embryos-polyembryony).

3.  Differentiate between albuminous and non-albuminous
seeds, giving one example of each.
Ans. Albuminous -(with residual) endosperm is not completely
used up during embryonic development eg,wheat /maize /
castor / sunflower.
Non albuminous - (without residual) endosperm is
completely consumed during embryonic development eg.
pea / groundnut.

4.  Draw a diagram of a male gametophyte of an
angiosperm. Label any four parts. Why is
sporopollenin considered the most resistant
organic material ?
 Sporopollenin can withstand high temperature /
strong acids / strong alkali.

5. (a) Draw a labeled diagram of the human female
reproductive system.
(b) Enumerate the events in the ovary of a human
female during : (i) Follicular phase (ii) Luteal phase
of menstrual cycle.
Ans: b) (i) Follicular phase-primary follicles grow and
mature, secretion of estrogen, first meiotic division.
(ii) Luteal phase - development of corpus luteum,
secretion of progesterone

6.  (a) Write the specific location and the functions of the
following cells in human males :
(i) Leydig cells
(ii) Sertoli cells
(iii) Primary spermatocyte
Ans. (a) (i) Leydig cells - found in interstitial spaces between
somniferous tubules ,secrete androgens / testosterone.
(ii) Sertoli cells -found in between spermatocyte inside
somniferous tubules, nourish developing spermatozoa /
sperms / germ cells.
(iii) Primary spermatocyte -found in the inner lining of
somniferous tubules,they undergo meiosis and form
sperms

7. (b) Explain the role of any two accessory glands in
human male reproductive system.
Ans:
The accessory glands are seminal vesicle, protstate
gland, bulbourethral gland Secretions of these glands
constitute seminal plasma which is rich in fructose,
Calcium and certain enzymes provide nourishment to
sperms / Secretions of bulbourethral glands also help in
lubrication of penis.

8.  Write the characteristic features of anther, pollen
and stigma of wind pollinated flower.
Ans: Pollen – light/ large number/ non-sticky.
 How do flowers rewards their insect pollinators?
Explain.
Ans: Provide nectar/ food for the larvae/ pollen grains/
safe place to lay eggs.

9.  Give a schematic representation showing the events
of spermatogenesis in human male.
Ans:
 Describe the structure of a human sperm.
Ans:
 Describe the sequence the events that lead to the
development of a 3 celled pollen grain from
microspore mother cell in angiosperms.
Ans: Microspore mother cell, meiosis, 4 haploid
microspores, tetrad, each microspore is a pollen grains,
with two layered wall- outer exine and inner intine, pollen
grains contains one larger vegetative cell, and a smaller
generative cell, which divides mitotically, into two male
gametes.

10. (a) Name the organic material exine of the pollen grain is
made up of. How is this material advantageous to
pollen grain ?
Ans: Sporopollenin.
Most resistant to high temperature / strong acids /
alkali / no enzymes can degrade it
(b) Still it is observed that it does not form a continuous
layer around the pollen grain. Give reason.
Ans: (Germs pores) to allow pollen tube to emerge out /
pollen germination.
© How are ‘pollen banks’ useful ?
Ans: Helps in storing pollen grains for years / for crop
breeding programmes

11. (a) Explain the menstrual phase in a human female. State the
levels of ovarian and pituitary hormones during this phase.
Ans: Menstrual phase occurs when released ovum not fertilized , break
down of endometrial lining (of the uterus) and its blood vessel form
the liquid that comes out through the vagina , lasts for 3 to 5 days .
Level of ovarian and pituitary hormones fall.
b) Why is follicular phase in the menstrual cycle also referred as
proliferative phase ? Explain.
Ans: Primary follicle grows into graafian follicle under the influence of
LH & FSH , regeneration of endometrium (under the influence of
estrogen)
c) Explain the events that occur in a graafian follicle at the time of
ovulation and there after.
Ans: Graafian follicle ruptures to release the ovum (secondary oocyte)
, remaining parts of the Graafian follicle transform into corpus luteum
d) Draw a graafian follicle and label antrum and secondary oocyte.

12. a) As a senior biology student you have been asked to
demonstrate to the students of secondary level in your
school, the procedure(s) that shall ensure cross-
pollination in a hermaphrodite flower. List the different
steps that you would suggest and provide reasons for
each one of them.
 Ans: Emasculation , removal of anthers from the flower bud
before the anther dehisce to avoid self pollination.
 Bagging , to prevent contamination of its stigma with
unwanted pollen grains.
 Rebagging , the stigma of the mature ovary are dusted with
desired pollen grains and rebagged to allow the fruit to
develop

13.  Draw a diagram of a section of a megasporangium of an
angiosperm and label funiculus, micropyle, embryo sac
and nucellus.

14. a) A pollen grain in angiosperm at the time of
dehiscence from an anther could be 2-celled or 3-
celled. Explain. How are the cells placed within the
pollen grain when shed at a 2-celled stage ?
Ans: In 2-celled stage the mature pollen grain contains a
generative and vegetative cell, whereas in 3-celled stage
one vegetative cell and two male gametes are present .
The generative cell floats in the cytoplasm of vegetative
cell

15. (a) Can a plant flowering in Mumbai be pollinated by
pollen grains of the same species growing in New
Delhi ? Provide explanations to your answer.
Ans: Yes, By artificial means.
b) Draw the diagram of a pistil where pollination has
successfully occurred. Label the parts involved in
reaching the male gametes to its desired destination.

16. a) Explain the following phases in the menstrual cycle of” a
human female: (i) Menstrual phase (ii) Follicular phase (iii)
Luteal phase.
Ans:
(i) Menstrual phase - first 3-5 days of the cycle where menstrual
flow occurs due to break down of endometrial lining of uterus,
if the released ovum is not fertilized.
(ii) Follicular phase - from 5th to 14th day of the cycle where the
primary follicles grow to become a fully mature Graafian follicle
, endometrium of uterus regenerates , Graafian follicle
ruptures to release ova (ovulation on 14th day)
(iii) Luteal Phase - During 15th to 28th day remaining parts of
graafian follicle transform into corpus luteum , secretion of
progesterone (essential for maintenance of endometrium)

17. b) A proper understanding of menstrual cycle can help
immensely in family planning. Do you agree with the
statement ? Provide reasons for your answer.
Ans: Yes , can take appropriate precautions between 10th
to 17th day of the menstrual cycle when the chances of
fertilization are high.