- (a) refer to the given figure
Xshowing structure of a mature
pollen grain.
What is the fate of the part
labelled 'X'?
(b) Despite occupying about 90% of earth's surface, oceans
contribute only 32% of the total productivity. Why?
- refer to the given figure showing a
method of contraception and answer
the accompanying questions.
(a) What does the given figure
represent?
(b) How does this method of
contraception work? - Haemophilia is a sex linked recessive disorder of humans.
The pedigree chart given below shows the inheritance of
haemophilia in one family. Study the pattern of inheritance
and answer the questions given.
2910 11 12 13 14 15413 5 6 7 8(a) Give all the possible genotypes of the members 4, 5 and 6
in the pedigree chart.
(b) a blood test shows that the individual 14 is a carrier of
haemophilia. The member numbered 15 has recently
married the member numbered 14. What is the probability
that their first child will be a haemophilic male?
OR
(a) Why Western Ghats have been declared as hot spots?
(b) How do chlorofluorocarbons reduce ozone to oxygen?
- The plant cells possess the unique properties of
dedifferentiation and redifferentiation. briefly describe
these processes with respect to plant tissue culture. - "Culture medium can be referred to as a highly enriched
laboratory soil." Justify this statement. - List various factors due to which pathogens develop
resistance to existing antibiotics. - (a) Why are gaseous nutrient cycles more perfect as
compared to sedimentary nutrient cycles?
(b) Over-exploitation of a species reduces the size of its
population eventually leading to its extinction? Give a
suitable example to justify this statement. - a plasmid DNa and a linear DNa (both of the same size)
have one site for restriction endonuclease. When cut and
separated on agarose gel electrophoresis, plasmid shows one
DNa band while linear DNa shows two bands. explain why?
SECTION - D- Mridul is a student of XII standard who is very good at
playing volleyball. He was selected as captain of the school
team for district level tournament.
Meanwhile he attended a blood donation camp to donate
blood and got to know that he was HIV positive. He became
very depressed and lost interest in everything. He remained
absent from school for a long time. His biology teacher
came to know about it. He visited Mridul's home and
counselled him. Mridul was back to school and also played
the tournament.
(a) What values have been reflected by the biology teacher?
(b) How is a person detected to be HIV positive different from
a person who has developed aIDS?
(c) Diagrammatically explain the events that the aIDS virus
undergo to increase its progeny after getting inside human
body.
SECTION - E - (a) Draw a flow chart depicting the steps that you would
follow to transfer a desirable gene of interest into a plant.
(b) What do you understand by the term biofertiliser? explain
the mode of action of a popular biofertiliser.
OR
explain the process of PCr and its working mechanism. - Draw a well labelled diagram of
(a) Transverse section of a mature dehisced anther.
(b) a section through human ovary.
OR
(a) When and how does placenta develop in a pregnant female?
(b) Why are human testes located outside the abdominal cavity? - (a) What will be the value of r (intrinsic rate of natural
increase) if a population growing exponentially doubles its
size in 3 years?
(b) Predators are considered as harmful animals as they harm
humans and livestock. Describe the ecological role of
predators in an ecosystem.
OR
Define somatic hybridisation. explain the steps involved in
somatic hybridisation with the help of suitable diagram.
SOLUTIONS - ancestral line of conifers amongst the given list of plants is
Psilophyton (primitive pteridophytes). - Population density of tigers can be measured on the basis
of their pug marks and faecal pellets. - In monosporic type of development of embryo sac, only
one megaspore of a tetrad remains functional and the
remaining three megaspores gradually degenerate. The
functional megaspore develops into female gametophyte,
e.g., Polygonum. - Nicotine present in tobacco stimulates the release of
adrenaline resulting in high blood pressure.