Embryo sac
3 cells3 cells- DNA packing of eukaryotes is carried out with help of lysine
and arginine rich basic proteins called histones. The unit of
compaction is nucleosome. There are five types of histone
proteins - H 1 , H 2 A, H 2 B, H 3 and H 4. Four of them (H 2 A, H 2 B,
H 3 and H 4 ) occur in pairs to produce histone octamer, called
nu body or core of nucleosome. Their positively charged ends
are towards the outside. They attract negatively charged
strands of DNA. DNA over nu body forms 13
4
turns to form
nucleosome core. A typical nucleosome contains 200 bp of^
DNA helix. DNA connecting two adjacent nucleosomes is
called interbead or linker DNA. It bears H 1 histone protein.
Nucleosome chain gives a bead on string appearance.
OR(a) Shrews-The first mammals evolved in the earth were like
shrews, who existed 2,00,000 years ago. Their fossils show
that they were small sized. They were viviparous, more
intelligent and avoided dangers because of better senses.
(b) Lobefins-Lobefins are fishes which were considered to be
extinct 65 million years ago, until one was captured in 1938
in South Africa. They are considered living fossils as they
were the first amphibians that lived both on land and water.
They were ancestors of modern day frog and salamander.
(c) Homo habilis - Homo habilis (able or skillful man, the tool
maker or handyman) was the transition man, who evolved
from Australopithecus. He lived in Africa about 2 million
years ago. The teeth and bipedal locomotion were like that
of modern man. Homo erectus evolved from them.
(d) Homo erectus - Homo erectus appeared about 1.7 million
years ago in middle pleistocene in central Java (1891). H.
erectus evolved from Homo habilis. His skull was flatter
than that of modern man. Also some primitive type of
speech had developed and use of fire may be known.
- Following resistant varieties of crop should be grown by
the farmers to get rid of the problem of crop diseases and
yield.
(a) White rust – Pusa Swarnim variety of Brassica
(b) Leaf and stripe – Himgiri variety of wheat
rust
(c) Black rot – Pusa Shubhra, Pusa Snowball K-1
varieties of Cauliflower
(d) Jassids – Pusa Sem-3 or Pusa Sem-2
varieties of flat beans- Many members of the genus Glomus form symbiotic
associations with plants to form mycorrhiza. The fungal
symbiont in these associations absorbs phosphorus
from soil and passes it to the plant. Plants having such
associations show other benefits also, such as resistance
to root-borne pathogens, tolerance to salinity and drought,
and an overall increase in plant growth and development.
Therefore, Glomus increases the farm yield. - (a) Algal bloom is the excess growth of planktonic algae
that causes colouration of water. It is caused due to passage
of sewage and run off from fertilised fields into ponds, lakes
and other water bodies. Nutrients present in sewage and
fertilisers cause nutrient enrichment or eutrophication
particularly with nitrogen and phosphorus. Algal blooms cut
off light and oxygen for submerged plants and aquatic life
causing their death. They cause deterioration of the water
quality and fish mortality.
(b) Farmers should find the alternates for fertilisers like manures
and compost. Domestic or industrial wastes with organic
nutrients must be treated before passing into water bodies. - (a) The three stages that angiosperms have to pass
through are:
(i) Vegetative phase
(ii) Reproductive phase
(iii) Senescence phase
(b) (i) Roots : Modified tuberous roots of sweet-potato,
tapioca, yam, Dahlia and Asparagus can be propagated
vegetatively when planted in soil. The buds present on
the roots grow into leafy shoots above ground and
adventitious roots at their bases. Adventitious buds
develop on the ordinary roots of Dalbergia sisso,
Populus, Guava, etc., and grow to form new plants.
(ii) Rhizomes : Rhizomes are underground modified
stem that serve as means of vegetative propagation
by perennating under unfavourable conditions. They
produce new aerial shoots during the favourable
season. Typha, Canna, ginger, turmeric, lotus,
Saccharum, water hyacinth and many other plants
propagate vegetatively with the help of rhizomes.
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