- Pyramid of numbers is a graphic representation of the
number of individuals per unit area at various trophic levels.
In most cases it is upright however this is not applicable
in all the cases. In a forest ecosystem, a single large sized
producer like tree can provide nourishment to several
herbivores (e.g., birds). The birds may support a still larger
population of ectoparasites which may further support a
still larger number of hyperparasites. Such a pyramid shall
be inverted. Small sized herbivorous birds are usually eaten
by falcon or eagle. The number of eagles is, however, very
small. This type of pyramid of numbers shall be spindle-
shaped. - (a) A - GnRH (Gonadotropin Releasing Hormone)
B - LH (Luteinising Hormone)
C - FSH (Follicle Stimulating Hormone)
(b) Inhibin is a protein hormone. It inhibits both hypothalamus
and pituitary gland to suppress FSH secretion thereby
affecting spermatogenesis.
(c) Sertoli cells support developing sperms and provide them
with nutrition. Sertoli cells secrete androgen binding protein
(ABP) that concentrates testosterone in the seminiferous
tubules. Sertoli cells also secrete inhibin which suppresses
FSH synthesis.
- Diagrammatic representation of pre-pollination development
of the male gametophyte (pollen grain) of angiosperms is
as:
23. (a) Anuradha reflects the values of awareness and concern
for the environment along with a good knowledge of bio-
control method.
(b) Anuradha wanted to make the farmers aware about
the harmful effects of pesticides on human health and
environment, and about the advantages of using bio-
control agents. So she asked her grandfather to organise
the meeting.
(c) Anuradha is talking about the bio-control method. The
natural method of pest and pathogen control involving
use of viruses, bacteria and insects (which are their natural
predators) is called bio-control (or biological control).
(d) Biopesticides are viruses, bacteria, protozoa, fungi, etc.
that are used for control of weeds, insects and pathogens.
These are of two types: bioherbicides and bioinsecticides.
Bioherbicides are chemicals used for inhibiting the growth
of plants in unwanted places e.g., Cactoblastis cactorum
and Chrysolina beetles have checked the growth of their
natural herbivores Opuntia and Hypericum perforatum
respectively. Bioinsecticides are biological agents that are
used to control harmful insects e.g., Baculovirus heliothis
and Bacillus thuringiensis are effective against cotton
bollworm and cabbage looper respectively.
24. Refer to answer 2, page no. 50, `MTG Excel in Biology’.
OR
DNA packing in eukaryotes is carried out with the help of
five types of histone proteins— H 1 , H 2 A, H 2 B, H 3 and H 4. The
unit of compaction is nucleosome. 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 (due to basic amino acids) are towards the outside.
They attract negatively charged strands of DNA. About
166 bp of DNA is wrapped over nu body for 1^3 / 4 turns to
form nucleosome of size 110 × 60Å (11 × 6 nm). DNA
connecting two adjacent nucleosomes is called interbead
or linker DNA, it bears H 1 histone protein. Lengh of linker
DNA is varied (about 145Å with 70bp). Nucleosome and
Manchineel (poison apple or poison guava), a tree of genus
Hippomane of family Euphorbiaceae is considered as one of
the most toxic trees. All parts of the tree contain toxins. It is
native to coastal beaches and mangroves of South Florida,
Caribbean, Central and Northern South America. It is a
round-crowned tree that grows up to 12 m in height with
60 cm thick trunk. It produces yellow to reddish, sweet-
scented fruits which contain toxins. When ingested, the
fruit is pleasantly sweet with subsequent strange peppery
feeling which gradually progresses to a burning sensation and
tightening of throat thereby disabling the victim to swallow
any food. Ingestion of toxic fruits may lead to the damage
of digestive tract if not treated in time. Manchineel is so
poisonous that smoke from its burning wood irritates eyes
and latex from its leaves and bark causes skin inflammation.