Most Important diagram of biology for class 12th Ncert cbse board
1.
Structure of
ovule –
The diagram of a typical angiosperm ovule is as follows :
Arising from the placenta are the megasporangia , commonly called ovules.
The number of ovules in one ovary may be one ( wheat , paddy , mango) to
many( papaya, water melon, orchids)
2 .
Embryo sac –
After the 8
nucleate stage , cell walls are laid down leading to the organization of the
typical female gametophyte or Embryo sac .
Observe the distribution of cells inside the embryo sac. Six of the eight
nuclei are surrounded by cell walls and organized into cells ; the remaining
two nuclei, called polar nuclei are situated below the egg apparatus in the
large central cell
3. Male reproductive system-
Male
reproductive system is located outside
of his body. These external structures
include the penis , the scrotum , and the testicles.
The organs of the male reproductive system are specialized for
the following function.
· To produce ,maintain and
transport sperm (the male reproductive
cells) and protective fluids( semen)
· To discharge sperm with in the female
reproductive tract
· To produce the secrete male sex
hormones.
4 .
Female reproductive system-
The female
reproductive system made up of internal organs and external structures. Its
function is to enable reproduction of the species . sexual maturation is the
process that this system undergoes in order to carry out its role in the
process of pregnancy and birth.
Let us examine the structure of a sperm . it is a microscopic structure composed of a head, a middle piece and tail . a plasma membrane envelops the whole body of sperm.
6 .
Menstrual cycle - the reproductive cycle in the
female primates ( monkeys , apes and human beings ) is called menstrual cycle .
the first menstruration beings at puberty and is called menarche . in human
female, menstruation is repeated at an average interval of about 28/30 days ,
and the cycle of events starting from one menstruation till the next one is
called menstrual cycle.
7. Double helicle structure of D.N.A –
Double helix is the description
of the structure of a DNA molecule . A DNA molecule consist of two strands that
wind around each other like a twisted ladder. Each strand has a backbone made
of alternating group of sugar ( deoxyribose) and phosphate groups. Attached to
each sugar is one of four bases: (A) adenine, (c) cytosine, (G) guanine or (T)
thymine . the two strands are held together by bonds between the bases ,
adenine forming a base pair with thymine, and cytosine forming a base pair with
guanine.
8. Nucleosome –
The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome.
9. D.N.A replication –
In molecular biology , DNA
replication is the biological process of producing two identical replicas of
DNA from one original DNA molecule . DNA replication occurs in a living
organisms acting as the most essential part for biological inheritance.
8.10. Structure
of t R.N.A –
Transfer RNAs or t
RNA are molecules that act as temporary carriers of amino acids, bringing the
appropriate amino acids to the ribosome based on the messenger RNA ( mRNA)
nucleotide sequence . in this way , they act as the intermediaries between
nucleotide and amino acid sequences.
811. Miller’s
experiment-
Miller
experiment was a chemical experiment that simulated the conditions thought at
time (1952) to be present on the early earth and tested the chemical origin of
life under those condition.
812. Structure
of biogas plant –
The biogas plant is dome
– like structure made of bricks and cement . it consists of the following five
compartments.
i.
Mixing tank
ii.
Inlet chamber/ tank
iii.
Digester
iv.
Outlet chamber/ tank
v.
Over flow tank
813. Structure
of antibody molecule-
Antibodies are
immune
System-related proteins called immunoglobulins. Each antibody consist of four polypeptides – two heavy chains and two light chains joined to form “Y” shaped molecule.
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