In humans, at the end of the first meiotic division, the male germ cells differentiate into the
Primary spermatocytes
Secondary spermatocytes
spermatids
spermatids
B.
Secondary spermatocytes
At sexual maturity, the germ cells in human male divide several times by mitosis to produce a large number of spermatogonia. In the growth phase, each spermatogonium actively grows to a larger primary spermatocyte by obtaining nourishment from the nursing cells. In maturation phase, each primary spermatocyte undergoes two successive division called maturation divisions. The primary spermatocyte undergoes first maturation division (meiotic) to producing tow haploid daughter cells called secondary spermatocytes undergo second maturation division to form four haploid spermatids. The transformation of spermatids into spermatozoa is called spermiogenesis or spermateliosis.
Which one of the flowing pairs of plants structures has haploid number of chromosomes?
Megaspore mother cell and antipodal cells
Egg cell and antipodal cells
Nucellus and antipodal cells
Nucellus and antipodal cells
A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this
(1) lost of urea and phosphate fertiliser were used in the crops in the vicinity.
(2) The area was sprayed with DDT by an aircraft.
(3) The lake water turned green and stinky/
(4) Phytoplankton populations in the lake declined initially thereby greatly reducing photosynthesis.
Which were two of above the main causes of fish mortality in the lake?
2, 3
3, 4
1,3
1,3
In the DNA molecule
the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
there are two strands, which run parallel in the 5' →3' direction
the proportion of adenine in relation to thymine varies with organism
the proportion of adenine in relation to thymine varies with organism
Gel electrophoresis is used for
cutting of DNA into fragments
separation of DNA fragments according to their size
construction of recombinant DNA by joining with cloning vectors
construction of recombinant DNA by joining with cloning vectors
The fruit is chambered, developed from inferior ovary and has seeds with succulent testa in
pomegranate
orange
guava
guava
Given below four methods (A - D) and their modes of action (1-4) in achieving contraception. Select their correct matching from the four options that follows
|
|
Method |
|
Mode of action |
|
A |
The Pill |
1 |
Prevents sperms reaching cervix |
|
B |
Condom |
2 |
Prevents implantation |
|
C |
Vasectomy |
3 |
Prevents ovulation |
|
D |
Copper – T |
4 |
Semen contains no sperms |
|
A |
B |
C |
D |
|
3 |
1 |
4 |
2 |
|
A |
B |
C |
D |
|
4 |
1 | 2 | 3 |
|
A |
B |
C |
D |
|
3 |
4 | 1 | 2 |
|
A |
B |
C |
D |
|
3 |
4 | 1 | 2 |
Polymase is formed by
several ribosomes attached to a single mRNA
many ribosomes attached to a strand of endoplasmic reticulum
a ribosome with several subunits
a ribosome with several subunits
In human adult females, oxytocin
is secreted by the anterior pituitary
stimulates the growth of mammary glands
stimulates pituitary to secrete vasopressin
stimulates pituitary to secrete vasopressin
A transgenic food crop, which may help in solving the problem of night blindness in developing countries is
Flavr savr tomatoes
Starlink maize
Bt soybean
Bt soybean
