Multiple Choice QuestionsHow many sperms are formed from a secondary
spermatocyte
4
8
2
1
C.
2
At sexual maturity, the undifferentiated primordial germ cells divide several times by I mitosis to produce a large number of spermatogonia. Each spermatogonium actively grows to a larger primary spermatocyte. Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic.
Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo second maturation division which is an ordinary mitotic division to form, four haploid spermatids. Thus each secondary spermatocyte gives rise to two spermatids that undergo transformation to form two sperms. Overall, both secondary spermatocytes give rise to four sperms.
Grey crescent is the area
at the point of entry of sperm into ovum
just opposite to the site of entry of sperm into ovum
at the animal pole
at the vegetal pole.
Even after killing the generative cell with a laser beam, the pollen grain of a flowering plant germinates and produces normal pollen tube because
laser beam stimulates pollen germination and pollen tube growth
the laser beam does not damage the region from which pollen tube emerges
the contents of killed generative cell permits germination and pollen tube growth
the vegetative cell has not been damaged
A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this
Lots of urea and phosphate fertilizer were used in the vicinity.
The area was sprayed with DDT by an aircraft.
The lake water turned green and stinky.
Phytoplankton populations in the lake declined initially thereby greatly reducing photosynthesis.
Which one of the following pairs of plant structures has haploid number of chromosomes
Nucellus and antipodal cells
Egg nucleus and secondary nucleus
Megaspore mother cell and antipodal cells
Egg cell and antipodal cells
When a man inhales air containing normal concentration of O2 as well as CO he suffers from suffocation because
CO reacts with O2 reducing its percentage in air
haemoglobin combines with CO instead of O2 and forms carboxyhaemoglobin
CO affects diaphragm and intercostal muscle
CO affects the nerves of the lungs.
Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason for considering N.sylvestris and N.tabacum to be separate species
They cannot interbreed in nature.
They are reproductively distinct.
They are physiologically distinct.
They are morphologically distinct.
Which one of the following is the correct statement regarding the particular psychotropic drug specified
Morphine leads to delusions and disturbed emotions.
Barbiturates cause relaxation and temporary euphoria.
Hashish causes alteration of thoughts, perceptions and hallucinations.
Opium stimulates nervous system and causes hallucinations.
The distance between two genes in a chromosome is measured in cross-over units which represent
ratio of crossing over between them
percentage of crossing over between them
number of crossing over between them
none of these.
In transgenics, expression of transgene in target tissue is determined by
enhancer
transgene
promoter
reporter.
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