XII BIOLOGY PRACTICAL-
Q.4- Spotting:
(Identify the following 10 spots-)10 Marks
Q. 4 Identify the stage of meiosis in the given slide.
Meiosis –I
prophase-I
Metaphase –I
Meiosis –II
Answer:The given spot is a
stage of meiosis –Leptotene.
Chromosomes appear
like long, thin, beaded thread.
In the leptotene stage the chromosomes divide
longitudinally to form pairs of sister chromatids.
Answer:
The given spot is a
stage of meiosis –Zygotene.
It is characterized
by pairing of homologous chromosomes called synapsis.Paired chromosomes are
called bivalents or tetrad.
Answer:The given spot is a stage of
meiosis –Pachytene.
Each chromosome is with 2 chromatids.
Crossing over occurs between non sister
chromatids of bivalent.
Exchange of genetic material takes
place which results in recombination.Recombination leads to variation and thus
the evolution of the organism.
Answer:The given spot
is a stage of meiosis –Diplotene.
Homologous
chromosomes start repelling from each other but remain attached at the
chiasmata.
Answer:
The given spot is a
stage of meiosis –Diakinesis.
Terminalizationtakes
place.
Nucleolusand nuclear
membrane completely disorganize and disappear
Answer:
The given spot is a
stage of meiosis –Anaphase –I.
Spindle fibres start
condensing, become shorter and pull homologous chromosomes towards opposite
poles.
Reduction division
takes place in this stage.
Answer:
The given spot is a stage of meiosis –Telophase –I.
Chromosomes reach the opposite pole.
Nucleolusgets reorganizedand then reappears.
Nuclear membranegets developedaround each set of
chromosomes, forming 2 daughter nuclei.
Answer:
The given spot is a
stage of meiosis –Prophase –II.
The nucleus enlarges.
Chromosome becomes
prominent, shorter and thicker.
Nucleolusand nuclear
membranedisappear.
Answer:
The given spot is a
stage of meiosis –Metaphase –II.
An imaginary line
develops forming the equatorial plane which is at right angle to previous
division.
Chromosomes get arrangedalong
the equatorial planein such a way that the centromere lie on the plane the arms
towards the poles.
At the end spindle
formationtakes place.
Answer:
The given
spot is a stage of meiosis –Anaphase –II.
Centromere
dividesand sister chromatidsget separatedwhich are now called daughter
chromosomes.
Spindle fibres start condensing becoming shorter and shorter pulling daughter chromosomes up to the opposite poles.
Answer:
The given spot is a stage of meiosis –Telophase –II.
Daughter chromosomes get collected at the opposite
poles.
Reappearance ofnucleolusand nuclear membraneresults in the formation of two daughter nuclei.
Q 4 H Identify the animal and comment on its xeric /
aquatic adaptations.
Xeric Animals:Camel (Camelus spp.)
Kangaroo rat (Dipodomys spp.)
Aquatic Animals:Fresh water fish Rohu (Labeo
rohita)
Dolphin (Delphinus spp)
H) It is Xeric adaptations in Camel-camelus spp
1.It is a xerocoles animal adapted to the desert conditions.
2. It can tolerate wide range of temperature fluctuations.
3.It excretes concentrated urine in order to conserve water.
4. It accumulates fat in the hump so that heat flows away from the body and inward flow of heat is prevent.
5.Camel can even close its nostrils to stop blowing sand from entering nostrils.
6. It is a two-toed ungulate showing presence of hooves instead of claws on the feet.
7 Flat and wide feet help it to walk easily over soft sand.
H) It
is Xeric Adaptations In Animals -Kangaroo rat (Dipodomys spp)
1. It is a Xerocoles rodent, which avoids heat by adopting nocturnal habits.
2. It seals its burrow by day to keep its chamber moist.
3. It goes into a 'move-freeze' mode which reduces predation at night.
4. It converses water, by lowering its metabolic rate, thus reducing the loss of water through its skin and respiratory system.
H) its aquatic adaptations In Animals. –Rohu-labeo rohita
A fresh water fish (ROHU)- Aquatic conditions with respect to their morphological adaption.
1.Body of fishes is stream-lined and laterally compressed to reduce friction and to allow swift passage in water while swimming.
2.It respires by gills which are specialized breathing organs to use gases dissolved in water.
3.It has air-bladder which acts as an accessory respiratory and
hydrostatic organ to maintain buoyancy. 4.Eyes
have no eyelids. Eyes are protected by hardened lens.
H) Its aquatic adaptations. In animal
Dolphin-Delphinus spp.
i. It is a mammal and not a fish.
ii. It has streamlined, smooth and furless body to reduce friction.
iii. It has a backward curving dorsal side and dorsal fin. Snout is beak like.
iv. The position of nostrils near the top of the head, facilitates easy breathing when animal reaches the surface of water for breathing,
v. Flippers in dolphin can control for steering, slowing and going up or
down or out of water.
I) It is part
an Embryo sac in V.S.of ovule.
1.Egg Apparatus: After fertilization, gives rise to
diploid zygote which later on develops into an embryo.
2.Polar nuclei: The two polar nuclei fuse to form single
diploid secondary nucleus. The secondary nucleus forms the triploid endosperm
nucleus, which produces endosperm in which food for the embryo is stored.
3. Antipodal cells: These are nutritive cell. They
degenerate during seed formation.
Answer:B –Antipodal cells
F –Egg cell / Female gamete
Q. 4 J Comment on the given pedigree chart.
•Colour Blindness
J) the given pedigree chart is Rolling of toungue.
The rolling of tongue is the ability of a person to roll the tongue inwards in 'U' shaped .
The rolling and folding of the tongue is often described as a dominant trait with simple mendelian inheritance.
The dominant gene is believed to be responsible for folding and rolling of the tongue while the inability to roll and fold the tongue is associated with recessive gene.
The inability to roll the tongue, is caused by autosomal recessive alle 'a'.
Both homozygous dominants (AA) and heterozygous (Aa) individuals are able to roll the tongue while homozygous recessive (aa) individuals are unable to roll the tongue
J) The given pedigree chart is Widows peak.
Widow's peak is a V-shaped hair line across the forehead.It is a dominant autosomal trait.
The gene responsible for widow's peak is dominant 'W'.
Therefore, both homozygous dominant (WW ) and heterozygous (Ww) individuals have widow's peak, while homozygous recessive (ww) individuals have straight hair line.
This feature is observed with both men and women.
Answer:The given spot is a pedigree chart of a genetic trait ‘colour blindness’.
Colour blindness is a sex / X linked recessive disorder of humans.
Due to recessive gene present on X chromosomes, colour sensitive cone cells are not formed.
This results in red-green colour blindness.
It is more common in male than female.
It follows criss-crossinheritance as this trait is transmitted from the father to the grandson through his carrier daughte