Biology class XII Question Anwser 2

12/18/2011 CBSE

Q.11 How would non-secretion of hydrochloric
acid in our stomach affect food digestion ? Explain ?

Ans11. Hydrochloric acid is responsible for the following :

(i) Activates pepsinogen, prorenin and other protease proenzymes.

(ii) Denatures food proteins and facilitates action of pepsin on them.

(iii) Stops the action of salivary amylase.

(iv) Disinfect the ingested food.

In the absence of HCl in the gastric juice no protein digestion would occur and
only carbohydrate digestion would continue.



Q.12 A farmer adds Azotobactor culture in the soil before sowing maize. How
does it increase the yield of maize.

Ans12.
Azotobacter is a free living non-symbiotic soil-bacteria, which can
fix atmospheric nitrogen. The fixed nitrogen becomes available to cereal crops.
The inoculation of maize seeds with Azotobacter will ensure simultaneous growth
of Azotobacter in the field and will provide better nitrogen availability,
better yields and saving of mineral nitrogen fertiliser's.



Q.13 Give one example of co-dominance in human genetics.

Ans13.
The ABO system of blood in humans is an example of both multiple
allelism and codominance. The gene exists as three alleles: IA, IB,
and i. Both IA and IB are dominant over i. Both the
dominant alleles confer AB phenotype when present together.
























Phenotype (Blood Group) Genotype
O ii
A IA IA or
IA i
B IB IB or
IB i
AB IA IB


Q.14 If abiotic origin of life is in process
on a planet other than the earth, what would be the conditions then ? Explain
them.

Ans.
If the abiotic origin of life has to take place on any planet :

(i) Hydrogen, nitrogen, water vapour, carbon dioxide, methane, and ammonia must
be present in its environment.

(ii) Sources of energy such as thermal energy, radiation, and lightening should
be available.

(iii) Atmosphere must be non-reducing.



Q.15 Explain the structure of a mammalian heart.

Ans.
A mammalian heart is a four chambered structure : two Atria
(auricles), and two Ventricles. The sinus venosus has totally fused with the
right auricle and does not form a separate chamber. The right and left halves of
the heart are completely partitioned off. The Interatrial Septum separates right
and left atria. Interventricular septum separates the two ventricles. The great
veins which return blood from body parts open in the right atrium and are called
Superior and Inferior Vana Cavae. Pulmonary veins pool oxygenated blood from
lungs in left atrium. Atrioventricular valves guard openings between respective
auricles and ventricles. Right AV valve is a Tricuspid valve and the left AV
valve is a Bicuspid (Mitral) valve.

The right ventricle opens into the pulmonary artery, which carries blood for
oxygenation to the lungs. Left ventricle opens into the Aorta , which supplies
blood to all the body parts. Semilunar valves guard openings of these great
arteries.

 


Q.16 Describe the mode of
infection, symptoms and preventive measure of Diphtheria, Tetanus and Measles.

Ans.




























Disease Mode of Infection Symptoms Preventive measures
Diphtheria Droplet infection, droplet
nuclei
Slight fever, sore throat,
oozing of semisolid material in the throat which develops in the tough
membrane and chokes the air passage.
DPT vaccination within the
first six months of the birth.

 

Tetanus Spores of the bacteria
infecting the wounds; spread through rusted, unsterlised surgical
instruments and unattended wounds.
Muscular rigidity (lock jaw
symptom) and painful muscular spasms.
Active immunisation, ATS
injection
Measles Droplet infection Eruption of small red spots (rubeola),
inflammation of the mucous membrane of the nose.
Acquired immunity,
vaccination, isolation.


Q.17 Describe two important
functions each of the elements P, B and S in green plants and also write the
deficiency symptoms of any two of them.

Ans17.
























Element Functions Deficiency symptoms
P (1) Constitutes cell membrane.


(2) Constituent of some proteins, all nucleic
acids and nucleotides.

Poor growth,


Leaves dull green

B (1) Required for uptake and
utilisation Ca2+.

(2)
Required for pollen germination.

Brown heart disease
S (1) Constituent of some
proteins and aminoacids.

(2)
Constitutes some vitamins.

Chlorosis


Q.18 Describe how our brain gets
a continuous supply of oxygen from the atmosphere.

Ans.
Respiratory gas exchange and the blood circulation provide a
continuous supply of oxygen from the atmosphere to the brain. Inhalation draws
in fresh air from the atmosphere into lungs through nostrils and via nasopharynx,
and trachea. In the alveoli of the lungs gaseous exchange occurs between blood
and the inhaled air. The high PO2 and low PCO2 in the
lungs cause diffusion of O2 into the RBCs where it combines loosely
with the Fe2+ ions of haemoglobin to form oxyhaemoglobin.
When the oxygenated blood reaches in the brain tissue, the lower PO2
and higher PCO2 there causes dissociation of oxyhemoglobin to
deoxyhemoglobin (reduced haemoglobin) and molecular oxygen.

The brain tissue picks up O2 and releases CO2 to blood.

 


Q.19 How would non-secretion of hydrochloric
acid in our stomach affect food digestion ? Explain ?


Ans. Hydrochloric acid is responsible for the following :

(i) Activates pepsinogen, prorenin and other protease proenzymes.

(ii) Denatures food proteins and facilitates action of pepsin on them.

(iii) Stops the action of salivary amylase.

(iv) Disinfect the ingested food.

In the absence of HCl in the gastric juice no protein digestion would occur and
only carbohydrate digestion would continue.



Q.20 A farmer adds Azotobactor culture in the soil before sowing maize. How
does it increase the yield of maize.

Ans.
Azotobacter is a free living non-symbiotic soil-bacteria, which can
fix atmospheric nitrogen. The fixed nitrogen becomes available to cereal crops.
The inoculation of maize seeds with Azotobacter will ensure simultaneous growth
of Azotobacter in the field and will provide better nitrogen availability,
better yields and saving of mineral nitrogen fertiliser's.



Q.21 Give one example of co-dominance in human genetics.

Ans.
The ABO system of blood in humans is an example of both multiple
allelism and codominance. The gene exists as three alleles: IA, IB,
and i. Both IA and IB are dominant over i. Both the
dominant alleles confer AB phenotype when present together.
























Phenotype (Blood Group) Genotype
O ii
A IA IA or
IA i
B IB IB or
IB i
AB IA IB


22 Describe the process of DNA replication.

Ans.
The DNA replication occurs in the following steps :



Origin : Replication starts from specific positions in the DNA helix,
called ‘Origin’. When the replication starts the DNA strands uncoil to expose
the template surface for synthesis of daughter strands on them. Helicase enzymes
help in unwinding the helix and Topoisomerases break and reseal one strand of
DNA to avoid supercoiling. The double stranded DNA unwinds as

a Y-shaped structure called ‘Replication fork’.



Primer formation : A short stretch of RNA is formed on the DNA template,
which serves as the primer for the DNA synthesis. Primase catalyses the
synthesis of RNA on the existing DNA.



DNA synthesis : DNA polymerase enzyme adds the building blocks to the
primer in a sequence as influenced by the template in 5’ to 3’ direction. On the
parental 5’-3’ strand daughter strand forms continuously in 5’ – 3’ direction;
but on the parental 3’ – 5’ strand daughter-strand forms discontinuously in
short stretches of 5’ – 3’ fragments, called ‘Okazaki Fragments’. These

fragments are then joined together. The continuous daughter-strand is called
‘Leading strand’, and the discontinuous daughter-strand is called ‘Lagging
strand’.



DNA Polymerase has proof-reading capacity and goes-back to any wrong base and
removes it to put new base in its position before it moves to a new base in 5’ –
3’ direction.

As the new strands grow from the fork and the replication proceeds, the point of
divergence at the replication fork moves away from origin.

.23 If abiotic origin of life is in process on a planet other than the earth,
what would be the conditions then ? Explain them.

Ans.
If the abiotic origin of life has to take place on any planet :

(i) Hydrogen, nitrogen, water vapour, carbon dioxide, methane, and ammonia must
be present in its environment.

(ii) Sources of energy such as thermal energy, radiation, and lightening should
be available.

(iii) Atmosphere must be non-reducing.



Q.24 Explain the structure of a mammalian heart.

Ans.
A mammalian heart is a four chambered structure : two Atria
(auricles), and two Ventricles. The sinus venosus has totally fused with the
right auricle and does not form a separate chamber. The right and left halves of
the heart are completely partitioned off. The Interatrial Septum separates right
and left atria. Interventricular septum separates the two ventricles. The great
veins which return blood from body parts open in the right atrium and are called
Superior and Inferior Vana Cavae. Pulmonary veins pool oxygenated blood from
lungs in left atrium. Atrioventricular valves guard openings between respective
auricles and ventricles. Right AV valve is a Tricuspid valve and the left AV
valve is a Bicuspid (Mitral) valve.

The right ventricle opens into the pulmonary artery, which carries blood for
oxygenation to the lungs. Left ventricle opens into the Aorta , which supplies
blood to all the body parts. Semilunar valves guard openings of these great
arteries.

 


25 Describe the mode of
infection, symptoms and preventive measure of Diphtheria, Tetanus and Measles.

Ans.




























Disease Mode of Infection Symptoms Preventive measures
Diphtheria Droplet infection, droplet
nuclei
Slight fever, sore throat,
oozing of semisolid material in the throat which develops in the tough
membrane and chokes the air passage.
DPT vaccination within the
first six months of the birth.

 

Tetanus Spores of the bacteria
infecting the wounds; spread through rusted, unsterlised surgical
instruments and unattended wounds.
Muscular rigidity (lock jaw
symptom) and painful muscular spasms.
Active immunisation, ATS
injection
Measles Droplet infection Eruption of small red spots (rubeola),
inflammation of the mucous membrane of the nose.
Acquired immunity,
vaccination, isolation.


Q.26 Describe two important
functions each of the elements P, B and S in green plants and also write the
deficiency symptoms of any two of them.

Ans.
























Element Functions Deficiency symptoms
P (1) Constitutes cell membrane.


(2) Constituent of some proteins, all nucleic
acids and nucleotides.

Poor growth,


Leaves dull green

B (1) Required for uptake and
utilisation Ca2+.

(2)
Required for pollen germination.

Brown heart disease
S (1) Constituent of some
proteins and aminoacids.

(2)
Constitutes some vitamins.

Chlorosis


Q.27 Describe how our brain gets
a continuous supply of oxygen from the atmosphere.

Ans.
Respiratory gas exchange and the blood circulation provide a
continuous supply of oxygen from the atmosphere to the brain. Inhalation draws
in fresh air from the atmosphere into lungs through nostrils and via nasopharynx,
and trachea. In the alveoli of the lungs gaseous exchange occurs between blood
and the inhaled air. The high PO2 and low PCO2 in the
lungs cause diffusion of O2 into the RBCs where it combines loosely
with the Fe2+ ions of haemoglobin to form oxyhaemoglobin.
When the oxygenated blood reaches in the brain tissue, the lower PO2
and higher PCO2 there causes dissociation of oxyhemoglobin to
deoxyhemoglobin (reduced haemoglobin) and molecular oxygen.

The brain tissue picks up O2 and releases CO2 to blood.

 



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