- (a) Congenital diseases are present
from birth. They may be caused due to a
single gene mutation, chromosomal
aberrations or environmental factors.
Sickle cell anaemia is caused due to
mutation in a single gene. Therefore,
both assertion and reason are true and
reason correctly explains the assertion.
- (b) Many microorganisms produce
powerful poisons called toxins which cause
diseases. They are of two types–exotoxins
and endotoxins. Exotoxins are released as
soon as they are secreted, while
endotoxins are released after the death of
the organism. Endotoxins are responsible
for dysentery, cholera, typhoid fever and
bubonic plague. Here, assertion and
reason both are true, but reason is not the
correct explanation of assertion.
Therefore, option (b) is correct.
- (e) The complement system is a
defensive system. It was named
complement by Ehrlich to denote its
activity of complementing the action of
antibody on antigen. It is a group of over
30 proteins, many of which are enzyme
precursors and are produced by the liver.
These proteins are present in the blood
plasma and on plasma membranes.
Therefore, assertion is false, but reason is
true.
- (a) In asthma the tissue surrounding
the bronchioles of the lungs swells up and
compresses the bronchioles. Hence, there
is difficulty in breathing. Therefore,
option (a) is correct.
- (e) In radiation therapy the cancerous
part of the body is exposed to X-rays
which destroy rapidly growing cells
without harming the surrounding tissue.
Rn-220, Co-60 and I-131 are radioisotopes,
which are generally used in radiotherapy.
Therefore, option (e) is correct.
- (c) Major Histocompatibility
Complexes (MHCs) is also referred to as
the HLA (Human Leucocyte Antigen)
system in humans. The MHC is a set of
molecules displayed on cell surfaces. It is
responsible for lymphocyte recognition
and antigen presentation. It is encoded
by several genes located on human
chromosome 6.
- (a) In leukemia (Leukaemia),
production of White Blood Corpuscles
(WBCs) increases in the bone marrow. It
causes abnormal increase of WBCs
count. Therefore, leukemias are
commonly called blood cancers.
- (d) Assertion and reason both are
false. An antigen carries more than one
epitope. Each Y-shaped antibody
molecule has at least two binding sites
that can attach to a specific epitope on an
antigen. An antigen can bind to identical
epitopes on two different cells at the
same time, which can cause
neighbouring cells to aggregate. - (c) Dendritic cells possess long
cytoplasmic processes. Their primary
role is to function as highly effective
antigen trapping and antigen presenting
cells. These cells are found in lymph
nodes, spleen, thymus and skin. They are
non-phagocytic in nature. - (b) Assertion and reason both are
correct, but reason is not the correct
explanation of assertion. HIV causes
AIDS. It is a retrovirus that attacks
helper T-cells. Its genome consists of a
single-stranded RNA filament
segmented into two identical filaments.
Its envelope possesses a lipid bilayer
derived from host cell membrane and
projecting knob like glycoprotein spikes. - (a) Drinking of excessive alcohol
impairs one’s physical, physiological and
psychological functions. Alcohol affects
co-ordination of limbs, head and eyes as
well as vision. By alcohol intake vision
becomes blurred and unsteady. Often the
field of vision is reduced. It is known as
tunnel vision. Therefore, drinking and
driving is not permitted together. - (e) Ganja is the dried unfertilised
female inflorescence of Cannabis sativa.
It is usually smoked in cigarettes. Its
effects are produced almost
instantaneously. - (b) Allergy is the hypersensitivity of
a person to some foreign substances
coming in contact with or entering the
body. It involves mainly IgE antibodies
and chemicals like histamine and
serotonin. IgE antibodies are produced in
response to an antigen, coat mast cells
and basophils. The allergic tendency is
genetically passed from parent to the
child and is characterised by the presence
of large quantities of IgE antibodies in
the blood.
14.(a) Cytotoxic T-cells are capable of
killing microorganisms and even some of
the body’s own cells directly hence, they
are called killer cells. After binding
with the foreign cells, they secrete
perforins that punch large round holes intheir membrane. The foreign cells
become greatly swollen due to the quick
flow of fluid into it. It usually dissolves
shortly thereafter.15.(c) Malaria is caused by the malarial
parasite, i.e. Plasmodium. It has two
hosts. Female Anopheles mosquito is
considered as the definitive or primary
host of malarial parasite as the sexual
phase of it occurs here. Human beings are
intermediate or secondary host as the
asexual phase of malarial parasite occurs
in man.- (d) Entamoeba histolytica causes
amoebic dysentery. It is dimorphic, i.e.
occurs in two forms, larger harmful
magna form and smaller harmless
minuta form. It is monogenetic, i.e.
requires a single host (humans). This
pathogen lives in the large intestine of
humans. - (a) The cells of the immune system
are derived from the pluripotent stem
cells in the bone marrow. Pluripotent
means a cell can differentiate into many
different types of tissue cells. The
pluripotent stem cells can form either
myeloid stem cells or lymphoid stem cells.
Thus, assertion and reason both are
correct and reason correctly explains the
assertion. - (c) Immunity is the ability of the
body to protect against all types of foreign
bodies like bacteria, virus, toxic
substances, etc., which enter the body.
Passive immunity is produced by a donor
other than the infected person or an
animal. It is short lived. Natural passive
immunity is the resistance passively
transferred from the mother to the foetus
through placenta. IgG antibodies can
cross placental barrier to reach the
foetus. - (b) Cancer is an abnormal and
uncontrolled division of cancer cells.
These cells do not remain confined to one
part of the body. They penetrate and
infiltrate into the adjoining tissues and
dislocate their functions. Both assertion
and reason are correct, but reason does
not explain assertion. Therefore, option
(b) is correct. - (d) Both assertion and reason are
false, carbon monoxide (CO) is a toxic gas
that interferes with oxygen transport and
utilisation. It affects by reducing the
amount of available oxyhaemoglobin and
Answers with Explanation