Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
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Chapter 11
1 a antigen: any large molecule (e.g. protein)
recognised by the body as foreign
antibody: a protein made by the immune
system in response to the presence of an
antigen, and targeted specifically at it
immune response: the response by the body
to the entry of a foreign antigen; it involves
the activity of phagocytes and B- and
T-lymphocytes
b A person who is blood group A recognises
red blood cells of type B as non-self and
produces anti-B antibodies. These will cause
clotting of the transferred blood which could
be fatal.
2 a Phagocytes originate in the bone marrow.
b i The lymphocyte nucleus takes up most
of the cell; there is very little cytoplasm.
Neutrophils have a lobed nucleus, with
a larger amount of cytoplasm. The
neutrophil is larger than the lymphocyte.
ii 10 µm
3 B-lymphocytes originate and mature in bone
marrow. T-lymphocytes originate in bone
marrow, but mature in the thymus gland.
4 By puberty, T cells have matured and left the
thymus gland. The thymus has no further
use, so decreases in size.
5 a 13.25 µm
b The cytoplasm of plasma cells is full of rough
endoplasmic reticulum where protein is
made. There are Golgi bodies for modifying
proteins to become antibody molecules and
packaging them into vesicles for exocytosis.
The mitochondria provide energy for protein
synthesis and for moving vesicles to the
cell surface membrane for secretion by
exocytosis.
6 The plasma cells will be identical to the
original B cell and will, therefore, all produce
exactly the same antibody molecules. Also,
the memory cells will be identical, so the
same antibody molecules will be produced
during any subsequent immune response to
the same antigen.
7 The primary response to an antigen is slow.
It can take several weeks to produce enough
antibody molecules to fight the infection
effectively. During this time, we usually show
the symptoms of the disease concerned.
8 Polysaccharides are made from only a small
number of different sugars – unlike proteins,
which are made from 20 different amino
acids. Polysaccharides would not give the
same huge number of different molecular
shapes in the variable region of antibodies as
is achieved with proteins.
9 Only some B and T cells have receptors of the
correct specificity.
10 Immunity to one strain does not provide
immunity to all of them, as they do not all
share the same antigens.
11 B-lymphocytes with antibody receptors
specific to the invading antigen divide by
mitosis to form plasma cells and memory
cells. The short-lived plasma cells secrete
antibody molecules. Helper T cells and killer
T cells with T cell receptors specific to the
invading antigen also divide by mitosis. The
helper T cells secrete cytokines to activate
appropriate B-lymphocytes to divide and
macrophages to carry out phagocytosis. The
killer T cells search for any infected cells in
the body and kill them.
12 a total red and white cells in males: 5 507 500
total red and white cells in females: 4 807 500
b males: 0.14%
females: 0.16%
c neutrophils in males and females = 60%
lymphocytes in males and females = 37%
d neutrophils = 4.5 × 10 9
lymphocytes = 2.8 × 10 9
Cambridge International AS and A Level Biology © Cambridge University Press 2014