Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
Answers to end-of-chapter questions
cytoplasm with granules / granular
cytoplasm;[3]
b presentation of antigen(s) by, macrophages /
other APCs;
some T-lymphocytes have receptors
complementary to antigen;
these are selected;
divide by mitosis;
helper T cells secrete cytokines;
to activate B-lymphocytes;
to secrete antibodies;
killer T cells search for cells infected by,
parasite / pathogen;
destroy host cell (and pathogen);
prevent reproduction of pathogen; [max. 6]
c B-lymphocytes can be activated by presence
of, antigen / pathogen alone;
without involvement of macrophages;
B-lymphocytes differentiate into plasma
cells;
secrete antibodies (T cells do not secrete
antibodies); [max. 2]
[Total: 11]
8 a i immunity is gained by the transfer of
antibodies from another source;
no immune response within the body;
antigen(s) / pathogen(s), have not entered
the body; [max. 2]
ii natural passive immunity:
antibodies cross the placenta;
in breast milk / colostrum;[2]
b i baby has passive immunity;
antibodies against measles antigens (from
mother) will interact with measles viruses /
antigens in vaccine;
so prevent an immune response;
therefore no memory cells will be formed;
[max. 3]
ii difficulty with timing first vaccination;
many children are not vaccinated at
appropriate time;
measles is highly infectious;
vaccination programmes concentrated on
other infectious diseases which have more
severe effect, such as smallpox and polio;
[max. 3]
c herd / mass, vaccination / immunity;
prevented spread through population;
surveillance for infected people;
very easy to identify infected people / no
symptomless carriers;
contact tracing to find people who may have
become infected;
ring vaccination / vaccination of all people in
surrounding area;
prevented spread from isolated infected
people;
one dose of the vaccine was enough to give
life-long immunity / no boosters required;
vaccine contained ‘live’ virus;
smallpox virus was stable / did not mutate;
no antigenic variation;
same vaccine was used for whole programme
/ did not need to be changed;
heat-stable / freeze-dried, vaccine;
suitable for hot countries / isolated areas /
rural areas;
bifurcated / steel, needle made vaccinating
easy;
did not need to be done by health
professionals; [max. 6]
[Total: 16]
9 a transcription (of DNA);
translation (of RNA);
assembly of amino acids to make four
polypeptides;
assembly of polypeptides to make antibody
molecule;
packaged in Golgi body into vesicles;
exocytosis; [max. 4]
b i X = variable region / antigen-binding site;
Y = constant region;[2]
ii disulfide;[1]
c variable region(s) are antigen-binding sites;
variable regions, are specific /
complementary, to antigen;
variable region has different amino acid
sequences for different antigens;
20 different amino acids can be arranged to
form different shapes;
disulfide bonds hold polypeptides together;
hinge region allows flexibility in binding to
antigen;
Cambridge International AS and A Level Biology © Cambridge University Press 2014