• Describe the process of endocytosis. (5)
Describe the process of endocytosis. (5)
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endocytosis occurs when a membrane encloses a target particle;
fluidity of membrane permits movement of membrane;
membrane sinks inwardly/forms pit/invaginates to enclose particle;
membrane seals back on itself / edges fuse;
one membrane layer / two phospholipid layers enclose particle
making vesicle;
inner phospholipid layer of (original) membrane becomes outer
phospholipid layer of vesicle membrane;
outer phospholipid layer of (original) membrane becomes inner
phospholipid layer of vesicle membrane;
vesicle breaks away from membrane/moves into cytoplasm;
changes in membrane shape require energy;
specific example of endocytosis (e.g. pinocytosis, phagocytosis);
• Accept any of the above points in an annotated diagram.
• Discuss the difference between prokaryote
and eukaryote reproduction
• Explain briefly why antibiotics are effective
against bacteria but not viruses. (3)
• antibiotics block specific metabolic pathways and
cell wall production in bacteria;
• viruses do not have metabolic pathways or cell
walls;
• viruses reproduce and obtain energy by using the
host cell metabolic pathways;
• (host cell) pathways are not affected by
antibiotics;
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• Describe how human skin and mucous
membranes act as barriers to pathogens.
• (Total 4 marks)
• To receive full marks, responses must have two answers for each.
Skin:
• lower pH / acid to keep bacteria from growing / chemical barrier;
• fatty acids / waxes antimicrobial;
• physical barrier to prevent entry / dry skin inhibits bacterial
growths;
• bacteria on skin prevent other bacteria from growing;
• antimicrobial / lysozyme in sweat and saliva (mucous membrane) to
keep bacterial growth in check;
mucous membranes:
• mucous traps bacteria / sticky / mucus slightly acidic ie vagina;
• cilia sweep mucous up to be swallowed to kill bacteria;
• contain macrophages / phagocytes;
• bacteria on mucous membranes prevent other bacteria from
growing;
• antimicrobial / lysozyme in sweat and saliva (mucous membrane) to
keep bacterial growth in check;
• Explain the production of antibodies.
• (8)
• antigens stimulate an immune response;
• antibodies are produced in response to specific antigens;
• antibodies are made by B-cells / lymphocytes / plasma
cells;
• First, antigen is engulfed by macrophages;
• Second antigen is presented on macrophage membrane;
• Third, helper T-cells bind to antigen (on macrophage);
• Forth helper T-cells are activated;
• Fifth, helper T-cells activate B-cells;
• Sixth, B-cells clone; into plasma cells and memory cells;
• The b-cells that become plasma cells produce specific
antibodies to the antigen;
• The b-cells that become memory cells are stored for longterm immunity;
• If there is a second infection by the same pathogen a faster
/ stronger response later; 8 max
• Explain antibody production(3)
• antigen causes an immune response to
produce antibodies specific for that antigen;
• antibodies produced in B-lymphocytes;
• B-lymphocytes produced in bone
marrow; carried in blood;
• antigen presenting cell / helper T cell present
antigen to B cell;
• Describe how phagocytic leucocytes may act
as a defense against disease.
• (4)
• phagocytic leucocyte occurs in blood and
body tissue fluids;
• phagocytic leucocyte detects
pathogen/foreign material;
• Phagocytic leucocyte surrounds/engulfs
pathogen / endocytosis / phagocytosis;
• The phagocytic leucocyte’s membrane forms
around pathogen to form a vacuole;
• lysosomes inside the phagocytic leucocyte
attach to the vacuole digest the pathogen
inside of the vacuoles;
• (a) Outline the cause and transmission of
AIDS.
• (5)
• HIV/human immunodeficiency virus reduces the effectiveness of the
immune system / reduction in the number of active lymphocytes /
infects T-(helper) cells/ lymphocytes;
• Because of the loss of helper T Cell, it causes the loss of the ability to
produce antibodies because the B cells are not activated;
• Losing the ability to produce antibodies causes the infected person
susceptible to other infectious diseases / AIDS is an accumulation of
opportunistic diseases;
• HIV can be transmitted by sexual intercourse/exchange of
body fluids with an infected person;
• HIV can be transmitted by blood transfusion/blood products
from infected person;
• mothers can transmit HIV to children while breast feeding/ during
pregnancy/birth;
• HIV can be transmitted by sharing hypodermic needles that have not
been sterilized;
• (c) Discuss the cause, transmission and social
implications of AIDS.
• (8)
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cause: [4 max]
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transmission: [3 max]
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AIDS caused by HIV;
penetrates (T) lymphocytes;
(envelope) (glyco)protein and cell receptors involved;
number of lymphocytes reduced over years;
results in lower immunity;
other illnesses develop (as result of lower immunity);
AIDS is the observed syndrome when final stages of infection develop / OWTTE;
HIV transmitted through blood/sexual contact/body fluids/placenta/ childbirth/breastfeeding;
distribution/transmission uneven around the world;
transmission risk increased depending on society’s traditions/beliefs/behaviour;
(rare minority of) individuals do not have cell receptors and do not develop AIDS;
condoms/latex barriers only protection against transmission through sexual contact;
social implications: [3 max]
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treatment expensive;
discrimination against victims
moral obligation of wealthy countries to help poorer countries;
economic consequences / loss of wage earners etc.;
increase in the number of orphans;
comment on traditions/beliefs/behaviour; (if not already awarded in transmission)
• State the difference between an antigen and
an antibody.(1)
• antigen is a substance / molecule that causes
antibody formation; antibody is a (globular)
protein / molecule that recognizes an
antigen; 1