The answers/markschemes are below each question. You can reorganize the document so that you do not see the answer/markschemes when you answer the questions.

1. Outline the process of endocytosis.
(Total 5 marks)














(Annotated diagram illustrating the process may be used to gain
some or all the marks.)
the mechanism whereby cells take in solids and / or solutions;
involves the formation of vesicles;
infolding of cell membrane;
called phagocytosis when solids / organisms are engulfed;
phagocytosis is called feeding in some unicellular organisms;
called pinocytosis when solutions are taken in
(vesicles are much smaller);
may be receptor-mediated (eg HIV);
requires energy / active process;
[5]


3. Compare, with the aid of a diagram, the structure of generalized prokaryotic and eukaryotic animal cells.
(Total 8 marks)











labelled diagram of generalized prokaryotic (P) and generalized eukaryotic
(E) animal cell 2 max
(Marks must be awarded if the following comparisons
are made as either annotations to the diagram or in narrative / table form.)
P is usually smaller in size, E is larger;
both have cytoplasm / protoplasm;
P has no nucleus / nucleoid region, E has (membrane-bound) nucleus;
P has one chromosome / circular, E has two or more chromosomes;
P has DNA only, E has DNA with protein (histones);
P has no membrane-bound organelles, E has some membrane-bound organelles;
E has mitochondria, P does not;
E has other example of organelle, P does not;
both can have a flagellum / flagella;
if flagella then E has 9+2 fibrils, P does not;
P can have pili / slime layer / capsule, E does not;
P can have plasmids, E does not;
both have ribosomes;
P has small ribosomes, E has larger ones;
both have cell membrane;
P has cell wall, E has no cell wall;
E has centriole, P has no centriole;
[8]


5. (a) Distinguish between diffusion and osmosis.
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(1)

(b) Explain how the properties of phospholipids help to maintain the structure of the cell surface membrane.
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(2)

(c) State the composition and the function of the plant cell wall.
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(2)
(Total 5 marks)


(a) Must have both for [1].
diffusion is the movement of molecules from an area of high
concentration to an area of low concentration;
osmosis is the diffusion of water across a partially
permeable membrane; 1

(b) hydrophillic head groups point outward;
hydrophobic tails form a lipid bilayer;
forms a (phospholipid) bilayer;
ions and polar molecules cannot pass through
hydrophobic barrier;
helps the cell maintain internal concentration
and exclude other molecules; 2 max

(c) cellulose;
structural support / protection / maintain turgor pressure; 2
[5]


7. According to cell theory all cells arise from pre-existing cells. The following diagram shows the cell cycle of a eukaryotic (body) cell of a diploid organism.


(a) Define the term diploid.
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(1)

(b) Identify the parts of the cell cycle labelled A and B.
A .................................................................................................................................
B .................................................................................................................................
(1)

(c) State three activities that occur during part A of the cell cycle.
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(3)


(d) Outline the differences in cytokinesis in animal and plant cells.
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(2)

(e) Explain the significance of complementary base pairing in relation to the cell cycle.
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(3)
(Total 10 marks)


(a) two sets of chromosomes / each chromosome represented twice;
pairs of homologous chromosomes;
Do not accept haploid number, having 46 chromosomes, 2n 1 max

(b) Both A and B must be correctly identified for [1].
A: interphase / G1, S, G2;
B: mitosis / phases of mitosis; 1


(c) Any three of the following [1] each.
protein synthesis / translation
DNA replication / chromosome replication;
cell growth / increase in cell volume;
organelle doubling;
microtubule formation;
respiration / glycolysis;
increase energy stores;
transcription / mRNA production;
Accept first three answers only. 3 max

(d) Award [1] each for the following.
animal cells:
pinching of cell membrane / form cleavage furrow;
centrioles;
plant cells:
cell plate formation;
cell wall built (during cytokinesis); 2 max

(e) "A" part of cycle / interphase involves DNA synthesis
replication of DNA requires complementary base pairing /
A-T, G-C; produces two identical copies of DNA /
sister chromatids;
sister chromatids split at anaphase;
each new cell gets a copy of each DNA molecule /
genetically identical wrong base pairing causes mutations;
mutations can lead to cancer (by uncontrolled cell division) 3 max
[10]


9. Distinguish between the structure of plant and animal cells.
(Total 6 marks)













Award [1] per difference,
plant cells:
have cell walls, animal cells do not;
have plastids / chloroplasts, animal cells do not;
have a large central vacuole, animal cells do not;
store starch, animal cells store glycogen;
have plasmodesomata, animal cells do not;

animal cells:
have centrioles, plant cells do not;
have cholesterol in the cell membrane, plant cells do not;
plant cells generally have a fixed shape / more regular whereas
animal cells are more rounded;
[6]


11. Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes.
(Total 9 marks)









phospholipid structure
hydrophobic tail / hydrophilic head;
head made from glycerol and phosphate;
tail made from two fatty acids;
saturated / unsaturated