Biology Paper 2 November 2023

1. Aa fat is liquid at room temperature while an oil is solid at the same temperature
2. Ba fat contains glycerol while an oil is built from fatty acid molecules alone
3. Ca fat is made only by animals while an oil is made only by bacteria and fungi
4. Da fat is solid at room temperature while an oil is liquid at the same temperature

1. Athe whole molecule mixes freely with water in every part of the cell
2. Bthe whole molecule repels water, which is why it is stored as a droplet
3. Cit dissolves in water only after it has been heated above forty degrees
4. Done end of the molecule mixes with water while the other end does not

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Answer this when you sit the paper.

1. Athree fatty acids join to one glycerol molecule and three molecules of water are taken in
2. Bthree fatty acids join to one another in a ring and one molecule of glycerol is released
3. Cthree fatty acids join to one glycerol molecule and three molecules of water are released
4. Done fatty acid joins to three glycerol molecules and three molecules of water are released

Answer this when you sit the paper.

1. Astaining and mounting respectively
2. Bclearing and dehydration respectively
3. Cdehydration and clearing respectively
4. Dfixation and sectioning respectively

1. Ait colours the different organelles so that they can be told apart under the objective
2. Bit kills the tissue quickly and preserves the structures close to their living state
3. Cit removes the water from the tissue so that the specimen will not decay in storage
4. Dit dissolves the cell walls so that the individual cells can be spread out on the slide

1. Ait uses a beam of electrons and has a much higher resolution, but living material cannot be examined with it
2. Bit uses a beam of electrons and has a much higher resolution, and living material is examined easily with it
3. Cit uses a beam of light focused by glass lenses, so it resolves detail down to a fraction of a nanometre
4. Dit uses a beam of electrons focused by glass lenses, so specimens can be viewed in their natural colours

1. Athe membrane must stay flexible enough for vesicles to form and transport proteins to work
2. Bthe membrane must stay completely rigid so that the cell keeps a fixed shape at all times
3. Cthe membrane must dissolve in the cytoplasm whenever the cell is about to divide in two
4. Dthe membrane must conduct heat away from the cytoplasm as fast as respiration produces it

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1. Aguanine and thymine
2. Badenine and cytosine
3. Cadenine and guanine
4. Dcytosine and thymine

1. Aa large purine pairs with a small pyrimidine, so the two strands stay an even distance apart
2. Btwo large purines pair together, so the helix is wide enough for the sugars to lie inside it
3. Cthe paired bases are joined by covalent bonds, so the strands cannot be parted for copying
4. Dthe paired bases carry opposite electrical charges, which holds the strands in a tight coil

1. Ahalf of the bases in each new strand are copied and the other half are guessed
2. Beach new molecule keeps one strand of the original and one strand newly built
3. Ceach new molecule is built entirely from nucleotides that were not there before
4. Done of the two new molecules is the original and the other is entirely new

1. Aa promise about which of their children will be affected and which will not be affected
2. Ba test that changes the sex of the embryo where the disorder is carried on the X chromosome
3. Cthe chance that a child of theirs will inherit a disorder, worked out from the family history
4. Da treatment that replaces the faulty allele in every cell of a child before it is born

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Athe difference between the observed and expected numbers is significant and needs another explanation
2. Bthe observed numbers match the expected ratio exactly, so no difference between them arose at all
3. Cthe cross must be repeated, because a chi-squared test gives no answer below the critical value
4. Dthe difference between the observed and expected numbers is not significant and is due to chance

1. Athe oxygen concentration of the air and the amount of nitrogen dissolved in the soil water
2. Bthe number of stomata that are closed and the thickness of the waxy cuticle on the leaf
3. Cthe mass of starch already stored in the leaf and the age of the roots holding the plant
4. Dthe carbon dioxide concentration of the air and the amount of chlorophyll in the leaf

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1. Alight intensity for curve A and carbon dioxide concentration for curve B
2. Blight intensity for curve A and temperature for curve B
3. Ctemperature for curve A and light intensity for curve B
4. Dcarbon dioxide concentration for curve A and temperature for curve B

1. Athe chlorophyll molecules are bleached, so light of every wavelength passes straight through the leaf
2. Bthe carbon dioxide in the air becomes too concentrated for the leaf to take any more of it in
3. Cthe light reaching the leaf is reflected once the temperature rises past the optimum for the plant
4. Dthe enzymes of photosynthesis are denatured, so their active sites no longer fit the substrate

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1. AB, because it lies to the right and so is less saturated than normal haemoglobin at a given tension
2. BB, because a curve to the right shows that the haemoglobin takes up oxygen at a lower tension
3. CA, because it lies to the left and so holds on to oxygen more tightly than normal haemoglobin
4. DA, because a curve to the left shows that the haemoglobin becomes saturated only at high tension

1. Athe first oxygen molecule to bind blocks the other three binding sites until the tension rises
2. Bhaemoglobin can carry oxygen only when carbon dioxide is present in the plasma around it
3. Cthe four polypeptide chains of a haemoglobin molecule take up oxygen one after the other slowly
4. Dthe binding of the first oxygen molecule changes the shape of the haemoglobin and eases the next

1. Athe low oxygen tension leaves the abnormal haemoglobin poorly saturated, so red cells may sickle
2. Bthe low oxygen tension makes the abnormal haemoglobin fully saturated, so the red cells return to normal
3. Cthe high air pressure at altitude forces extra oxygen into the red cells, which then rupture at once
4. Dthe cold air at altitude thickens the plasma, so the sickle shaped cells pass through capillaries easily

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1. Athe cell surface membrane and the vacuole respectively
2. Bthe cell wall and the nucleus respectively
3. Cthe cellulose cell wall and the chloroplast respectively
4. Dthe middle lamella and the nucleolus respectively

1. Athey fuse there and their contents form the cell plate that becomes the new wall between the cells
2. Bthey fuse there and release enzymes that digest the old cell wall so the two cells can separate
3. Cthey carry the chromosomes to the two poles of the cell before the new wall is laid down
4. Dthey store the water that is needed to fill the two vacuoles of the newly formed daughter cells

1. Athe large permanent vacuole fills the cell completely and leaves no room for a furrow
2. Bplant cells divide by meiosis alone, and a cleavage furrow forms only after mitosis
3. Cthe rigid cellulose wall cannot be drawn inwards by a ring of contracting microfilaments
4. Dthe plant cell has no cell surface membrane that a ring of microfilaments could pull on

1. Asupply testosterone so that the woman's muscles and bones are strengthened during her later years
2. Bsupply oestrogen, and often progesterone, to relieve the symptoms of the woman's own falling levels
3. Csupply follicle stimulating hormone so that the ovaries begin to release eggs once again each month
4. Dsuppress the remaining oestrogen so that menstruation is brought to an end more quickly than usual

1. Aher uterus lining becomes too thick for an egg to implant, so the cycle comes to a stop
2. Bher body begins to produce antibodies against her own eggs, which are then destroyed
3. Cher ovaries run out of follicles able to respond to FSH, so the oestrogen level falls
4. Dher pituitary gland stops producing FSH and LH, so the follicles she still has cannot ripen

1. Amenstruation ends, bone density rises steadily and the risk of heart disease falls year by year
2. Boestrogen levels rise, the skin becomes more elastic and the ovaries release two eggs a month
3. Cthe ovaries enlarge, hot flushes cease within a week and the uterus lining thickens permanently
4. Dmenstruation ends, contraception is no longer needed and the risks of a late pregnancy are avoided

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1. ABryophyta
2. BConiferophyta
3. CFilicinophyta
4. DAngiospermophyta

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1. Athe gametophyte and the sporophyte respectively
2. Bthe sporophyte and the gametophyte respectively
3. Cthe sporophyte and the protonema respectively
4. Dthe zygote and the gametophyte respectively

1. Aa waxy cuticle that limits water loss, rhizoids that anchor the plant, and spores with resistant walls
2. Ba waxy cuticle that limits water loss, xylem vessels that carry water, and seeds with a food store
3. Ctrue roots that reach deep water, lignified stems that stand upright, and flowers that attract insects
4. Da thick woody bark that resists drying, a taproot that stores starch, and pollen carried on the wind

1. Aeating food grown in soil that has been contaminated, and walking barefoot over infected ground
2. Bcontact with the blood or other body fluids of an infected person, and handling infected bushmeat
3. Cthe bite of a mosquito that has fed on an infected person, and drinking untreated river water
4. Dbreathing air in a room where an infected person has been, and touching a surface days afterwards

1. Athe region has more mosquitoes than anywhere else, and it is the mosquito that carries the virus about
2. Bthe forest holds the fruit bat reservoir, bushmeat is widely hunted, and health services are stretched thin
3. Cthe climate there is dry enough for the virus to survive on open ground for months between outbreaks
4. Dthe population there has no immune system response to any virus, so every person exposed is infected