Biology 0610 | Paper 1 Mock 01 | Multiple Choice (Core)

The decisive clue is the absence of a true nucleus. Only prokaryotes (bacteria) have their genetic material as a loop of DNA free in the cytoplasm rather than enclosed in a nuclear membrane, and their cell wall is not made of cellulose. Protoctists and fungi are ruled out because, although they can be simple, their cells do contain a true nucleus, and plant cells have both a nucleus and a cellulose wall. Whenever an organism is described as single-celled with no nucleus, classify it as a bacterium.

The correct statement about DNA is that it is made of two strands, matching the double-helix structure. The other statements are false: base A pairs with T (not C), genes are made of DNA (not protein), and chromosomes do contain DNA (they are made of it). So the true statement is the one saying DNA is made of two strands.

Genes are lengths of DNA, and the DNA is found on the chromosomes inside the nucleus, so the genes are stored in the part described as the nucleus containing the chromosomes. The ribosome, mRNA and amino acids are all involved in building proteins, not in storing the genes, so the genes are held in the nucleus.

Maltose is broken down to glucose by the enzyme maltase, found on the membranes lining the small intestine, so maltase completes the digestion into an absorbable sugar. Amylase produces maltose from starch but does not act on maltose, lipase acts on fats and pepsin on protein, so none of those finishes maltose digestion; maltase does.

While food and space are plentiful and nothing limits growth, each cell divides and the population doubles again and again, giving very rapid growth. This is the exponential phase, also called the log phase. It is not the lag phase (slow start), the stationary phase (numbers level off), or the death phase (numbers fall); the steady doubling under ideal conditions is the log phase.

Coal formed from ancient plants that had removed carbon dioxide from the air by photosynthesis, fixing the carbon into their tissues; that carbon stayed locked in the fuel until now. So the carbon released by burning the coal was originally taken from the air by photosynthesis in those ancient plants. Nitrogen fixation belongs to a different cycle, ancient animals respired carbon out rather than removing it, and combustion adds carbon dioxide rather than removing it. Photosynthesis is the only process that takes carbon dioxide out of the air.

Fertilisation is defined as the fusion of the nuclei of a male gamete (sperm) and a female gamete (egg cell). It must involve one sperm and one egg, because each gamete carries one set of chromosomes and their fusion restores the full set in the zygote. Two sperm or two egg cells would not be fertilisation, and a uterus-lining cell is a normal body cell, not a gamete, so joining a sperm to it does not fit the definition. Always state fertilisation as the fusion of a sperm nucleus and an egg nucleus.

An automatic, rapid response like pulling the hand away before pain is felt is a reflex action. It happens without conscious thought because the impulse passes through a short reflex arc in the spinal cord. It is not a voluntary action (which needs a conscious decision), a hormonal response (which is slower and chemical), or a tropism (a growth response in plants).

The scent reaches the far side because its molecules are in constant random motion and, overall, move from where they are concentrated to where they are dilute, down the concentration gradient; this is diffusion. It does not need a draught, and osmosis refers only to water crossing a partially permeable membrane, not scent spreading through air. Diffusion always proceeds from high to low concentration, never the reverse.

Sensitivity is the ability to detect and respond to changes in the environment. The plant detects the direction of light coming through the glass and responds by growing towards it over several days, which demonstrates sensitivity. Although the bending also involves movement of part of the plant, the underlying process being shown is the detecting of and responding to a stimulus, so the answer is sensitivity.

When soil becomes waterlogged it runs short of oxygen, and these low-oxygen conditions favour denitrifying bacteria. They break down soil nitrates and release nitrogen gas, which escapes into the atmosphere; this is the only step that removes usable nitrogen from the soil. Nitrogen-fixing bacteria do the reverse (gas to compounds), nitrifying bacteria turn ammonium into nitrate, and decomposers break down dead matter, so none of those cause the loss of nitrogen gas. This is why farmers prefer well-drained soil, to keep denitrification low.

Yeast fermenting sugar without air produces ethanol and carbon dioxide (glucose to ethanol and carbon dioxide). Lactic acid is the product in animal muscle, not yeast; oxygen is a reactant of aerobic respiration and is not produced; so only the ethanol-and-carbon-dioxide pair is correct.

A dichotomous key identifies organisms through a series of steps, each offering two contrasting statements about a feature; the choice made at each step leads onward until the organism is named. That step-by-step pairing of statements is precisely what is described here. A food chain or food web shows feeding relationships (who eats what), and a pyramid of numbers shows how many organisms are at each feeding level; none of these is used to identify an unknown animal. The word to hold onto is dichotomous, meaning divided into two at each step.

Producers capture energy at the start of the chain, so they hold the most energy of any trophic level; energy then falls at each step upward. The table shows Level 1 has the greatest energy at 10000 kJ, decreasing to just 10 kJ at Level 4, so Level 1 contains the producers. The highest level number here has the least energy, which is the consumers at the top, not the producers. The producers are always the level with the most available energy.

At night there is no light, so the maize cannot photosynthesise; the only process happening in the sealed box is respiration. Living plant cells respire day and night, breaking down carbohydrates and releasing carbon dioxide, so with the box sealed this gas builds up and its concentration rises. In the light, photosynthesis would remove carbon dioxide, so it cannot explain a rise; nitrogen fixation and combustion of soil are not what is producing this gas here. Remember that plants respire continuously, and at night respiration is the only gas-exchange process going on.

This shows enzyme specificity: each enzyme has an active site whose shape is complementary to only one type of substrate, like a key that fits only one lock. An enzyme that breaks down starch cannot act on protein because the protein molecule does not fit its active site, so no enzyme-substrate complex forms. Enzymes lower activation energy rather than raise it, and although enzymes are indeed unchanged by reactions, that property is not what this observation demonstrates. The clue is that one enzyme acts on one substance but not another.

Correct answer: into the cell by osmosis

The grid shows one parent giving gametes T and t and the other giving T and t, so this is Tt \(\times\) Tt. The four boxes are TT, Tt, Tt and tt. The homozygous recessive (tt) box is one of the four, so the fraction that is tt is \(\tfrac{1}{4}\). One half would be the heterozygous (Tt) fraction, and 'none' would apply only if at least one parent could not donate a recessive allele, which both can here.

Anaemia is caused by a shortage of iron, so the row pairing anaemia with iron is the correct match. The other rows are wrong: scurvy is caused by a lack of vitamin C (not iron), rickets by a lack of vitamin D or calcium (not vitamin C), and constipation by a lack of fibre (not calcium). Learning each deficiency with its specific missing substance lets you reject the mismatched rows and select the anaemia-iron pairing.

Growing towards light is positive phototropism, and its survival value is that it brings the leaves into the light so more photosynthesis can take place. It is not about moving away from water, staying short to save energy, or gripping soil (that is the root's role), so the photosynthesis advantage is the correct reason.

Concentrated salt solution has a lower water potential than the cytoplasm of the organism. Water therefore moves out of the cell by osmosis, across the partially permeable membrane, into the more concentrated surroundings, so the organism shrinks. Water would only enter if the outside were more dilute; salt particle size is irrelevant to whether water moves; and osmosis does not depend on respiration.

At each feeding level organisms respire, and respiration releases energy as heat that escapes to the surroundings and cannot be passed on, so most of the energy is lost as heat released by respiration. It is not lost as minerals in the soil or as reflected sunlight, and it is not turned into new producer plants (energy flows one way and is not recycled); the main route by which energy leaves each level is heat from respiration.

The table shows atmospheric carbon dioxide rising steadily over the decades. The human activity that best accounts for this is the increased burning of fossil fuels, which releases carbon that had been locked away for millions of years and adds it to the air faster than photosynthesis can remove it. More photosynthesis by forests would lower carbon dioxide, reduced animal respiration would not raise it, and rainfall does not control it. Fossil-fuel combustion is the main driver of the rising trend.

The glomerulus is a knot of capillaries in the kidney where high blood pressure filters small molecules such as water, glucose, urea and ions out of the blood into the nephron capsule; blood cells and proteins are too big to pass. The ureter and collecting duct carry fluid onwards, and the bladder only stores urine, so none of these is where filtration under pressure happens.

Foot lengths measured to the nearest millimetre form a smooth range of values with all intermediates, which is continuous variation. It does not fall into just two categories, it is not caused by diet alone, and it is not discontinuous, because there are no separate groups; the values grade into one another, so the variation is continuous.

About ninety per cent of the energy is lost at each transfer between trophic levels, mostly through respiration, faeces and excretion, so very little of the original energy reaches the top of the chain. Because only a small amount of energy is left, it can support only a small number of top carnivores, far fewer than the producers that captured the energy at the start. Their larger body size or being hunted are not the reason; the limiting factor is the energy remaining after repeated losses.

Because the alveolus and capillary walls are each only one cell thick, the gases have a very short distance to diffuse, so exchange is rapid. Diffusion is faster over shorter distances, which is why the thinness speeds, rather than slows, exchange. The gases move by diffusion down their concentration gradients, not by active pumping.

Fertilisation follows a fixed sequence: pollen lands on the stigma, the pollen tube grows down through the style, the male nucleus is carried to the ovule, and finally the two nuclei fuse. The order in the table that lists these steps in this sequence is the correct one. The other orders put fusion or the tube growth before the pollen even lands, which is impossible. Keep pollination (pollen reaching the stigma) first and fusion of nuclei last.

The storms act as a selection pressure that removes weak fliers, which tend to be the shorter-winged insects. Longer-winged insects fly more strongly, so more of them survive and reproduce and pass on their alleles for longer wings, which is why the mean wing length rises from 9.1 mm to 11.4 mm. The best-supported conclusion is therefore that insects with longer wings survived and reproduced, so the mean rose. Insects do not grow longer wings because they need them, the storms do not create a mutation for longer wings, and wind cannot stretch the wings of individual insects. The population mean shifts because selection changes which alleles are passed on, not because individuals change during their lives.

Large carbohydrates such as starch are made by joining many glucose units together, so glucose is the sub-unit that builds starch. Amino acids build proteins, while fatty acids and glycerol build fats; these are not carbohydrate units. The repeating building block of starch (and glycogen and cellulose) is glucose.

Passive immunity is a short-term defence in which antibodies are acquired ready-made from another individual, such as across the placenta or in breast milk. The baby receives its mother's antibodies through breast milk but makes none of its own and forms no memory cells, so once the borrowed antibodies break down the protection fades, which is exactly passive immunity. Active immunity, from a vaccine or infection, would involve the baby making its own antibodies and memory cells for long-term protection, so this short-lived, borrowed protection is passive.

Every substance entering an animal cell must cross the thin boundary that surrounds the cytoplasm, the cell membrane. It is described as partially permeable because it "decides" what passes through, controlling entry and exit. A common mistake is to choose the cell wall, but animal cells have no cell wall, and where a wall does exist (in plant cells) it is fully permeable and does not select what crosses. The cytoplasm lies inside this boundary and the nucleus controls the cell, so neither is the surrounding layer that regulates entry.

Since DNA base sequences are inherited, closely related organisms that branched apart recently have had little time to accumulate changes, so their matching genes show only a small number of base differences. Finding few differences between corresponding genes is therefore the direct evidence that two organisms share a recent common ancestor. The other observations are irrelevant to ancestry: differences in the number of legs concern outward form, and where or in which year the organisms were collected tells you nothing about how similar their DNA is.

The table shows glucose falling from high to low and lactic acid rising from low to high, which matches anaerobic respiration in muscle: glucose is used up and lactic acid is produced. Oxygen is not used in anaerobic respiration, and ethanol is a yeast product, so the other combinations do not fit the data.

When a continuous characteristic such as height is plotted and forms a symmetrical bell shape, that shape is called a normal distribution. A bar chart is used for discontinuous categories, and a random scatter or discontinuous pattern does not describe a smooth bell curve, so the symmetrical bell shape is a normal distribution.

In a solution more concentrated than the cell sap, water leaves the cell by osmosis. So much water can be lost that the cytoplasm and cell membrane shrink and pull away from the rigid cell wall; this state is called plasmolysis. A turgid cell is the opposite (full of water and firm), fully permeable describes a membrane not a cell, and actively respiring is unrelated to water loss.

Strong salt solution has a lower water potential than the onion cell sap, so water leaves the cells by osmosis. The cytoplasm and cell membrane shrink and pull away from the cell wall (plasmolysis), so under the microscope you see the cell membrane pulled away from the wall. Plant cells with walls do not burst, and chloroplasts dividing or the nucleus leaving are not osmotic effects.

In a root the xylem is arranged in the centre as a star (or cross) shape, whereas in a stem the vascular bundles are arranged in a ring near the outside. So the organ whose xylem forms a central star is the root, described here as the organ with xylem in a central star shape. The organ with xylem in separate bundles around a ring is the stem, so it is not the one with the central star; the root is.

Mayfly larvae live only in clean, well-oxygenated water, so their absence signals pollution, while bloodworms tolerate low oxygen, so their abundance signals pollution. Sample B has no mayfly larvae and many bloodworms, both pointing to low oxygen and heavy pollution, making it the more polluted sample. Sample A, with many mayfly larvae and few bloodworms, is the cleaner water, so the two indicator species together show B is more polluted rather than the result being undecidable.

If the strips get longer, the cells must have taken in water and swollen. Water enters potato cells by osmosis when the surrounding solution has a higher water potential than the cell sap. Losing water would shorten the strips, and active transport of salt or release of sugar do not increase length. The extra length is direct evidence that the cells gained water by osmosis.