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

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.

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.

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.

Mineral ions such as magnesium are absorbed at the roots and travel dissolved in water within the xylem up to the leaves, where magnesium is used to make chlorophyll. So the route is dissolved in the water carried by the xylem. Phloem carries sucrose rather than mineral ions, the waxy cuticle is a waterproof outer layer rather than a transport route, and companion cells support the phloem, so the ions reach the leaves through the xylem.

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.

Distilled water has a higher water potential than the cell sap, so cylinder P gains water by osmosis and increases in mass. Concentrated sugar solution has a lower water potential than the cells, so water leaves cylinder Q and it loses mass. Hence P gains mass and Q loses mass; the other predictions get the direction of water movement wrong for one or both cylinders.

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.

In well-aerated soil, nitrifying bacteria oxidise the ammonium compounds released by decay into nitrates, the form plants absorb most readily; this step is called nitrification. Nitrogen-fixing bacteria act on nitrogen gas, not ammonium, and denitrifying bacteria do the opposite by turning nitrate back into nitrogen gas; there is no such thing as carbon-fixing bacteria in this cycle. Keep the two easily confused steps apart: fixation is gas to compound, while nitrification is ammonium to nitrate.

A species is defined by breeding, not by appearance: it is a group of organisms that can reproduce together to produce fertile offspring. Two animals that look alike yet never produce fertile young fail this test, so the observation best suggests they belong to two different species. It is tempting to call them the same species because they resemble each other, but the definition depends on producing fertile offspring, not on looks. Belonging to the same genus while being in different kingdoms is impossible, since a genus already sits inside a single kingdom.

A cylinder shows no change in mass only when there is no net movement of water. This happens when the surrounding solution has the same water potential as the cylinder, so water enters and leaves at equal rates. In pure water the cylinder would gain mass, in the most concentrated solution it would lose mass, and it would not dissolve.

A gene is a length of DNA that codes for a protein, so when a cell follows the instructions in a gene, the large molecule it builds is a protein. It does not build a single base, a second gene, or a chromosome; those are not the product coded for by a gene. The core idea is that genes code for proteins, so the product made from a gene is a protein.

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.

This is a mutually beneficial partnership. The nitrogen-fixing bacteria in the root nodules supply the bean plant with nitrogen compounds, and in return the plant supplies the bacteria with carbohydrates (sugars) that it made in photosynthesis, which the bacteria use as an energy source. The plant does not give the bacteria nitrogen gas, nitrates or carbon dioxide; those would not be a food supply. Remember that the plant provides the organic food, made by photosynthesis, that powers the bacteria.

A defining feature of insects is having three pairs of legs, that is six legs in total, attached to the thorax. This is one of the quickest ways to separate insects from other arthropods: arachnids have four pairs, crustaceans have many pairs, and myriapods have legs on many segments. None of the larger or smaller numbers fits an insect, so the reliable count to remember is three pairs.

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 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 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.

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.

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.

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.

Correct answer: into the cell by osmosis

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.

A good gas exchange surface needs a large surface area (so more gas can diffuse at once) and a thin, moist lining (so the diffusion distance is short and gases can dissolve before crossing). The alveoli have both, which makes them efficient. Thick walls with a small area, a dry surface with no blood supply, or a cartilage ring covered in cilia would all slow or prevent exchange, so the large moist area is what makes the alveoli work.

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.

When a person sweats heavily and drinks little, the body is short of water, so the kidneys reabsorb more water back into the blood and produce only a small volume of concentrated urine. Producing large, dilute urine would waste water the body needs. Healthy urine does not contain protein or glucose, so those options describe abnormal results rather than the effect of water shortage.

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 liquid rising on the sugar side shows water has moved into the more concentrated sugar solution. Osmosis moves water from the dilute side (pure water, higher water potential) to the concentrated side (lower water potential), so water moves towards the more concentrated side. It is not an equal two-way movement, it does not move towards the dilute side, and the sugar molecules do not need to cross for water to move.

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.

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.

Roots are negatively phototropic, tending to grow away from light rather than towards it, so the claim is incorrect: roots grow away from light. Roots do respond to stimuli (they are positively gravitropic), and they are not positively phototropic like shoots, so the other evaluations are wrong.

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.

Both lengths are already in millimetres, so apply the formula directly: \[\text{magnification} = \frac{\text{image size}}{\text{actual size}} = \frac{96}{0.8} = 120.\] The magnification is \(\times 120\) and carries no units. Dividing 96 by 0.8, not by 8, is the key step; misplacing the decimal point gives the wrong values.

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.

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.

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.

As the lamp is moved away the light reaching the pondweed becomes dimmer, and the bubble count falls from 40 to 18 to 8. Because bubble rate reflects photosynthesis, the data show that the rate of photosynthesis falls as light intensity decreases with distance. There is a clear change, and the plant is still producing bubbles, so it has not died.

Sulfur dioxide and nitrogen oxides from burning coal dissolve in the water in rain clouds to form acids, so the rain that falls is acidic. This acid rain damages trees and makes lakes too acidic, harming or killing the organisms living in them. Acid rain is a distinct problem from ozone depletion, and it lowers rather than raises the pH and oxygen quality of affected lakes; eutrophication of the open ocean is caused by nutrient runoff, not by these acidic gases.

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.

With the soil and pot sealed inside a bag, no water can escape from the soil, so the only way the set-up can lose mass is through the exposed leaves. The steady fall in mass is caused by water vapour lost from the leaves by transpiration. Roots absorbing gases would not reduce mass, a plant cannot respire away its whole mass, and mineral ions do not evaporate; the lost mass is transpired water.

The warmth in the middle of a compost heap comes from the respiration of the microorganisms that are breaking down the grass cuttings and vegetable peelings; respiration is an energy-releasing process that gives out heat. Photosynthesis does not occur in the dark interior and does not release heat, nitrogen fixation does not warm the heap, and evaporation would cool the surface rather than heat the centre. Decomposers respiring as they feed is what makes a compost heap warm.