OCR GCSE Biology Revision

Its DNA is present as a circular loop in the cytoplasm; prokaryotes do not enclose DNA in a nucleus.

8 mm = 8000 µm; 8000 ÷ 40 = ×200.

Its higher resolving power can separate structures that are too close together to appear distinct under a light microscope.

Active transport, because ions move against their concentration gradient and energy is needed.

Bonds maintaining the protein structure break, changing the active site so the substrate no longer fits.

It breaks large fat globules into small droplets, increasing the surface area on which lipase can act.

Alveolar walls are damaged, reducing exchange area, so oxygen diffuses into blood more slowly.

It must generate greater pressure to pump blood around the whole body rather than only to the lungs.

Phloem, by translocation from the source leaf to the sink root.

Another factor such as carbon dioxide or temperature has become limiting, so light is no longer the rate-limiting factor.

Additional oxygen is taken in to help remove or process lactate and restore the body to its resting state.

It reduces transfer of pathogens from hands but does not remove pathogens already reproducing inside the body.

Influenza is caused by a virus, and antibiotics target bacterial structures or processes rather than viruses.

A neurotransmitter chemical diffuses across the synaptic gap and binds to receptors on the next neurone.

It promotes glucose uptake by cells and conversion of glucose to glycogen, especially in liver and muscle.

More ADH makes collecting ducts more permeable, so more water is reabsorbed and urine volume falls while it becomes more concentrated.

Pollination transfers pollen to a stigma; fertilisation is fusion of the male and female gamete nuclei.

The combinations are AA, Aa, Aa, aa, so one of four outcomes is aa: 25% for each conception.

A resistant variant survives antibiotic treatment and reproduces; its resistance allele is passed on, increasing in frequency.

Organisms use energy in respiration and movement, and material is lost in waste, so not all biomass is transferred to the next level.

Repeats reveal variation or anomalies and allow a more reliable mean estimate at each temperature.

Only a small set of parents is chosen each generation, so fewer alleles are passed on and harmful recessive alleles may become common.

A peak in luteinising hormone (LH) triggers ovulation.

A pollen tube grows down the style towards an ovule, carrying the male nucleus.

They respire while breaking down organic material and release carbon dioxide.

It can reconnect habitats, allowing organisms to move between groups and maintaining gene flow.

The transect samples a defined gradient, showing how abundance changes with distance from the shore.

It gives a wider field of view and makes the specimen easier and safer to locate before magnifying further.

There is no net water movement, so the external solution and tissue have similar water potential.

The changed codon may still specify the same amino acid, or the altered amino acid may not affect the protein's function. Another substitution could change an amino acid at an enzyme active site, altering substrate binding and therefore the phenotype.

It is J247/04. It assesses B4–B6 and B7, with assumed knowledge of B1–B3 and synoptic links.

One distance gives little range, so measure several planned distances while controlling other factors. A single reading cannot show variation or an anomaly, so repeat each distance and calculate a mean after checking anomalous results.

(2.20 − 2.50) ÷ 2.50 × 100 = −12%. The negative sign means the tissue lost mass, consistent with net water leaving the cells.

24 mm = 24,000 µm; 24,000 ÷ 80 = ×300.

It supports the presence of reducing sugar. It does not identify which sugar is present or give its concentration without a calibrated quantitative method.

Use a transect from the path to the stream with quadrats at consistent intervals, and measure soil moisture at each point. Replicate transects to check that the pattern is not unique to one line.

12 ÷ 40 = 0.30 cm³ s⁻¹. Record several gas volumes at short, equal time intervals near the start and use the gradient of that early section.

The rate rises when the lamp is closer, so light may have been limiting. It does not follow the simple inverse-square expectation exactly; another limiting factor, heating, or measurement variation could explain the smaller increase.

Different workloads and measurement times change the response, so they would confound the comparison. A common protocol makes recovery patterns more fairly comparable.

Zone size also depends on concentration and diffusion through agar. A plate test does not account for safe dose, absorption, the patient's body or clinical outcomes.

(3.30 − 3.00) ÷ 3.00 × 100 = +10%. The tissue gained mass, consistent with net water entering its cells.

6 mm = 6000 µm; 6000 ÷ 30 = ×200.

Chloroplasts contain chlorophyll to absorb light; the cellulose cell wall supports the cell and resists expansion.

Their greater resolving power makes much smaller, closely spaced sub-cellular structures distinguishable.

A nucleotide, containing a sugar, phosphate group and base.

A double helix.

T-G-C-A.

In the nucleus; it produces a complementary mRNA copy of the gene.

It may alter a triplet codon and amino acid, changing the enzyme's folding and active-site shape so substrate binding or catalysis changes.

The 20 s reaction; for a fixed endpoint, rate is proportional to 1/time, so it was about twice as fast.

At high concentration, enzyme active sites are occupied most of the time; enzyme concentration becomes limiting.

Yes. Respiration occurs continuously in living plant cells; photosynthesis needs light, respiration does not.

A measured temperature rise in the surroundings, compared with a suitable control.

Both use glucose; muscle produces lactate, while yeast produces ethanol and carbon dioxide.

A polymer; it contains many linked glucose monomers.

Amino acids.

Fatty acids and glycerol.

They make organic food from carbon dioxide and water using light energy, supplying biomass to the rest of a food chain.

Carbon dioxide and water.

Endothermic: it absorbs energy from light.

To use up starch already stored before the investigation, so starch detected afterward is evidence made during the test.

One quarter, because inverse-square intensity varies as 1/distance².

Carbon dioxide was limiting at the plateau; extra light alone could not raise the rate.

By active transport using energy and membrane transport proteins, against the concentration gradient.

Two genetically identical daughter cells.

It produces specialised cell types that perform tasks efficiently and can be organised into tissues and organs.

In meristems, regions such as root and shoot tips where cells divide for growth.

They divide and differentiate to replace or repair cells in particular tissues.

Embryonic stem cells.

SA = 6×9 = 54 cm²; volume = 27 cm³; ratio = 54:27 = 2:1 (2 cm⁻¹).

Urea, carried to the kidneys for removal in urine.

Blood passes through the heart twice in one complete journey around both the pulmonary and systemic circuits.

The pulmonary artery.

Plasma, with urea dissolved in it.

Root cells use active transport, powered by respiration, through membrane transport proteins.

Translocation through phloem.

Phloem.

It removes moist air near the leaf, maintaining a steep water-vapour gradient from inside to outside.

12 ÷ 3 = 4 mm min⁻¹; convert to volume rate only if the capillary area is known.

A motor neurone.

An effector, such as a muscle or gland.

A relay neurone.

Ciliary muscles contract and suspensory ligaments slacken, making the lens thicker/more curved.

A convex (converging) lens.

The cerebellum.

Other tissue may be damaged and individual cases differ, so a single observation cannot isolate cause.

Nervous tissue has limited repair and damage can be irreversible; the affected region may be difficult to access.

Only cells with the matching receptor respond to it.

Pituitary/hypothalamic stimulation of the thyroid is reduced, bringing thyroxine production down.

Progesterone.

Luteinising hormone (LH).

A condom, when used correctly.

It is transferred to the uterus for implantation and development.

More auxin accumulates on the shaded side, whose cells elongate more, bending the shoot toward light.

Common: auxin is linked to tropisms. Higher extension: ethene is associated with fruit ripening.

Treatment can induce parthenocarpy, fruit development without normal fertilisation and seed formation.

Enzyme-controlled metabolic reactions work effectively only within a suitable temperature range.

More blood flows near the skin, increasing heat transfer to the surroundings.

It falls as cells take up glucose and liver/muscle store some as glycogen.

It promotes its breakdown to glucose, which enters the blood.

Pancreatic beta cells produce little or no insulin.

Water leaves by osmosis, so the cell shrinks.

Its volume falls and it becomes more concentrated.

The collecting duct.

More ADH is released, increasing water reabsorption and making urine more concentrated.

Blood water potential falls, ADH rises and more water is reabsorbed, so urine volume decreases and concentration increases.

The atmosphere as carbon dioxide, oceans, soil or carbonate rock.

They secrete digestive enzymes onto the material, break it down, then absorb soluble products.

Respiration, decomposition or combustion.

Microorganisms need water for metabolism and enzyme reactions, so low water content reduces their activity.

No. It includes populations of different species; the ecosystem includes the community and abiotic environment.

Abiotic: it is a non-living chemical condition.

Both interacting species.

The producer.

Respiration uses organic molecules and converts some matter into products such as carbon dioxide and water. The heat released is energy transfer, not biomass.

64 ÷ 800 × 100 = 8%.

Genotype; it records the alleles.

No. It means the organism's entire genetic material.

Continuous; values form a range.

No. Most have no effect; some influence phenotype and very few determine it.

It may change an amino acid and active-site shape, affecting substrate binding/catalysis.

Sexual reproduction, because alleles from two parents are combined.

Haploid; they carry one set of 23 chromosomes.

Two gametes fuse at fertilisation; 23 + 23 restores the diploid total of 46.

One quarter (25%), because one of four equally likely allele combinations is bb.

3 ÷ 4 × 100 = 75%.

One half (50%).

No. It is polygenic and also influenced by environment.

Counts of characteristics in offspring from controlled crosses over generations.

Between individuals within a species as well as between species.

Natural classification uses many shared characteristics to reflect relationships; an artificial system groups by a limited convenient feature that may not reflect evolutionary relatedness.

No. Populations change over generations as some inherited variants lead to greater reproductive success.

No. It describes change in inherited population characteristics over generations.

Susceptible bacteria are killed more often; resistant ones survive and reproduce, passing on resistance.

Natural selection acting on heritable variation.

40 × 30 ÷ 10 = 120 animals, assuming a well-mixed closed population and marks retained.

It can remove or fragment habitats, reducing resources and isolating populations.

To determine whether biodiversity targets are achieved and to detect problems or unintended effects.

Other factors may vary too; correlation alone does not rule out confounding causes.

It can reduce yield and supply, potentially raising prices and limiting access.

A natural enemy preys on, parasitises or infects the pest, reducing its abundance.

It narrows the gene pool and makes harmful alleles more likely to be inherited together.

Engineering directly modifies DNA; selective breeding chooses parents with existing traits across generations.

It joins the gene fragment to the plasmid DNA.

Effects depend on the engineered trait; a pest-resistant trait could change or reduce pesticide use, so evidence must be crop-specific.

People may still lack access or affordability, and production may be environmentally or economically unsustainable.

No. It includes mental and social wellbeing as well as physical health.

No; it is a non-communicable disease.

No. HPV infection can be transmitted; the cancer that may develop is not passed between people.

18 ÷ 90 = 0.20, so an estimate is 0.20 × 2,000 = 400 cases; the estimate depends on a representative sample.

No. It detects pathogen genetic material; separate control measures are needed to reduce spread.

A virus.

A physical barrier.

It inhibits or kills microorganisms, reducing infection.

Its DNA or an antigen.

Phagocytes, a type of white blood cell.

They move mucus containing trapped particles/pathogens toward the throat for removal.

Memory lymphocytes remain and rapidly produce the matching immune response.

The lymphocyte makes the specific antibody; the tumour cell enables rapid division so many copies can be produced.

Human chorionic gonadotrophin (hCG).

No. Antibiotics target bacteria, not viruses.

To reduce airborne contamination and exposure to microorganisms.

To compare outcomes and separate a medicine effect from expectation or natural recovery.

No. It changes likelihood; outcomes also depend on other factors.

It holds a narrowed artery open to improve blood flow.

Other factors may confound the relationship; stronger evidence and biological mechanism are also considered.

Changes disrupt control of growth and division, causing uncontrolled multiplication.

Its antigens may be recognised as foreign by the recipient's immune system.

Consent, genetic privacy, fairness of access or potential effects on future generations.

No. It estimates likelihood; environment, other genes and chance also matter.