GCSE Biology Higher Short Paper B
Covers Respiration and Exercise, The Nervous System and Reflexes, Hormones and Homeostasis and 3 more.
Questions
Question 1 [4 marks]
Genetics and Inheritance
In snapdragon plants, flower colour shows codominance. The allele for red flowers (R) and the allele for white flowers (W) are both expressed if present together, producing pink flowers.
A red-flowered plant (RR) is crossed with a white-flowered plant (WW). Use a genetic diagram to determine the genotype and phenotype of all the offspring, and explain why this phenotype appears.
Question 2 [4 marks]
Hormones and Homeostasis
A patient's blood glucose concentration was 5.5 mmol/l at 08:00 and rose to 9.5 mmol/l at 08:30 after breakfast.
Calculate the mean rate of increase in blood glucose concentration, in mmol/l per minute, over this time.
Question 3 [4 marks]
Ecosystems and Material Cycles
A student estimates the population of snails in a garden using the mark-release-recapture method. On the first day, 40 snails are caught, marked, and released. The next day, 50 snails are caught, of which 8 are found to be marked.
Calculate an estimate of the total population of snails in the garden, using population estimate = (number marked in first sample x total number in second sample) / number of marked individuals recaptured.
Question 4 [5 marks]
The Nervous System and Reflexes
A student repeated a computer reaction time test five times, recording (in seconds): 0.31, 0.29, 0.33, 0.58, 0.30.
Identify the anomalous result and explain why it should be excluded, then calculate the mean reaction time using the remaining four results.
Question 5 [5 marks]
Genetics and Inheritance
In humans, sex is determined by the sex chromosomes: XX in females and XY in males.
Using a genetic diagram, explain why the probability of a baby being born male is normally about 50%.
Question 6 [6 marks]
Evolution and Natural Selection
Two populations of the same species become separated by a new river, and cannot interbreed for many thousands of years.
Explain how this separation could eventually lead to the formation of two separate species, and explain how scientists could use DNA evidence to confirm that speciation has occurred.
Question 7 [6 marks]
Respiration and Exercise
Aerobic respiration of one mole of glucose releases about 2900 kJ of energy. Anaerobic respiration (producing lactic acid) of one mole of glucose releases only about 120 kJ of energy.
Calculate how many times more energy is released by aerobic respiration than anaerobic respiration of the same amount of glucose, and explain why muscle cells still respire anaerobically during vigorous exercise despite this being far less efficient.
Question 8 [6 marks]
The Nervous System and Reflexes
Explain, in terms of the lens and ciliary muscles, how the eye focuses on a near object rather than a distant object.
Model solutions
| Question 1[4 marks] | |
|---|---|
| Answer or working | Marks |
| a correctly completed genetic diagram (Punnett square) crossing RR with WW | M1 |
| all offspring having the genotype RW | A1 |
| all offspring having a pink phenotype | A1 |
| explaining that because R and W are codominant, both alleles are expressed together in a heterozygous plant, producing a blended pink phenotype rather than a plant being purely red or white | B1 |
| Final answer: All offspring have the genotype RW and a pink phenotype, because in codominance both the red and white alleles are expressed together | |
| Question 2[4 marks] | |
|---|---|
| Answer or working | Marks |
| finding the change in concentration = 9.5 - 5.5 = 4 mmol/l | M1 |
| identifying the time taken = 30 minutes | M1 |
| using rate = change / time | M1 |
| a rate of 4/30 = 0.13 mmol/l per minute (2 significant figures) | A1 |
| Final answer: 0.13 mmol/l per minute | |
| Question 3[4 marks] | |
|---|---|
| Answer or working | Marks |
| using the given formula, population estimate = (number marked in first sample x total in second sample) / number recaptured marked | M1 |
| substituting (40 x 50) / 8 | M1 |
| calculating 40 x 50 = 2000 | M1 |
| 250 snails | A1 |
| Final answer: An estimated population of 250 snails | |
| Question 4[5 marks] | |
|---|---|
| Answer or working | Marks |
| identifying 0.58 seconds as the anomalous result | B1 |
| explaining it is much higher than (does not fit the pattern of) the other four results, likely reflecting an error such as a lapse in concentration rather than a genuine reaction time | B1 |
| summing the remaining four results (0.31 + 0.29 + 0.33 + 0.30 = 1.23) | M1 |
| dividing the sum by 4 | M1 |
| a mean reaction time of 0.31 seconds (2 significant figures) | A1 |
| Final answer: 0.58 s is anomalous and should be excluded; the mean of the remaining four results is 0.31 seconds (2 s.f.) | |
| Question 5[5 marks] | |
|---|---|
| Answer or working | Marks |
| the mother's eggs all carry an X chromosome | B1 |
| the father's sperm carry either an X chromosome or a Y chromosome, in roughly equal numbers | B1 |
| a correctly completed genetic diagram (Punnett square) showing XX, XX, XY, XY offspring | M1 |
| 2 out of 4 (or 1 out of 2) combinations are XY (male) | A1 |
| this gives a probability of about 50% for each sex at each fertilisation | B1 |
| Final answer: Eggs always carry X, sperm carry X or Y in equal numbers; a Punnett square shows XX and XY combinations occur equally often, giving about a 50% chance of a male baby | |
| Question 6[6 marks] | |
|---|---|
| Answer or working | Marks |
| the two populations are geographically isolated and cannot interbreed | B1 |
| each population experiences different environmental conditions or independently accumulates different mutations | B1 |
| natural selection acts differently on each population, favouring different characteristics in each | B1 |
| over many generations the two populations become increasingly genetically different | B1 |
| eventually, the two populations become so different that they can no longer interbreed to produce fertile offspring, meaning they have become separate species | B1 |
| scientists can compare DNA sequences between the two populations, and a large enough difference confirms they can no longer be classified as the same species | B1 |
| Final answer: Geographic isolation stops interbreeding, so each population evolves separately by natural selection until they can no longer produce fertile offspring together, forming two species; comparing their DNA sequences can confirm how different they have become | |
| Question 7[6 marks] | |
|---|---|
| Answer or working | Marks |
| using ratio = 2900 / 120 | M1 |
| approximately 24 times more energy | A1 |
| during vigorous exercise, the heart and lungs cannot supply oxygen to the muscles fast enough to meet the high demand for aerobic respiration | B1 |
| anaerobic respiration not requiring oxygen, so it can continue to release some energy even when oxygen supply is insufficient | B1 |
| this allowing muscle contraction (and exercise) to continue, even though anaerobic respiration releases far less energy per glucose molecule | B1 |
| the resulting build-up of lactic acid needing to be broken down using oxygen later (an oxygen debt repaid during recovery) | B1 |
| Final answer: Aerobic respiration releases about 24 times more energy than anaerobic respiration from the same glucose; muscles still respire anaerobically during vigorous exercise because oxygen cannot be supplied fast enough, and this lets contraction continue despite being far less efficient, though it creates an oxygen debt that must later be repaid | |
| Question 8[6 marks] | |
|---|---|
| Answer or working | Marks |
| to focus on a near object, the ciliary muscles contract | B1 |
| this reduces the tension in the suspensory ligaments (they become slack) | B1 |
| the lens, no longer being pulled taut, becomes fatter/more rounded, increasing its power to refract (bend) light | B1 |
| this greater refraction is needed to focus light from a nearby object (which diverges more) onto the retina | B1 |
| to focus on a distant object, the ciliary muscles instead relax and the suspensory ligaments become taut | B1 |
| this pulls the lens thin, reducing its power, which is enough to focus the more parallel light rays from a distant object | B1 |
| Final answer: For a near object, ciliary muscles contract, slackening the suspensory ligaments so the lens becomes fatter and more powerful, refracting light strongly enough to focus it on the retina; for a distant object the ciliary muscles relax, the ligaments pull the lens thin, and its lower power is enough to focus the more parallel light | |