Edexcel iGCSE Biology 4BI1 - Paper 2B -Co-ordination and response- Exam Style Questions- New Syllabus
▶️ Answer/Explanation
(a) C (Y)
A is not the answer as W does not contain xylem
B is not the answer as X does not contain xylem
D is not the answer as Z does not contain xylem
(b)(i) • 8.16(4) (2)
One mark for:
÷ by 5
OR
× 52
OR
× 0.25
OR
0.8(164)
OR
40.82 (allow between 40.82 and 40.85)
Working:
Convert length to mm: \( l = 5.2 \text{ cm} = 52 \text{ mm} \)
Volume = \( \pi r^2 l = 3.14 \times (0.50)^2 \times 52 = 3.14 \times 0.25 \times 52 = 40.82 \text{ mm}^3 \)
Rate = \( 40.82 \div 5 = 8.164 \text{ mm}^3/\text{min} \)
(b)(ii) A description that makes reference to four of the following points:
1. set up potometer underwater / cut stem underwater / dry leaves / eq (1)
2. use a fan at different distances / with and without fans / different fan speeds / eq (1)
3. leave for set time / stated time (1)
4. measure distance bubble moves / distance water moves (on scale) / eq (1)
5. keep other factors constant (1)
6. repeat / reset bubble with reservoir / eq (1)
(c) An answer that makes reference to four of the following points:
1. at start / for first two days, ABA is low / is 0.5 OR at start / for first two days water loss is high / is 100 (1)
2. after two days / from three days ABA increases OR after two days / from three days percentage water loss decreases / eq (1)
3. after five days / after watering / ABA decreases OR after five days / after watering water loss increases / eq (1)
4. as ABA increases water loss decreases / inverse relationship / negative correlation / eq (1)
5. ABA closes stomata / stomata open when ABA low / eq (1)
6. stomata close from two days / stomata close from three days / eq (1)
7. stomata closing reduces transpiration / water loss / evaporation / stomata closing prevents wilting / stomata closing prevents loss of turgidity / ABA reduces transpiration / eq (1)
8. light intensity may change / humidity may change / wind may change / eq (1)
▶️ Answer/Explanation
(a) A (P)
B is not the answer as Q is the cornea
C is not the answer as R is the iris
D is not the answer as S is the conjunctiva
(b)(i) 8.2 (2)
Only one mark for: 24.7 OR division by 3 OR 8.23…
(b)(ii) A description that makes reference to two of the following points:
• (diameter) decreases / pupil smaller / eq (1)
• small decrease between 4(au) and 5(au) / starts to level off after 3(au) / starts to level off from 4(au) / large decrease between 2 and 3 (au) / calculated fall / eq (1)
(b)(iii) An explanation that makes reference to three of the following points:
• less light enters (eye) / passes through pupil / eq (1)
• to prevent damage to retina / eq (1)
• (as pupil narrows) circular muscles (of iris) contract (1)
• (as pupil narrows) radial muscles (of iris) relax (1)
(b)(iv) An explanation that makes reference to one of the following points:
• distance from camera (1)
• same student / person / same eye / left or right eye (1)
• food / drinks / caffeine consumed / eq (1)
• recovery time / time spent with mask on (1)
• noise in room (1)
• other light sources / distance from light (1)
• (type of) mask (1)
• colour of light / wavelength of light (1)
(b)(v) An explanation that makes reference to two of the following points:
1. using a camera (to record) / takes a photograph / uses an image / eq (1)
2. waiting 20 s (each time) / waiting same time / eq (1)
3. pupil is not changing size / is stationary / eye has adjusted / eq (1)
▶️ Answer/Explanation
(a) An answer that makes reference to one of the following points:
• maintenance of constant (internal) conditions in body / eq (1)
• control / regulating / maintaining internal conditions / eq (1)
• control / regulating / maintaining internal environment / eq (1)
• keeping conditions in body the same / within a (narrow) range / eq (1)
(b) • 250 (1)
Calculation: \( \frac{300000}{1200} = 250 \)
(c)(i) A (cell wall and cytoplasm only)
B is not the answer as bacteria do not have nuclei
C is not the answer as bacteria do not have nuclei
D is not the answer as bacteria do not have nuclei
(c)(ii) An explanation that makes reference to the following points:
1. fertilisers / animal waste / minerals / nitrates / phosphates (run off / leach) / eq (1)
2. algal growth / eutrophication / eq (1)
3. less light (penetrates) / competition for light / less photosynthesis / eq (1)
4. decomposition / decay (of dead algae / plants / organisms / organic waste / manure / faeces / sewage) eq (1)
5. less oxygen / only anaerobic species grow / eq (1)
6. bacteria respire / other species cannot respire / reduced respiration / eq (1)
7. pesticides kill organisms / eq (1)
(d)(i) An answer that makes reference to one of the following points:
• eggs / ova / follicles, do not mature / do not grow / eq (1)
• (FSH is required to) mature eggs / ova / follicles (1)
• (low FSH leads to) less oestrogen / (FSH) stimulates oestrogen release (1)
(d)(ii) An answer that makes reference to one of the following points:
• no ovulation occurs / egg not released / ova not released / eq (1)
• LH / it stimulates ovulation / LH / it stimulates egg release / eq (1)
• (lower LH leads to) less progesterone / LH / it stimulates progesterone (1)
(e)(i) An explanation that makes reference to two of the following points:
• less water absorbed / less water enters blood / less water enters capillaries / eq (1)
• (water moves by) osmosis (1)
• water potential in blood is high(er) / water potential in gut / faeces / lumen is low(er) / eq (1)
(e)(ii) An explanation that makes reference to three of the following points:
1. mutation (1)
2. (only resistant bacteria) survive / are not killed / non-resistant bacteria die / eq (1)
3. bacteria reproduce / multiply / eq (1)
4. pass on allele / gene / mutation / eq (1)
(f)(i) An explanation that makes reference to two of the following points:
• (denitrifying bacteria convert) nitrate into nitrogen (1)
• so less eutrophication / less algal growth / more oxygen in river / lower BOD / eq (1)
• wood chips have large surface area (for bacteria) / wood chips are biodegradable (so do not pollute) / eq (1)
(f)(ii) An explanation that makes reference to two of the following points:
1. trees / roots absorb water / trees intercept water / eq (1)
2. (more) transpiration (1)
3. less runoff / slows down water flow / more soil permeability / more infiltration / eq (1)
4. less soil erosion / roots hold onto soil / roots stabilise soil / eq (1)
5. rivers do not get blocked (with soil) / eq (1)
▶️ Answer/Explanation
(a)
• W = lens (1)
• X = cornea (1)
• Y = retina (1)
(b) A description that makes reference to the following:
• circular muscles relax (1)
• radial muscles contract (1)
• pupil dilates / gets wider (1)
▶️ Answer/Explanation
(a) An explanation that makes reference to two of the following:
- Exercise increases body temperature / eq (1)
- (More) sweat / eq (1)
- To cool down / lose heat / eq (1)
- By evaporation (of sweat) (1)
(b)(i) An explanation that makes reference to three of the following:
- Blood concentration increases / less water in blood / eq (1)
- (Detected by) hypothalamus / osmoreceptors / pituitary gland (1)
- Releases ADH (1)
- Collecting duct becomes more permeable / eq (1)
- Increased water reabsorption (so less urine produced) (1)
(b)(ii) An explanation that makes reference to two of the following:
- With (pure water) blood becomes more dilute / less concentrated / has high water concentration / eq (1)
- Less / no ADH released when drinking water / eq (1)
- Less water reabsorbed (by kidney) when water drunk / eq (1)
- Salt / sugar absorbed into blood (in intestine) (from isotonic drink) / eq (1)
Accept converse arguments for the isotonic drink (e.g., more ADH released, more water reabsorbed).
▶️ Answer/Explanation
(a)(i) D (T)
A is not correct as Q is not the pore of a sweat gland
B is not correct as R is not the pore of a sweat gland
C is not correct as S is not the pore of a sweat gland
(a)(ii) B (R)
A is not correct as P is not the structure that carries blood
C is not correct as S is not the structure that carries blood
D is not correct as T is not the structure that carries blood
(a)(iii) A description that makes reference to four of the following points:
1. vasoconstriction (1)
2. arterioles supplying capillaries near skin surface constrict / blood vessels supplying skin narrow (1)
3. less blood flows to skin surface (1)
4. hair erector muscle contracts / hair stands up (1)
5. traps air / insulates (1)
6. less heat loss by radiation / convection / evaporation (of sweat) (1)
7. less sweating (1)
(b) An answer that makes reference to five of the following points:
1. (mean) skin temperature is higher in young (1)
2. (mean) skin temperature is higher with heat strain (1)
3. mean sweating rate higher in young (1)
4. mean sweating rate higher in moderate/higher heat strain (1)
5. smaller difference in sweating rate between low and moderate strain in young (1)
6. no information on sweat rate with no heat strain / at rest (1)
7. more sweat glands in young / each gland produces more sweat in young (1)
8. young can reduce (core) body temperature faster / young less likely to overheat (1)
9. numbers very small / not repeated / unreliable / no information on age (1)
10. no information on BMI / fat layers / health / diet (1)
▶️ Answer/Explanation
(a) D (homeostasis)
A is not correct as it is not absorption
B is not correct as it is not diffusion
C is not correct as it is not egestion
(b)(i) Calculation method:
Insensible loss = gas exchange + sweating = \(0.4 + 0.5 = 0.9\) litres
Total water loss = urine + gas exchange + sweating + faeces = \(1.5 + 0.4 + 0.5 + 0.1 = 2.5\) litres
Percentage insensible loss = \(\frac{0.9}{2.5} \times 100 = 36\%\)
(b)(ii) Calculation method:
Water input from food for 70 kg person = 0.5 litres
Water input per kg = \(\frac{0.5}{70} = 0.007142857\) litres/kg
For 110 kg person: \(0.007142857 \times 110 = 0.7857\) litres ≈ \(0.79\) litres (accept \(0.77–0.80\))
(b)(iii) An explanation that makes reference to four of the following points:
1. more water lost / less water in body /eq (1)
2. water / liquid lost in vomiting / faeces / diarrhoea / eq (1)
3. (more) sweating / eq (1)
4. concentration of blood increases / water potential lowered / eq (1)
5. (more) ADH produced / secreted / eq (1)
6. by hypothalamus / pituitary (1)
7. permeability of collecting duct increases / eq (1)
8. more water reabsorbed / less water lost in urine / more concentrated urine / less urine / eq (1)
(c) An answer that makes reference to four of the following points:
In winter:
1. body mass lower / eq (1)
2. as fewer plants available / less food / hibernating / eq (1)
3. less sunlight / lower temp / less photosynthesis / eq (1)
4. (much) more water intake / eq (1)
5. as more rainfall/ eq (1)
6. less concentrated urine in winter / more urine / eq (1)
7. (so) more water lost in urine / eq (1)
8. Ref to data for urine 3× less concentrated in winter / water input 4 × higher in winter / eq (1)
In summer: converse of above points applies.
▶️ Answer/Explanation
(a)(i) A (P)
Explanation: The sweat gland is correctly identified as structure P. Sweat glands are coiled tubular structures found in the dermis layer of the skin that produce sweat, which helps regulate body temperature through evaporation.
(a)(ii) D (T)
Explanation: Capillaries are the smallest blood vessels where exchange of gases, nutrients, and waste products occurs between blood and tissues. In skin diagrams, capillaries are typically shown as tiny vessels near the skin surface, which matches structure T.
(a)(iii) Vasodilation occurs, increasing blood flow to the skin surface for heat loss.
Explanation: When a person moves to a hot environment, several changes occur in the blood vessels of the skin to facilitate heat loss. Vasodilation occurs, where the arterioles and small arteries supplying the skin widen. This allows more blood to flow through the capillaries near the skin surface. The increased blood flow brings more heat to the skin surface where it can be radiated away. This process helps cool the blood and ultimately reduces core body temperature. These changes are part of the body’s thermoregulatory response to prevent overheating in hot conditions.
(b)(i) Sweating rate (in litres per hour)
Explanation: The dependent variable is the factor being measured in response to changes in the independent variable. In this investigation, scientists are measuring how sweating rate changes with running speed and environmental conditions, making sweating rate the dependent variable.
(b)(ii) 0.425 litres
Explanation: From the graph, at 220 m/min in hot/humid conditions, the sweating rate is approximately 1.7 L/hour. To find the volume in 15 minutes (which is 0.25 hours): Volume = Rate × Time = 1.7 L/hour × 0.25 hour = 0.425 L. This calculation shows that the person would release 0.425 litres of sweat in 15 minutes under these conditions.
(b)(iii) Sweating rate increases with running speed in both environments, but is consistently higher in hot/humid conditions.
Explanation: The graph shows several important relationships: In both environments, sweating rate increases with running speed, indicating that higher exercise intensity generates more body heat that needs to be dissipated. The hot and humid environment consistently results in higher sweating rates across all running speeds compared to the cool and dry environment. This occurs because in humid conditions, sweat evaporates less efficiently, so the body produces more sweat to achieve the same cooling effect. The similar slope of both lines suggests that the relationship between running speed and sweating rate is consistent regardless of environmental conditions, though the baseline sweating rate is higher in hot/humid conditions. These findings demonstrate how both internal factors (exercise intensity) and external factors (environmental conditions) influence the body’s thermoregulatory response through sweating.
▶️ Answer/Explanation
2 (a)(i) C
Explanation: The cornea is the transparent front part of the eye that covers the iris and pupil. In the diagram, label C points to this structure. Label A is the retina (incorrect), B is the conjunctiva (incorrect), and D is the lens (incorrect).
2 (a)(ii) An explanation that makes reference to two of the following:
- Circular muscles contract (1)
- Radial muscles relax (1)
- (So) pupil narrows / gets smaller / constricts / iris widens (1)
Detailed Explanation: Structure X is the iris. In bright light, the circular muscles of the iris contract. Simultaneously, the radial muscles of the iris relax. This coordinated action causes the pupil (the hole in the center of the iris) to constrict or become smaller. This reduces the amount of light entering the eye, protecting the retina from potential damage caused by excessive light intensity.
2 (b)(i) Using one eye or both eyes / number of eyes used.
Explanation: The independent variable is the factor that the investigator deliberately changes. In this experiment, the student is comparing the results when the volunteer uses one eye versus when they use both eyes. Therefore, the number of eyes used (one or two) is the independent variable.
2 (b)(ii) Any one from: light intensity, distance from the block, size/shape/colour of pins, size/shape/angle of the block or grid.
Explanation: A controlled variable is a factor that must be kept constant to ensure a fair test. For this investigation, many variables could affect the volunteer’s ability to judge distance. For example, the light intensity must be the same in all trials, as poor lighting would make it harder to see the pins regardless of how many eyes are used. Similarly, the distance between the volunteer and the block must be kept constant.
2 (b)(iii)
Explanation:
Mode is the value that appears most frequently.
- One eye: The scores are: 0, 0, 1, 1, 2, 2, 3, 3, 3. The number 3 appears most often (three times), so the mode is 3.
- Both eyes: The scores are: 3, 4, 4, 6, 6, 6, 6, 6, 6. The number 6 appears most often (six times), so the mode is 6.
Median is the middle value when all values are arranged in order.
- One eye (ordered): 0, 0, 1, 1, 2, 2, 3, 3, 3. The fifth value (out of nine) is the median, which is 2.
- Both eyes (ordered): 3, 4, 4, 6, 6, 6, 6, 6, 6. The fifth value is the median, which is 6.
2 (b)(iv) An explanation that makes reference to three of the following:
- Better distance judgement (with two eyes) / better depth perception (1)
- Large area seen by both eyes / large overlapping visual field (1)
- To locate prey / catch prey (1)
- Do not need wide field of view as not preyed upon (1)
Detailed Explanation: The results in Table 2 show a higher mode and median (both 6) when using both eyes compared to using one eye (mode=3, median=2). This means the volunteer was significantly better at correctly judging the distance of the pins with two eyes. This is due to binocular vision. The diagram shows that predators like cats have a large area of overlap (seen by both eyes) in front of them. This overlapping field of view allows the brain to compare the slightly different images from each eye (a process called stereopsis) to calculate precise depth and distance. This accurate depth perception is crucial for predators to successfully judge the distance to their prey before pouncing or chasing. They sacrifice a wide total field of view (which is more important for prey animals to spot predators) for this superior forward-facing depth perception, which is a key adaptive feature for a hunting lifestyle.
▶️ Answer/Explanation
(a)
A. Oviduct (or Fallopian tube) (1)
B. Ovary (1)
C. Cervix (1)
Explanation: The diagram shows key parts of the female reproductive system. Label A points to the tube connecting the ovary to the uterus, which is the oviduct (or Fallopian tube). Label B points to the organ that produces eggs, which is the ovary. Label C points to the narrow opening at the base of the uterus, which is the cervix.
(b) Structure D is the uterus (womb). Its roles include:
- It is the site of implantation of the embryo. (1)
- The placenta grows in the uterus, which provides nutrition to and removes waste from the developing embryo/foetus. (1)
Explanation: The uterus is a muscular organ. After an egg is fertilised, the resulting embryo travels to the uterus and implants into its thickened lining (endometrium). The uterus then supports the developing baby throughout pregnancy. The placenta, which forms on the uterine wall, is crucial for exchanging oxygen, nutrients, and waste between the mother’s blood and the baby’s blood.
(c)(i) From the typical patterns on the graph:
- Hormone M is oestrogen. (1)
- Hormone N is progesterone. (1)
The importance of their changes is:
- Oestrogen (M) increases in the first half of the cycle (before day 14). It repairs and builds up the uterine lining (endometrium) after menstruation, preparing it for a potential pregnancy. It also stimulates the release of LH which triggers ovulation. (1)
- Progesterone (N) increases significantly after ovulation (after day 14). Its main role is to maintain the thickened uterine lining, making it suitable for the implantation of a fertilised egg. It also inhibits further ovulation. If pregnancy does not occur, its level falls, leading to the breakdown of the lining and menstruation. (1)
Explanation: The menstrual cycle is precisely controlled by hormones. Oestrogen dominates the follicular phase (first half), preparing the body for ovulation and pregnancy. Progesterone dominates the luteal phase (second half), maintaining the conditions needed for a potential pregnancy. The drop in progesterone is the direct signal for the period to start if no embryo implants.
(c)(ii) Another hormone is FSH (Follicle-Stimulating Hormone). (1)
- FSH is released by the pituitary gland. It stimulates the development of follicles (which contain eggs) in the ovary. It also stimulates the ovaries to produce oestrogen. (1)
OR Another hormone is LH (Luteinizing Hormone). (1)
- LH is also released by the pituitary gland. A surge in LH around the middle of the cycle triggers ovulation – the release of a mature egg from the ovary. After ovulation, LH stimulates the remains of the follicle to develop into the corpus luteum, which produces progesterone. (1)
Explanation: FSH and LH are gonadotropins released from the brain that directly act on the ovaries. FSH kickstarts the cycle each month by causing a follicle to mature. The LH surge is the essential trigger for ovulation. These hormones work in concert with oestrogen and progesterone in a complex feedback system to regulate the cycle.
▶️ Answer/Explanation
Solution
(a)(i) Pituitary (gland)
Explanation: Follicle-Stimulating Hormone (FSH) is produced and secreted by the pituitary gland, a small gland located at the base of the brain. The pituitary gland is often called the ‘master gland’ because it controls many other hormone glands in the body.
(a)(ii) D
Explanation: Progesterone is a hormone that is crucial in the second half of the menstrual cycle, after ovulation. Its main role is to prepare the lining of the uterus (endometrium) to receive and support a fertilized egg. If pregnancy does not occur, progesterone levels fall, leading to menstruation. On the graph, line D shows a hormone that peaks in the middle of the cycle and remains high for the second half before dropping sharply, which matches the pattern of progesterone. Line A represents oestrogen (peaks just before ovulation), line B represents LH (sharp mid-cycle peak triggering ovulation), and line C represents FSH (rises in the first half to stimulate follicle development).
(a)(iii)
FSH:
- Stimulates the growth and development of egg-containing follicles in the ovaries.
- Triggers the ovaries to produce and release the hormone oestrogen.
LH:
- Triggers ovulation – the release of a mature egg from the ovary around the middle of the menstrual cycle.
- Stimulates the remains of the follicle in the ovary (after the egg is released) to develop into the corpus luteum, which then produces progesterone.
Explanation: FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) work in a coordinated way to regulate the menstrual cycle. FSH kickstarts the cycle by promoting the growth of follicles. As these follicles mature under the influence of FSH, they secrete increasing amounts of oestrogen. This rising oestrogen level eventually triggers a surge in LH. This LH surge is the direct cause of ovulation. After ovulation, LH stimulates the transformation of the ruptured follicle into the corpus luteum, which secretes progesterone to maintain the uterine lining.
(b)
Overall Comparison:
- Oral tablets have a slightly wider range of effectiveness (91-99%) compared to injections and implants (94-99%), suggesting they might be slightly less reliable on average or more dependent on correct use.
- A significant disadvantage common to all these hormonal methods is that they offer no protection against sexually transmitted infections (STIs), including HIV.
- All methods can also potentially cause side effects, which vary from person to person.
Oral Tablets:
Advantages:
- They are easy to use and do not require a medical procedure for each dose.
- They are a good option for people who are afraid of needles.
- It is relatively easy to stop taking them if someone changes their mind and wants to try to conceive, allowing the menstrual cycle to return to normal quickly.
Disadvantages:
- They must be taken at the same time every day without fail; forgetting a pill can reduce its effectiveness significantly.
- Their effectiveness can be reduced by vomiting, diarrhoea, or by taking certain other medications.
Injection:
Advantages:
- It is long-lasting (effective for 12 weeks per dose), so you don’t need to remember to take a pill daily.
- You cannot forget to take it once it has been administered.
Disadvantages:
- It must be administered by a healthcare professional, requiring regular clinic visits.
- The injection itself can be painful, and some people have a fear of needles.
- After stopping the injections, it can take a longer time for fertility to return to normal compared to stopping the pill.
Implant:
Advantages:
- It is the longest-lasting method (up to 3 years), requiring very little ongoing effort after insertion.
- Like the injection, you cannot forget to use it.
- It is highly effective and can be ideal for people who have limited access to healthcare facilities, as it only needs attention every three years.
Disadvantages:
- Insertion and removal are minor surgical procedures that must be performed by a trained healthcare professional.
- The procedure involves minor risks like infection, pain, or scarring at the implant site.
- It can be less easy to reverse quickly if someone changes their mind about wanting to conceive, as it requires a removal procedure.
Explanation: The choice of contraceptive method is highly personal and depends on an individual’s lifestyle, ability to adhere to a schedule, access to healthcare, fear of medical procedures, and future family planning goals. Each method has a trade-off between convenience, duration of action, and the level of medical intervention required.
▶️ Answer/Explanation
(a) In a test tube / culture dish / jar / glass / petri dish / container / in culture solution / in a lab / outside a living organism.
Explanation: The term “in vitro” literally means “in glass” in Latin, referring to biological processes that are conducted outside of a living organism in an artificial laboratory environment, such as in test tubes or petri dishes. This contrasts with “in vivo” experiments which are conducted within living organisms.
(b) Plant cells can differentiate into all/different types of tissues or specialized cells throughout the plant’s life and can form/regenerate a whole new plant.
Explanation: Plant cells exhibit totipotency, meaning that even mature, differentiated plant cells retain the ability to dedifferentiate and then redifferentiate into any cell type needed to regenerate an entire plant. This is why you can grow a new plant from a cutting. In contrast, human cells have much more limited differentiation capabilities. While stem cells can differentiate into various cell types, most human cells become permanently specialized during development and cannot revert back or form entirely new organisms.
(c)
1. Nitrate – for making amino acids/proteins/DNA/nucleic acids
2. Magnesium – for making chlorophyll/chloroplasts/photosynthesis
Explanation: Plant tissue culture media must contain essential minerals that support plant growth and development. Nitrate is crucial as it provides nitrogen, which is a fundamental component of amino acids, proteins, and nucleic acids (DNA and RNA). Without adequate nitrogen, plants cannot synthesize these essential biomolecules. Magnesium is a central component of the chlorophyll molecule, which is vital for photosynthesis as it captures light energy. Without magnesium, plants cannot produce chlorophyll effectively, leading to chlorosis (yellowing of leaves) and impaired photosynthesis.
(d) Enzymes are affected by pH/ work best at optimum pH. If pH changes, the shape of the active site can change/be denatured so substrates can no longer bind.
Explanation: Maintaining a constant pH is critical because enzymes, which catalyze all biochemical reactions in plant cells, are highly sensitive to pH changes. Each enzyme has an optimal pH range where it functions most efficiently. If the pH deviates from this range, the enzyme’s three-dimensional structure can be altered, changing the shape of its active site. This prevents substrates from binding properly, effectively denaturing the enzyme and halting the metabolic reactions it catalyzes. This would severely disrupt plant growth and development in the culture media.
(e) Place a shoot in light from one side/unidirectional light and another shoot in darkness/light all around. Leave both for a stated time/use shoots of same type/same temperature/other control variable. Observe/measure bending or growing towards light.
Explanation: To demonstrate phototropism (growth response to light), you would set up two identical young plant shoots. One would be placed in a location with light coming from only one direction (e.g., near a window), while the control would be placed in either complete darkness or with light evenly distributed from all sides. Both plants should be kept under the same temperature and watering conditions to ensure any differences are due to light direction only. After a few days, you would observe that the shoot exposed to unilateral light has bent toward the light source. This bending occurs because auxin hormone accumulates on the shaded side of the stem, promoting more cell elongation on that side and causing the stem to curve toward the light.
(f) To maintain biodiversity/reduce damage to ecosystems and to prevent extinction/keep species for future generations/for medicinal properties.
Explanation: Conserving endangered plant species is crucial for several reasons. Firstly, it maintains biodiversity, which ensures ecosystem stability and resilience. Each plant species plays a unique role in its ecosystem, and losing one can disrupt food webs and ecological balance. Secondly, it prevents extinction, preserving genetic diversity that might be valuable for future breeding programs, especially as climate changes. Many plants contain compounds with medicinal properties; for example, aspirin originated from willow bark. By conserving endangered species, we preserve potential future medicines and genetic resources that could be vital for human well-being.
(g) Agitation mixes contents/mixes oxygen/with plant cells. Light is for photosynthesis. Suitable temperature is for enzyme action.
Explanation: Suspension cultures require specific conditions to mimic optimal natural environments. Agitation (shaking or stirring) ensures that cells and nutrients are evenly distributed throughout the liquid media, preventing sedimentation. It also promotes gas exchange, ensuring oxygen (needed for respiration) is available and carbon dioxide (a product of respiration) is removed. Light is essential for photosynthetic plant cells to produce their own energy through photosynthesis. Maintaining a suitable temperature is critical because temperature affects enzyme activity; most plant enzymes function optimally around 25-30°C. Temperatures that are too high can denature enzymes, while temperatures that are too low can slow down metabolic processes to inadequate levels.
▶️ Answer/Explanation
(a)(i) C (S)
Explanation: The Bowman’s capsule (S) is the cup-like sac at the beginning of the nephron that surrounds the glomerulus and receives the filtrate.
(a)(ii) B (Q)
Explanation: The loop of Henle (Q) is a U-shaped tubule that descends into and ascends from the medulla of the kidney. It is crucial for creating a concentration gradient for water reabsorption.
(a)(iii) A (P)
Explanation: ADH (Antidiuretic Hormone) affects the collecting duct (P). ADH increases the permeability of the collecting duct walls to water, allowing more water to be reabsorbed back into the blood, producing more concentrated urine.
(b)(i) An explanation that makes reference to three of the following points:
• Glucose passes from the blood in the glomerulus (R) into the Bowman’s capsule / renal capsule (S) during ultrafiltration. (1)
• (All) glucose is (then) reabsorbed / absorbed back into the blood / eq. (1)
• This reabsorption occurs in the proximal convoluted tubule / PCT (T). (1)
• It is reabsorbed by active transport (which requires energy). (1)
Explanation: During ultrafiltration, small molecules like glucose enter the nephron. The body cannot afford to lose this valuable energy source, so 100% of filtered glucose is normally reclaimed from the filtrate in the proximal convoluted tubule via active transport against its concentration gradient.
(b)(ii) A description that makes reference to two of the following points:
• Add Benedict’s solution to the urine sample (and heat). (1)
• A positive result is indicated by a colour change to green / yellow / orange / brick-red. (1)
Alternative: Use a test strip (e.g., Clinistix) which changes colour (e.g., to brown) in the presence of glucose. (1 each)
Explanation: Benedict’s test is a standard biochemical test for reducing sugars like glucose. Heating with Benedict’s reagent causes a reduction reaction, producing a coloured precipitate of copper(I) oxide.
(c) A description that makes reference to two of the following points:
• Less urine is produced / lower volume. (1)
• The urine becomes more concentrated / contains less water / appears darker in colour. (1)
• (It may contain) a higher concentration of urea / other solutes. (1)
Explanation: Dehydration lowers the water potential of the blood. This is detected by osmoreceptors, leading to increased secretion of ADH. ADH causes more water to be reabsorbed from the collecting duct back into the blood, conserving water. This results in a smaller volume of more concentrated, darker yellow urine.
▶️ Answer/Explanation
(a)
The completed table is as follows:
Explanation:
To complete the table, we need to recall the key hormones involved in human reproductive systems and their functions.
- FSH (Follicle-Stimulating Hormone): This hormone is released by the pituitary gland and its target cells are in the ovaries. Its primary effect is the growth of the follicle which contains the developing egg cell.
- LH (Luteinizing Hormone): Also released by the pituitary gland and targeting the ovaries, LH’s crucial role is to trigger ovulation, which is the release of a mature egg from the ovary.
- Progesterone: This hormone is produced by the ovaries (specifically by the corpus luteum after ovulation). It travels to the uterus where its main effect is to thicken and maintain the lining of the uterus, preparing it for a potential pregnancy.
- Testosterone: The missing hormone for the final row is testosterone. It is released by the testes. Its target cells are in various body locations like the skin (e.g., armpit, groin), and one of its many effects is the growth of body hair, which is a secondary sexual characteristic.
(b)
Three differences between hormones and neurotransmitters are:
1. Site of Production and Release: Hormones are produced by endocrine glands (e.g., pituitary, thyroid, adrenal) and released directly into the bloodstream. Neurotransmitters are produced in and released from the endings of nerve cells (neurons) into the synaptic cleft.
2. Mode of Transport: Hormones are transported throughout the body via the blood plasma. Neurotransmitters diffuse across the narrow synaptic gap between two neurons.
3. Scope and Speed of Effect: Hormones generally have a widespread effect, influencing many target cells in different parts of the body, and often produce slower, longer-term responses (e.g., growth, menstrual cycle). Neurotransmitters have a very localized effect, typically acting on the adjacent neuron or muscle cell, and produce very rapid, short-term responses (e.g., muscle contraction, nerve impulse transmission).
Explanation:
Hormones and neurotransmitters are both chemical messengers, but they operate in fundamentally different ways. Hormones are part of the endocrine system, which is slow-acting but has long-lasting and widespread effects. Think of it like a broadcast – the hormone is released into the blood and can reach almost any cell in the body, but only target cells with the correct receptors will respond.
Neurotransmitters are part of the nervous system, which is fast-acting and precise. It’s like a direct, private phone line between two specific cells. The message is delivered quickly and locally across the tiny synapse, leading to an immediate but short-lived effect. This difference in transport and scope directly leads to their different roles in coordinating body functions.
▶️ Answer/Explanation
(a) Explain how layer A is adapted for its role.
Answer: Layer A (the waxy cuticle/epidermis) is adapted by being transparent to allow light through, having a waxy coating to reduce water loss, and having few chloroplasts as it is not photosynthetic.
Detailed Explanation:
Layer A represents the upper epidermis and its waxy cuticle. This layer has several key adaptations for its protective role. First, it is transparent, allowing sunlight to pass through to the underlying palisade mesophyll cells where most photosynthesis occurs. Second, it secretes a waxy, waterproof substance called the cuticle that forms a protective barrier. This cuticle significantly reduces water loss through evaporation from the leaf surface, which is crucial for preventing the plant from wilting, especially in dry conditions. Additionally, the cells of the epidermis typically contain few or no chloroplasts since their primary function is protection rather than photosynthesis. This combination of transparency and waterproofing makes the epidermis highly efficient at protecting inner tissues while still enabling the essential process of photosynthesis to occur.
(b) Explain how layers B and C are adapted for photosynthesis and gas exchange.
Answer: Layer B (palisade mesophyll) is adapted with many chloroplasts and tightly packed cells for efficient light absorption. Layer C (spongy mesophyll) has air spaces and loosely packed cells to facilitate gas exchange.
Detailed Explanation:
Layer B is the palisade mesophyll layer, which is perfectly adapted for its role as the main photosynthetic tissue. The cells are elongated and arranged vertically in a tightly packed formation, positioned close to the upper epidermis where light intensity is highest. This arrangement maximizes light capture. Furthermore, these cells contain a high density of chloroplasts – the organelles where photosynthesis actually occurs – making them extremely efficient at converting light energy into chemical energy.
Layer C is the spongy mesophyll layer, which is specialized for gas exchange. Unlike the tightly packed palisade cells, the spongy mesophyll cells are irregularly shaped and loosely arranged, creating numerous interconnected air spaces between them. These air spaces create a large surface area for the diffusion of gases. Carbon dioxide (\(CO_2\)), which is needed for photosynthesis, can diffuse freely from the stomata through these air spaces to reach the photosynthetic cells. Simultaneously, oxygen (\(O_2\)), produced as a byproduct of photosynthesis, can diffuse out of the cells into these air spaces and eventually exit the leaf. The loose arrangement and abundant air spaces thus create an optimal environment for the efficient exchange of these vital gases.
(c) State the role of guard cells.
Answer: Guard cells control the opening and closing of stomata to regulate gas exchange and water loss.
Detailed Explanation:
Guard cells are highly specialized cells that surround each stoma (plural: stomata), which are tiny pores on the leaf surface. Their primary role is to regulate the opening and closing of these stomatal pores. When guard cells are turgid (swollen with water), they bend and create an opening between them, allowing the stoma to open. This opening enables carbon dioxide (\(CO_2\)) to enter the leaf for photosynthesis during daylight hours. Conversely, when guard cells lose water and become flaccid, they relax and close the stoma. This closure helps to conserve water by reducing transpiration (water vapor loss), particularly during hot, dry conditions or at night when photosynthesis isn’t occurring. Therefore, guard cells perform the crucial balancing act of allowing sufficient \(CO_2\) intake for photosynthesis while minimizing excessive water loss.
(d) Discuss whether an anti-transpirant spray will promote plant growth.
Answer: Anti-transpirant sprays may not consistently promote plant growth because while they reduce water loss, they may also limit carbon dioxide intake and mineral transport.
Detailed Explanation:
The effect of anti-transpirant sprays on plant growth involves a complex trade-off. On one hand, these sprays can be beneficial because they form a waterproof coating that reduces transpiration (water loss from the leaves). By conserving water, they help prevent wilting and water stress, especially during drought conditions or in windy environments. This water conservation could potentially support growth by maintaining turgor pressure and physiological processes.
However, there are significant drawbacks that may hinder growth. Although the spray allows other gases like carbon dioxide (\(CO_2\)) to pass through, it might still create an additional barrier that slightly reduces the rate of \(CO_2\) diffusion into the leaf. Since \(CO_2\) is essential for photosynthesis, any reduction in its uptake could limit the plant’s ability to produce glucose and other carbohydrates, ultimately slowing growth. Additionally, the transpiration stream plays a vital role in transporting mineral ions from the roots to the shoots. By reducing transpiration, the spray might also reduce the upward movement of these essential nutrients, potentially causing nutrient deficiencies that impair growth. Furthermore, transpiration provides a cooling effect for leaves; reducing it might lead to overheating in bright sunlight, damaging plant tissues. Therefore, whether an anti-transpirant promotes growth depends on the specific environmental conditions – it might be helpful in water-scarce situations but detrimental when water is plentiful and maximum photosynthetic rate is desired.
▶️ Answer/Explanation
(a) C
Explanation: Both Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) are gonadotropins. They are not produced in the ovaries. Instead, they are both synthesized and released by the anterior pituitary gland in the brain. The pituitary gland acts as the control center, sending these hormones via the bloodstream to act on the ovaries. Therefore, the correct row is C, where both sources are listed as the pituitary.
(b) 800%
Explanation: To calculate the percentage increase, we first find the actual increase in concentration. The concentration increases from 5 arbitrary units (unlikely) to 45 arbitrary units (likely). The increase is therefore 45 – 5 = 40 units. The percentage increase is calculated by taking this increase, dividing it by the original value (when unlikely), and then multiplying by 100. So, the calculation is (40 / 5) × 100 = 8 × 100 = 800%.
(c)
FSH (Follicle-Stimulating Hormone):
- Stimulates the growth and development of follicles in the ovary. Each follicle contains an immature egg cell (oocyte).
- Stimulates the ovaries to produce and release the hormone oestrogen. As the follicles grow under the influence of FSH, the cells surrounding them produce increasing amounts of oestrogen.
LH (Luteinizing Hormone):
- Triggers ovulation, which is the release of a mature egg from the ovary. There is a sharp surge in LH levels around the middle of the menstrual cycle, which causes the dominant follicle to rupture and release the egg.
- Stimulates the remains of the follicle (after the egg has been released) to develop into a structure called the corpus luteum.
- Stimulates the corpus luteum to produce and release the hormone progesterone, which is vital for preparing and maintaining the uterine lining for a potential pregnancy.
Explanation: FSH and LH work in a tightly coordinated cycle. FSH initiates the process by starting follicle development, which then leads to oestrogen production. The rising oestrogen levels eventually trigger the LH surge. This LH surge is the direct cause of ovulation. After ovulation, LH’s role shifts to maintaining the corpus luteum, which produces progesterone. In summary, FSH is primarily responsible for the first half of the cycle (follicular phase), while LH’s key actions are triggering ovulation and supporting the second half of the cycle (luteal phase).
▶️ Answer/Explanation
(a) An explanation that makes reference to two of the following points:
- less oxygen (1)
- (less) respiration (1)
- (less) energy / ATP (1)
Detailed Explanation: When red blood cells burst (haemolysis), they can no longer carry oxygen effectively. Oxygen is essential for cellular respiration, which releases energy in the form of ATP. Reduced oxygen leads to less respiration and less ATP. Since foetal development requires energy for growth and cell division, a lack of ATP directly hinders development.
(b) An explanation that makes reference to three of the following points:
- DNA unzips / separates / one strand copied (1)
- complementary / base pairing (1)
- template (1)
- mRNA produced (1)
- transcription (1)
Detailed Explanation: Transcription occurs: the DNA double helix unwinds, one strand acts as a template, RNA nucleotides pair complementarily (A-U, C-G), and mRNA is formed by RNA polymerase, carrying the code from the gene to the ribosome.
(c) no nucleus / DNA / no ribosomes / mitochondria (1)
Detailed Explanation: Mature red blood cells lack a nucleus (and therefore DNA) and ribosomes. Protein synthesis requires DNA for instructions and ribosomes for assembly, so they cannot make proteins.
(d) can pass across placenta (1)
Detailed Explanation: The passage states antibodies pass across the placenta, a selective barrier. Red blood cells cannot cross normally, indicating antibodies are smaller.
(e)(i) An answer that makes reference to the following points:
- parent genotype dd x Dd (1)
- gamete d (and d) and D or d (1)
- offspring genotype Dd and dd (1)
Detailed Explanation: Mother: dd, Father: Dd. Gametes: mother → d only; father → D or d. Possible offspring: Dd (Rhesus positive) or dd (Rhesus negative).
(e)(ii) 50% / 0.5 / half / 50:50 (1)
Detailed Explanation: From a Punnett square, 2 out of 4 possibilities are Dd (Rhesus positive), so probability = ½ or 50%.
(f) An explanation that makes reference to three of the following points:
- memory cells (1)
- remain in mother’s blood (1)
- recognise / identify antigen / binds with antigen (1)
- more antibodies produced / produced faster / sooner (1)
- secondary immune response (1)
Detailed Explanation: During the first pregnancy, memory cells are made. In a second pregnancy, these memory cells quickly recognise the Rhesus antigen and trigger a rapid, strong secondary immune response, producing large amounts of antibody quickly.
(g) in the uterus / womb (1)
Detailed Explanation: “In utero” means inside the uterus (womb), referring to procedures performed on the foetus before birth.
(h) (adult) (rhesus) negative / negative (1)
Detailed Explanation: The foetus is being attacked by anti-Rhesus antibodies. Transfusing Rhesus negative blood (lacking the antigen) ensures the new cells are not attacked, allowing them to survive and carry oxygen.
▶️ Answer/Explanation
(a) So that the sperm can swim effectively to reach the egg and so that they are capable of fertilizing the egg. This ensured that all men in the study were initially fertile, so any failure to conceive later could be attributed to the contraceptive treatment rather than pre-existing fertility issues.
(b)(i) Progesterone plays two key roles: it thickens and maintains the uterine lining (endometrium) to prepare it for a potential pregnancy, and it inhibits the production of FSH and LH, which prevents further eggs from maturing and prevents ovulation.
(b)(ii) The injections contain testosterone because the progestin in the injection reduces the body’s natural production of testosterone. The added testosterone helps to maintain normal male hormone levels and prevent side effects associated with low testosterone.
(b)(iii) Testosterone is produced in the testes, specifically in the Leydig cells located in the interstitial tissue between the seminiferous tubules.
(c)(i) The purpose of the initial suppression phase was to reduce sperm production to a very low level (below 1 million per cm³) before testing the contraceptive’s effectiveness.
(c)(ii) The sperm count is monitored during the suppression phase to measure if and when the sperm count falls below the required threshold (1 million per cm³), indicating that the treatment is successfully suppressing fertility.
(c)(iii) Alternative contraception was used during the suppression phase to prevent pregnancy because sperm production might not yet be fully suppressed, meaning the men could still be fertile during this initial period.
(d) Sperm count continues to be monitored during the testing phase to ensure that it remains below the effective threshold (1 million per cm³) and to confirm that the treatment continues to work reliably throughout the study.
(e) The number of men whose partners became pregnant is 5.
Calculation: The injection was 98.4% effective, meaning 1.6% of the men’s partners became pregnant. With 320 men in the study, the calculation is 1.6% of 320 = (1.6 / 100) × 320 = 5.12. Since we are counting men, we round to the nearest whole number, which is 5.
(f) Evaluation:
Advantages: The injections are highly effective (98.4% success rate), are reversible for most men, do not require daily remembering like a pill, and shift some of the responsibility for contraception to men.
Disadvantages: There are significant side effects like acne and mood disorders. It does not protect against sexually transmitted infections. The suppression phase is long (26 weeks), and for a small percentage of men (5%), fertility did not return to normal within a year after stopping, raising concerns about long-term reversibility.
Overall, while the method shows promise, the side effects and potential irreversibility for some are important considerations.
▶️ Answer/Explanation
(a) The walls of the heart are less able to contract/pump effectively.
Explanation: Cardiomyopathy causes the heart muscle to become abnormal – either stretched, thickened, or stiff. This structural change directly impairs the heart’s ability to contract forcefully and pump blood efficiently around the body. When the heart cannot pump enough blood to meet the body’s demands, it leads to heart failure.
(b) The atria receive blood and pump/push it into the ventricles. The right atrium receives deoxygenated blood from the body (via the vena cava), and the left atrium receives oxygenated blood from the lungs (via the pulmonary veins).
Explanation: The atria act as the receiving chambers and priming pumps for the heart. Their main function is to collect blood returning to the heart and then contract to push this blood into the more powerful ventricles below. This ensures the ventricles are adequately filled before they perform the major work of pumping blood out of the heart to the lungs and the rest of the body.
(c) The pulmonary artery carries deoxygenated blood, while the aorta carries oxygenated blood. The pulmonary artery carries blood away from the heart to the lungs, whereas the aorta carries blood away from the heart to the rest of the body.
Explanation: These two major arteries have completely different roles. The pulmonary artery is the only artery in the body that carries deoxygenated blood. It transports this blood from the right ventricle to the lungs to pick up oxygen. In contrast, the aorta is the body’s main artery, carrying freshly oxygenated blood from the left ventricle to supply all tissues and organs.
(d) The heart-lung bypass machine oxygenates the blood and removes carbon dioxide (acting like artificial lungs), and it pumps this oxygenated blood around the body (acting like an artificial heart). This allows the patient’s tissues and cells to continue respiring and provides the surgeon with a still, blood-free heart to operate on.
Explanation: During a heart transplant, the patient’s own heart and lungs are temporarily bypassed. This machine is crucial for life support. It takes over the function of the heart by pumping blood and the function of the lungs by adding oxygen to the blood and removing carbon dioxide. This maintains circulation and gas exchange, keeping the patient’s organs alive while the surgeon removes the old heart and attaches the new one.
(e) Immunosuppressants prevent rejection of the transplanted heart. They do this by reducing the immune response, stopping the immune system from recognizing the new heart as foreign and attacking it.
Explanation: The immune system is designed to identify and destroy foreign cells, like those from a donor organ, based on their different antigens. Immunosuppressant drugs are essential to dampen this immune response. Without them, the patient’s white blood cells would recognize the new heart as “non-self” and mount an attack, leading to transplant rejection and failure.
(f) Smoking reduces oxygen in the blood and damages artery walls. It can lead to narrowed arteries, increased risk of blood clots, and higher blood pressure, all of which are dangerous for a transplanted heart.
Explanation: Smoking is particularly harmful after a transplant. The carbon monoxide in smoke binds to haemoglobin, reducing the blood’s oxygen-carrying capacity. Chemicals in tobacco also damage the lining of arteries, promoting atherosclerosis (fatty deposits), which can narrow the coronary arteries supplying the new heart muscle. This increases the risk of heart attacks, strokes, and failure of the transplant.
(g) A diet that contains all the required nutrients/food groups in the correct proportions.
Explanation: A balanced diet isn’t about eating specific “health foods” but about consuming the right amounts and varieties from all the major food groups: carbohydrates, proteins, fats, vitamins, minerals, fibre, and water. This ensures the body gets all the essential nutrients it needs to function optimally, support the immune system, and maintain a healthy weight.
(h) number of patients = 150
Explanation: The passage states that 200 transplants are done each year and that 75% of patients live at least five years. To find the number, we calculate 75% of 200. This can be done as (75/100) × 200 = 0.75 × 200 = 150. Therefore, we can expect 150 of the 200 patients to be alive after five years.
(i) Strenuous activities put extra pressure on the heart, increasing heart rate and blood pressure, which could strain the new heart during the recovery period.
Explanation: After major surgery like a transplant, the body, and especially the new heart, needs time to heal and adapt. Strenuous activities like heavy lifting cause a sudden, significant increase in the heart’s workload. This could be too stressful for the recovering heart muscle and the surgical connections (sutures), potentially leading to complications like a heart attack or damage to the surgical site.
(j) Because their immune system is weakened by the immunosuppressant drugs, making them less able to fight off infections from pathogens in food.
Explanation: Immunosuppressants, while vital for preventing rejection, have the side effect of reducing the overall activity of the immune system. This means the body’s defences against bacteria, viruses, and other pathogens are lowered. Harmful bacteria like Salmonella or E. coli, which might be fought off by a healthy person, can more easily cause food poisoning in a transplant patient because their white blood cells are less effective at destroying the invaders.
▶️ Answer/Explanation
(a) spinal cord
(b)(i) C (0.5)
A is incorrect because 0.5 is the answer
B is incorrect because 0.5 is the answer
D is incorrect because 0.5 is the answer
Cross: Hh (heterozygous, HD) × hh (homozygous recessive, no HD). Probability of child inheriting H (HD) allele from heterozygous parent is \( \frac{1}{2} = 0.5 \).
(b)(ii) A diagram that makes reference to the following points:
• one circle and one square shown (1)
• two shapes unshaded (1)
For each of the two additional children, the predicted sex ratio is 1:1 (one male, one female). The predicted phenotype ratio for children from this cross is 1 with HD : 1 without HD. Therefore, for two more children, one is predicted to have HD and one without, with sexes not specified by probability.
(c) An explanation that makes reference to three of the following points:
• prevents translation / no translation (1)
• prevents ribosomes attaching (to mRNA) (1)
• prevents / no, codon binding to anticodon (1) Allow tRNA does not bind to mRNA
• prevents amino acids joining / amino acid chain not made (1)
• huntingtin / protein / polypeptide not made (1) Allow less huntingtin / protein made
The drug binds to the mutated mRNA, blocking the process of protein synthesis (translation). This prevents the formation of the harmful huntingtin protein, thereby reducing damage to nerve cells.