2025 Cambridge IGCSE Biology (0610) 模拟试题及答案详解

(a) Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by the diffusion of water vapour through the stomata.

(b) (i) The reservoir allows the air bubble to be pushed back to the start of the capillary tube (scale) so that the measurement can be repeated.

(ii) 1. Cut the stem of the shoot under water to prevent air from entering the xylem.
2. Seal all joints of the potometer apparatus with petroleum jelly to ensure it is completely airtight.

(c) Description: As the wind speed increases, the rate of transpiration increases (from 1.5 mm/min in calm air to 6.4 mm/min in strong wind).
Explanation: Moving air blows away the water vapour that accumulates on the surface of the leaf (boundary layer). This maintains a steep water vapour concentration gradient between the inside of the leaf air spaces and the outside atmosphere, leading to faster diffusion of water vapour out through the stomata.

(d) Any two from: temperature, humidity, light intensity.

(a) max [2]:
- loss of water vapour from leaves / aerial parts of plant [1]
- by evaporation from surfaces of mesophyll cells [1]
- followed by diffusion of water vapour through stomata [1]

(b) (i) max [2]:
- to return the air bubble to the start / zero mark [1]
- allows repeats / multiple measurements to be taken [1]

(b) (ii) max [2]:
- cut shoot under water [1]
- seal joints with Vaseline / grease / petroleum jelly [1]
- ensure leaves are dry before starting [1]

(c) max [5]:
- rate increases as wind speed increases / describe trend with data quotes [1]
- wind removes the saturated layer of air / boundary layer / water vapour outside the leaf [1]
- this maintains / increases the water vapour concentration gradient [1]
- between the air spaces inside the leaf and the external air [1]
- leading to faster diffusion of water vapour through stomata [1]

(d) max [2]:
- temperature [1]
- humidity [1]
- light intensity [1]

(a)
- Petals: Insect-pollinated are large and brightly coloured; wind-pollinated are small, green or dull-coloured.
- Stigmas: Insect-pollinated are sticky and enclosed within the flower; wind-pollinated are long, feathery and hang outside the flower.
- Pollen: Insect-pollinated are larger, sticky or spiky, produced in smaller quantities; wind-pollinated are small, light, smooth, produced in massive quantities.

(b) (i) Magnification = Image size (size of drawing) / Actual size

(b) (ii) Convert units: 40 mm = 40 * 1000 = 40000 micrometres.
Magnification = 40000 / 80 = x500.

(c) 1. The pollen grain germinates on the sticky stigma.
2. A pollen tube grows down through the style towards the ovary.
3. The growth of the pollen tube is controlled by the pollen tube nucleus.
4. The pollen tube enters the ovary and reaches an ovule, entering through the micropyle.
5. The male gamete nucleus travels down the pollen tube.
6. The male nucleus fuses with the female gamete nucleus (egg cell nucleus) inside the ovule to form a diploid zygote.

(a) max [3]:
- Petals: large/brightly coloured vs small/dull/green [1]
- Stigmas: sticky/inside flower vs feathery/hanging outside flower [1]
- Pollen: sticky/spiky/large/few vs smooth/light/small/many [1]

(b) (i) [1]:
- Magnification = Image size / Actual size [1]

(b) (ii) max [3]:
- conversion of 40 mm to 40000 micrometres [1]
- correct substitution: 40000 / 80 [1]
- correct calculation: x500 or 500 [1]

(c) max [6]:
- pollen grain germinates / produces pollen tube [1]
- pollen tube grows down the style [1]
- enters the ovary / enters the ovule [1]
- through the micropyle [1]
- male nucleus / gamete travels down the tube [1]
- male and female nuclei fuse / join [1]
- to form a zygote / diploid cell [1]

(a) A double circulatory system means that for every complete circuit of the body, blood passes through the heart twice (pulmonary circuit and systemic circuit).

(b) 1. Keeps oxygenated and deoxygenated blood separate, preventing mixing and maximizing oxygen delivery to tissues.
2. Allows blood to be pumped at a higher pressure to body tissues, ensuring faster delivery of oxygen and glucose for aerobic respiration.
3. Blood to the lungs can be pumped at a lower pressure, preventing damage to the delicate lung capillaries while still allowing efficient gas exchange.

(c) (i) 1. Arteries have thick muscular and elastic walls, whereas veins have thin walls with less muscle and elastic tissue.
2. Arteries have a narrow lumen, whereas veins have a wide lumen (and contain valves to prevent backflow).

(c) (ii) 1. The thick layer of muscle and elastic fibers allows the wall to stretch and recoil to withstand and maintain high blood pressure from the heart's pumping action.
2. The elastic recoil helps to smooth out the pulse of blood.
3. The narrow lumen maintains high blood pressure to transport blood quickly to body tissues.

(d) (i) Pulmonary artery.
(ii) Renal artery.

(a) max [2]:
- blood passes through the heart twice [1]
- for one complete circuit / round of the body [1]

(b) max [4]:
- oxygenated and deoxygenated blood are kept separate / do not mix [1]
- blood can be pumped at high pressure to the body [1]
- blood is pumped at a lower pressure to the lungs [1]
- faster / more efficient delivery of oxygen / glucose to respiring tissues [1]
- supports higher metabolic rate / active lifestyle / warm-bloodedness [1]

(c) (i) max [2]:
- Arteries: thicker wall / more muscle / more elastic tissue vs Veins: thinner wall [1]
- Arteries: narrow lumen vs Veins: wide lumen [1]
- Arteries: no valves vs Veins: have valves [1]

(c) (ii) max [4]:
- thick muscular wall withstands high blood pressure [1]
- elastic tissue stretches and recoils [1]
- recoil maintains / regulates blood pressure / smooths blood flow [1]
- narrow lumen maintains high pressure [1]

(d) (i) [1]:
- pulmonary artery [1]

(d) (ii) [1]:
- renal artery [1]

(a) Proteins / amino acids.

(b) 1. High nitrate levels cause rapid growth of algae on the water surface (algal bloom).
2. This layer of algae blocks sunlight from reaching submerged aquatic plants.
3. Submerged plants cannot photosynthesise and therefore die.
4. Aerobic bacteria (decomposers) multiply rapidly as they feed on the dead plant matter.
5. These bacteria respire aerobically, using up the dissolved oxygen in the water.
6. The lack of dissolved oxygen causes fish and other aquatic animals to suffocate and die.

(c) (i) Decomposers (or bacteria/fungi).

(c) (ii) Untreated sewage contains high levels of organic matter. Decomposing bacteria feed on this organic matter, multiply rapidly, and consume large amounts of dissolved oxygen through aerobic respiration.

(d) (i) Nitrogen fixation is the process of converting inert atmospheric nitrogen gas into nitrogen-containing compounds, such as ammonia or nitrates, that can be absorbed and used by plants.

(d) (ii) Nitrification.

(a) [1]:
- proteins / amino acids [1]

(b) max [6]:
- algal bloom / rapid growth of algae on surface [1]
- blocks sunlight from entering water [1]
- submerged plants cannot photosynthesise [1]
- submerged plants die [1]
- bacteria / decomposers feed on dead plants and multiply [1]
- bacteria respire aerobically [1]
- dissolved oxygen concentration decreases [1]
- fish / aquatic animals suffocate / die [1]

(c) (i) [1]:
- decomposers / bacteria / fungi [1]

(c) (ii) max [2]:
- sewage provides organic matter / food for bacteria [1]
- bacteria undergo aerobic respiration [1]
- using up oxygen / oxygen depletion [1]

(d) (i) max [2]:
- conversion of atmospheric nitrogen gas [1]
- into ammonia / ammonium / nitrates / compounds plants can use [1]

(d) (ii) [2]:
- nitrification [1]

(a) (i) The binomial system is an internationally agreed system in which the scientific name of an organism is made up of two parts: the genus name and the species name.

(a) (ii) First word: Genus.
Second word: Species.

(b) 1. Amphibians have moist, scale-less skin, whereas reptiles have dry skin with scales.
2. Amphibians lay soft, jelly-like eggs in water, whereas reptiles lay eggs with leathery/rubbery shells on land.

(c) 1. Morphological features can be misleading due to convergent evolution, where unrelated organisms evolve similar structures (analogous structures) to adapt to similar environments.
2. DNA sequences provide a direct record of genetic inheritance and evolutionary history.
3. The closer the DNA base sequences are between two species, the more recently they shared a common ancestor.

(d) (i) Cell wall, chloroplasts (or large permanent vacuole).

(d) (ii) The cellulose cell wall is fully permeable and rigid. It resists turgor pressure inside the cell, preventing the cell from bursting when it takes up water by osmosis, and provides structural support to the plant.

(a) (i) max [2]:
- internationally agreed system of naming [1]
- using two names / genus and species [1]

(a) (ii) [2]:
- First word: genus [1]
- Second word: species [1]

(b) max [2]:
- skin: moist/no scales vs dry/scales [1]
- reproduction: jelly-like eggs in water vs leathery/shelled eggs on land [1]
- larval stage: aquatic gills vs lungs from birth [1]

(c) max [3]:
- physical traits can look similar due to environmental adaptation / convergent evolution [1]
- DNA base sequence is more accurate / objective [1]
- more similar DNA indicates more recent common ancestor / closer evolutionary relationship [1]

(d) (i) max [2]:
- cell wall [1]
- chloroplasts [1]
- large permanent vacuole [1]

(d) (ii) max [2]:
- prevents cell from bursting (due to osmosis / turgor pressure) [1]
- provides structural support / maintains shape of cell [1]

(a) (i) Trachea.

(a) (ii) 1. Massive number of alveoli provides a very large total surface area for diffusion.
2. The walls of the alveoli are only one cell thick, which reduces the diffusion distance.
3. A moist lining allows gases to dissolve before diffusing across the membrane.
4. A dense network of blood capillaries maintains a steep concentration gradient by constantly bringing deoxygenated blood and carrying away oxygenated blood.

(b) 1. Goblet cells produce and secrete sticky mucus, which traps inhaled dust particles, bacteria, and pathogens.
2. Ciliated cells have hair-like projections called cilia on their surface.
3. Cilia beat rhythmically to move the mucus (carrying trapped pathogens) upwards away from the lungs toward the throat, where it is swallowed and destroyed by stomach acid.

(c) (i) A gene is a length of DNA that codes for a specific protein.

(c) (ii) 1. The sequence of bases in a gene determines the sequence of bases in mRNA (via transcription).
2. In the cytoplasm, ribosomes read the base sequence in triplets (codons).
3. Each triplet codes for a specific amino acid.
4. This determines the order in which amino acids are joined together to form a polypeptide chain, which then folds into a specific 3-dimensional protein shape.

(a) (i) [1]:
- trachea [1]

(a) (ii) max [4]:
- large surface area [1]
- thin wall / one cell thick / short diffusion distance [1]
- moist lining allows gases to dissolve [1]
- dense capillary network / rich blood supply [1]
- ventilation / blood flow maintains concentration gradient [1]

(b) max [3]:
- goblet cells secrete/produce mucus [1]
- mucus traps dust / bacteria / pathogens [1]
- cilia (on ciliated cells) beat / wave [1]
- to sweep mucus away from lungs / to throat [1]

(c) (i) [2]:
- length of DNA [1]
- that codes for a (specific) protein [1]

(c) (ii) max [3]:
- base sequence determines the sequence of amino acids [1]
- three bases (triplet/codon) code for one amino acid [1]
- amino acids are joined in a specific order [1]
- folding determines specific 3D shape / function of the protein [1]