Edexcel GCSE Combined Science CB8 and CB9: a complete overview of exchange and transport in animals and ecosystems and material cycles

What CB8 and CB9 actually demand

These two topics, examined on Biology Paper 2, cover how substances are exchanged and transported in animals, and how organisms interact and recycle materials in ecosystems. The examiners reward the alveolus adaptations, the path of blood through the heart, the carbon cycle, and confident use of the quadrat core practical.

This guide walks through both topics and ties together the matching dot-point pages, each with its own practice questions.

Exchange and transport in animals

Large organisms have a small surface area to volume ratio, so they need exchange surfaces and a transport system. The lungs exchange gases in the alveoli, which have a large surface area, thin walls, a moist lining and a rich blood supply.

Humans have a double circulatory system: the right side of the heart pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body. Arteries carry blood away at high pressure, veins return it with valves, and capillaries allow exchange. Blood is plasma, red cells (haemoglobin), white cells and platelets.

Ecosystems

An ecosystem is a community of organisms interacting with abiotic (non-living) factors. Food chains start with a producer. Organisms show interdependence and compete for resources.

Material cycles

• Carbon cycle: removed by photosynthesis; returned by respiration, combustion and decomposition.
• Water cycle: evaporation and transpiration, condensation, precipitation.
• Nitrogen cycle: nitrogen-fixing bacteria make usable compounds; decomposers release nitrogen; denitrifying bacteria return nitrogen gas.

Biodiversity is reduced by deforestation, pollution and global warming, and protected by conservation.

How CB8 and CB9 are examined

• Structure to function. Explaining alveolus and blood-vessel adaptations.
• Sequencing. The path of blood through the heart.
• Cycles. Describing the carbon and nitrogen cycles.
• Core practical. Using quadrats and transects to estimate populations.

Check your knowledge

A mix of recall and application questions covering CB8 and CB9. Attempt them under timed conditions, then check against the solutions.

1. State two adaptations of the alveoli for gas exchange. (2 marks)
2. Name the part of the blood that carries oxygen. (1 mark)
3. Why is the wall of the left ventricle thicker than the right? (1 mark)
4. Name the process that removes carbon dioxide from the air. (1 mark)
5. Name two processes that return carbon dioxide to the air. (2 marks)
6. Give one example of an abiotic factor. (1 mark)
7. Name the bacteria that turn nitrogen gas into compounds plants can use. (1 mark)
8. State why quadrats should be placed randomly. (1 mark)