Describe how the carbon in a dead animal returns to the air.

Decomposers feed on the remains and release carbon dioxide as they respire.

Describe the two ways water enters the atmosphere in the water cycle.

It evaporates from oceans, lakes and soil, and it is lost from plant leaves by transpiration.

What happens to water vapour as it rises and cools in the water cycle?

It condenses into droplets that form clouds, and the water later falls as precipitation.

Explain why the water cycle provides land organisms with fresh water.

Evaporation leaves dissolved salts behind, so the water that condenses and falls as rain is fresh and can be used by organisms on land.

OCR GCSE Biology A J247

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Protein synthesis and the triplet code Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition and trophic levels Pyramids of biomass and the efficiency of transfer

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations How genetic variants influence phenotype Asexual and sexual reproduction compared Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination, multiple genes and Mendel's work Variation within a population, and classification Natural selection and evolution Evidence for evolution, and the work of Darwin and Wallace

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, and evidence for environmental change Food security, agricultural and biotechnological solutions Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples Physical and chemical plant defences Detecting plant disease; white blood cells and platelets Non-specific defences and the immune system Monoclonal antibodies and their uses Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc The eye and its common defects The structure and function of the brain Investigating and treating the brain Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Plant hormones and their commercial uses Homeostasis, and the skin in temperature control Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes Osmotic changes in body fluids, and the kidneys The kidney tubule and the effect of ADH Responding to temperature and osmotic challenges

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Community Level Systems

The carbon and water cycles, and decomposition

3 things to know
Paper 4

Overview

How photosynthesis removes carbon dioxide and respiration, combustion and decomposers return it, how water evaporates, transpires, condenses and falls as fresh rain, why the carbon and water cycles matter to organisms and habitats, what aerobic and anaerobic mean, how temperature, water and oxygen affect the rate of decomposition, turning a compost heap, and calculating rates of decay.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain why decomposition almost stops at very high temperatures, is slow in dry or waterlogged conditions, and is fast in well-aerated soil.

Process

Which process removes carbon dioxide from the air in the carbon cycle?

Process

Name two processes that return carbon dioxide to the air in the carbon cycle.

Questions from this subtopic

Each one with the model answer underneath.

1
Which process removes carbon dioxide from the air in the carbon cycle?
Model answer
Photosynthesis by plants and algae.
2
Name two processes that return carbon dioxide to the air in the carbon cycle.
Model answer
Respiration by living organisms and the combustion of fuels.
3
Describe how the carbon in a dead animal returns to the air.
Model answer
Decomposers feed on the remains and release carbon dioxide as they respire.
4
Describe the two ways water enters the atmosphere in the water cycle.
Model answer
It evaporates from oceans, lakes and soil, and it is lost from plant leaves by transpiration.
5
What happens to water vapour as it rises and cools in the water cycle?
Model answer
It condenses into droplets that form clouds, and the water later falls as precipitation.
6
Explain why the water cycle provides land organisms with fresh water.
Model answer
Evaporation leaves dissolved salts behind, so the water that condenses and falls as rain is fresh and can be used by organisms on land.

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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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Algae and .

phytoplanktonfungianimals

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AThe blood becomes too dilute.

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Egestion means passing out of undigested food as faeces.

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