A cube has sides of 2 cm. State its surface area, its volume and its surface area to volume ratio.

Its surface area is 24 cm², its volume is 8 cm³, and the ratio is 3:1.

A cube has sides of 4 cm. State its surface area, its volume and its surface area to volume ratio.

Its surface area is 96 cm², its volume is 64 cm³, and the ratio is 1.5:1.

One cube has sides of 1 cm and another has sides of 3 cm. Which has the larger surface area to volume ratio, and what are the two ratios?

The 1 cm cube, at 6 cm² to 1 cm³, a ratio of 6:1, against 54 cm² to 27 cm³, a ratio of 2:1.

A block measures 4 cm by 2 cm by 1 cm. State its surface area, its volume and its surface area to volume ratio.

Its surface area is 28 cm², its volume is 8 cm³, and the ratio is 3.5:1.

What happens to the surface area to volume ratio of an organism as it gets larger?

It gets smaller, because volume increases faster than surface area does.

Why can a single-celled organism rely on diffusion across its surface alone?

Its surface area to volume ratio is very large and no part of it is far from the surface, so diffusion supplies its needs fast enough.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides 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, mutualism and parasitism

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination and characteristics controlled by many genes Variation within a population, and classification Natural selection and evolution Evidence for evolution from fossils and antibiotic resistance

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism 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 White blood cells, antibodies and platelets Non-specific defences and the immune system 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 Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Homeostasis and control systems in the body Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes

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

Scaling Up

Surface area to volume ratio and exchange surfaces

3 things to know
Paper 7 (Biology)

Overview

Calculating the surface area, volume and surface area to volume ratio of cubes and blocks, how the ratio falls as organisms get larger, why single-celled organisms rely on diffusion while large animals need exchange surfaces and transport systems, what makes an exchange surface efficient, and the oxygen, carbon dioxide, urea, water, food molecules and mineral ions that organisms take in, transport or remove.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Name three features that make an exchange surface efficient.

Key term

Why does an organism need water transported around it?

Key term

In what form are food molecules carried around an animal's body?

Questions from this subtopic

Each one with the model answer underneath.

1
A cube has sides of 2 cm. State its surface area, its volume and its surface area to volume ratio.
Model answer
Its surface area is 24 cm², its volume is 8 cm³, and the ratio is 3:1.
2
A cube has sides of 4 cm. State its surface area, its volume and its surface area to volume ratio.
Model answer
Its surface area is 96 cm², its volume is 64 cm³, and the ratio is 1.5:1.
3
One cube has sides of 1 cm and another has sides of 3 cm. Which has the larger surface area to volume ratio, and what are the two ratios?
Model answer
The 1 cm cube, at 6 cm² to 1 cm³, a ratio of 6:1, against 54 cm² to 27 cm³, a ratio of 2:1.
4
A block measures 4 cm by 2 cm by 1 cm. State its surface area, its volume and its surface area to volume ratio.
Model answer
Its surface area is 28 cm², its volume is 8 cm³, and the ratio is 3.5:1.
5
What happens to the surface area to volume ratio of an organism as it gets larger?
Model answer
It gets smaller, because volume increases faster than surface area does.
6
Why can a single-celled organism rely on diffusion across its surface alone?
Model answer
Its surface area to volume ratio is very large and no part of it is far from the surface, so diffusion supplies its needs fast enough.

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Cell Level Systems

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Genes, Inheritance and Selection

Global Challenges

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AA diet high in sugar and fat leads to obesity.

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