Organisation
Organisation is the GCSE biology topic that explains how cells are organised into tissues, organs and organ systems, focusing on the human digestive and cardiovascular systems and how enzymes speed up digestion. It also covers how plants transport water and dissolved sugars through xylem and phloem tissue.
Method
- Learn the hierarchy of organisation: cells group together to form tissues, tissues form organs, and organs work together in organ systems (for example, the digestive system).
- For enzyme questions, use the lock-and-key model: an enzyme's active site has a shape that is complementary to one specific substrate, so each enzyme only catalyses one reaction.
- Learn the effect of temperature and pH on enzyme activity: rate increases as temperature rises towards the optimum, then falls rapidly as the enzyme denatures and its active site changes shape.
- Memorise which organ produces which digestive enzyme, and where each type of food is chemically broken down (for example, amylase in the mouth and small intestine, protease in the stomach and small intestine, lipase in the small intestine).
- Learn the structure and role of the heart, blood vessels and blood in the double circulatory system, and how each part is adapted to its function.
- For plant transport questions, learn how xylem carries water and dissolved minerals upwards from the roots, and how phloem transports (translocates) dissolved sugars around the plant in both directions.
Worked example
A student investigates the effect of pH on the rate of reaction between amylase and starch, using a colour change with iodine. At pH 6, the starch was fully broken down after 150 seconds. Calculate the rate of reaction at pH 6, using the equation: rate = 1000 / time. Give your answer to 3 significant figures.
- Write down the equation: rate = 1000 / time.
- Substitute the time given: rate = 1000 / 150.
- Calculate: 1000 / 150 = 6.666...
- Round to 3 significant figures: 6.67.
- Final answer: the rate of reaction is 6.67 (s^-1).
Practice questions
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Q1Name the organ system responsible for breaking food down into small, soluble molecules.Show answer
Answer: The digestive system.
Q2State the type of large biological molecule that all enzymes are made from.Show answer
Answer: Protein.
Q3Name the plant tissue that transports water and dissolved minerals from the roots to the leaves.Show answer
Answer: Xylem.
Q4An amylase reaction is complete after 200 seconds. Calculate the rate of reaction using rate = 1000 / time.Show answer
Answer: 5 (1000/200 = 5)
Q5State two ways that bile aids the digestion of fats.Show answer
Answer: It neutralises stomach acid (makes conditions alkaline for enzymes in the small intestine) and emulsifies fat into small droplets, increasing the surface area for lipase to act on.
Q6Explain why the rate of an enzyme-controlled reaction decreases sharply above the enzyme's optimum temperature.Show answer
Answer: The enzyme denatures: its active site changes shape so the substrate can no longer bind, so fewer (or no) enzyme-substrate complexes form.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
State two ways in which a red blood cell is adapted to carry oxygen efficiently.
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A student carried out the required practical into the effect of pH on the rate of reaction between amylase and starch. At pH 8 the reaction was complete after 250 seconds. (a) Calculate the rate of reaction at pH 8, using rate = 1000 / time. Give your answer to 3 significant figures. (b) The rate of reaction at pH 7 was 12.5. Explain, in terms of enzyme structure, why the rate of reaction is lower at pH 8 than at pH 7.
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A student examines a microscope slide showing villi in the small intestine. Explain how the structure of the small intestine, including villi, is adapted to maximise the absorption of digested food molecules into the blood.
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Free printable worksheet
Want more practice on paper? Download the organisation worksheet pack - 18 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 2 of GCSE Biology Workbook, the whole course as one free printable PDF.
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