lesson
Break down, then absorb
1 · Learn
Digestion breaks large food molecules into smaller soluble molecules that can be absorbed. Physical breakdown, such as chewing, increases exposed surface; enzymes are biological catalysts that help chemical reactions proceed.
The small intestine has a large surface for absorbing digested nutrients into the body. The large intestine absorbs remaining water. Food, digestive contents and blood occupy different spaces; food pieces do not simply enter blood vessels whole.
2 · Worked example
I distinguish breaking a biscuit into crumbs from digesting its starch molecules. Smaller crumbs are still made of the same large molecules until chemical digestion changes them.
3 · Your turn
Is chewing alone the same as completing chemical digestion? Explain.
Check your answer
No. Chewing breaks food into smaller pieces; chemical digestion breaks large molecules into smaller absorbable molecules.
4 · Apply your learning
Use a supplied digestive-system diagram to trace food and separately mark where absorption occurs.
Adult guidance and safety
Use supplied data and diagrams unless a qualified adult has approved the practical, equipment and risk assessment. No tasting substances, culturing unknown microbes, mains electricity, flames or hazardous chemical experiments at home. Models simplify reality; ask which assumptions affect the conclusion.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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