lesson
One population connects to several others
1 · Learn
A food web links feeding relationships. Arrows conventionally show transfer from food to consumer. Producers build food molecules; consumers obtain them by feeding. A species can be part of several chains, so one change can have several effects.
In a model web, grass feeds rabbits and grasshoppers; grasshoppers feed frogs; rabbits and frogs feed foxes. Fewer grasshoppers may reduce food for frogs, but this alone does not prove exactly how many frogs will remain.
2 · Worked example
I trace grass -> grasshopper -> frog. If grasshoppers decline, frogs lose one listed food source. Other unlisted factors could also influence frog numbers.
3 · Your turn
In the supplied web, which two consumers feed directly on grass?
Check your answer
Rabbits and grasshoppers.
4 · Apply your learning
Draw the complete supplied web and explain one direct and one possible indirect effect of a change, labelling uncertainty.
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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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