Year 8 Science · Unit 1 · Lesson 11
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Learning Goals
Match each part to its job
Write the matching letter in the middle column. Each letter is used once.
| Part of the gut | Letter | Job |
|---|---|---|
| Mouth | A. Mixes food with acid and enzymes and churns it into a thick liquid. | |
| Oesophagus | B. Absorbs most of the nutrients into the blood through its villi. | |
| Stomach | C. A muscular tube that pushes swallowed food down to the stomach. | |
| Small intestine | D. Absorbs water; what is left forms faeces. | |
| Large intestine | E. Teeth chew the food and saliva starts chemical digestion. |
Odd one out
In each row, three things belong together and one does not. Circle the odd one out and give your reason.
| Row | Four things | Reason it is the odd one out |
|---|---|---|
| 1 | chewing · saliva mixing with food · food shaped into a soft ball · nutrients taken in by villi | |
| 2 | kidney · mouth · stomach · large intestine | |
| 3 | absorbs water · has villi that absorb most nutrients · leftover waste becomes faeces · the last section before the anus |
1. State the difference between digestion and absorption.
Cause and effect
Complete the chain for a bite of bread. Each box follows from the box before it.
2. Some people do not make enough of the enzyme that breaks lactose (the sugar in milk) into smaller sugars. Use the words digestion and absorption to explain why much of the lactose they drink is not taken into their blood.
Investigation: modelling villi with paper towel
A group lined three identical 10 cm plastic tubes with paper towel. Tube A had a flat strip that just covered the inside. Tubes B and C had longer strips folded into pleats so they still fitted in the same 10 cm. The group poured 50 mL of water slowly through each tube and worked out how much water the paper held.
| Tube | Lining | Trial 1 | Trial 2 | Trial 3 | Mean |
|---|---|---|---|---|---|
| A | flat strip | 4 | 5 | 3 | 4 |
| B | 5 pleats | 9 | 8 | 10 | 9 |
| C | 10 pleats | 12 | 13 | 11 | 12 |
Source: sample class results.
3. How many times as much water did the lining in tube C hold as the lining in tube A? Show your working.
Answer times
4. What part of the small intestine do the pleats model? Use the pattern in Table 1 to explain why the small intestine has millions of these, not a smooth lining.
5. Give one way this model is not like a real small intestine.
6. Tayla eats a large bowl of pasta five minutes before her 5 km race, saying it will give her muscles energy for the run. Her coach says she should have eaten it a few hours earlier. Evaluate who is right. Use digestion, absorption and the circulatory system in your answer.
Match each part to its job
Mouth → E; Oesophagus → C; Stomach → A; Small intestine → B; Large intestine → D.
Odd one out
Row 1: nutrients taken in by villi (small intestine; the rest happen in the mouth). Row 2: kidney (not part of the gut). Row 3: has villi that absorb most nutrients (small intestine; the rest describe the large intestine).
1. Digestion breaks food into smaller, usable parts; absorption moves those materials from the gut into the blood. [2 marks]
Cause and effect
Box 2: stomach acid and enzymes break the food down further. Box 3: in the small intestine, small sugar particles are absorbed through the villi into the blood.
2. Without the enzyme, lactose is not digested into smaller sugars, so its particles stay too large to be absorbed in the small intestine and pass on through the gut. [2 marks: 1 not digested; 1 too large to be absorbed]
Go Deeper
3. 12 ÷ 4 = 3 times as much. [2 marks: 1 using the two means, 1 answer]
4. The villi. More pleats in the same 10 cm held more water (4, 9, then 12 mL) because there was more surface; millions of villi give a huge surface, so nutrients are absorbed into the blood much faster than through a smooth lining. [3 marks: villi; pattern with data; more surface, faster absorption]
5. Any one: paper just soaks up water; real villi are living cells with blood vessels inside; the gut absorbs nutrients, not only water; villi are far smaller and more numerous. [1 mark]
Show What You Know
6. Marking guide (points expected): 1 starch in pasta is too large for cells to use; 1 it must be digested (mouth, stomach, small intestine) into small sugar particles; 1 the sugar is absorbed through the villi into the blood; 1 this takes hours, not minutes; 1 the blood (circulatory system) carries the sugar to her muscles; 1 judgement: the coach is right, as food eaten five minutes before cannot reach her muscles in time. [6 marks]
Common error to watch for: thinking food is “in the body” once it is in the stomach. It is still inside the gut until it is absorbed into the blood.