Grade 7 · Body Systems · Digestive and Circulatory Systems
Digestion and Nutrient Transport
From a mouthful of food to glucose reaching a muscle cell.
Learning objectives
- Sequence the organs of the digestive system.
- Explain the role of enzymes in digestion.
- Trace glucose from the small intestine to a body cell.
NGSS alignment
MS-LS1-3
Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.
MS-LS1-7
Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
Chewing bread until it turns sweet
Chew a piece of plain bread slowly for a minute and it begins to taste sweet, even though no sugar was added.
Think about it
- What could have changed in your mouth?
- Where does the sweetness come from?
EXPLAIN
From food to fuel
Digestion breaks large food molecules into small ones that can pass through the wall of the small intestine into the blood.
| Organ | What happens |
|---|---|
| Mouth | Teeth cut and grind; salivary amylase begins starch digestion |
| Oesophagus | Muscular waves (peristalsis) push food down |
| Stomach | Acid and protease begin protein digestion |
| Small intestine | Enzymes finish digestion; villi absorb nutrients |
| Large intestine | Water is absorbed; waste is compacted |
Enzymes
- Amylase breaks starch into glucose
- Protease breaks protein into amino acids
- Lipase breaks fats into fatty acids and glycerol
Careful
Enzymes are catalysts, not ingredients. They speed up reactions and are not used up.
Glucose absorbed by a villus enters the blood, travels through the heart and is delivered to respiring cells.
INVESTIGATION
Testing amylase activity
research question
How does temperature affect the time amylase takes to digest starch?
hypothesis
Activity will increase up to about 37 degrees Celsius and then fall as the enzyme denatures.
variables
Independent: temperature (10, 20, 37, 50, 70 degrees Celsius). Dependent: time until iodine no longer turns blue-black. Controlled: enzyme and starch concentration, volumes, pH.
method
Mix starch and amylase in a water bath at each temperature. Every 30 seconds transfer a drop to iodine on a tile and record when the blue-black colour disappears.
safety
Wear eye protection. Iodine stains; handle hot water baths with care.
analysis
Plot time against temperature and identify the optimum. Explain the shape of the curve using enzyme shape.
Watch
Human Body Systems Functions Overview
Amoeba Sisters · 9 min
Places digestion in the context of the whole body.
Before you watch: Where do you think most absorption happens?
- Which organ absorbs most nutrients?
- How does glucose reach a muscle cell?
Interactive simulation · PhET
Concentration
Dissolve a solute and watch how concentration changes as you add water.
While you explore
- How does a concentration difference help absorption in the small intestine?
- What happens to concentration when more water is added?
Key vocabulary
- Villi
- Tiny finger-like folds that soak up nutrients.
- Enzyme
- A protein that speeds up a reaction in your body.
Practice questions
0/2 correct
Level 1 · Criterion A
Which enzyme digests starch?
Level 2 · Criterion A
Most nutrient absorption happens in the:
MYP criterion tasks
Level 3 · Criterion C
A student found that starch digestion took 90 s at 37 degrees Celsius but was not complete after 10 minutes at 70 degrees Celsius. Analyse these results.
Reflect & track
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