Human Diet And Digestion

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Lesson notes

Balanced Diet

A balanced diet contains all food groups in correct proportions.
Essential food groups: carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre, and water.
Individual needs vary with age, gender, activity level, and pregnancy.

Vitamin Deficiencies

Scurvy results from severe vitamin C deficiency (e.g., in sailors).
Symptoms of scurvy: anaemia, exhaustion, bleeding, limb pain, gum ulcers, tooth loss.
Rickets in children is caused by vitamin D deficiency, leading to soft, weak bones.
Vitamin D is needed for calcium absorption; treatment includes supplements and sunlight.

Digestive System Overview

The alimentary canal processes food through: ingestion, mechanical digestion, chemical digestion, absorption, assimilation, and egestion.
Key organs: mouth, oesophagus, stomach, small intestine (duodenum & ileum), large intestine, rectum, anus.
Accessory organs: salivary glands, pancreas, liver, gall bladder.

Organs of the human digestive system

Physical (Mechanical) Digestion

Breaks food into smaller pieces without chemical change.
Increases surface area for enzyme action.
Includes chewing (teeth), stomach churning, and emulsification of fats by bile.

Chemical Digestion

Breaks down large, insoluble molecules into small, soluble ones.
Produces molecules that can be absorbed into the blood.

Digestive Enzymes

Amylase (mouth & pancreas) digests starch → smaller sugars.
Proteases (stomach & pancreas) digest proteins → amino acids.
Lipase (pancreas) digests lipids → fatty acids + glycerol.

The digestion of starch by amylase

Hydrochloric Acid in Stomach

Hydrochloric acid in gastric juice kills bacteria and provides low pH (~2).
Low pH denatures bacterial enzymes and optimises pepsin (a protease) activity.

Bile & Emulsification

Bile is produced by liver, stored in gall bladder, released into duodenum.
Bile is alkaline – neutralises stomach acid for small intestine enzymes.
Bile emulsifies fats (mechanical digestion), increasing surface area for lipase.

Bile production and secretion

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Practice questions

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1.Which food group provides the main source of energy in a balanced diet?
Easy
- ACarbohydrates
- BProteins
- CLipids
- DVitamins
2.Scurvy is caused by a deficiency of vitamin D.
Easy
True or false?
3.Name the mineral required for the development of strong bones and teeth.
Easy
4.Complete the sentence about digestion.
Easy
The breakdown of large, insoluble molecules into small, soluble molecules is called ____ digestion.
5.Match each enzyme to the type of food it digests.
Medium
- Amylase
- Protease
- Lipase
- Proteins
- Lipids
- Starch
6.Arrange the following stages of food breakdown in the correct order, starting from ingestion.
Medium
- Absorption
- Chemical digestion
- Egestion
- Ingestion
- Mechanical digestion
7.Which organ produces bile?
Easy
- AGall bladder
- BLiver
- CPancreas
- DStomach
8.Which of the following is a role of hydrochloric acid in the stomach?
Medium
- Akills bacteria
- Bmechanically breaksdown food
- Cprovides optimum pH for pepsin
- Ddetoxifies poisons

More questions

9.Which of the following is a symptom of rickets?
Easy
- AAnaemia
- BBone pain
- CTooth loss
- DSpontaneous bleeding
10.Emulsification of fats is an example of chemical digestion.
Medium
True or false?
11.The optimum pH for the enzyme pepsin in the stomach is approximately pH 2. What is the hydrogen ion concentration in mol/dm³ at this pH?
Hard
- A-0.99
- B2.01
- C1.01
- D0.01
12.Name the process by which bile breaks down large fat droplets into smaller ones.
Easy
13.Which of the following is a symptom of scurvy?
Easy
- ABone pain
- BSpontaneous bleeding
- CSoft, weak bones
- DTooth decay
14.Bile is produced in the gall bladder.
Easy
True or false?
15.Which enzyme is produced in the mouth and the pancreas and digests starch?
Easy
- ALipase
- BProtease
- CAmylase
- DPepsin
16.Arrange the following stages of food breakdown in the correct order, starting from the first stage.
Easy
- Absorption
- Chemical digestion
- Ingestion
- Egestion
17.Which of the following are roles of bile? (Select all that apply)
Medium
- ANeutralises hydrochloric acid in the duodenum
- BEmulsifies fats
- CDigests proteins into amino acids
- DStores vitamins
18.Which of the following are roles of hydrochloric acid in the stomach? (Select all that apply)
Medium
- AKills bacteria in food
- BDigests starch into sugars
- CProvides an acid pH for pepsin to work
- DEmulsifies fats
- ENeutralises alkaline bile
19.Which of the following is an example of physical digestion?
Medium
- AAmylase breaking down starch
- BEmulsification of fats by bile
- CPepsin breaking down proteins
- DAbsorption of amino acids
20.Which of the following are produced in the pancreas? (Select all that apply)
Medium
- AAmylase
- BPepsin
- CLipase
- DHydrochloric acid
- EProtease
21.Arrange the following in the correct order as food passes through the digestive system:
Medium
- Duodenum
- Ileum
- Mouth
- Oesophagus
- Stomach
22.A student is investigating the effect of pH on the activity of the enzyme pepsin. At which pH would pepsin be most active?
Easy
- ApH 2
- BpH 7
- CpH 9
- DpH 12
23.Which of the following are roles of bile in digestion? (Select all that apply)
Medium
- ANeutralises stomach acid
- BEmulsifies fats
- CDigests proteins
- DStores glucose
24.Match each enzyme to the food type it digests.
Easy
- Amylase
- Protease
- Lipase
- Starch
- Proteins
- Lipids
25.A student measures the pH of stomach contents as 1.5. What is the hydrogen ion concentration in mol/dm³?
Hard
- A0.0316 mol/dm³
- B0.316 mol/dm³
- C3.16 mol/dm³
- D31.6 mol/dm³
26.A student is investigating the effect of pH on the activity of the enzyme pepsin. They set up test tubes with pepsin and protein solution at different pH values and measure the time taken for the protein to be digested. Which pH would result in the fastest digestion?
Easy
- ApH 2
- BpH 7
- CpH 9
- DpH 12
27.Emulsification of fats by bile is an example of chemical digestion.
Easy
True or false?
28.Match each enzyme to the food substance it digests.
Easy
- Amylase
- Protease
- Lipase
- Starch
- Proteins
- Lipids
29.The diagram shows the human digestive system. Which labelled part produces bile?
Easy
- ALiver
- BGall bladder
- CPancreas
- DStomach
30.Which food group is the main source of energy in a balanced diet?
Easy
- AProteins
- BLipids
- CCarbohydrates
- DVitamins
31.Match each food group to its primary function in the body.
Easy
- Carbohydrates
- Proteins
- Lipids
- Dietary Fibre
- Provide energy
- Growth and repair
- Insulation and energy store
- Help prevent constipation
32.Bile is produced in the:
Easy
- AGall bladder
- BLiver
- CPancreas
- DStomach
33.A student investigates the effect of pH on the activity of the enzyme pepsin. They set up four test tubes each containing pepsin and a protein solution at different pH values. After 10 minutes at 37°C, they measure the concentration of amino acids produced. The results are shown in the table: | pH | Amino acid concentration (g/dm³) | |----|----------------------------------| | 1 | 2.5 | | 2 | 4.8 | | 4 | 1.2 | | 7 | 0.1 | At which pH is pepsin most active?
Medium
- ApH 1
- BpH 2
- CpH 4
- DpH 7
34.A student sets up an experiment to investigate the effect of temperature on the digestion of starch by amylase. They add starch solution and amylase to test tubes at different temperatures and test for starch using iodine after 5 minutes. The results are shown in the table: | Temperature (°C) | Colour with iodine | |------------------|--------------------| | 10 | Blue-black | | 20 | Blue-black | | 30 | Brown | | 40 | Brown | | 50 | Blue-black | | 60 | Blue-black | At which temperature(s) was the starch completely digested?
Medium
- A10°C and 20°C
- B30°C and 40°C
- C50°C and 60°C
- DAll temperatures
35.In an experiment to investigate the effect of pH on the digestion of protein by pepsin, a student sets up four test tubes each containing pepsin and protein solution at different pH values. After 30 minutes at 37°C, the amount of digested protein is measured. Which pH is likely to show the greatest digestion?
Easy
- ApH 2
- BpH 7
- CpH 10
- DpH 4
36.Which of the following are roles of hydrochloric acid in the stomach? (Select all that apply.)
Medium
- AKills bacteria in food
- BProvides optimum pH for pepsin
- CEmulsifies fats
- DDigests starch
37.A student investigates the effect of temperature on the digestion of starch by amylase. They add starch solution and amylase to test tubes at different temperatures and test for starch using iodine after 10 minutes. At which temperature is starch most likely to be completely digested?
Easy
- A0°C
- B37°C
- C60°C
- D100°C
38.Which of the following are produced in the pancreas? (Select all that apply.)
Medium
- AAmylase
- BLipase
- CPepsin
- DBile
39.Which of the following is a role of bile in digestion?
Medium
- AIt digests lipids into fatty acids and glycerol.
- BIt neutralises the acidic pH from the stomach entering the duodenum.
- CIt kills bacteria in the stomach.
- DIt provides an acidic pH for enzymes in the small intestine.
40.A student investigates the effect of pH on the digestion of protein by pepsin. Four test tubes each contain pepsin and protein solution at different pH values. After 10 minutes at 37°C, the amount of amino acid produced is measured. The results are shown in the table. | pH | Amino acid produced (mg) | |---|---| | 2.0 | 12.5 | | 4.0 | 8.2 | | 6.0 | 3.1 | | 8.0 | 0.5 | At which pH is pepsin most active?
Medium
- ApH 2.0
- BpH 4.0
- CpH 6.0
- DpH 8.0
41.Arrange the following stages of food breakdown in the correct order, starting from the first stage that occurs after food enters the mouth.
Medium
- Absorption
- Chemical digestion
- Mechanical digestion
- Egestion
42.Complete the sentence about physical digestion.
Easy
Physical digestion is the breakdown of food into smaller pieces without ____ change to the food molecules.
43.State one function of hydrochloric acid in the stomach.
Easy
44.A student measures the pH of stomach contents as 1.5. What is the hydrogen ion concentration in mol/dm³? Give your answer to 3 significant figures.
Hard
45.A sample of stomach contents has a hydrogen ion concentration of 0.0316 mol/dm³. Calculate the pH of this sample. Give your answer to 2 decimal places.
Hard
46.Complete the sentence:
Easy
The breakdown of large fat droplets into smaller droplets by bile is called ____.
47.State two functions of hydrochloric acid in the stomach.
Easy
48.Complete the sentence about a balanced diet.
Easy
A balanced diet contains the correct proportions of carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre and ____.
49.Complete the sentence about bile.
Easy
Bile is produced in the L____ and stored in the G____ B____.
50.Explain why the stomach produces hydrochloric acid.
Easy
51.Describe how the structure of the small intestine is adapted for absorption of digested food.
Medium
52.A student measures the pH of stomach contents as 1.5. What is the hydrogen ion concentration in mol/dm³? Give your answer to 3 significant figures.
Hard
- A1.0316 mol/dm³
- B2.0316 mol/dm³
- C0.0316 mol/dm³
- D-0.9684 mol/dm³
53.A sample of stomach contents has a hydrogen ion concentration of 0.0316 mol/dm³. Calculate the pH of this sample. Give your answer to 2 decimal places.
Medium
- A0.5
- B3.5
- C1.5
- D2.5

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