Human Diet And Digestion

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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.

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.

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.

Structure of a triglyceride (lipid) – broken down by lipase into glycerol and fatty acids.

Benedict's test for reducing sugars: colour change from blue to green/yellow/orange/red indicates glucose concentration.

Iodine test for starch: blue-black colour indicates starch present.

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.
Medium
4.Complete the sentence about digestion.
Medium
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.
Hard
- Absorption
- Chemical digestion
- Egestion
- Ingestion
- Mechanical digestion
7.Which organ produces bile?
Medium
- AGall bladder
- BLiver
- CPancreas
- DStomach
8.State two roles of hydrochloric acid in the stomach.
Hard

Slides

Balanced Diet

A balanced diet contains carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre and water in correct proportions.
Each food group has a specific function: carbohydrates for energy, proteins for growth and repair, lipids for energy storage and insulation, etc.
Dietary needs vary with age, gender, activity level and pregnancy.

Which of the following is NOT a component of a balanced diet?

Carbohydrates
Proteins
Cholesterol
Dietary fibre

Vitamin Deficiencies: Scurvy and Rickets

Scurvy is caused by a severe lack of vitamin C. Symptoms include anaemia, exhaustion, bleeding and tooth loss.
Rickets is caused by a lack of vitamin D, which is needed for calcium absorption. Symptoms include soft, weak bones and bone pain.
Vitamin D is obtained from sunlight and foods like fish, eggs and butter.

Scurvy is caused by a deficiency of vitamin ____. Rickets is caused by a deficiency of vitamin ____.

The Digestive System

The digestive system includes the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus.
Accessory organs: salivary glands, pancreas, liver and gall bladder.
Food passes through five stages: ingestion, digestion (mechanical and chemical), absorption, assimilation and egestion.

Which of these are stages of food breakdown?

Ingestion
Digestion
Respiration
Egestion

Physical Digestion

Physical digestion breaks food into smaller pieces without changing the molecules chemically.
It increases surface area for enzyme action.
Examples: chewing by teeth, churning in the stomach, emulsification of fats by bile.

Which of the following is an example of physical digestion?

Amylase breaking down starch
Chewing food with teeth
Protease digesting protein
Absorption of amino acids

Chemical Digestion

Chemical digestion breaks large, insoluble molecules into small, soluble ones using enzymes.
Small soluble molecules can be absorbed into the blood.
It involves hydrolysis reactions catalysed by specific enzymes.

Chemical digestion breaks down large, ____ molecules into small, ____ molecules.

Enzymes in Digestion

Amylase (from mouth and pancreas) digests starch into sugars.
Proteases (from stomach and pancreas) digest proteins into amino acids.
Lipase (from pancreas) digests lipids into fatty acids and glycerol.

Which enzyme digests starch?

Amylase
Protease
Lipase
Pepsin

Hydrochloric Acid in the Stomach

The stomach produces hydrochloric acid as part of gastric juice.
It kills bacteria in food and provides an acidic pH (around 2) for enzymes like pepsin to work.
Pepsin has an optimum pH of about 2.

What is the role of hydrochloric acid in the stomach?

Emulsify fats
Kill bacteria and provide acidic pH for enzymes
Digest starch
Neutralise bile

Bile and Emulsification

Bile is produced by the liver and stored in the gall bladder.
It is alkaline and neutralises stomach acid entering the duodenum.
Bile emulsifies fats (breaks large drops into smaller ones), increasing surface area for lipase action.

Which statements about bile are true?

Bile is produced by the gall bladder.
Bile neutralises stomach acid.
Bile emulsifies fats.
Bile contains lipase.

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