All Class Five Science Topics
Class Five Science notes for primary schools in Tanzania. Topic 1, Digestive System, is free to read below: types of digestion, parts of the digestive system and their functions, digestive juices and enzymes, absorption and assimilation, and common digestive problems, with end-of-topic questions. The other four topics are available in the Click Online Academy app.
- Topic 1Digestive SystemRead below · Free
- Topic 2Growth and Development in Plants and AnimalsContinue in the app
- Topic 3Reproductive SystemContinue in the app
- Topic 4MagnetismContinue in the app
- Topic 5Computer CodingContinue in the app
Chapter One: Digestive System
Science • Class Five • How Your Body Uses Food
🔑 Key Terms and Concepts
- Digestion
- The process by which food is broken down into simpler substances that can be absorbed into the blood and used by the body.
- Mechanical Digestion
- Physical breakdown of food into smaller pieces without changing its chemical nature (e.g. chewing, churning).
- Chemical Digestion
- Breaking down food into simpler substances using digestive juices and enzymes.
- Enzyme
- A special substance that acts like “scissors” to cut large food molecules into smaller usable ones.
- Absorption
- The process by which digested food passes through the walls of the small intestine into the blood or lymph.
- Assimilation
- The process where absorbed nutrients are used by body cells for energy, growth and repair.
- Villi
- Tiny finger-like projections in the small intestine that increase the surface area for absorption.
- Emulsification
- Breaking fats into tiny droplets so enzymes can act on them more easily (done by bile).
🍽️ Concept of Digestion
The food we eat contains large molecules such as starch (carbohydrates), proteins and fats. These cannot be used directly by the body.
Digestion changes them into small molecules:
- Starch → Glucose
- Proteins → Amino acids
- Fats → Fatty acids and glycerol
These smaller molecules can then pass through the walls of the intestine into the blood and be transported to all parts of the body.
• When we eat ugali (starch), our body changes it into glucose for energy.
• When we eat beans (proteins), they are changed into amino acids to build muscles.
• When we eat oily foods (fats), they are broken into fatty acids and glycerol for stored energy.
✏️ Quick Revision – Concept
1. What is digestion?
2. What are the end products of starch, proteins and fats?
⚙️ Types of Digestion
(a) Mechanical Digestion
Physical breakdown of food into smaller pieces without changing its chemical nature. This makes food easier to swallow and gives enzymes a larger surface area to act on.
Examples: Chewing by teeth; churning and squeezing by stomach muscles.
(b) Chemical Digestion
Breaking down food into simpler substances using digestive juices and enzymes. Enzymes act like “scissors” that cut large molecules into smaller ones.
Examples:
- Salivary amylase changes starch into maltose (sugar).
- Pepsin in the stomach breaks proteins into smaller pieces.
- Lipase changes fats into fatty acids and glycerol.
✏️ Quick Revision – Types
1. What is the difference between mechanical and chemical digestion?
🫁 Parts of the Digestive System and Their Functions
Mouth
- First part of the digestive system – contains teeth, tongue and salivary glands.
- Teeth cut and grind food (mechanical digestion).
- Tongue mixes food with saliva and helps in swallowing.
- Saliva softens food and contains amylase which digests starch into sugar.
Oesophagus (Food Pipe)
A muscular tube that pushes food from the mouth to the stomach by wave-like movements (peristalsis).
Stomach
- A muscular bag that churns food (mechanical digestion).
- Produces gastric juice containing pepsin (digests proteins) and hydrochloric acid (kills germs and helps enzymes work).
Small Intestine
- The longest part – where most digestion is completed and absorption takes place.
- Receives bile, pancreatic juice and intestinal juice.
- Has villi that increase surface area for absorption.
Large Intestine
Absorbs water and minerals from undigested food. The remaining waste becomes faeces.
Rectum and Anus
Faeces are stored in the rectum and passed out through the anus.
✏️ Quick Revision – Parts
1. Where does most absorption of digested food take place?
2. What is the function of the oesophagus?
🧪 Digestive Juices and Enzymes
| Juice / Source | Main Action |
|---|---|
| Saliva (mouth) | Amylase: starch → maltose |
| Gastric juice (stomach) | Pepsin: proteins → smaller pieces; HCl kills germs |
| Bile (liver / gall bladder) | No enzymes – emulsifies fats into tiny droplets |
| Pancreatic juice (pancreas) | Amylase, lipase, trypsin – digest starch, fats and proteins |
| Intestinal juice (small intestine) | Completes digestion of sugars, proteins and fats |
🩸 Absorption and Assimilation
End Products of Digestion
- Carbohydrates → Glucose
- Proteins → Amino acids
- Fats → Fatty acids and Glycerol
Absorption
Takes place mainly in the small intestine. Villi increase the surface area. Glucose and amino acids pass into blood vessels; fatty acids and glycerol pass into lymph vessels first.
Assimilation
Absorbed nutrients are used by body cells:
- Glucose → energy through respiration
- Amino acids → build new tissues, enzymes and hormones
- Fatty acids and glycerol → stored as energy reserves and insulation under the skin
✏️ Quick Revision – Absorption & Assimilation
1. What is assimilation?
⚠️ Defects of the Digestive System and Prevention
- Diarrhoea – frequent watery stool (infection or contaminated food)
- Constipation – difficulty passing stool (lack of fibre or water)
- Ulcers – painful sores in the stomach lining
- Indigestion – discomfort from overeating or eating too fast
- Tooth decay – damage to teeth caused by bacteria and sugary foods
Ways to Prevent These Problems
- Eat a balanced diet with enough fibre.
- Drink clean water.
- Brush teeth regularly (oral hygiene).
- Avoid overeating and contaminated food.
📝 End of Topic Questions
Test yourself! Answer first, then click to see the suggested answer.
Part A: Multiple Choice Questions
1. Digestion is the process of:
A. Storing food only B. Breaking food into simpler substances that can be absorbed C. Making food taste better D. Cooling the body2. Chewing food is an example of:
A. Chemical digestion B. Mechanical digestion C. Absorption D. Assimilation3. Starch is broken down into:
A. Amino acids B. Glucose C. Fatty acids D. Vitamins4. Most absorption of digested food takes place in the:
A. Mouth B. Stomach C. Small intestine D. Large intestine5. Bile is produced by the:
A. Pancreas B. Liver C. Stomach D. Mouth6. Villi help to:
A. Produce enzymes B. Increase surface area for absorption C. Chew food D. Store faeces7. Proteins are broken down into:
A. Glucose B. Amino acids C. Fatty acids D. Water8. Assimilation is:
A. Breaking food into pieces B. Using absorbed nutrients by body cells C. Passing out waste D. Producing saliva9. Constipation can be prevented by:
A. Eating less fibre B. Eating enough fibre and drinking water C. Avoiding all food D. Eating only sugar10. Pepsin works in the:
A. Mouth B. Stomach C. Large intestine D. OesophagusPart B: Short Answer Questions
11. Define digestion and name the two main types.
12. List the main parts of the digestive system in order.
13. What are the end products of digestion of carbohydrates, proteins and fats?
14. Explain the role of bile in digestion.
15. Name three defects of the digestive system and one way to prevent each.
✅ Suggested Answers & Summary
Click the buttons above to reveal answers. Always try answering first!
Remember: Digestion breaks food into simple substances. Mechanical and chemical digestion work together. Nutrients are absorbed in the small intestine and used by cells (assimilation). Take care of your digestive system with a balanced diet, clean water and good hygiene.
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