CIE iGCSE Biology-7.3 Physical digestion- Study Notes- New Syllabus
CIE iGCSE Biology-7.3 Physical digestion- Study Notes – New syllabus
CIE iGCSE Biology-7.3 Physical digestion- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe physical digestion as the breakdown of food into smaller pieces without chemical change to the food molecules
- State that physical digestion increases the surface area of food for the action of enzymes in chemical digestion
- Identify in diagrams and images the types of human teeth: incisors, canines, premolars and molars
- Describe the structure of human teeth, limited to: enamel , dentine, pulp , nerves, blood vessels , cement and understand that teeth are embedded in bone and the gums
- Describe the functions of the types of human teeth in physical digestion of food
- Describe the function of the stomach in physical digestion
Supplement
- Outline the role of bile in emulsifying fats and oils to increase the surface area for chemical digestion
Physical Digestion
What is Physical Digestion?
Physical digestion (also called mechanical digestion) is the breakdown of large pieces of food into smaller ones without changing the chemical structure of the food.
🧠 Why is Physical Digestion Important?
- It increases the surface area of food.
- This makes it easier for enzymes to reach and chemically digest the food.
- Without physical digestion, chemical digestion would be too slow.
🦷 Where Does Physical Digestion Happen?
| Organ | What Happens |
|---|---|
| Mouth | Teeth cut, tear, and grind food (chewing or mastication) |
| Stomach | Muscles churn and mix food to break it up further |
🦷 Types of Teeth Involved in Physical Digestion:
| Tooth Type | Function |
|---|---|
| Incisors | Cut food into smaller pieces |
| Canines | Tear and hold food |
| Molars & Premolars | Crush and grind food |
⚠️ Physical vs Chemical Digestion – Difference
| Feature | Physical Digestion | Chemical Digestion |
|---|---|---|
| Changes food’s shape? | Yes | No |
| Changes food’s molecules? | No | Yes |
| Examples | Chewing bread, churning in stomach | Enzymes breaking starch into sugars |
📌 Quick Summary:
Physical digestion is the first step in the digestive process. It helps make food easier to swallow, more exposed to enzymes, and faster to digest overall.
How Physical Digestion Helps Enzymes
Key Statement:
Physical digestion increases the surface area of food for the action of enzymes in chemical digestion.
🧠 What Does This Mean?
- When you chew food or it’s churned in the stomach, large pieces are broken into smaller fragments.
- This does not change the chemical structure, but it exposes more surface area.
- More surface area means enzymes can act faster and more efficiently.
🔬 Example:
Imagine breaking a loaf of bread into crumbs – the crumbs have more surface area than the whole loaf.
This lets enzymes like amylase reach and break down the starch in the bread much quicker.
🔄 Why Is This Important?
- Increases digestion speed
- Helps ensure nutrients are fully broken down
- Supports efficient absorption of food in the intestine
Identifying Types of Human Teeth in the Image
Human Teeth Structure
Teeth are not just for chewing – they are complex structures with multiple layers and functions. Each part of the tooth plays an important role in digestion and oral health.
1. Enamel
- Definition: Enamel is the hard, white outer covering of the tooth crown (the visible part above the gum).
- Made of: Mostly calcium phosphate, a rock-hard mineral.
- Function:
- Acts as a protective shield against physical damage, acids, and bacteria.
- Prevents wear and tear during chewing.
- Important fact: Enamel contains no living cells, so it cannot repair itself once damaged.
2. Dentine
- Definition: Dentine lies under the enamel and forms the bulk of the tooth.
- Texture: Softer than enamel but still hard and yellowish in color.
- Function:
- Supports enamel.
- Has tiny tubules that can carry temperature and pain signals to the pulp.
- Makes the tooth sensitive when enamel is worn down.
3. Pulp (Pulp Cavity)
- Definition: The pulp is the soft inner part of the tooth found in the center.
- Made of: Connective tissue, blood vessels, and nerves.
- Function:
- Keeps the tooth alive by supplying nutrients and oxygen.
- Senses pain and temperature through nerve endings.
- Helps in forming dentine during development.
4. Nerves
- Location: Inside the pulp.
- Function:
- Detect pain, pressure, and temperature.
- Trigger protective reflexes (e.g., avoiding biting too hard).
5. Blood Vessels
- Location: Also, inside the pulp.
- Function:
- Carry oxygen and nutrients to the living cells of the tooth.
- Remove waste products.
6. Cementum
- Definition: A bone-like layer covering the tooth root.
- Function:
- Anchors the tooth to the periodontal ligament (fibers that connect tooth to jawbone).
- Helps maintain tooth position in the jaw.
7. Periodontal Ligament (PDL)
- Location: Between the cementum and jawbone.
- Function:
- Acts as a shock absorber during chewing.
- Holds the tooth firmly but flexibly in the socket.
8. Bone (Jawbone)
- Definition: The alveolar bone of the jaw holds the roots of teeth.
- Function:
- Provides a firm base for the teeth.
- Responds to pressure and can remodel itself with age or dental movement (like braces).
9. Gums
- Definition: The soft pink tissue that surrounds and supports the teeth.
- Function:
- Protects the roots and bone.
- Helps seal the tooth and prevent bacterial entry.
🧠 Summary of Tooth Parts and Functions:
| Structure | Location | Function |
|---|---|---|
| Enamel | Outer layer | Protects tooth, hardest part of the body |
| Dentine | Under enamel | Supports enamel, carries pain signals |
| Pulp | Center of tooth | Contains blood vessels and nerves, keeps tooth alive |
| Nerves | Inside pulp | Detect pain, pressure, temperature |
| Blood Vessels | Inside pulp | Provide nutrients, oxygen, remove waste |
| Cementum | Around root | Connects tooth to jaw via ligament |
| PDL | Between root & bone | Anchors tooth, absorbs shock |
| Bone | Jaw | Holds roots in place |
| Gums | Surround tooth base | Protect and support teeth and jaw |
📚Fact:
Teeth are not bones, but they are made of many hard tissues. Once your permanent teeth are formed, they don’t regrow – so taking care of them is essential!
Functions of the Types of Human Teeth in Physical Digestion
Physical digestion is the mechanical breakdown of food into smaller pieces without any chemical change. This increases the surface area for enzymes to act during chemical digestion.
Different types of teeth in humans are specialized for different roles in breaking down food physically.
1. Incisors
Location: Front of the mouth (4 upper, 4 lower – total 8).
Shape: Flat, sharp-edged teeth.
Function:
- Cut and slice food (like biting into an apple).
- First teeth to make contact with food.
- Help form small, manageable pieces for further chewing.
2. Canines
Location: On either side of the incisors (2 upper, 2 lower – total 4).
Shape: Pointed and sharp (fang-like).
Function:
- Used to tear and pierce food (especially meat).
- Help grip and pull food apart.
- Especially important in carnivorous animals – still useful in humans.
3. Premolars (Bicuspids)
Location: Behind canines (4 upper, 4 lower – total 8).
Shape: Broad, flat surface with ridges.
Function:
- Help crush and grind food into smaller pieces.
- Prepare food for swallowing and enzyme action.
- Combine tearing and grinding actions.
4. Molars
Location: At the very back (6 upper, 6 lower – total 12 including wisdom teeth).
Shape: Large, flat surfaces with multiple cusps.
Function:
- Grind and mash food thoroughly.
- Final stage of chewing before food is swallowed.
- Provide most of the mechanical force in digestion.
🔍 Summary Table: Types of Teeth and Functions
| Type of Tooth | Location in Mouth | Shape/Feature | Main Function in Physical Digestion |
|---|---|---|---|
| Incisors | Front (4 top, 4 bottom) | Flat, sharp | Cutting and slicing food |
| Canines | Beside incisors | Pointed/fang-like | Tearing and piercing food |
| Premolars | Behind canines | Broad with ridges | Crushing and grinding |
| Molars | Back of the mouth | Large, multi-cusped | Heavy grinding and mashing |
Physical digestion by teeth helps increase surface area of food particles, making chemical digestion faster and more efficient as enzymes can work on a larger exposed surface.
Function of the Stomach in Physical Digestion
What is Physical Digestion?
Physical digestion is the mechanical breakdown of food into smaller pieces without changing the chemical structure of the food molecules.
This process is important because it increases surface area, making it easier for enzymes to act on food during chemical digestion.
🟠 So, What Does the Stomach Do in Physical Digestion?
The stomach is more than just a storage bag. It plays an active role in physically breaking down food.1. Churning Action
- The stomach has thick muscular walls that contract and relax in a coordinated way.
- This movement is called churning.
- Churning mixes the food with digestive juices and breaks it into smaller pieces.
- 🌀 Think of it like a washing machine – it tosses food around to make it soft, broken down, and easier to digest.
2. Food Turns into Chyme
- As a result of churning and mixing, the solid food turns into a semi-liquid mixture called chyme.
- Chyme is much easier to move into the small intestine and digest further.
- 🔁 It’s smoother, softer, and more uniform – perfect for enzymes to do their job next!
3. Improving Enzyme Efficiency
- Physical digestion in the stomach increases the surface area of the food.
- This means enzymes like pepsin (involved in chemical digestion of protein) can act more effectively and quickly.
📌 Summary: Stomach’s Role in Physical Digestion
| Action | Description |
|---|---|
| Churning | Muscular contractions mix and break down food |
| Mixing with Juices | Combines food with acid and enzymes for better digestion |
| Formation of Chyme | Solid food becomes semi-liquid, making it easier to digest |
| Increased Surface Area | Helps enzymes act faster during chemical digestion |
💡 Quick Tip:
Physical digestion in the stomach = churning by muscular walls
Chemical digestion in the stomach = enzymes like pepsin + hydrochloric acid
Role of Bile in Emulsifying Fats and Oils
What is Bile?
Bile is a greenish-yellow fluid made by the liver and stored in the gall bladder.
It is released into the small intestine (specifically the duodenum) when fatty food enters.
Note: Bile is not an enzyme – it doesn’t break down fats chemically, but it helps enzymes do their job better.
Main Role: Emulsification of Fats
Emulsification means breaking up large fat droplets into many smaller ones, without changing the fat’s chemical structure.
🔍 Why Is This Important?
- Fats and oils don’t mix well with water and tend to form large globules.
- Enzymes like lipase (which digests fat) can only work on the surface of these droplets.
- So, large fat droplets = small surface area → slow digestion.
🟩 Bile Solves This Problem By:
- Breaking up large fat globules into tiny droplets.
- This process increases the surface area available for lipase to act.
- As a result, fat digestion becomes faster and more efficient.
💡 Think of it Like This:
If you pour oil into water, it floats on top in blobs.
Bile acts like a natural detergent, breaking the blobs into tiny droplets that mix better and give enzymes more surface to work on.
📌 Summary Table
| Function of Bile | Details |
|---|---|
| Emulsifies fats | Breaks large fat droplets into smaller ones |
| Increases surface area | More area for lipase enzymes to work |
| Aids chemical digestion | Makes fat digestion faster and more efficient |
| Alkaline in nature | Also neutralizes stomach acid entering the small intestine |