Life Processes & Systems
The Digestive System
Breaking down food for energy
Interactive Digestive System
Click on each organ to learn about its function in digestion:
Click an organ to see details
Nutrition & Balanced Diet
What your body needs
Components of a Balanced Diet
Your body needs seven components for good health:
🍞 Carbohydrates
Main energy source. Found in bread, rice, pasta, potatoes.
🥩 Proteins
Growth and repair. Found in meat, fish, eggs, beans, pulses.
🧈 Lipids (Fats)
Energy store, insulation. Found in butter, oil, nuts, cheese.
🥦 Vitamins
Healthy immune system. Found in fruits and vegetables.
🥛 Minerals
Strong bones, teeth, blood. Calcium, iron, etc.
🌾 Fibre
Healthy digestion. Found in whole grains, vegetables, fruit.
💧 Water
Essential for all body functions. About 60% of your body is water.
Malnutrition
Malnutrition means having a poor diet - either too little or too much of certain nutrients.
Undernutrition: Not enough food or specific nutrients. Can cause starvation, vitamin deficiencies, stunted growth.
Overnutrition: Too much food. Can cause obesity, heart disease, type 2 diabetes, high blood pressure.
Breathing & Respiration
Two different but related processes
Breathing
The physical process of moving air in and out of your lungs.
- • Inhalation: Diaphragm contracts, chest cavity expands, air rushes in
- • Exhalation: Diaphragm relaxes, chest cavity shrinks, air pushed out
- • A mechanical process involving muscles
Respiration
The chemical reaction that releases energy from glucose in your cells.
- • Happens in every cell, all the time
- • Uses oxygen and glucose
- • Produces carbon dioxide and water
- • Releases energy for life processes
The Word Equation for Aerobic Respiration
Important: This is NOT the same as breathing! Respiration happens in cells. Breathing gets oxygen INTO the body.
The Respiratory System
How gas exchange works
Pathway of Air
Gas Exchange in Alveoli
How Gas Exchange Works
-
1Oxygen diffuses from the alveolus (high concentration) into the blood (low concentration).
-
2Carbon dioxide diffuses from the blood (high concentration) into the alveolus (low concentration).
-
3Carbon dioxide is then breathed out when you exhale.
Key term: Diffusion is the movement of particles from high to low concentration.
Cell Organisation
Specialised cells and diffusion
Cell Adaptations
Cells are adapted for their specific functions. Here are two important examples:
Ciliated Epithelial Cells
Found in the airways (trachea, bronchi).
- • Have tiny hair-like structures called cilia
- • Cilia beat in waves to move mucus
- • Mucus traps dust and bacteria
- • Helps keep lungs clean and healthy
Cells with Microvilli
Found lining the small intestine.
- • Have tiny finger-like projections called microvilli
- • Greatly increase surface area
- • More space for absorbing nutrients
- • Makes absorption much faster
Diffusion Gradients
Diffusion happens faster when there's a bigger difference in concentration:
High concentration → Low concentration
Steeper gradient = Faster diffusion
Example in lungs: Blood constantly flowing maintains the gradient for gas exchange.
Plants: Transport of Water & Minerals
How plants move substances
Xylem
Transports water and minerals UP from roots to leaves.
- • Made of dead cells joined end-to-end
- • Forms hollow tubes (like straws)
- • Strong cell walls provide support
- • Water evaporates from leaves (transpiration)
Phloem
Transports sugars (food) UP and DOWN throughout the plant.
- • Made of living cells
- • Has sieve plates with pores
- • Transports glucose from leaves
- • Process called translocation
Root Hair Cells
Specialised cells on plant roots that increase surface area for water absorption.
Adaptation: Long, thin extension (hair) that sticks out into soil.
Benefit: Large surface area means more space for water to enter by osmosis.
Ecosystems
Food webs and pyramids
Energy Flow in Ecosystems
Energy flows through ecosystems from producers to consumers. At each level, some energy is lost as heat, movement, or waste.
Pyramid of Biomass: Shows the total mass of organisms at each level. Always pyramid-shaped because energy is lost at each step.
Energy Loss: About 90% of energy is lost between each trophic level (used for respiration, movement, heat, or lost in waste).
Bioaccumulation
Some toxins build up in food chains and become more concentrated at higher levels.
Example: If water contains tiny amounts of mercury, plankton absorb it. Small fish eat many plankton, accumulating more mercury. Large fish eat many small fish, concentrating it further. The top predator ends up with dangerous levels of toxin.
Practice Questions
Test your understanding
Digestive System [4 marks]
Name two organs that produce digestive enzymes and state what each enzyme breaks down.
Answer:
Salivary glands: Produce amylase which breaks down starch into sugars. [2 marks]
Pancreas: Produces several enzymes including amylase (starch), protease/trypsin (proteins), and lipase (fats). [2 marks]
Also acceptable: Stomach (produces pepsin/protease for proteins), Small intestine (produces various enzymes)
Breathing vs Respiration [3 marks]
Explain the difference between breathing and respiration.
Answer:
Breathing is a physical process of moving air in and out of the lungs using muscles (diaphragm and intercostal muscles). [1 mark]
Respiration is a chemical process that happens in all cells, where glucose reacts with oxygen to release energy, producing carbon dioxide and water. [1 mark]
Key difference: Breathing is mechanical (moving air); respiration is chemical (releasing energy). [1 mark]
Gas Exchange [3 marks]
Describe how the structure of alveoli is adapted for efficient gas exchange.
Answer:
• Thin walls: One cell thick for short diffusion distance [1 mark]
• Large surface area: Millions of alveoli provide a huge surface area for exchange [1 mark]
• Good blood supply: Surrounded by capillaries to maintain concentration gradient [1 mark]
Also acceptable: Moist lining, close to capillaries
Pyramid of Biomass [3 marks]
Explain why a pyramid of biomass is always pyramid-shaped, unlike a pyramid of numbers.
Answer:
A pyramid of biomass shows total mass of organisms at each level. [1 mark]
Energy is lost at each trophic level (about 90%) through respiration, movement, heat, and waste. [1 mark]
This means there must always be more biomass at lower levels to support the level above - the producer level has the most biomass, decreasing up the pyramid. [1 mark]
Continue Learning
Explore Year 8 Chemistry or Physics to continue your science journey.