Study sheet: IGCSE Biology Core Concepts

📋 Course Outline

1. Photosynthesis and Cell Structures
2. Gas Exchange and Breathing
3. Digestion and Nutrition
4. Respiration and Osmosis
5. Experiments and Yeast Variables
6. Biological Calculations

📖 1. Photosynthesis and Cell Structures

★ Must-know

📐 Formula — The balanced equation for photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

📌 The rate of photosynthesis increases with light intensity until another factor, such as carbon dioxide concentration or temperature, becomes limiting.

• The chloroplast contains chlorophyll for photosynthesis.

• Ribosomes are the site of protein synthesis.

Further detail

• The permanent vacuole contains cell sap, while the cell wall strengthens and supports plant cells.

💡 Memory Hook

More light increases photosynthesis until CO₂ or temperature becomes limiting.

📖 2. Gas Exchange and Breathing

🔑 Key Concepts & Definitions

• Alveoli : the main site of gas exchange

★ Must-know

• The trachea carries air to the bronchi and is supported by cartilage rings.

• Cartilage rings prevent the trachea and bronchi from collapsing.

Further detail

📌 A collapsed lung reduces oxygen uptake because less surface area is available for gas exchange.

📌 A chest puncture may cause the lung to collapse and fail to inflate.

💡 Memory Hook

Trachea → bronchi → alveoli.

📖 3. Digestion and Nutrition

🔑 Key Concepts & Definitions

• Peristalsis : a wave of muscular contraction that moves food through the gut

★ Must-know

• The oesophagus carries food from the mouth to the stomach.

• The small intestine is the main site of nutrient absorption.

📌 Young animals need more protein for growth and the production of new cells and tissues.

• If an organism eats 2.0 g of food and egests 0.50 g, it absorbs 1.5 g and assimilates 75%.

Further detail

📌 Excess carbohydrate is stored as fat.

💡 Memory Hook

Mouth → oesophagus → stomach → small intestine.

📖 4. Respiration and Osmosis

🔑 Key Concepts & Definitions

• Anaerobic respiration in yeast : produces carbon dioxide and ethanol
• Osmosis : the movement of water through a partially permeable membrane from a dilute solution to a concentrated solution

★ Must-know

📌 A red blood cell in concentrated salt solution loses water and shrinks, while a red blood cell in very dilute solution gains water and may burst.

Further detail

📌 An oil layer prevents oxygen from entering and maintains anaerobic conditions.

• Boiling the glucose solution removes dissolved oxygen, and allowing oxygen to reach the yeast switches the conditions to aerobic.

💡 Memory Hook

Aerobic respiration uses oxygen, whereas anaerobic yeast respiration produces ethanol and carbon dioxide.

📖 5. Experiments and Yeast Variables

★ Must-know

📌 Reliability can be improved by using several organisms and calculating a mean.

• Shell height is the dependent variable when measuring snail growth.

📌 Glucose solution should be cooled before yeast is added because a hot solution may kill yeast or denature its enzymes.

Further detail

• A gas syringe can be used to measure gas produced by yeast accurately.

💡 Memory Hook

Independent variables are changed, whereas dependent variables are measured.

📖 6. Biological Calculations

★ Must-know

📌 Smaller cells have a larger surface-area-to-volume ratio than larger cells.

📐 Formula — Light intensity is calculated using $\text{Intensity} = \frac{1}{\text{distance}^2}$.

Further detail

• A cube with a side length of 0.040 mm has a surface-area-to-volume ratio of 150:1.

• When light intensity is 0.0625, the distance is 4 cm.

📊 Synthesis Tables

Gas Exchange Structures

Structure	Function	Key feature
Trachea	Carries air to the bronchi	Supported by cartilage rings
Bronchi	Receive air from the trachea	Cartilage rings prevent collapse
Alveoli	Main site of gas exchange	Provide surface area for oxygen uptake