GCSE Biology Paper 2 Revision Notes

This is your complete guide to smashing GCSE Biology Paper 2. You'll find all the key concepts broken down into manageable chunks that won't overwhelm you.

The notes cover everything from basic cell biology to complex processes like photosynthesis. Each topic builds on the last, so you'll develop a solid understanding step by step.

Top tip: Use these notes alongside your textbook and past papers for the best results. Don't try to memorise everything at once - focus on understanding the concepts first.

Key Concepts in Biology - Cells

Every living thing has eight key characteristics that you need to remember: Movement, Respiration, Sense, Growth, Reproduction, Excretion, Nutrition, and Coordination. Think of them as life's essential requirements.

All living things are made of cells, but not all cells are the same. Eukaryotic cells (like yours) are complex and have a proper nucleus, whilst prokaryotic cells (like bacteria) are much simpler and smaller. Plant and animal cells have different structures because they do different jobs.

Organelles are like tiny organs inside cells, each with specific functions. The nucleus contains DNA and controls the cell, mitochondria provide energy through respiration, and chloroplasts (only in plants) carry out photosynthesis. The cell membrane acts like a bouncer, controlling what gets in and out.

Remember: Plant cells have three extra structures that animal cells don't - a cell wall for strength, a large vacuole for support, and chloroplasts for making food.

Bacteria and Cell Adaptations

Bacterial cells are quite different from plant and animal cells. They have a capsule for protection, plasmids (extra DNA rings), and a flagellum that spins like a propeller to help them move around.

Cells don't stay the same - they differentiate to become specialists at particular jobs. Sperm cells are built for speed with long tails and lots of mitochondria for energy. Egg cells are packed with nutrients and have special defences to stop multiple sperm getting in.

Ciliated epithelial cells line your airways and have tiny hairs called cilia that sweep mucus upwards. It's like having millions of tiny brushes cleaning your lungs.

Understanding diffusion rates is crucial - they're faster when you have high temperatures, thin membranes, large surface areas, and steep concentration gradients. Think of it like water flowing downhill - the steeper the slope, the faster it flows.

Quick check: Can you explain why sperm cells have so many mitochondria? It's all about providing energy for that epic journey to the egg!

Microscopy Basics

Microscopes are your window into the invisible world of cells. Light microscopes have been around since the 1590s and work by passing light through specimens. They're perfect for looking at living cells and can show you nuclei and chloroplasts clearly.

Electron microscopes arrived in the 1930s and are much more powerful. They use beams of electrons instead of light, giving incredible detail of internal structures. The downside? They're expensive and can't be used on living specimens.

The key measurements you need are: bacteria (0.5µm), human cells $10-33µm$, and plant cells $10-few hundred µm$. Remember the magnification formula: Magnification = Image size ÷ Actual size.

When using a microscope, always start with the lowest power objective lens and use stains to make transparent specimens visible. The total magnification equals eyepiece magnification × objective lens magnification.

Pro tip: When drawing what you see under a microscope, use a pencil and only draw the outlines of main features. No shading or colouring needed!

Using Microscopes and Enzymes Introduction

Following the proper specimen preparation technique is essential for clear results. Cut thin slices, add a drop of water, place carefully with tweezers, add stain if needed, and use a cover slip to avoid air bubbles.

Resolution is just as important as magnification - it's the minimum distance two parts need to be apart to appear separate. Higher resolution means clearer, more detailed images with better clarity.

Enzymes are biological catalysts made from chains of amino acids. Each enzyme has a unique active site where substrates bind, and this shape determines which reaction it can catalyse. Think of it like a lock and key - only the right key fits.

There are 20 different types of amino acids, creating thousands of possible enzyme combinations. Without enzymes, the chemical reactions in your body would be far too slow to keep you alive.

Key insight: Enzymes speed up reactions without being used up themselves - they can be reused over and over again, making them incredibly efficient.

Enzyme Function and Specificity

Enzyme specificity means each enzyme only works on one particular substrate because of its unique active site shape. It's like having a specialist tool for each specific job - a hammer won't work as a screwdriver.

Enzymes can both break down large molecules and synthesise (build up) new ones from smaller parts. Amylase breaks down starch into sugars, whilst catalase breaks down harmful hydrogen peroxide into water and oxygen.

In digestion, three key enzymes do the heavy lifting: protease breaks proteins into amino acids, amylase turns starch into glucose, and lipase splits fats into fatty acids and glycerol. These smaller molecules can then pass through your digestive system walls.

Synthesis enzymes work in reverse, building complex molecules. Starch synthase in plants builds starch from glucose for energy storage, whilst DNA polymerase constructs new DNA strands.

Remember: Your food molecules are too big to absorb directly - enzymes must break them down into smaller, soluble pieces first.

Enzyme Activity and Food Tests

Temperature and pH dramatically affect enzyme activity. Human enzymes work best at 37°C (body temperature). Go too hot and the enzyme denatures - it unfolds and can't work anymore, and this damage is permanent.

pH changes affect the bonds holding enzymes together, changing their shape. Each enzyme has an optimum pH where it works best. More substrate or enzyme concentration means more collisions and faster reactions, but only up to a point.

You can test for different nutrients using simple chemical tests. Benedict's reagent detects sugars, turning from blue through green, yellow, and orange to brick red as sugar concentration increases. Iodine tests for starch, changing from brown to dark blue-black.

For lipids, mix with ethanol then add water - a milky precipitate shows fats are present. The biuret test for proteins uses potassium hydroxide and copper sulphate, turning purple if protein is detected.

Lab tip: When testing enzyme activity with different pH values, remember to calculate the rate as 1000/time to get your answer in s⁻¹.

Energy in Food and Transport Processes

You can measure energy content in food by burning it and seeing how much it heats water. The formula is: Energy = Mass of water × Temperature change × 4.2. This tells you how many joules per gram your food contains.

Diffusion is the net movement of particles from high to low concentration - no energy needed, just natural particle movement. Only small molecules can diffuse across cell membranes, and it happens faster with higher temperatures and concentration gradients.

Osmosis is specifically about water movement across semi-permeable membranes. Water moves from areas of high water concentration to low water concentration. Think of it as water trying to balance things out.

Active transport is different - it moves particles against the concentration gradient using energy. This is crucial when your gut needs to absorb nutrients even when there's more in your blood than in your food.

Key difference: Diffusion and osmosis are passive (no energy needed), but active transport requires energy to work against the natural flow.

Investigating Osmosis

The potato osmosis experiment perfectly demonstrates water movement. Cut identical potato cylinders, weigh them, then place in different concentration solutions for 40 minutes. The mass changes tell you which way water moved.

When potato cylinders gain mass, water has moved in by osmosis - the solution was more dilute than the potato cells. When they lose mass, water moved out because the solution was more concentrated. Isotonic solutions cause no change.

Turgid cells have taken in water and become firm (good for plant support). Plasmolysed cells have lost water and become limp. This is why plants wilt when they don't get enough water.

The key to understanding osmosis is remembering that dilute solutions have high water concentrations, whilst concentrated solutions have low water concentrations. Water always moves towards lower water concentration.

Exam tip: Always dry potato cylinders with paper towel before reweighing to remove surface water - this prevents errors in your mass measurements.