Cell Structure and Microscopy Basics

Every living thing is made up of cells, but not all cells are the same! Animal cells contain a nucleus (the control centre with DNA), mitochondria for energy production, and ribosomes for making proteins. Plant cells have all of these plus some extras - chloroplasts for photosynthesis, a large vacuole for support, and a rigid cell wall.

Bacterial cells are completely different - they're much simpler with no proper nucleus. Instead, their DNA floats freely in the cytoplasm, and they often have flagella to help them move around.

When using a microscope, remember this key formula: Total magnification = eyepiece magnification × objective magnification. This tells you how much bigger the image appears compared to real life.

Quick Tip: Think of animal cells as basic models, plant cells as the deluxe version with solar panels (chloroplasts), and bacterial cells as the stripped-down, no-frills option!

Enzymes and How They Work

Enzymes are like biological matchmakers - they speed up chemical reactions without getting used up themselves. Every enzyme works best at specific conditions, particularly temperature and pH levels.

The lock and key mechanism explains how enzymes work - each enzyme (the lock) only fits with one specific substrate (the key). Human body enzymes work best at 37°C, but stomach enzymes prefer acidic conditions whilst small intestine enzymes like it more alkaline.

Substrate concentration affects reaction speed too. More substrate molecules mean faster reactions, until all the enzyme's active sites are busy - then it plateaus.

Food Tests You Need to Know

Learning to test for different biological molecules is essential lab work. The Benedict's test detects reducing sugars - you'll see colour changes from blue through green, yellow, orange to brick red as sugar concentration increases.

Biuret reagent tests for proteins, turning purple when proteins are present. The emulsion test for lipids involves shaking your sample with ethanol, then adding water - a milky colour means lipids are there.

Iodine solution tests for starch, turning blue-black when starch is detected. Finally, calorimetry measures energy in food using the formula: Energy = mass of water × temperature change × 4.2.

Exam Tip: Remember the colour changes for Benedict's test - they follow the colours of a traffic light system from blue $stop/no sugar$ to red $go/lots of sugar$!