GCSE AQA Combined Science Trilogy Higher: Comprehensive Notes on Cells and Microscopy

Microscopy: Your Window into the Cell World

Want to see inside a cell? You'll need the right tool for the job. Light microscopes have been around since the mid-17th century and use light to create images - they're cheap, let you observe living specimens, but only magnify up to 2000x with fairly low resolution (200nm).

Electron microscopes are the superstars of the microscopy world, developed in the 1930s. They use electrons instead of light, giving incredible magnification (up to 2,000,000x) and amazing resolution (0.2nm). The trade-off? They're expensive and can't view living specimens.

Quick Tip: Remember that higher magnification and better resolution mean you can see smaller structures more clearly - that's why electron microscopes let scientists study subcellular structures in detail.

Animal vs Plant Cells: Spotting the Differences

Both animal and plant cells share some key components. The nucleus acts like the cell's control centre, containing DNA and directing all activities. The cell membrane works as a selective barrier, controlling what enters and leaves. Mitochondria are the powerhouses where aerobic respiration happens, whilst ribosomes manufacture proteins.

Plant cells have some extra features that animals don't. Chloroplasts contain chlorophyll for photosynthesis, the cell wall made of cellulose provides structural support, and the vacuole filled with cell sap keeps the plant rigid and upright.

The cytoplasm in both cell types is where most chemical reactions occur - think of it as the cell's busy workshop where everything gets done.

Memory Trick: Plants need extra support to stand upright, so they have cell walls and vacuoles that animal cells don't need.

Eukaryotes vs Prokaryotes: The Great Cell Divide

All life falls into two main categories. Eukaryotic cells include animals, plants, fungi, and protists - they all have their genetic material neatly packaged inside a nucleus, plus all the usual organelles like mitochondria and ribosomes.

Prokaryotic cells (basically bacteria) are much simpler. Their DNA floats freely in the cytoplasm as a single loop, not tucked away in a nucleus. They might have extra bits like plasmids (bonus DNA), flagella for swimming about, or slime layers for protection.

Here's the key difference: prokaryotes lack the membrane-bound organelles that eukaryotes have. No mitochondria, no chloroplasts, just the basics needed to survive and reproduce.

Exam Focus: Remember that bacteria are the main example of prokaryotes you'll encounter - they're ancient, simple, but incredibly successful organisms.