AQA A Level Biology: Eukaryotic Cell Structure Notes for Year 12

Mitochondria and Golgi Apparatus

Think of mitochondria as your cell's power stations - they're where all the energy gets made! These oval-shaped organelles have a clever double membrane design with the inner layer folded into cristae (like accordion folds) to create more surface area. Inside the matrix, special enzymes work flat out during aerobic respiration to produce ATP, which is basically your cell's currency for energy.

You'll find loads of mitochondria in really active cells like muscle cells because they need tons of energy to function properly. The more active the cell, the more mitochondria it needs - it's that simple!

The Golgi apparatus is like your cell's post office and packaging centre rolled into one. It's made up of stacked, flattened sacs called cisternae that look a bit like pancakes piled on top of each other.

Quick Tip: Remember that proteins enter at the cis face (receiving side) and leave at the trans face (shipping side) - think of it like a conveyor belt system that processes and packages lipids and proteins before sending them off to where they're needed.

Endoplasmic Reticulum and Ribosomes

The endoplasmic reticulum (ER) is basically your cell's highway system - a massive network of membranes that transport stuff around. There are two types, and they're dead easy to tell apart.

Rough ER looks bumpy because it's covered in ribosomes stuck to its surface. Its main job is folding and processing all the proteins that those ribosomes have just made - think of it as a protein finishing school where everything gets properly shaped and prepared.

Smooth ER has no ribosomes attached, so it looks, well, smooth! Instead of dealing with proteins, it focuses on making and processing lipids - the fats and oils your cell needs.

Ribosomes are the tiny protein-making machines of your cell. They're made of proteins and RNA and can either float freely in the cytoplasm or attach to the rough ER. What's interesting is they don't have a membrane around them like most other organelles.

Memory Trick: Rough ER = Ribosomes = pRotein processing. Smooth ER = Synthesises lipids. The alliteration makes it stick!

Ribosomes and Chloroplasts

Ribosomes might be small, but they're absolutely crucial - they're the site where proteins are made. Each ribosome has two parts: a large subunit and a small subunit that work together like a perfectly coordinated team to build proteins from amino acids.

Chloroplasts are the green powerhouses found only in plant cells, and they're where photosynthesis takes place. Like mitochondria, they've got a double membrane, but inside there's something really special - stacks of membranes called granum (plural: grana) connected by lamellae.

The thylakoids (the individual disc-like structures in each granum) are where the light reactions of photosynthesis happen, whilst the stroma (the fluid-filled space around them) is where the darker reactions take place. It's like having two different workshops in the same factory!

Chloroplasts even have their own DNA and ribosomes, which suggests they might have once been independent organisms that got incorporated into plant cells millions of years ago.

Fun Fact: Chloroplasts are basically solar panels for plants - they capture sunlight and convert it into chemical energy that the whole plant can use!