AQA 4.1.1.1 Eukaryotes vs. Prokaryotes

Welcome to GCSE Science Unlocked. I’m Lottie, and after a decade in marketing, I’ve decided to head back to college to finally get my science GCSE. I’m discovering that "common sense" and "AQA mark schemes" are two very different languages. And I’m Mr. H. I’ve spent twenty years teaching this spec, and Lottie is right—the examiner doesn't care about your life experience; they care about your vocabulary. If the word isn't precise, the mark isn't yours. He’s a tough mentor, but someone has to keep me from writing "blobs" when I mean "organelles." Today, we’re tackling AQA Specification 4.1.1.1: Eukaryotes and Prokaryotes. [clears throat] Let’s start with the big hitters. Eukaryotic cells. These are the cells that make up you, me, and the salad I had for lunch. Lottie, what defines them? Right, so from my pre-reading: Eukaryotes are complex. Animal and plant cells fall into this category. The main "must-have" is the nucleus. It’s like the CEO’s office—it keeps the DNA protected and separate. Exactly. In a prokaryotic cell, the genetic material is ABSOLUTELY NOT enclosed in a nucleus. It is a single DNA loop floating freely in the cytoplasm. But they also possess EXTRAS -- structures that students consistently forget when they see a comparison question. The PLASMIDS! I actually found this fascinating in the textbook -- they're these little bonus rings of DNA. And bacteria can just pass them to each other? Like handing a colleague a thumb drive with cheat codes on it. "Thumb drive with cheat codes" is highly informal, but the biological mechanism of transferring genetic traits, like antibiotic resistance, is sound. AQA specifically requires you to state that prokaryotes may contain one or more small rings of DNA called PLASMIDS. If an exam asks for the differences between a human cell and a bacterial cell, "plasmids" is a high-level answer that gets you the mark every time. So plasmids get the marks. And SCALE gets the marks too, right? Because eukaryotic cells are typically 10 to 100 micrometers, but these prokaryotic bacteria are... what... 0.1 to 5 micrometers? Correct. They are orders of magnitude smaller. But do not trip over the similarities. Students get so obsessed with the differences that they forget both types of cells have a cell membrane and cytoplasm. And here is the Mr. H Mark Scheme Warning. Let's test you. What else do prokaryotes share with plant cells? A cell wall. Bacteria have a cell wall around the outside to keep their shape. Precisely, But here is the trap, What is a plant cell wall made of? Cellulose. And if you draw a bacterial cell and label its wall as "cellulose", the examiner will have a fit. That is a one-way ticket to zero marks. Plant cell walls are cellulose. Bacterial cell walls are NOT. The specification demands you know they have a cell wall, but you must NEVER conflate the materials. So a bacterial cell wall is a completely different material. Okay... mental checklist for a prokaryote: [listing them off] orders of magnitude smaller, cell membrane, cytoplasm, a STRICTLY non-cellulose cell wall, a single DNA loop, and those bonus plasmids. Spot on. If you memorize that manifest exactly as you've said it, you have effectively BULLETPROOFED yourself against the first section of the exam. Smaller, simpler, but with those sneaky plasmids. Got it. That’s 4.1.1.1 cleared off my revision list. Excellent. Next time, we’ll be looking at the specific sub-cellular structures. And Lottie? Yes Don’t call the mitochondria a "powerhouse." We aren't in a 1990s textbook. I’ll bring my "aerobic respiration" definitions ready. See you then!