AQA Biology 4.1.1.1 · Contrast
Eukaryotes and prokaryotes
A bacterium and one of your liver cells are both alive. What does the bacterium not have, and how many of them would fit across your cell?
Triple Science · Higher tier
Start here
A liver cell and a bacterium, drawn to the same scale.
Both are living cells, and both need DNA to make their proteins. The liver cell keeps its DNA inside a nucleus.
If you had to guess, is the bacterium’s DNA inside a nucleus too, or loose in the cell?
Plant and animal cells are eukaryotic: each has a cell membrane, cytoplasm and genetic material enclosed in a nucleus. The cells of fungi and protists are eukaryotic too. Bacterial cells are prokaryotic. Below, an animal cell and a bacterium are drawn side by side. Decide where each structure belongs before it appears.
Build the two cells · structure 1 of 7
Nucleus
Which cell has it?
Cells are measured in tiny units. Milli means a thousandth, micro a millionth and nano a thousand-millionth of a metre, so 1 mm = 1000 µm and 1 µm = 1000 nm (and centi, a hundredth: 1 cm = 10 mm). An order of magnitude is a factor of ten. If one thing is about 10ⁿ times bigger than another, it is n orders of magnitude bigger. Put both sizes in the same unit before you divide.
Estimate · comparison 1 of 3
Bacteria (2 µm) across a liver cell (20 µm)
How many fit across, to the nearest power of ten?
Equation
Actual size = Image size ÷ Magnification
Units first
Image size and actual size must be in the same unit. Magnification has no unit: write it as ×2000.
Command words in this lesson
- Compare
- Both cells in every sentence: “a bacterium has no nucleus, whereas an animal cell does”.
- Calculate
- Show every line, units matched before you divide, unit on the answer.
- Estimate
- An approximate answer, here to the nearest power of ten.
Key fact
Eukaryotic cells keep their genetic material in a nucleus. Prokaryotic cells are about an order of magnitude smaller, with a single DNA loop, possibly plasmids, and a cell wall around the membrane.
Key note · AQA 4.1.1.1
Eukaryotes and prokaryotes
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
Connects to
Ask MrBadmus
Not sure which structures a bacterium has, or how to convert µm?
Cells are drawn as flat outlines. In the builder the bacterium is drawn about ten times larger than the animal cell's scale so its parts can be seen; the hook and the size comparisons are drawn to scale. Sizes are typical values: real cells vary.