Eukaryotes and Prokaryotes – AQA GCSE Biology Revision Notes

All cells share fundamental components including a cell membrane, cytoplasm, and ribosomes. Organisms such as plants and animals are composed of eukaryotic cells, while bacteria are examples of prokaryotic cells. The primary distinction between these two types lies in the organization of their genetic material.

Eukaryotic cells, such as plant and animal cells, are characterized by having their genetic material (DNA) enclosed within a nucleus. They possess a full set of cellular components and typically range in size from 10 to 100 micrometers (µm).

Prokaryotic cells, exemplified by bacteria, lack a nucleus; their genetic material is found as a single loop of DNA in the cytoplasm. They may also contain smaller, circular DNA pieces called plasmids. Prokaryotic cells are surrounded by a cell wall and are significantly smaller than eukaryotic cells, often measuring around 1 µm.

Cell sizes are measured in micrometers (µm), with 1 mm equivalent to 1000 µm. It is crucial to understand how to convert between millimeters and micrometers. Differences in cell size can be described in terms of 'order of magnitude', referring to differences by factors of ten. Many eukaryotic subcellular structures are comparable in size to, or larger than, entire prokaryotic cells.

Biologists frequently use standard form to represent very small or very large numbers, ensuring clarity and avoiding confusion. For example, converting 1.5 µm to millimeters (0.0015 mm) would then be expressed as 1.5 x 10^-3 mm in standard form. Careful attention to units is required when dealing with cell measurements.