Cell structure

All living organisms are made up of cells, which are the basic units of life. There are two main types of cells:

• Eukaryotic cells: Found in plants and animals, these cells are larger and more complex. They contain genetic material (DNA) enclosed within a nucleus and other membrane-bound organelles, like mitochondria (for energy production) and chloroplasts (for photosynthesis in plant cells).

• Prokaryotic cells: Found in bacteria, these cells are smaller and simpler. Their DNA is not enclosed in a nucleus but instead exists as a single loop within the cytoplasm. Bacterial cells may also contain plasmids, which are small rings of extra DNA.

Cells function like tiny factories, with various sub-cellular structures (organelles) that have specialised roles to keep the cell alive and functional.

Animal cell structure

Animal Cells typically contain:

• Nucleus: Stores genetic material and controls cell activities.

• Cytoplasm: The site of most chemical reactions.

• Cell membrane: Regulates the movement of substances in and out of the cell.

• Mitochondria: The site of aerobic respiration, where energy is released.

• Ribosomes: Where proteins are synthesised.

Plant cell structure

Plant Cells also contain the following additional structures:

• Chloroplasts: The site of photosynthesis, producing glucose.

• Permanent vacuole: Filled with cell sap, which helps maintain cell structure.

• Cell wall: Made of cellulose, providing extra strength and support to the cell.

Bacterial cell structure

Bacterial Cells have:

• Cell membrane and cytoplasm.

• Cell wall (not made of cellulose) for structure and protection.

• Genetic material that floats freely in the cytoplasm, as a single loop of DNA, without a nucleus.

• Plasmids, which are small rings of DNA that provide extra genetic traits, such as antibiotic resistance.

Additional maths skills

Cells and their structures vary greatly in size, requiring different units for measurement:

• Meters (m) for large areas, like fields.

• Millimeters (mm) for larger structures, like a leaf.

• Micrometers (µm) for cells (1 µm = 0.001 mm).

• Nanometers (nm) for smaller parts, like viruses (1 nm = 0.000001 mm).

To make it easier to compare these sizes, we use standard form (scientific notation). For example:

• 10 µm = 1 x 10⁻⁵ m (10 to the power of -5 meters)

• 0.2 µm = 2 x 10⁻⁷ m

Order of magnitude calculations help us understand size differences between objects. For instance, an animal cell (10 µm) is roughly one order of magnitude, or 10 times, larger than a bacterial cell (1 µm).