Cell structure

To describe the key structural differences between eukaryotic and prokaryotic cells.
To identify and state the functions of the main sub-cellular structures in animal, plant, and bacterial cells.
To apply mathematical skills to understand the scale and size of cells and their organelles.

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.

A typical animal cell

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.

A typical plant cell

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.

A typical bacterial cell

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).
Estimations can help us understand the relative size and proportions of cell components. This is useful when:
- Precise measurements aren’t required, like comparing the sizes of different organelles.
- Accurate measurements are challenging due to the tiny size of these structures.
Microscopy allows us to view cells and their organelles at high magnification, often with a scale bar to provide a reference for measuring sizes within the image.
Understanding cell structure, size, and scale is essential in biology, helping us appreciate the diversity and complexity of life at the cellular level.

Eukaryotic cell: A cell that contains genetic material enclosed within a nucleus and other membrane-bound organelles, typically found in plants and animals.
Prokaryotic cell: A simpler cell, such as a bacterium, whose genetic material is not enclosed in a nucleus and lacks membrane-bound organelles.
Nucleus: A large organelle in eukaryotic cells that stores genetic material (DNA) and controls cell activities.
Cytoplasm: The jelly-like substance where most chemical reactions occur within a cell.
Cell membrane: A partially permeable barrier that surrounds the cell, regulating the movement of substances in and out.
Mitochondria: Organelles in eukaryotic cells where aerobic respiration takes place, releasing energy for the cell.
Ribosomes: Tiny structures responsible for protein synthesis within cells.
Chloroplasts: Organelles found in plant cells (and some protists) that are the site of photosynthesis.
Cell wall: A rigid outer layer found in plant and bacterial cells (but not animal cells) that provides structural support and protection.
Plasmid: Small, circular rings of extra DNA found in bacterial cells, often carrying genes for traits like antibiotic resistance.

Research Deep Dive: Choose one specific organelle (like the mitochondrion or chloroplast) or a type of prokaryote (like E. coli or Cyanobacteria). Research its detailed structure, specific functions, and importance to the cell or organism, perhaps creating a fact file or short presentation.
Cell Model Challenge: Using materials you have at home (like playdough, balloons, or even household items), create a 3D model of either an animal cell, a plant cell, or a bacterial cell. Label the key organelles and explain their roles.