Cell Structure (AQA GCSE Biology Combined Science): Revision Notes
Specialised animal cells
Animal cells can become specialised to do specific jobs in the body. This means they develop particular structures that help them carry out their function really well.
What is specialisation?
When organisms grow and develop, their cells change to become specialised cells with different jobs. This process happens mainly when animals are young and growing. In adult animals, most cell division is just for repairing damaged tissue or replacing old cells.
Different specialised cells have developed unique structures that make them perfect for their specific role. The shape and parts of each cell type are perfectly matched to what that cell needs to do.
The key principle of cell specialisation is that structure matches function - every feature of a specialised cell is designed to help it do its specific job effectively.
Ciliated cells
Ciliated cells are found lining your trachea (windpipe) and other parts of your respiratory system. These cells have a very important job - they help keep your lungs clean and healthy.
Key features:
- Cilia - these are tiny hair-like structures that stick out from the cell surface
- Normal cell parts - nucleus, cytoplasm, cell membrane, ribosomes, and mitochondria
How they work: The cilia can move in coordinated waves, a bit like a field of wheat blowing in the wind. This movement pushes mucus (which traps dirt and bacteria) up and away from your lungs. The mucus gets swept up to your throat where you can cough it out or swallow it.
This sweeping action is really important because it stops harmful particles from getting deep into your lungs where they could cause infections or damage.
Sperm cells
Sperm cells have one main job - to carry the male parent's genetic information to the female's egg cell. They need to travel quite a long distance to reach the egg, so they're specially designed for this journey.
Key features:
- Long tail - this whips back and forth to help the sperm swim towards the egg
- Many mitochondria - these provide lots of energy needed to power the tail for swimming
- Acrosome - this contains special enzymes that help the sperm break through the outer layers of the egg cell
- Nucleus - contains the genetic information that will combine with the egg
The streamlined shape of sperm cells helps them move efficiently through liquid. Everything about their structure is designed to help them complete their journey to fertilise an egg.
Nerve cells
Nerve cells (also called neurones) carry electrical messages around your body. These messages might need to travel from your brain to your toe, or from your finger to your spinal cord - sometimes quite long distances!
Key features:
- Long axon - this is like a long cable that carries electrical signals over long distances
- Dendrites - these are tiny finger-like branches that connect with other nerve cells
- Nucleus - controls the cell like in other cells
The long, thin shape of nerve cells is perfect for carrying messages quickly from one part of the body to another. The dendrites allow nerve cells to form networks, passing messages between different nerve cells.
Worked Example: Muscle Cell Structure and Function
Muscle cells demonstrate how structure perfectly matches function:
Step 1: Energy requirements
- Contain many mitochondria to provide the energy needed for movement
Step 2: Contraction mechanism
- Have special protein fibres that can slide over each other, making the muscle cell contract (get shorter)
Step 3: Coordinated movement
- When lots of muscle cells contract together, they make your whole muscle move
Key Points to Remember:
- Specialised cells have structures that match their specific job
- Ciliated cells use tiny hairs (cilia) to sweep mucus and dirt away from lungs
- Sperm cells have tails for swimming and enzymes to break into egg cells
- Nerve cells have long axons to carry electrical messages over long distances
- Most cell specialisation happens when organisms are young and developing