Cell Structure (AQA GCSE Biology): Revision Notes
📚Revision Notes
Specialised animal cells
What are specialised animal cells?
Some animal cells become specialised. This means they develop specific features to do particular jobs really well. Each type of specialised cell has a special shape and contains particular parts that help it carry out its function.
Note
The process of cells becoming specialised allows organisms to be more efficient. Instead of all cells doing everything, different cells can become experts at specific tasks. This is similar to how people in society have different jobs and specialise in different skills.
Ciliated cells
Ciliated cells are found lining your trachea (windpipe). They have a very important job keeping your lungs clean.
Key features:
- Cilia - These are like tiny moving hairs on the cell surface
- Standard cell parts - They still have a nucleus, cytoplasm, cell membrane, ribosomes and mitochondria
How they work: The cilia move in organised waves. This sweeps mucus up and away from your lungs. The mucus traps dirt and bacteria, so the ciliated cells help remove harmful substances from your respiratory system.
Important
Smoking damages ciliated cells by destroying the cilia. This means mucus and harmful particles can't be cleared from the lungs effectively, leading to breathing problems and increased risk of infection.
Sperm cells
Sperm cells are the male reproductive cells. They need to travel a long way to reach the female egg cell, so they have special adaptations for movement.
Key features:
- Long tail - This swims to move the sperm cell forwards
- Many mitochondria - These provide the energy needed for the tail to keep moving
- Acrosome - This contains enzymes that help the sperm break through the outer layers of the egg cell
- Carries genetic information - The nucleus contains the male parent's DNA
Example
How sperm cell features work together:
Step 1: The mitochondria provide energy for movement Step 2: The long tail propels the sperm towards the egg Step 3: The acrosome releases enzymes to break through the egg's outer layer Step 4: The nucleus delivers the male genetic material to fertilise the egg
This shows how each specialised feature contributes to the sperm's overall function of reproduction.
Nerve cells
Nerve cells carry electrical messages around your body. They can be very long because they need to connect different parts of your body that may be far apart.
Key features:
- Long axon - This is like a wire that carries electrical signals over long distances
- Dendrites - These are tiny finger-like branches that connect with other nerve cells
- Nucleus and standard cell parts - Located in the cell body
How they work: The electrical impulse travels along the axon from one end of the nerve cell to the other. The dendrites help the nerve cell connect with many other nerve cells to form networks.
Note
Some nerve cells can be over a metre long! For example, nerve cells that carry signals from your spinal cord to your toes need to span almost the entire length of your body.
Muscle cells
Muscle cells are specialised for contraction (getting shorter and fatter). This creates movement in your body.
Key features:
- Protein fibres - These can slide over each other to make the muscle cell contract
- Many mitochondria - Muscle cells need lots of energy to keep contracting, so they contain many mitochondria to supply this energy
Cell differentiation
When organisms develop and grow, their cells become specialised through a process called differentiation.
Key points about differentiation:
- Most animal cells differentiate at an early stage of development
- Cells develop different structures so they can do particular jobs
- In adult animals, cell division mainly happens for repair and replacement
- Once cells are specialised, they usually stay that way
Important
Cell differentiation is crucial for complex organisms. Without it, we would just be a blob of identical cells that couldn't perform the many different functions needed for life. Differentiation allows for the division of labour between different cell types.
Summary
Key Points to Remember:
- Specialised cells have specific features that help them do particular jobs really well
- Ciliated cells sweep mucus away from lungs using moving cilia
- Sperm cells have a tail for swimming, mitochondria for energy, and enzymes to penetrate egg cells
- Nerve cells have long axons to carry electrical signals and dendrites to connect with other cells
- Muscle cells contain protein fibres for contraction and lots of mitochondria for energy
- Differentiation is the process where cells develop specialised features during growth and development