GCSE Biology · Biology
Cells: a clear study guide
Cells are the basic units of living organisms. Learn the structures by linking each one to its job, then use magnification and transport equations carefully in exam questions.
Animal and plant cells
Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cellulose cell wall, chloroplasts and a permanent vacuole.
The nucleus contains genetic material. Mitochondria are the site of aerobic respiration, while ribosomes join amino acids to make proteins. Chloroplasts absorb light for photosynthesis.
Movement across membranes
Diffusion is the net movement of particles from a higher concentration to a lower concentration. Osmosis is the movement of water through a partially permeable membrane from a dilute solution to a more concentrated solution.
Active transport moves substances against a concentration gradient and requires energy from respiration.
- A steeper concentration gradient usually increases diffusion rate.
- Higher temperature gives particles more kinetic energy.
- A larger surface area can increase the rate of exchange.
Microscopy and magnification
Use magnification = image size รท actual size. Keep units consistent before calculating, and convert millimetres to micrometres when needed. Show the conversion step so your method is clear.
Quick check
Which organelle contains genetic material?
Answer: The nucleus.
What energy source powers active transport?
Answer: Energy released by respiration, usually supplied as ATP.
Common questions
What is the difference between diffusion and osmosis?
Diffusion is the movement of particles down a concentration gradient; osmosis specifically describes water moving through a partially permeable membrane.
Why do cells have specialised structures?
Each structure is adapted to carry out a particular function efficiently.