Revision:Gcse biology - cells

Cells

Robert hook discovered cells in the 1665. A typical cell is 20 micrometers wide.


Animal cells have four things:

  • A Nucleus – controls the cell and contains genetic information
  • A cell membrane – Decides what gets in and out of the cell and holds it together
  • Cytoplasm – Where the cell’s enzyme work (In animals there are granules of glycogen which is stored food. In plants there are starch grains which are also stored food)
  • Mitochondria – Where the cell respires, during glucose and oxygen into energy and water


However, plant cells contain three extra things:

  • Rigid cell wall – this is made of cellulose and supports the cell, and stops it exploding when osmosis occurs
  • Vacuole – Contains the cell sap (a weak solution of sugar and salts)
  • Chloroplasts – Contain chlorophyll, which is used in photosynthesis. (EQ = CO2 + H2O  O2 + C6H12O6)
  • Chloroplasts and starch grains are examples of plastids, small bodies within the cell which hold a chemical
Cells and tissues
  • Epidermis (in plants) and epithelium (they both look very similar). The epidermis covers the plant, while epithelium in animals lines tubes and forms the skin
  • Muscle tissue. Lots of strands packed tightly together (bad drawing) all going in one direction.
  • Nerve tissue. A network of nerve cells connected together.
Name of tissue What it is Function
Epidermal tissue Sheets of cells To line and protect the outside of the plant
Photosynthetic tissue Cells with chloroplasts in them To provide glucose (food) for the plant via photosynthesis
Packing tissue Large balloon like cells To fill the spaces inside the plant (but often leave space for gas diffusion)
Vascular (conducting) tissue Long tubes Transporting food and water around the plant
Strengthening tissue Bundles of tough fibres To strengthen the plant and provide support

The body is able to work by the division of labour between cells, and this can only occur in multi cellular organisms.


All living things are made up of cells. However, most cells are specified to do a particular job. Some important examples of specialized cells are as follows.


Palisade cells are specified to absorb the maximum amount lf light for photosynthesis. They are packed with chloroplasts, are long and tall to maximize surface area for carbon dioxide absorption. It also means there is a bigger chance of light hitting it.


Cells that line the oviducts have hairs which “waft” the egg along both backwards and forwards.


Guard cells (which are on the bottom of cells and “guard” the stoma (plural stomata)) can open and close to let air in (which carries carbon dioxide in for photosynthesis).When the cells are turgid they are open, when they are flaccid they are closed (Turgid = full of water, flaccid = dryish). They also have thin outer walls and thick inner walls.


Red blood cells have a large surface area (donut shape) for maximum oxygen absorption by the haemoglobin. They are smooth so they can easily go through the capillaries and have no nucleus for maximum space for haemoglobin,


Sperm cells have a long tail for mobility and a short lifespan so only the fittest sperm get to the egg (natural selection)

Egg cells have a huge food reserve and when the sperm fuses with the egg the egg membrane changes instantly to become impenetrable to other sperm.

Also See

Here are the other comprehensive GCSE Biology notes by Prometheus:

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