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Life and Cells

Plant and Animal cells have similarities and differences

  • Nucleus- contains genetic material that controls the activities of the cell
  • Cytoplasm- where chemical reactions occur. It contains enzymes that control the reactions.
  • Cell Membrane- holds cell together and controls what goes in and out
  • Mitochondria- where most of the reactions for respiration's occur. Respiration releases energy that the cell needs to work
  • Ribosomes- where proteins are made in the cell.

Cells make up tissues, organs and systems

Cells have structures specialised so they can carry out their function. Similar cells are grouped together to make a tissue, different tissues work together as an organ. Groups of organs working together make up an organ system.All the groups of organs and organ systems work together make up a full organism - human.

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Specialised Cells

Palisade leaf cells are adpated for photosynthesis

  • Packed with chloroplasts which are crammed at the top of the cell- so they are nearer the light
  • Tall shape means more surface area for absorbing CO2
  • Thin shape means you can stack them on top of a leaf
  • Guard cells are adapted to open and close pores
  • Special kidney shape which opens and closes the stomata (pores)
  • When the plant has lots of water the guard cell fill with it and go plump. This makes the stomata open so gases can be exchanged for photosynthesis.
  • When a plant is short of water, the guard cells lose water and become flaccid, making the stomata close.
  • Thin outer walls and thickened inner walls make the opening and closing work
  • They are sensitive to light and close at night to save water.
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Specialised Cells

Red blood cells are adpated to carry oxygen

  • Concave shape gives a big surface areaa for abosrobing oxygen. It also helps them pass smoothiy through capilliraries to reach body cells
  • Theyre packed with haemoglobin- the pigment that abosorbs the oxygen.
  • They have no nucleus. to leave even more room for harmoglobin.

Sperm and Egg cells are specialised for reproduction

  • Egg cell- carry the female DNA, nourish the developing embryo and contains huge food reserves to feed embryo
  • When sperm fuses with the egg, the egg membrane instantly changes its structure to stop more sperm getting in..
  • Sperm- male DNA to the female DNA. long tail and streamlined head. Lots of Mitchondria too provide eneergy.
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Diffusion meaning

  • Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration.
  • It happens in both liquid and gases- thats because the particles in these rubstances are free to move around.  

Cell membranes

  • They hold the cell together and let things in and out.
  • Substances can move in and out of cells by diffusion and osmosis.Only very small molcules can diffuse through cell membranes e.g glucose, amino acides, water and oxygen. while big molcules dont fit in.
  • Particles flow through membrane from where there high concentration to low concentration.
  • The rate of diffusion depends on 3 main things: 
  • Distance- substances diffuse more quickly when they havent as far to move
  • Concentration didderence- substances diffuse faster if theres a big difference in concentration.
  • Surface area- the more surface there is available for molecules to move across.
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Osmosis is a special case of diffusion.

  • Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentraion to a region of low water concentration.
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