Diffusion and Specialised Cells

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  • the gradual movement of particles from places with lots of particles to where there are fewer particles
  • Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration
  • happens in both solutions and gases, the particles in these substances are free to move
  • the bigger the difference in concentration, the faster the diffusion rate

Cell Membranes:

  • hold the cell together but let stuff in and out
  • dissolved substances can move in and out of cells by diffusion 
  • only very small molecules can diffuse through cell membranes - oxygen, water, glucose and amino acids
  • bigger molecules such as starch and proteins cant fit through
  • particles flow through a cell membrane from a high concentration to a low concentration 
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Specialised Cells

1. Palisade Leaf Cell - photosynthesis 

  • packed with chloroplasts for photosynthesis, near the top of the cell for light 
  • tall chapes means more surface area is exposed down the side for carbon dioxide from the air
  • thin shape means more towards the top of the leaf 
  • grouped together at the top of the leaf for photosynthesis 

2. Guard Cell - open and close pores

  • kidney shape opens and closes stomata in the leaf
  • if the plant holds lots of water, the guard cells are filled and expand, this causes the stomata to open so gases are able to be exchanged for photosynthesis 
  • when the plant is short of water, the guard cells lose water making the stomata close - helps to stop water vapour escaping
  • thin outer walls and thickened inner walls make opening and closing work 
  • sensitive to light and close at night to save water without losing photosynthesis 
  • guard cells are adapted to their function of allowing gas exchange and control water loss in the leaf
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Specialised Cells

3. Red Blood Cells

  • concave shape gives big surface area to absorb oxygen, no nucleus
  • helps them pass smoothly through the capillaries to reach body cells 
  • packed with haemoglobin (pigment absorbing oxygen)
  • adapted to carry oxygen, important part of the blood

4. Sperm and Egg Cell:

  • important in reproduction
  • egg cell - carry female DNA and nourish developing embryo in early stages, contains food reserves to feed the embryo
  • when a sperm cell fuses with egg, eggs membrane changes structure to stop sperm getting in, making sure the offspring end up with the right amount of DNA
  • sperm cell - get male DNA to female DNA, has a long tail and streamlined head(easy to swim) a lot of mitochondria to provide energy 
  • carries enzymes in heads to digest through egg cell membrane 
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Cell Organisation

  •  Specialised cells carry out a particular funtion = differentiation - occurs during development of multicellular organism
    • specialised cells form tissues --> form organs --> form organ systems 
    • Large multicellular organisms have different systems inside for exchanging and transporting materials 
  • Cells are organised into tissues: 
    • tissue = group of similar cells that work together to carry out a particular function, includes more than one type of cell
    • 1. muscular tissue - contracts to move 
    • 2. glandular tissue - makes and secretes chemicals like enzymes and hormones
    • 3. epithelial tissue - covers some parts of the body
  • Tissues are organised into organs:
    • organ = group of different tissues working together to perform a certain funtion, stomach organ is made of:
    • 1. muscular tissue - moves the stomach wall to churn up food
    • 2. glandular tissue - makes digestive juices (digestion of food)
    • 3. epithelial tissue - covers outside and inside of stomach 
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Cell Organisation

  • Organs are organised into Organ Systems 
    • organ system = group of organs working together to perform a perticular function
    • digestive system breaks down food and made up of these organs:
    • 1. glands (pancreas and salivary) - produce digestive juices
    • 2. stomach and small intestine - digest food
    • 3. liver - produces bile
    • 4. small intestine - absorbs soluble food molecules
    • 5. large intestine - absorbs water from undigested food leaving faeces 
    • digestive system exchanges materials with the environment by taking in nutrients and releasing substances, eg..bile. 
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