Diffusion and Specialised Cells
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- Created by: amieparlour
- Created on: 14-04-14 15:47
Diffusion
- 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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