GCSE AQA Biology 2 Cells & Diffusion

GCSE AQA Biology 2 Cells & Diffusion

1. Animal & plant cells

   • Animal cells have...
     • Nucleus
       • Contains genetic material that conrols activities of cell
     • Cytoplasm
       • Gel-like substance where most chemical reactions happen - contains enzymes
     • Cell membrane
       • Hold cell together & controls what goes in/out
     • Mitochondria
       • Where reactions for respiration take place - releases energy
     • Ribosomes
       • Where proteins are made - protein synthesis
   • Plant cells have the same plus...
     • Cell wall
       • Rigid, made of cellulose - supports & strengthens cell
     • Permanent vacuole
       • Contains cell sap - weak solution of sugars & salts
     • Chloroplasts
       • Where photosynthesis happens (makes food for the plant) - contain green substance (chlorophyll)

2. Diffusion

   • Definition
     • The spreading out of particles from an area of high concentration to an area of low concentartion
   • Happens in both solutions & gases
   • The bigger the difference in concentration, the faster the diffusion rate
   • Cell membranes
     • Allow small molecules through (e.g. oxygen, glucose, amino acids, & water)
     • Don't allow big molecules through (e.g. starch & proteins)
     • Particles move randomly but net movement from high to low concentration

3. Specialised cells

   • Palisade leaf cells
     • Packed with chloroplasts - for photosynthesis
     • Tall shape - large surface area exposed down side for absorbing carbon dioxide
     • Thin shape - can pack lots at top of leaf
   • Guard cells
     • Open & close stomata in leaf
     • When plant has lots of water...
       • Guards cells fill with water & become turgid, making stomata open - gases can be exchanged for photosynthesis
     • When plant is short of water...
       • Guard cells lose water & become flaccid, making stomata close - stops too much water vapour escaping
     • Thin outer walls & thick inner walls
     • Sensitive to light & close at night
       • To save water - adapted to function of allowing gas exchange & controlling water loss within leaf
   • Red blood cells
     • Concave shape
       • Big SA for absorbing oxygen & helps them move smoothly through capillaries
     • Packed with haemoglobin
       • Pigment that absorbs oxygen
     • No nucleus
       • More room for haemoglobin
   • Sperm & egg cells
     • Sperm cells
       • Long tail & streamlined head
         • Help it swim to egg
       • Lots of mitochondria
         • Energy needed to swim
       • Carry enzymes
         • In head - to digest egg cell membrane
     • Egg cells
       • Huge food reserves
         • To feed embryo
       • Membrane can change structure
         • To stop more sperm getting in - offspring ends up with right amount of DNA

4. Cell organisation

   • Cell differentiation
     • Process by which cells become specialised for a particular job
     • Occurs during development
   • Tissue - group of similar cells
     • That work together to carry out a particular function
     • Examples of tissues
       • Muscular tissue - contracts to move
       • Glandular tissue - makes & secretes chemicals e.g. enzymes & hormones
       • Epithelial tissue - covers parts of the body
   • Organ - group of different tissues
     • That work together to perform a certain function
     • e.g. Stomach is made of...
       • Muscular tissue - moves stomach wall to churn food
       • Glandular tissue - makes digestive juices to digest food
       • Epithelial tissue - covers outside and inside of stomach
   • Organ system - group of organs
     • Working together to perform a particular function
     • e.g. Digestive system is made of these organs...
       • Glands
         • Produce digestive juices
       • Stomach & small intestine
         • Digest food
       • Liver
         • Produces bile
       • Small intestine
         • Absorbs soluble food molecules
       • Large intestine
         • Absorbs water from undigested food - leaving faeces

5. Single-celled microorganisms

   • Bacterial cells
     • Has cytoplasm, cell membrane & wall
       • No nucleus - strands of genetic material instead
     • Have flagella
       • Long protein strands - to move about
   • Yeast cells
     • Have a nucleus, cytoplasm, cell membrane & wall