Bio topics

• Differentiation


  The process by which cells become specialised for a particular function
• In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised
• Lots of plant cells don't ever lose this ability to differentiate
• Undifferentiated cells


  Cells that have not become specialised, also called stem cells
• The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells
• Examples of Specialised Cells

  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Sperm cells


  • Specialised for reproduction
  • Have a long tail and streamlined head to help swim to the egg
  • Have lots of mitochondria to provide energy
  • Carry enzymes in head to digest through egg cell membrane
• Nerve cells


  • Specialised for rapid signalling
  • Long to cover more distance
  • Branched connections at ends to connect to other nerve cells
• Muscle cells


  • Specialised for contraction
  • Long to have space to contract
  • Contain lots of mitochondria to generate energy for contraction
• Root hair cells


  • Specialised for absorbing water and minerals
  • Grow into long "hairs" that stick out into the soil to increase surface area
• Phloem and xylem cells


  • Specialised for transporting substances
  • Form tubes by being long and joined end to end
  • Xylem cells are hollow, phloem cells have few subcellular structures to allow flow
• Plants transport food substances from the leaves to growing parts of the plant through phloem tubes
• The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it
• The alveoli in the lungs are specialised to maximise the diffusion of oxygen and carbon dioxide
• Alveoli


  • Have an enormous surface area (about 75 m² in humans)
  • Have a moist lining for dissolving gases
  • Have very thin walls
  • Have a good blood supply
• The villi in the small intestine increase the surface area to assist quick absorption of digested food into the blood
• Villi


  • Have a single layer of surface cells
  • Have a very good blood supply to assist quick absorption
• Digested food moves into the blood by diffusion and by active transport
• Leaves


  • Have stomata (holes) on the underside to allow carbon dioxide to diffuse in
  • Allow oxygen and water vapour produced in photosynthesis to diffuse out
  • Have guard cells to control the size of the stomata
• The flattened shape of the leaf increases the surface area for gas exchange
• Gills


  • Made of lots of thin plates called gill filaments to increase surface area
  • Have lots of finger-like structures called lamellae to increase surface area even more
  • Have a thin surface layer of cells to minimise the distance gases have to diffuse
  • Have blood flowing in the opposite direction to the water flow to maintain a large concentration gradient
• The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood
• Digestive enzymes are produced by cells and then released into the gut to mix with food
• Carbohydrases


  Enzymes that break down carbohydrates into simple sugars
• Proteases


  Enzymes that break down proteins into amino acids
• Lipases


  Enzymes that break down lipids into glycerol and fatty acids
• Amylase is an example of a carbohydrase that breaks down starch
• Places where amylase is made

  • Salivary glands
  • Pancreas
  • Small intestine
• Places where proteases are made

  • Stomach (as pepsin)
  • Pancreas
  • Small intestine
• Places where lipases are made

  • Pancreas
  • Small intestine
• Bile produced in the liver is stored in the gall bladder before being released into the small intestine
• Bile


  Alkaline substance that neutralises stomach acid and emulsifies fats
• The enzymes in the small intestine work best in the alkaline conditions created by bile
• Humans have a double circulatory system with two circuits - one for the lungs and one for the rest of the body
• How the heart pumps blood

  1. Blood flows into the atria

  2. Atria contract, pushing blood into ventricles

  3. Ventricles contract, forcing blood out of the heart
• Coronary arteries branch off the aorta to supply the heart muscle with oxygenated blood
• Cardiovascular disease


  Diseases of the heart or blood vessels, e.g. coronary heart disease
• Coronary heart disease


  1. Coronary arteries that supply blood to the heart muscle get blocked by fatty material

  2. Arteries become narrower

  3. Blood flow is restricted

  4. Lack of oxygen to the heart muscle

  5. Can result in a heart attack
• Stents


  Tubes inserted inside arteries to keep them open and allow blood flow
• Stents are inserted


  They keep arteries open and allow blood to pass through to the heart muscle