B3 and B4 Organisation

• Levels of organisation in living organisms

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organisms
• Cells


  Basic building blocks
• Tissues

  Groups of cells that have similar structures and functions
• Organs

  Groups of tissues working together to perform a specific function
• Organ systems

  Groups of organs working together
• Organisms

  Organ systems work together, forming an organism
• Enzymes

  Large proteins that catalyse (speed up) reactions. Enzymes are not changed in the reactions they catalyse.
• Lock and key theory

  1. The enzyme's active site (where the reaction occurs) is a specific shape.

  2. The enzyme (the lock) will only catalyse a specific reaction because the substrate (the key) fits into its active site.

  3. At the active site, enzymes can break molecules down into smaller ones or bind small molecules together to form larger ones.

  4. When the products have been released, the enzyme's active site can accept another substrate molecule.
• Parts of the digestive system

  • Mouth
  • Salivary glands
  • Oesophagus
  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Small intestine
  • Large intestine
  • Rectum
  • Anus
• Salivary glands

  Make saliva containing the enzyme amylase
• Stomach

  Churns food, releases protease to digest proteins, releases hydrochloric acid to kill pathogens
• Liver

  Makes bile
• Gall bladder

  Stores bile, which is alkaline to neutralise hydrochloric acid from the stomach and emulsifies fat to form small droplets with a large surface area
• Pancreas

  Makes enzymes: amylase, lipase, and protease
• Small intestine

  Where digested food is absorbed into the blood
• Large intestine

  Where water and minerals are absorbed into the blood
• Digestive enzymes

  • Amylase
  • Proteases
  • Lipases
• Amylase

  Breaks down starch into glucose
• Proteases

  Break down proteins into amino acids
• Lipases

  Break down lipids into fatty acids and glycerol
• Optimum pH

  The pH at which an enzyme's activity is greatest
• As temperature increases

  The rate of enzyme reaction increases until it reaches the optimum temperature, then decreases as the enzyme becomes denatured
• Denatured

  The shape of an enzyme's active site is changed by heat or extreme pH, so the substrate can no longer bind to it and the enzyme cannot catalyse the reaction
• Transpiration


  Movement of water from the roots to the leaves through the xylem
• Translocation


  Movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Factors affecting the rate of transpiration

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
• Effect of temperature on transpiration

  Higher temperatures increase the rate of transpiration
• Effect of humidity on transpiration

  Lower humidity increases the rate of transpiration
• Effect of wind speed on transpiration

  More wind increases the rate of transpiration
• Effect of light intensity on transpiration

  Higher light intensity increases the rate of transpiration
• Stomata


  Tiny openings in the undersides of leaves that control gas exchange and water loss
• Guard cells


  Used to open and close the stomata
• Palisade mesophyll


  Tightly packed cells with lots of chloroplasts to absorb light for photosynthesis
• Spongy mesophyll


  Spherical cells with lots of air spaces to allow gases to diffuse quickly, and a large surface area-to-volume ratio to increase gas exchange
• Xylem


  Transports water and mineral ions from the roots to the rest of the plant
• Xylem


  • Made of dead cells with no end walls between them
  • Walls strengthened by lignin to withstand pressure
• Phloem


  Transports dissolved sugars from the leaves to the rest of the plant
• Transpiration stream


  Constant movement of water up the plant
• Heart


  Organ that pumps blood around the body
• Heart


  • Made from cardiac muscle tissue
  • Supplied with oxygen by the coronary artery