Biology Notes

• Structure of the leaf

  1. Epidermis has few chloroplasts covered by the cuticle to reduce water loss and stops bacteria

  2. Stomata opens to allow gas exchange

  3. Guard Cell controls whether the stomata is open or closed

  4. Palisade Mesophyll Layer-Contains many chloroplasts and is the main sites of photosynthesis

  5. Spongy Mesophyll Layer-Main gas exchange surface of the leaf

  6. Xylem carries water and minerals up the plant

  7. Phloem- Transports sugars from photosynthesis up and down the plant
• Leaves adapted for gas exchange

  • Thin and short diffusion pathway
  • Flat and large surface area
  • Many stomata which allow movement of gases in and out of the airspaces inside the leaf to maintain a steep concentration gradient
• Internal structure of the leaf adapted for gas exchange

  1. Air Spaces- Allow movement of gases around the mesophyll layer

  2. Many Stomata-Open in sunlight to allow gas exchange

  3. Thin Cell Walls-Allow gas is to move easily into the cells

  4. Moist Air-Needed for gases to dissolve

  5. Close contact between cells and air which allows efficient gas exchange for respiration and photosynthesis
• Formula for Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
• Formula for Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O
• Diffusion- Movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient
• Hydrogen Carbonate Indicator turns purple if there are low levels of CO2 and turns yellow if there are high levels of CO2
• Osmosis-Movement of water molecules from a high water potential to a low water potential down a water potential gradient through a partially permeable membrane
• Active Transport-Movement of molecules from a low concentration to a high concentration against the concentration gradient so energy is needed
• Transpiration is the loss of water vapor from the parts of the plant that are above ground
• Loss of water from the spongy mesophyll layer to the airspaces decreases the water concentration (or potential) in their cytoplasm causing water to move into the cell (from surrounding cells) by osmosis