CB6 Photosynthesis

• carbon dioxide + water      =          glucose + oxygen
• Photosynthesis is the process that plants and algae use to make their own food.
• Plants are the main producers of food and therefore biomass. 
• Photosynthesis happens in the LEAF chloroplasts but only when there is light energy.

  It is an endothermic reaction as energy has to be put in to make the products.
• Air spaces are inside the leaf  so that gases can move through to cells.
• in the leaf the palisade cells trap most light so most photosynthesis happens here. They contain lots of chloroplasts containing green chlorophyll to this.
• The bottom layer of the leaf contains tiny holes called STOMATA . They allow the gases involved in photosynthesis to enter and leave the leaf.
• 3 limiting factors will affect the RATE of photosynthesis:

  1. Temperature
  2. Light intensity
  3. Carbon dioxide concentration

  These can make photosynthesis faster or slower.
• If the temperature is too high, enzymes start to denature and the rate of photosynthesis slows down.
• Temperature is a limiting factor because it increases the kinetic energy of molecule and increases the rate of enzyme activity making  photosynthesis faster.
• • ROOT HAIR CELLS have a large surface area for absorbing water and minerals have long extensions that stretch out into the soil. The hair means that they have a bigger surface area take in more water from the soil.
• • Water enters the root hair cells by OSMOSIS. The water moves from a high concentration to a low concentration through a semi-permeable membrane.
• • Plants also need to get nutrients called MINERAL IONS from the soil.
• The mineral ions enter the root hair cells by a process called ACTIVE TRANSPORT.
• • ACTIVE TRANSPORT is movement from a low concentration to a high concentration and needs ENERGY to happen as proteins in the cell membrane are used to move the mineral ions in.
• TRANSLOCATION – process of transporting sucrose around a plant
• Plants make sucrose sugar from the glucose made during photosynthesis.
• Sucrose travels UP AND DOWN the plant stem in the SIEVE TUBES of PHLOEM tissue. These tubes have very little cytoplasm so that there’s lots of space to transport sucrose and other nutrients.
• COMPANION CELLS pump sucrose into the sieve tubes. This increases the pressure  and creates a flow of sucrose. These cells have lots of mitochondria which supply energy from respiration for active transport of sucrose into and out of the sieve tubes.
• Xylem vessels are dead cells which have no cytoplasm or cell contents. This means there’s more space for water containing mineral ions to move UP the plant from the root to the leaves.
• Xylem are adapted because they:

  1. have lignin in the wall to keep them rigid and very strong, preventing them from collapsing.
  2. have no end walls between cells so a long tube is created that water can flow through easily.
  3. contain tiny pores called pits in their walls to allow water and mineral ions to move out.
• Transpiration is the loss of water by evaporation from leaves.
• A TRANSPIRATION STREAM set up by water evaporating from the stomata in the leaves makes this happen.
• As water evaporates from the stomata in the leaves, it creates a ‘pull’ which draws more water through the xylem tubes from the roots. This causes water to enter the roots by osmosis.
• In the light, water flows into pairs of guard cells by osmosis, making them rigid / swell. This opens the stoma.

  At night in the dark, water flows out of the guard cells. They lose their rigidity and the stoma shuts.
• The following factors make transpiration faster:

  1. High temperature – particles move faster so transpiration is faster 

  2. High light intensity – makes the stomata open wider. This increases the rate of evaporation of water from the leaf so more water is taken up to replace this.

  3. Windy – moves water molecules away from the stomata so a greater diffusion gradient is created

  4. Low humidity – little water vapour in the air so a greater diffusion gradient
• can measure the rate of transpiration using a potometer.
• The rate can be measured as:

  distance moved by the air bubble/time taken
• adaptations of xylem

  lignin, no end walls, pits