Plants and photosynthesis

• Root hair cells absorb water and mineral ions from the soil
• upper epidermis (waxy cuticle) - reduces water loss and allows light through
• palisade cell layer (mesophyll) - top of leaf, lots of chloroplast, more photosynthesis
• spongy cell layer (mesophyll) - air spaces which allow diffusion of gas
• xylem of vascular bundle (vein) - transports water
• phloem of vascular bundle (vein) - transports glucose and nutrients - phood
• stomata (stoma or pore) - reduces water loss
• guard cells - open and close stomata (closes at night, open during the day)
• lower epidermis (cuticle) - has waxy cuticle
• The upper epidermis of a leaf contains a waxy cuticle that reduces water loss and allows light to pass through.
• the xylem is the main supporting tissue in plants and is distributed differently in stems and roots
• in stems the xylem is found as distint oval patches arranged in a circle
• in roots the xylem is found at the centre
• the xylem transports water using transpiration and has a thickened wall (dead)
• the phloem uses translocation to transport nutrients and glucose
• the guard cells open and close the stomata
• the stomata provide an entry and exit point for gases such as oxygen and carbon dioxide - water has the tendency to evaporate out of the stomata when they are open, espicially on a hot day - this process is known as transpiration
• A transpiration stream is the flow of water up xylem tubes, due to the loss of water by transpiration through the leaves
• abiotic factor = non - living
• factors affecting transpiration

  • light intensity - increased light intensity opens stomatas to allow co2 into plant, wider stomata = faster transpiration
  • temperature - hotter temp = molecules have more energy which means water molecules will evaporate faster
  • humidity - drier air = steeper concentration gradient, water will move out quicker
  • air movement - faster air movement = water vapour removed quicker, steeper concentration gradient of water vapour between the inside + outside of the leaf
• xylem is made out of dead cells
• the wall of xylem is strengthened with lignin
• carbon dioxide + water = glucose + oxygen
• 6CO2 + 6H2O → C6H12O6 + 6O2
• light provides energy
• chlorophyll absorbs light
• photosynthesis is an endothermic reaction because it takes in heat
• plants use light energy in photosynthesis
• turgid means the guard cell is swollen with water
• stomata become flaccid due to water leaving
• uses of glucose

  • respiration - releases energy for life processes
  • starch - storage - glucose is stored by joining molecules together in a polymer; the starch is broken back down when the plant needs it
  • fat/oil - long time storage - can be converted into lipids + stored in seeds; the fat is broken back down into glucose when the plant needs it
• uses of glucose

  • transport - glucose converts into sucrose to be carried around the plant in the phloem
  • protein - growth and enzymes - glucose is combined with nitrate mineral ions (absorbed from soil through root hairs) to make amino acids; amino acids make proteins for growth/enzymes
  • cellulose - structure - cell walls; glucose is used to make cellulose which gives shape/support to the plant
• the plant material made by growth is known as biomass
• biomass is useful to us because it can be used for food, fuel, building materials, drugs and fibres
• plants obtain nitrate by absorbing it from soil through root hairs, into the xylem
• nitrate is needed by plants because glucose + nitrate = amino acids = proteins (for enzymes/growth)
• if a plant was deficient in nitrate, it would have stunted growth and the leaves would go yellow
• the test for starch is iodine - a positive result is blue/black, a negative one is brown
• glucose test: benedicts + heat - positive test is brick red
• protein test = biuret test - postive test = purple