Plant Biology

• Stomata - Small holes under leaf letting in CO2, on shaded side so water doesn’t evaporate
• Guard cells - lots of water makes cells turgid (gap increases), little water makes cells flaccid (gap decreases to conserve water)
• Spongy mesophyll - lots of gaps between cells (easier for gas to diffuse through)
• Phloem - carries sugars to plant
• Waxy cuticle - thin layer of lipids prevents water loss
• Palisade mesophyll - lots of chloroplasts for photosynthesis
• Translocation - movement of sugars from leaf to plant (cell sap moves through pores in phloem tubes)
• Transpiration - evaporation of water from leaf (water moves through hollow xylem tubes in stream, when water evaporates water moves up xylem tubes)
• Transpiration rate change - High heat = High rate (water has more energy to evaporate), more light = high rate (stomata stay open), high wind = high rate (wind blows water away)
• Photosynthesis: Carbon Dioxide/CO2 + Water/H20 → Glucose/C6H12O6 + Oxygen/O2
• Uses of Glucose:

  Cellular respiration - breaks glucose to release energy

  Cellulose - made from glucose to strengthen cell walls

  Starch - stored for long term, compact and insoluble, broken into glucose if photosynthesis isn’t happening

  Amino acids - glucose + nitrate ions → proteins

  Oils & Fats - stored as future energy source for seeds
• Chlorophyll: plants have different levels of this, disease decreases chlorophyll
• Light intensity: rate increases until there’s not enough CO2
• Carbon dioxide: rate increases until there’s not enough light
• Temperature: rate increases, then decreases when enzymes denature
• Greenhouses: traps sun heat to increase temp, artificial light in night to increase rate, paraffin heater releases heat and carbon dioxide as it burns, pests an pathogens don’t get in
• Fertilisers: gives plant enough essential minerals
• Auxin: hormone controlling growth at ends of shoots and roots, produced in tips, dissolves backwards on shaded side
• Auxin in shoots:

  Positive phototropism, negative gravitropism, auxin expands cells in shaded side to bend towards light
• Auxin in roots: Negative phototropism, positive gravitropism, auxin lets upper side grow faster for roots to grow to gravity
• Use of Auxin:

  Weed killer: weeds have broad leaves, plant grows uncontrollably and dies, crops have narrow leaves, less surface area means no death
• Gibberllin - promotes growth of stems

  Sugarcanes: sprayed during growth to increase length
• Ethene - promotes ripening of fruit

  Bananas: exposed to ethene in ripening chambers
• Plants infected by TMV and rose black spot have poor growth due to:

  • Infection causing discolouration of leaves, hindering photosynthesis
  • Reduced photosynthesis leading to decreased glucose production
  • Decreased availability of glucose resulting in reduced respiration and energy for growth
  • Less energy and glucose leads to reduced production of molecules necessary for growth, especially proteins
• PRACTICAL 6:

  1. place boiling tube 10 cm from LED (doesn’t change heat)
  2. fill boiling tube with sodium hydrogen carbonate which releases CO2, add pondweed
  3. count number of bubbles in minute OR catch bubbles using funnel and measuring cylinder to measure volume
  4. repeat and move boiling tube further