GCSE AQA Biology 2 Plants & Photosynthesis

GCSE AQA Biology 2 Plants & Photosynthesis

1. Plant tissues & organs

   • Organs in a plant...
     • Stem
     • Roots
     • Leaves
   • Tissues in a leaf...
     • Mesophyll - where most of photosynthesis happens
     • Xylem & phloem - transport water, mineral ions & sucrose
     • Epidermal - covers the plant

2. Photosynthesis equation

3. How photosynthesis works

   • Photosynthesis produces 'food' - glucose
   • Happens inside chloroplasts
     • Chloroplasts contain chlorophyll which absorbs sunlight & uses its energy to...
       • Convert carbon dioxide and water into glucose, oxygen is produced as by-product
   • Happens in the leaves of all green plants

4. The rate of photosynthesis

   • Affected by 3 factors...
     • Light
       • Provides energy needed for photosynthesis
       • Too little slows down rate
       • As light level increased, rate increases steadily up to certain point
         • Past that point, increasing light levels further won't make any difference
           • Carbon dioxide or temperature has become a limiting factor
     • Carbon dioxide
       • One of the raw materials needed for photosynthesis
       • Too little slows down rate
       • Increasing levels will only increase rate up to certain point
         • After that, carbon dioxide is no longer limiting factor
     • Temperature
       • Has to be right
       • If temp. is limiting - usually because too low
         • Enzymes needed work more slowly at lower temp.
       • If plant is too hot - enzymes denatured
         • Happens at about 45 degrees C

5. Creating the ideal conditions for growing crops in a greenhouse

   • Heat
     • Greenhouses trap Sun's heat - temp. isn't limiting
     • In winter, farmers might use heaters
     • In summer, farmers might use shades and ventilation
   • Light
     • Supply artificial light at night
   • Carbon dioxide
     • Use paraffin heaters to heat greenhouse - makes carbon dioxide as by-product
   • Pests & diseases
     • Keeping plants enclosed makes it easier to keep them free from pests & diseases
     • Can add fertilisers to soil to provide minerals

6. How plants use glucose

   • For respiration
     • Releases energy enabling plant to convert rest of glucose into other useful substances
       • Need minerals from soil as well
   • Making cell walls
     • Glucose converted into cellulose for making strong cell walls
       • Especially in rapidly growing plant
   • Making proteins
     • Glucose combined with nitrate ions (from soil) to make amino acids which are made into proteins
   • Storing in seeds
     • Glucose turned into lipids for storing in seeds
   • Storing as starch
     • Glucose turned into starch & stored in roots, stems & leaves for when photosynthesis isn't happening
       • Starch is insoluble - better for storing than glucose

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