photosynthesis

• photosynthesis uses energy to change carbon dioxide and water into glucose and oxygen
• photosynthesis takes place in the chloroplasts - they contain a green pigment called chlorophyll that absorb light
• energy is transferred to the chloroplasts from the environment by light
• photosynthesis is endothermic - this means energy is transferred from the environment in the process
• the word equation for photosynthesis:

  $carbon dioxide +$$water -> glucose +$$oxygen (+energy)$
• the symbol equation for photosynthesis:

  $6CO2 +$$6H2O -> C6H12O6 +$$6O2$
• plants use glucose in five main ways:

  • for respiration
  • making cellulose
  • making amino acids
  • stored as oils or fats
  • stored as starch
• 1 - for respiration

  this transfers energy from glucose which enables the plants to convert the rest of the glucose into various other useful substances
• 2 - making cellulose

  glucose is converted into cellulose for making strong plant cell walls
• 3 - making amino acids

  glucose is combined with nitrate ions (absorbed form the soil) to make amino acids, which are then made into proteins
• 4 - stored as oils or fats

  glucose is turned into lipids (fats and oils) for storing in seeds
• 5 - store as starch

  glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn't happening, like in the winter.
• starch is insoluble, which makes it better for storing than glucose - a cell with lots of glucose in would draw in loads of water and swell up
• limiting factors affect the rate of photosythesis
• a limiting factor is something that stops photosynthesis from happening quickly
• these factors have a combined effect on the rate of photosynthesis, but which factor is limiting at a particular time depends on the environmental conditions:

  • at night - light is the limiting factor
  • in winter - temperature is the limiting factor
  • if its warm enough and bright enough, the amount of CO2 is the limiting factor
  • chlorophyll can be a limiting
• the amount of chlorophyll in a plant can be affected by disease or environmental stress such as lack of nutrients
• the factors affecting chlorophyll can cause chloroplasts to become damaged or to not make enough chlorophyll - this means the rate of photosynthesis is reduced because they can't absorb as much light
• light provides the energy needed for photosynthesis
• as the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point. Beyond that, it won't make any difference
• beyond the certain point, it won't make any difference if the light intensity increases as the rate will no longer increase
• this is because it'll either be the temperature or the CO2 level which is now the limiting factor - not light
• the amount of CO2 will only increases the rate of photosynthesis up to a point - after this the graph flattens out, as the amount of CO2 increases, the rate no longer increases ( this shows that CO2 is no longer the limiting factor)
• as long as light and CO2 are in plentiful supply then the factor limiting photosynthesis must be temperature
• usually if the temperature is the limiting factor its because the temp is too low - the enzymes needed for photosynthesis work more slowly at low temperatures
• if the plants get too hot, the enzymes it needs for photosynthesis and tis other reactions will be damaged - this happens at about 45 degrees
• graphs show the limiting factors when the graph is a straight line
• you can artificially create the ideal conditions for farming
• the most common way to artificially create the ideal environment for plants, is to grow them in greenhouses
• greenhouses help to trap the sun's heat, and make sure that the temperature is not a limiting factor
• in winter a farmer or gardener might use a heater as well to keep the temperature at the ideal level
• in summer it might get too hot, so they might use shades and ventilation to cool things down
• farmers often supply artificial light after the sun goes down to give their plants more quality photosynthesis time
• farmers can also increase the level of CO2 by using a paraffin heater - as the paraffin heater burns, it makes CO2 as a by-product
• keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases
• farmers can add fertilisers to the soil as well, to provide all the minerals needed for healthy growth
• this equipment can cost a lot of money -n but if the farmer can keep the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested more often and can be sold