Chapter 8

• What is photosynthesis?


  Photosynthesis is the process that plants use to make glucose. It uses energy to change carbon dioxide and water into glucose and oxygen
• Where does photosynthesis happen?


  Photosynthesis happens in the chloroplasts in green plant cells-they contain pigments like chlorophyll that absorb light. Energy is transferred to the chloroplasts from the environment by light. It is endothermic
• What is the word equation for photosynthesis?

  Carbon dioxide + water -> glucose + oxygen
• What is the symbol equation for photosynthesis?

  
• What are the leaf adaptations?


  -most leaves are broad, giving them a big surface area for light to fall on

  -most leaves are thin so the diffusion distance for gases is short

  -they contain chlorophyll in the chloroplasts to absorb light energy

  -they have veins, which bring plenty of water in the xylem, to the cells of the leaves and remove the products of photosynthesis in the phloem

  -they have air spaces to allow carbon dioxide to get to the cells and for oxygen to leave by diffusion

  -they have guard cells that open and close the stomata to regulate gas exchange.
• Why is glucose used for respiration?


  Respiration is where energy is released from the breakdown if glucose. Plants use this energy to convert the rest of the glucose into various other useful substances , which they can use to build new cells and grow
• Why is glucose used for making cellulose


  Glucose is converted into cellulose for making strong cell walls especially in a rapidly growing plant. These cell walls support and strengthen the cells
• Why is glucose used for making amino acids?


  In plant cells, glucose is combined with nitrate ions to make amino acids. Amino acids are the building blocks for making up proteins. When they are joined together in a particular sequence they make up a particular protein
• How can glucose be stored?


  Lipids- Plants can convert some of the glucose they produce into lipids. Plants store lipids in seeds

  Starch- Plants can convert glucose into starch. Glucose is stored as starch so it's ready for use when photosynthesis isn't happening as much. Starch is stored in the roots, stems, seeds and leaves
• What is a limiting factor?

  The rate of photosynthesis is affected by the intensity of light, the volume of carbon dioxide and the temperature. All of these factors need to be at the right level to allow a plant to photosynthesise ad quickly as possible.

  If one of these factors is too low or high, it will become a limiting factor. This means it's the factor that is stopping photosynthesis from happening faster.
• How does light intensity affect the rate of 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- as light intensity increases, the rate will no longer increase. This is because it'll be either the temperature or the carbon dioxide level which is now the limiting factor, not light

  
• How does the carbon dioxide level affect photosynthesis?

  As with light intensity, the amount of carbon dioxide will only increase 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 carbon dioxide is no longer the limiting factor

  
• How does temperature affect photosynthesis?

  Enzymes are proteins which increase the speed of chemical reactions in living things- so enzymes increase the rate of photosynthesis in plant cells. The speed at which enzymes work is affected by temperature

  
  

  Usually, if temperature is the limiting factor in photosynthesis, it's because it's too low. But if plants get too hot, the enzymes it needs for photosynthesis will get damaged, this generally happens at 45 degrees celcius

  
• How does chlorophyll affect photosynthesis?


  If a plant doesn't get enough sunlight, it cannot make chlorophyll. If a plant doesn't get enough chlorophyll, its rate of photosynthesis will drop, and the plant will eventually die
• How would you investigate the affect of light intensity on photosynthesis?


  -To investigate the effect of different light intensities on the rate of photosynthesis, you need to be able to measure the rate. One way to do this, is using an aquatic plant. The rate at which it produces oxygen corresponds to the rate at which it's photosynthesising- the faster the rate of oxygen production, the faster the rate of photosynthesis

  
• Describe the method for investigating the affect of light intensity on photosynthesis


  -A source of white light is placed at a specific distance from the pondweed.

  -Leave it for a couple of minutes to adjust to the new light intensity before starting the experiment

  -to start, the pondweed is left to photosynthesise for a set amount of time. The oxygen it releases will collect in the capillary tube

  -At the end, the syringe is used to draw the gas bubble in the tube alongside a ruler, and the length of the gas bubble is measured

  -Repeat this at different distances away from the light source

  
• What are the controlling variables in this experiment?

  independent variable- light intensity

  dependant variable- amount of oxygen produced
• How do you calculate the rate of photosynthesis?

  divide the total length of the bubble by the time taken to produce it
• What is the inverse square law?

  The inverse square law means that if you have the distance, the light intensity will be four times greater and if you third the distance the light intensity will be nine times greater and if you double the distance the light intensity will be four times smaller

  
• How can you grow plants in a greenhouse?

  -clear glass to maximise the light available

  -ventilation vents to allow the plants to access carbon dioxide

  -removable netting or whitewash to reduce the intense sunlight of summer

  -electric lighting to provide light for the plants during winter or at night

  -automatic watering system to supply the correct amount of water for photosynthesis

  -gravel under plants to allow drainage of water out of pots

  -paraffin heater increases the temperature and gives out carbon dioxide