Edexcel GCSE 9-1 Biology Topic 6-
Plant Structures and their Functions
Exam Questions With Assured
Answers
Photosynthesis - ANSPhotosynthetic organisms such as green plants and algae use energy from the
sun to make glucose.
Some of the glucose is used to make large complex molecules the plants or algae need to grow.
These make up the organisms biomass or living material.
The energy stored in the biomass then works its way through the food chain as animals eat them and
each other. So photosynthetic organisms are the main producers of food and life.
Photosynthesis Equation - ANSPhotosynthesis occurs inside chloroplasts which contain chlorophyll to
absorb light.
Carbon Dioxide + Water -(light and chlorophyll)--> Glucose + Oxygen
6CO2 + 6H20 --> C6H12O6 + 6O2
This is an endothermic reaction meaning energy is taken into the cell.
The rate of photosynthesis is affected by the light intensity, the concentration of CO2 and the
temperatures. Any of these 3 factors can become a limiting factor. This stops photosynthesis from
happening faster.
CORE PRACTICAL
Light Intensity and the Rate of Photosynthesis - ANSPondweed can be used to measure the effect of
light intensity on the rate of photosynthesis. The rate at which the pondweed produces oxygen
corresponds to the rate at which photosynthesis is happening:
The faster the rate of oxygen production, the faster the rate of photosynthesis.
, Method:
1)The apparatus is set up according to the image. The gas syringe should be empty to start with.
Sodium hydrogencarbonate may be added to the water to make sure the plant has enough carbon
dioxide as sodium hydrogencarbonate releases carbon dioxide in solution.
2)A source of white light is placed at a measured distance from the pondweed.
3)Leave to photosynthesise for a set amount of time.
4)As it photosynthesises, the pondweed releases oxygen which is collected in a gas syringe which
allows you to accurately measure the volume of oxygen produced. 5)The whole experiment is
repeated at different distances from the pondweed. The rate of oxygen production at each distance
can then be calculated.
6)For this experiment, any variable that could affect the results should be controlled. e.g. the
temperature (conical flask/ test tube in a water bath) and the carbon dioxide (a set amount of
hydrogencarbonate to a set volume of water)
Notes: This experiment can also be used as a test for the affects of temperature and carbon dioxide.
Have a control test tube, covered in foil to make sure the experiment is occurring correctly.
What if I added a pH indicator to the core practical? - ANSThe further from the light source the test
tube gets, the more acidic the solution gets as there is more CO2 that is released compared to the
amount of oxygen.
Distance cm Colour at end pH at Start pH at End 0 Purple 8.4 9.0
20 Magenta 8.4 8.8 40 Red 8.4 8.6
60 Orange 8.4 8.4
80 Yellow 8.4 8.2
The further away the pondweed from the light source, the less oxygen was produced showing a
negative correlation.
Limiting Factors for Photosynthesis
Light Intensity - ANSLight transfers the energy needed for photosynthesis.
At first, as the light level is raised, the rate of photosynthesis increases steadily (the rate is directly
proportional to light intensity).
Plant Structures and their Functions
Exam Questions With Assured
Answers
Photosynthesis - ANSPhotosynthetic organisms such as green plants and algae use energy from the
sun to make glucose.
Some of the glucose is used to make large complex molecules the plants or algae need to grow.
These make up the organisms biomass or living material.
The energy stored in the biomass then works its way through the food chain as animals eat them and
each other. So photosynthetic organisms are the main producers of food and life.
Photosynthesis Equation - ANSPhotosynthesis occurs inside chloroplasts which contain chlorophyll to
absorb light.
Carbon Dioxide + Water -(light and chlorophyll)--> Glucose + Oxygen
6CO2 + 6H20 --> C6H12O6 + 6O2
This is an endothermic reaction meaning energy is taken into the cell.
The rate of photosynthesis is affected by the light intensity, the concentration of CO2 and the
temperatures. Any of these 3 factors can become a limiting factor. This stops photosynthesis from
happening faster.
CORE PRACTICAL
Light Intensity and the Rate of Photosynthesis - ANSPondweed can be used to measure the effect of
light intensity on the rate of photosynthesis. The rate at which the pondweed produces oxygen
corresponds to the rate at which photosynthesis is happening:
The faster the rate of oxygen production, the faster the rate of photosynthesis.
, Method:
1)The apparatus is set up according to the image. The gas syringe should be empty to start with.
Sodium hydrogencarbonate may be added to the water to make sure the plant has enough carbon
dioxide as sodium hydrogencarbonate releases carbon dioxide in solution.
2)A source of white light is placed at a measured distance from the pondweed.
3)Leave to photosynthesise for a set amount of time.
4)As it photosynthesises, the pondweed releases oxygen which is collected in a gas syringe which
allows you to accurately measure the volume of oxygen produced. 5)The whole experiment is
repeated at different distances from the pondweed. The rate of oxygen production at each distance
can then be calculated.
6)For this experiment, any variable that could affect the results should be controlled. e.g. the
temperature (conical flask/ test tube in a water bath) and the carbon dioxide (a set amount of
hydrogencarbonate to a set volume of water)
Notes: This experiment can also be used as a test for the affects of temperature and carbon dioxide.
Have a control test tube, covered in foil to make sure the experiment is occurring correctly.
What if I added a pH indicator to the core practical? - ANSThe further from the light source the test
tube gets, the more acidic the solution gets as there is more CO2 that is released compared to the
amount of oxygen.
Distance cm Colour at end pH at Start pH at End 0 Purple 8.4 9.0
20 Magenta 8.4 8.8 40 Red 8.4 8.6
60 Orange 8.4 8.4
80 Yellow 8.4 8.2
The further away the pondweed from the light source, the less oxygen was produced showing a
negative correlation.
Limiting Factors for Photosynthesis
Light Intensity - ANSLight transfers the energy needed for photosynthesis.
At first, as the light level is raised, the rate of photosynthesis increases steadily (the rate is directly
proportional to light intensity).
