Year 10 Biology Final Exam
Topic 8: Photosynthesis
Adaptations of a leaf for photosynthesis
Characteristics of a leaf to help with photosynthesis
- most leaves are broad, which gives them a big surface area to absorb light
- most leaves are thin so diffusion of gases are short
- the palisade layer of the leaf are closely packed together and contain the most chloroplasts
- this is to absorb more sunlight as it is located at the top of the leaf
- also to trap the sunlight in its tightly packed spaces
- the spongy mesophyll layer has a lot of air spaces to aid gas exchange
- allows carbon dioxide to get to the cells and oxygen to leave by diffusion
- guard cells at the bottom of the leaf can open and close the stomata for gas exchange
Photosynthesis
- an endothermic reaction, the light energy from the environment is transferred
- to the chloroplasts, the energy is used to carbon dioxide and water to glucose
- oxygen is formed as a by-product
- Carbon dioxide + Water → Glucose + Oxygen + Water
- 6CO2 + 6H2O → C6H12O6 + 6O2
Chlorophyll
- the green pigment found in chloroplasts of a leaf
- chlorophyll acts as a catalyst for photosynthesis
- it speeds up the rate of photosynthesis without using itself up
- it exists as a biological catalyst
,The Rate of Photosynthesis
Bubbling Pondweed Practical (6 marker)
- Set up a boiling tube containing 45 cm³ of sodium hydrogen carbonate solution
- Allow the tube to stand for a few minutes
- Shake to disperse any air bubbles that might form
- Cut a piece of the pondweed into 5 cm long at the end uppermost
- Use forceps to place the pondweed in the boiling tube carefully
- Make sure that you don't damage the pondweed or cause the liquid to overflow
- Position the boiling tube under a light source, with distances of 0, 5, 10, 15, 20, 25 cm apart
- Count the number of bubbles emerging from the cut end of the stems in one minute
- Repeat the count and record your results
- Calculate the average number of bubbles produced per second
- Compare the rate of photosynthesis of all your results
- Make sure the temperature, piece of pondweed and concentration of solution is the same
Conclusion
- The greater the distance of the lamp, the less the pondweed will photosynthesize
- This is because of the decrease in light intensity
Independent variable- the variable that is changed
Dependent
Dependent variable- the variable that we are testing for (title) variable
Control variable- the variable that is kept the same
Independent variable
Inverse square law
- the rate of photosynthesis is inversely proportional to the distance from the light source
- the surface area the light shines on increases
- the light energy intensity stays the same
, Factors affecting the rate of photosynthesis
- amount of sunlight shone onto the leaves
- surface area of the leaf
- amount of water absorbed
- amount of chlorophyll present in the plant
- amount of carbon dioxide in the environment
- temperature of the surroundings
Limiting factors for the rate of photosynthesis
- Light intensity
- Carbon dioxide
- Temperature
- As concentration of carbon dioxide / light intensity increases, the rate of
photosynthesis will increase until any of the three above runs out
- As the temperature increases, the rate of photosynthesis increases until the
temperature is too high and denatures the enzymes in the plant, causing the rate of
photosynthesis to decrease
Topic 8: Photosynthesis
Adaptations of a leaf for photosynthesis
Characteristics of a leaf to help with photosynthesis
- most leaves are broad, which gives them a big surface area to absorb light
- most leaves are thin so diffusion of gases are short
- the palisade layer of the leaf are closely packed together and contain the most chloroplasts
- this is to absorb more sunlight as it is located at the top of the leaf
- also to trap the sunlight in its tightly packed spaces
- the spongy mesophyll layer has a lot of air spaces to aid gas exchange
- allows carbon dioxide to get to the cells and oxygen to leave by diffusion
- guard cells at the bottom of the leaf can open and close the stomata for gas exchange
Photosynthesis
- an endothermic reaction, the light energy from the environment is transferred
- to the chloroplasts, the energy is used to carbon dioxide and water to glucose
- oxygen is formed as a by-product
- Carbon dioxide + Water → Glucose + Oxygen + Water
- 6CO2 + 6H2O → C6H12O6 + 6O2
Chlorophyll
- the green pigment found in chloroplasts of a leaf
- chlorophyll acts as a catalyst for photosynthesis
- it speeds up the rate of photosynthesis without using itself up
- it exists as a biological catalyst
,The Rate of Photosynthesis
Bubbling Pondweed Practical (6 marker)
- Set up a boiling tube containing 45 cm³ of sodium hydrogen carbonate solution
- Allow the tube to stand for a few minutes
- Shake to disperse any air bubbles that might form
- Cut a piece of the pondweed into 5 cm long at the end uppermost
- Use forceps to place the pondweed in the boiling tube carefully
- Make sure that you don't damage the pondweed or cause the liquid to overflow
- Position the boiling tube under a light source, with distances of 0, 5, 10, 15, 20, 25 cm apart
- Count the number of bubbles emerging from the cut end of the stems in one minute
- Repeat the count and record your results
- Calculate the average number of bubbles produced per second
- Compare the rate of photosynthesis of all your results
- Make sure the temperature, piece of pondweed and concentration of solution is the same
Conclusion
- The greater the distance of the lamp, the less the pondweed will photosynthesize
- This is because of the decrease in light intensity
Independent variable- the variable that is changed
Dependent
Dependent variable- the variable that we are testing for (title) variable
Control variable- the variable that is kept the same
Independent variable
Inverse square law
- the rate of photosynthesis is inversely proportional to the distance from the light source
- the surface area the light shines on increases
- the light energy intensity stays the same
, Factors affecting the rate of photosynthesis
- amount of sunlight shone onto the leaves
- surface area of the leaf
- amount of water absorbed
- amount of chlorophyll present in the plant
- amount of carbon dioxide in the environment
- temperature of the surroundings
Limiting factors for the rate of photosynthesis
- Light intensity
- Carbon dioxide
- Temperature
- As concentration of carbon dioxide / light intensity increases, the rate of
photosynthesis will increase until any of the three above runs out
- As the temperature increases, the rate of photosynthesis increases until the
temperature is too high and denatures the enzymes in the plant, causing the rate of
photosynthesis to decrease
