Photosynthesis and Respiration Experiments
Topic 7 — Photosynthesis and Respiration Experiments
1. Photosynthesis
Definition
Photosynthesis is the process by which plants make glucose using:
-
carbon dioxide
-
water
-
light energy
-
chlorophyll
2. Photosynthesis Equation
carbon dioxide + water → glucose + oxygen
(light and chlorophyll required)
3. Common ATP Photosynthesis Experiments
Frequently Tested
-
starch test on leaves
-
oxygen bubble counting
-
pondweed experiments
-
limiting factor investigations
-
hydrogencarbonate indicator experiments
Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.
4. Starch Test on Leaves
Purpose
To test whether photosynthesis occurred.
5. Starch Test Method
Step 1
Boil leaf in water
Purpose:
kills leaf / stops reactions
Step 2
Boil leaf in ethanol
Purpose:
remove chlorophyll
Leaf becomes pale.
Step 3
Wash leaf in warm water
Purpose:
softens leaf
Step 4
Add iodine solution
6. Starch Test Results
Positive Result
blue-black
(starch present)
Negative Result
yellow-brown
(no starch)
7. Common ATP Questions on Starch Test
Why Remove Chlorophyll?
To see colour change clearly.
Why Use Water Bath with Ethanol?
Ethanol is flammable.
Why Boil in Water First?
Stops enzyme reactions.
8. Limiting Factors of Photosynthesis
Factors
-
light intensity
-
carbon dioxide concentration
-
temperature
9. Effect of Light Intensity
More light →
more photosynthesis
Until another factor becomes limiting.
10. Pondweed Experiments
Used to estimate photosynthesis rate.
Measured By
-
counting oxygen bubbles
-
gas volume produced
11. Common Variables in Pondweed Experiments
Independent Variable
-
light intensity
-
distance from lamp
-
temperature
Dependent Variable
-
bubble count
-
oxygen volume
Controlled Variables
-
plant size
-
time
-
carbon dioxide concentration
-
temperature
12. Distance from Lamp Experiments
Closer lamp →
higher light intensity →
more photosynthesis
Further lamp →
lower photosynthesis
13. Common Sources of Error
-
bubble size differs
-
counting mistakes
-
lamp heats water
-
unequal pondweed size
14. Improvements
-
use gas syringe instead of bubble counting
-
use water bath
-
repeat readings
-
use same pondweed length
Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.
15. Hydrogencarbonate Indicator
Used to detect carbon dioxide levels.
16. Indicator Colours
| Colour | Carbon Dioxide Level |
|---|---|
| Purple | low CO₂ |
| Red/orange | atmospheric CO₂ |
| Yellow | high CO₂ |
17. Respiration
Definition
Respiration is the chemical process that releases energy from glucose.
18. Aerobic Respiration
Requires
oxygen
Equation
glucose + oxygen → carbon dioxide + water + energy
19. Anaerobic Respiration
In Plants and Yeast
glucose → ethanol + carbon dioxide + energy
In Humans
glucose → lactic acid + energy
20. Common ATP Respiration Experiments
Frequently Tested
-
germinating seeds
-
yeast respiration
-
temperature effect
-
limewater test
-
respirometer investigations
21. Germinating Seed Experiments
Why Germinating Seeds?
Actively respiring.
Dead seeds often used as control.
22. Limewater Test
Positive Result
limewater turns milky/cloudy
Shows:
carbon dioxide present
23. Yeast Respiration Experiments
Usually involve:
-
sugar solution
-
yeast
-
warm temperature
24. Why Warm Temperature Used?
Increases enzyme activity in yeast.
Too high temperature:
yeast enzymes denature
25. Why Oil Layer Sometimes Added?
Prevents oxygen entering.
Ensures anaerobic respiration.
Very common examiner point.
Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.
26. Respirometers
Used to measure:
respiration rate
Usually by:
oxygen uptake
27. Variables in Respiration Experiments
Independent Variables
-
temperature
-
sugar concentration
-
oxygen availability
Dependent Variables
-
gas volume
-
bubble movement
-
carbon dioxide production
28. Common ATP Graph Trends
Photosynthesis
increase to plateau
Respiration
higher temperature →
faster respiration
until enzymes denature
29. ATP Comparison Questions
Photosynthesis vs Respiration
| Photosynthesis | Respiration |
|---|---|
| requires light | occurs all the time |
| stores energy | releases energy |
| produces oxygen | uses oxygen |
30. ATP Conclusions
Strong Conclusion
“As light intensity increased, photosynthesis rate increased because more light energy was available.”
Weak Conclusion
“Light affected photosynthesis.”
31. Common Examiner Complaints
-
forgetting control setup
-
confusing photosynthesis and respiration
-
not mentioning chlorophyll
-
vague graph descriptions
-
incorrect starch test order
-
forgetting ethanol is flammable
32. ATP Frequently Tested Skills
Candidates may need to:
-
complete results tables
-
draw graphs
-
interpret trends
-
explain colour changes
-
identify variables
-
suggest controls
-
calculate rates
-
explain improvements
33. Quick ATP Summary Table
| Test | Positive Result |
|---|---|
| Iodine test | Blue-black |
| Limewater | Milky/cloudy |
| Hydrogencarbonate indicator | Yellow = high CO₂ |
Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.