B1.4 Flashcards
What is photosynthesis?
The process of making glucose from sunlight in the leaves of the plant.
Is photosynthesis endothermic or exothermic?
Endothermic — it requires energy input from the environment.
Where does the energy for photosynthesis come from?
From light, which is transferred to the chloroplasts.
In which part of the plant does photosynthesis take place?
In the leaves, specifically within chloroplasts.
What is the word equation for photosynthesis?
Carbon dioxide + Water → Glucose + Oxygen (in the presence of light)
What is the symbol equation for photosynthesis?
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
What is the chemical formula for: Carbon dioxide?
CO₂
What is the chemical formula for: Water?
H₂O
What is the chemical formula for: Glucose?
C₆H₁₂O₆
What is the chemical formula for: Oxygen?
O₂
How can you measure the rate of photosynthesis in a lab experiment?
By measuring the oxygen production of a plant, e.g. pondweed.
What plant is commonly used to investigate photosynthesis?
Pondweed
What equipment is used in the practical to measure oxygen production?
A test tube full of water, a bung, a capillary tube connected to a syringe.
What is the role of the capillary tube and syringe?
The capillary tube collects the gas (oxygen); the syringe allows control of water movement
What is used as the light source for photosynthesis?
A lamp placed at a measured distance from the test tube.
How is oxygen production measured?
By measuring the distance a gas bubble moves using a ruler.
What are examples of variables that can be changed in the pondweed experiment?
• Temperature (controlled using a water bath)
• Light intensity (by varying the lamp distance)
• Time the pondweed is left
Why is it important to control all variables except the independent variable?
To ensure a valid experiment — only the independent variable should affect the result.
What is the independent variable in the pondweed experiment?
The one factor you are changing to observe its effect (e.g. light intensity).
How does temperature affect the rate of photosynthesis?
As temperature increases, the rate increases — up to a certain point.
Why does the rate of photosynthesis decrease at high temperatures?
Enzymes controlling the reaction begin to denature, causing the rate to fall.
How does light intensity affect photosynthesis?
The rate of photosynthesis increases with light intensity.
What experiment proves photosynthesis requires light?
- Cover half of a small leaf with foil.
- Place plant on windowsill for 48 hours.
- Boil the leaf to kill it.
- Place in hot ethanol for 10 minutes to remove chlorophyll.
- Dip back in boiling water to soften.
- Cover with iodine solution in a Petri dish.
What is the result of the light-required experiment?
• Foil-covered half remains brown.
• Exposed half turns blue-black (starch present).
What happens to light intensity as distance increases?
It decreases.
What is the relationship between light intensity and distance?
Light intensity is inversely proportional to the square of the distance.
What is the inverse square law formula?
Light intensity ∝ 1 ÷ distance²
How does carbon dioxide concentration affect photosynthesis?
As CO₂ concentration increases, the rate of photosynthesis increases.
What is a limiting factor in photosynthesis?
An environmental condition that restricts the rate of photosynthesis when in short supply.
How can farmers use knowledge of limiting factors?
To improve conditions in greenhouses and maximise photosynthesis for better crop growth and higher profits.
What does the graph for effect of light intensity on photosynthesis look like?
Steady curved increase starting from 0 but after a certain point it levels off flat - photosynthesis reaches its maximum rate
What does the graph for effect of carbon dioxide on photosynthesis look like?
Steady curve increasing starting from 0 but after a certain point it levels off flat
What does the graph for effect of temperature on photosynthesis look like?
Increase not starting from 0 up to a peak but sudden drop after optimum temperature - enzymes denatured
