Photosynthesis
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of plant cell structure and tissues in a leaf.
What part of the plant carries water to the leaves?
The xylem vessels
What gas do plants take in for photosynthesis?
Carbon dioxide
Where in the plant cell does photosynthesis happen?
In the chloroplasts
What is the main pigment that absorbs light energy for photosynthesis?
Chlorophyll
Topic Explainer Video
Check out these @JoeDoesBiology and @lauradoesbiology videos that explain photosynthesis, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Photosynthesis
What is Photosynthesis?
Photosynthesis is the process by which green plants use sunlight to make their own food (glucose). As light energy is required, this is an endothermic reaction.
Word Equation:
carbon dioxide + water → glucose + oxygen
(in the presence of light and chlorophyll)
Symbol Equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Where the Reactants Come From
- Carbon dioxide (CO₂): Enters the leaf from the air through small pores called stomata via diffusion.
- Water (H₂O): Absorbed from the soil by root hair cells, then transported to the leaves via the xylem.
- Light energy: Absorbed from sunlight by chlorophyll in chloroplasts.
The Role of Chlorophyll
- Chlorophyll is a green pigment found in chloroplasts.
- Most chloroplasts are found in the leaf, mainly in the palisade mesophyll layer.
- It absorbs light energy needed to drive the chemical reactions in photosynthesis.
- Without chlorophyll, plants cannot perform photosynthesis effectively.
What Happens to the Products?
- Glucose (C₆H₁₂O₆):
- Used for respiration to release energy.
- Converted to starch for storage.
- Used to make cellulose for cell walls.
- Used to make amino acids and lipids.
- Oxygen (O₂):
- Some is used in respiration.
- The rest diffuses out of the leaf into the air through the stomata.
Key Terms and Definitions
|
Term |
Definition |
|---|---|
|
Photosynthesis |
Process in which green plants make glucose using light, CO₂ and water. |
|
Chlorophyll |
Green pigment that absorbs light energy. |
|
Stomata |
Small pores in leaves where gas exchange happens. |
|
Xylem |
Tissue that transports water from the roots to the leaves. |
|
Endothermic |
Reactions that require an input of energy. |
No answer provided.
Exam Tips
Remember, photosynthesis can only happen when light energy is available, so look out for experiments done in the dark! Photosynthesis will not be occurring (but respiration still will be).
Make sure you can correctly balance the chemical equation for photosynthesis.
No answer provided.
Practice Question
Describe the process of photosynthesis and explain where the reactants come from. (4 marks)
Model Answer:
- In photosynthesis, carbon dioxide and water are used to make glucose and oxygen (1).
- Carbon dioxide enters the leaf through stomata from the air (1).
- Water is absorbed by the roots and transported to the leaves through the xylem (1).
- Light energy is absorbed by chlorophyll in the chloroplasts, which provides energy for the reaction (1).
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!