REVISION NOTES
IGCSE Edexcel Biology
2.5 Nutrition (in Plants)
2.5.1 Understand the process of photosynthesis and its importance in the conversion of light energy to chemical energy
Photosynthesis:
- Endothermic reaction
- Occurs in the chloroplast
- Require energy from sunlight to convert CO2 and H2O into glucose
- By product is oxygen
Importance of photosynthesis:
- Produces glucose
- Uses of glucose:
- Production of starch
- Conversion into lipids
- Conversion into sucrose
- Production of cellulose
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_003_Photosynthesis-Equation-2-1.png)
2.5.2 Know the word equation and the balanced chemical symbol equation for photosynthesis
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_002_Photosynthesis-Equation-1.png)
2.5.3 Understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis
Effect of CO2 concentration:
- The more CO2 present, the faster the rate of photosynthesis
- This trend continues unless another limiting factor is low in supply
Effect of light intensity:
- As light intensity increases, rate of photosynthesis increases
- Increasing intensity increases energy available for photosynthesis
- Light intensity is inversely proportional to distance between light and plant
- This trend continues unless another limiting factor is low in supply
Effect of temperature:
- Towards optimum:
- Increasing temperature increases kinetic energy
- Increases successful collisions between the reactants and enzymes
- Increases the rate of photosynthesis
- Above optimum:
- Enzymes start to denature
- Rate of reaction decreases
- Below optimum:
- Less kinetic energy in enzymes and molecules
- Successful collision rate decreases
- Photosynthesis rate decreases
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_004_Temperature-and-Rate-of-Photosyntesis.png)
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_005_Light-Intensity-and-Rate-of-Photosyntesis.png)
2.5.4 Describe the structure of the leaf and explain how it is adapted for photosynthesis
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_007_Cross-Section-of-Leaf.png)
2.5.5 Understand that plants require mineral ions for growth, and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids
Magnesium
- Absorbed from the soil by root hair cells
- Required to make chlorophyll
- Causes chlorosis
- Veins of leaves start turning yellow
Nitrate
- Absorbed from the soil by root hair cells
- Required to make proteins
- Nitrogenous component of amino acids
Causes leaves to turn yellow and stunted growth
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_008_Mineral-Deficiencies-in-Plants.png)
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_011_Starch-in-Leaf-and-Light.png)
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_012_Starch-in-Leaf-and-Carbon-Dioxide.png)
2.5.6 Practical: investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll
Evolution of oxygen practical:
- Submerge a bundle of shoots of a water plant in a beaker of water under an unturned funnel
- Add a boiling tube with water over the end of the funnel
- Oxygen is produced as a by product of photosynthesis
- The gas bubbles will collect in the boiling tube to displace the water
Evolution of oxygen explanation:
- Demonstrates process of photosynthesis in water plants such as Elodea or Camboba (pondweed)
- Oxygen is a by-product of photosynthesis
- In water, oxygen released is observed as bubbles
- Confirm that the gas collected is oxygen
- A splint previously put out can be inserted into the boiling tube
- In the presence of oxygen, it will light on fire again.
Requirement of light practical:
Method 1:
- Place a plant in the dark for 24 hours to use up the starch storage
- Place another plant under light for 24 hours
- Pluck a leaf from each plant
- Test the leaves of both plants for starch by adding a drop of iodine
Results:
- Iodine solution for the plant in darkness should remain orange/brown
- No sunlight could be absorbed
- Photosynthesis could not occur
- Iodine solution for the plant in sunlight should turn blue/black
- Received enough sunlight to photosynthesize
- Creates glucose that can replace the starch storage
Requirement of CO2 practical:
- Place 2 plants in the dark for 24 hours so that the starch storage gets used up
- Post destarching, cover 1 plant with a plastic bag containing KOH
- KOH absorbs the carbon dioxide in the surrounding environment
- Cover another plant with a plastic bag not containing anything to use as a control
- Place the plants in bright light for 8 hours
- Remove the coverings and test both plants for starch in the following manner:
- Put leaves from the plant in water at 90OC
- Transfer the leaves into hot ethanol for 10 mins
- Dip the leaves in a 90OC water bath again
- Spread the leaves on a white tile
- Add iodine solution to the leaves
- Observe the colour change
Results:
- Leaf surrounded by potassium hydroxide will remain orange/brown
- Photosynthesis should not occur due to the lack of carbon dioxide
- Leaf not surrounded by potassium hydroxide should turn blue/black
- It has all the raw materials required to photosynthesise
Requirement of chlorophyll practical:
- Put a variegated leaf (partially green and white) in water at 95oC
- Transfer the leaf into hot ethanol for 10 mins
- Dip the leaf in 95oC water
- Spread the leaf on a white tile and cover it with iodine solution
Results:
- Areas of the leaf that are white:
- Do not contain chlorophyll
- Remain orange/brown as no photosynthesis can occur
- No starch accumulated
- Areas of the leaf that are green:
- Contain chlorophyll
- Turn blue/black as photosynthesis would occur
- Accumulates starch
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_009.png)
![](https://resource.studiaacademy.com/wp-content/uploads/2023/03/IGED_BIO_TOPIC-7_010_Testing-Leaf-for-Starch.png)