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, AQA GCSE Biology notes Topic 4 - Bioenergetics
4.1 Photosynthesis
4.1.1 Photosynthetic reaction
Photosynthesis
• An endothermic reaction in which energy comes from sunlight is transferred from environment to
the chloroplasts by light
Equation
Adaptations of leaves
1. Large surface area - absorb light
2. Thin walls - short diffusion distance
3. Chlorophyll in chloroplasts - absorb light
4. Veins - transport water in xylem & glucose in phloem
5. Air spaces - CO2 in, O2 out by diffusion
Uses of glucose
1. Respiration - release energy
2. Produce amino acid - make protein
3. Produce cellulose - strengthen cell wall
4. Store as lipids in seeds
5. Store as insoluble starch in root, stem & leaves
How do plants make proteins?
• Amino acids made from glucose and plants combine these with nitrate ions absorbed from the soil
to make proteins.
4.1.2 Rate of photosynthesis
What will affect rate of photosynthesis? (limiting factors)
Light intensity • ↑light, ↑rate
CO2 concentration • ↑CO2, ↑rate
• Rate stays constant at 200 arbitrary units
2
, AQA GCSE Biology notes Topic 4 - Bioenergetics
Temperature • Reaction controlled by enzymes
• ↑CO2, ↑rate coz molecules moves faster,
↑chemical reaction
• If too high (45℃), enzymes denatured, ↓rate
Amount of chlorophyll • Light absorption
Greenhouse
• Increase light, temp, CO2 - increase crop yield
• Gain max rate of photosynthesis while maintaining profit
Light intensity ∝ 1/d2
How can you measure the rate of photosynthesis?
• Place the plant underwater and measure the volume of oxygen made or count the number of
bubbles in a given time. The more gas made, the faster the rate of photosynthesis.
How can you test if a plant for starch?
• Boil in ethanol to destroy waxy cuticle and remove the colour. Then add iodine to the leaf. If the
iodine turns blue it contains starch
Investigate pop size of plant species using random sampling with quadrats
1. Place two 20m tape measure (labelled X & Y) at right angles to each other to form a square area
2. Use a random number generator and pick 2 numbers as a coordinate.
3. Place quadrat on ground at the co-ordinates
4. Count & record all no of plants you are investigating inside quadrat
5. Repeat 1-4 for 10 times
6. Calculate mean no of organisms per quadrat
7. Estimate pop of species using
Distribution
• Place randomly
• At random no
Investigate effect of light intensity on plant distribution using transect line
1. Stretch tape measure to mark out a line (transect) in area you want to study
2. Place quadrat at exactly 2m on tape measure (to get data about position of organism in relation to
distance from sea)
3. Count & record all no of plants you are investigating inside quadrat
4. Use light meter to measure light intensity at the position
5. Repeat 1-5 for more than 3 times
3
, AQA GCSE Biology notes Topic 4 - Bioenergetics
How to improve accuracy?
• Repeat experiment in different area randomly in the same field
4.1.3 Uses of glucose from photosynthesis
The glucose produced in photosynthesis may be
• used for respiration
• converted into insoluble starch for storage
• used to produce fat or oil for storage
• used to produce cellulose - strengthens the cell wall
• used to produce amino acids - protein synthesis
To produce proteins, plants also use nitrate ions that are absorbed from the soil
4.2 Respiration
4.2.1 Aerobic and anaerobic respiration
4
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