Photosynthesis Flashcards
Where does photosynthesis happen?
Inside chloroplasts, found in leaf cells. Chloroplasts contain chlorophyll which absorbs sunlight and converts this light energy into chemical energy. This chemical energy is released when glucose is broken down during respiration
What is the word equation for photosynthesis?
Carbon dioxide + water -> glucose + oxygen
(Above the arrow there is light and chlorophyll)
What is the chemical equation for photosynthesis?
6CO2 + 6H20 -> C6H12O6 + 6O2
What are limiting factors for photosynthesis?
Something which stops photosynthesis from happening any faster. This can be light intensity, CO2 concentration and temperature
How does light intensity (or carbon dioxide) affect the rate of photosynthesis?
If light intensity is increased, then the rate of photosynthesis will increase steadily until a certain point when light intensity is no longer the limiting factor.
How does temperature affect the rate of photosynthesis?
As temperature increases, so does the rate of photosynthesis to a point. If the temperature is too high (over around 45°C), the plant’s enzymes will be denatured, so the rate of photosynthesis rapidly decreases.
How are leaves adapted for photosynthesis?
- leaves are broad, large SA exposed to light
- most chloroplasts found in the palisade layer, close to the top of the leaf where they can get the most light
- upper epidermis is transparent so light can pass through to the palisade layer
- network of vascular bundles deliver water and nutrients to the leaf and remove glucose produced
- waxy cuticle reduces water loss by evaporation
- lower surface full of stomata, lets CO2 diffuse directly into the leaf
- spongy mesophyll contain air spaces for diffusion of oxygen and CO2
What is photosynthesis?
The process of plant producing food - glucose
Testing that photosynthesis is happening by testing for starch - glucose is stored in plants as starch
- Place the leaf in boiling water (hold with forceps) – stops and chemical reactions happening inside the leaf
- Place leaf in a boiling tube with some ethanol and heat in a water bath until it boils – gets rid of any
chlorophyll (makes the leaf a white ish colour) - Rinse the leaf in cold water and add a few drops of iodine solution – if starch is present the leaf will turn a blue-black colour
This test shows whether photosynthesis is taking place
Testing for chlorophyll
You can show that chlorophyll is needed for photosynthesis using variegated (green and white) leaves.
Chlorophyll
1. Take a variegated leaf from a plant that’s been exposed to light. Record which bits are green and which parts are not
2. Test the leaf for starch, and the parts of the leaf that were green should turn blue-black
3. This suggests that only parts of the leaf that contained chlorophyll are able to photosynthesise and produce starch
Testing that CO2 is needed for photosynthesis
CO2
1. The soda lime will absorb CO2 out of the air in the jar
2. If you leave the plant in the jar for a while, then test for starch, it won’t turn blue-black
3. This shows that no starch has been produced in the leaf, which means that CO2 is needed for photosynthesis
Testing that light is needed for photosynthesis
Light
1. Take a plant that has been grown without any light (in a cupboard for 48 hours) – it will have used up its starch stores
2. Cut a leaf from the plant and test for starch using iodine solution – the leaf shouldn’t turn blue-black
3. This shows that light is needed for photosynthesis, as no starch has been made
Investigating effect of light intensity on the rate of photosynthesis
Oxygen production shows the rate of photosynthesis
Canadian pondweed is used to measure the effect of light intensity on the rate of photosynthesis
- The gas syringe should be empty to start with. Sodium hydrogen-carbonate may be added to the water to make sure the plant has enough carbon dioxide (releases CO2 in solution)
- A source of white light is placed at a specific distance from the pondweed
- The pondweed is left to synthesise for a set amount of time. The oxygen produced by photosynthesis will collect in the capillary tube
- At the end, the syringe is used to draw the
gas bubbles in the tube up alongside a
ruler and the length of the gas bubble is measured. This is proportional to the volume of O2 produced - Any variables that could affect the results should be controlled
- This test is repeated with the light source placed at different distances from the pondweed
What is the glucose from photosynthesis used for?
- Converted into starch
- Cellulose for cell walls
- Proteins for growth
- Sucrose, stored in fruits
- Sugar in respiration
(Oils for storage in seeds)
What are nitrate and magnesium ions needed for?
Plants use nitrates as a supply of nitrogen, which is needed to make amino acids to make proteins for healthy growth. Plants absorb nitrates in water through their roots. Nitrates are present in high levels in plant fertilisers.
Plants use magnesium ions to make chlorophyll in their leaves.
