Topic 4 - Bioenergetics - Photosynthesis Flashcards
What is the word equation for photosynthesis?
Carbon dioxide + water –> glucose + oxygen
What is the symbol equation for photosynthesis?
6CO2 + 6H2O –> C6H12O6 + 6O2
What is photosynthesis?
- Photosynthesis uses energy to convert carbon dioxide and water into glucose and oxyen.
Where does photosynthesis happen?
- It takes place in chloroplasts in green plant cells. They contain pigments like chlorophyll that absorb light.
What type of reaction is photosynthesis?
- Endothermic - energy is transferred from the surroundings in the process.
How are leaves adapted for photosynthesis?
- Large surface area for light to fall onto
- Thin so diffusion distances are short for gases
- They contain chlorophyll in the choloroplasts to absorb light
- They have guard cells that open and close the stomata to regulate gas exchange
- They have veins that bring plenty of water in xylem to the cells of the leaves and remove the products of photosynthesis in the phloem
What are the five main ways glucose is used in plants?
- For respiration
- For making cellulose
- For making amino acids
- To be stored as oils or fats
- To be stored as starch
What is the glucose use for respiration?
- Respiration transfers energy from glucose which enables the plans to convert the rest of the glucose into other useful substances.
What is the use of glucose for making cellulose?
- Glucose is converted into cellulose for making strong plant cell walls.
What is the use of glucose for making amino acids?
- Glucose is combined with nitrate ions from the soil to make amino acids.
- Amino acids are then turned into proteins for growth.
What is the use of glucose for being stored as oils or fats?
- Glucose is turned into lipids for storing in seeds.
What is the use of glucose for being stored as starch?
- Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn’t happening like in the winter.
- Starch is insoluble, which makes it much better for storing than glucose.
- A cell with lots of glucose in it would take in lots of water and swell up.
What are the three limiting factors of photosynthesis?
- Carbon dioxide concentration
- Light intensity
- Temperature
What does limiting factor of photosynthesis mean?
- Any of these three factors can be the limiting factor - this just means it is stopping photosynthesis from happening any faster
- These factors have a combined effect on the rate of photosynthesis, but which factor is limiting at a particular time depends on environmental conditions
- E.g. at night, light is the limiting factor. In the winter, temperature if often the limiting actor. If it is warm and bright, CO2 is usually limiting
How can chlorophyll be a limiting factor of photosyntehsis?
- The amount of chlorophyll in a plant can be affected by disease or environmental stress such as lack of nutrients
- These factors can cause chloroplasts to become damaged or not make enough chlorophyll
- This means the rate of photosynthesis is reduced because they cant absorb as much light
How does light affect photosynthesis?
- Not enough light slows down the rate of photosynthesis
- As the light level is raised, the rate of photosynthesis increases steadily, but only up to a certain point
- Beyond that it wont make any difference, as light increases the rate of photosynthesis no longer increases
- This is because it is either temperature or CO2 levl which is now the limiting factor
How does carbon dioxide affect photosynthesis?
- Too little CO2 slows down the rate of photosynthesis
- As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a point
- After this, the graph flattens out - as CO2 increases, the rate of photosynthesis no longer increases
- This shows that CO2 is no longer the limiting factor - as long as light and CO2 are in plentiful supply then the factor limiting photosynthesis must be temperature
How does temperature affect photosynthesis?
- The temperature has to be just right
- If it is too cold, the enzymes work more slowly. If it is too hot, the enzymes are denatured
- This happens at about 45 degrees celcius
Photosynthesis practical?
- Place a source of white light a specific distance from the pondweed
- Leave the pondweed to photosynthesise for a set amount of time. The oxygen released will collect in the capillary tube
- At the end of the experiment, use the syringe to draw the gas buble in the tube up alongside the ruler and measure the length of the gas bubble. This is proportional to the volume of oxygen produced
- Repeat the experiment with the light source at different distances from the pondweed
- Repeat the experiment at each distance twice to calculate a mean volume of oxygen
- Keep the temperature and time allocated for pondweed to photosynthesise the same
- Repeat the experiment at each distance twice to calculate a mean volume of oxygen
What is the inverse square law?
Light intensity is proportional to 1 / distance squared
What is the unit for light intensity?
Arbitrary units
Function of a greenhouse?
The most common way to artificially create the ideal environment for plants to grow
What do greenhouses do?
- Greenhouses help to trap the suns heat
- This is to make sure the temperature doesn’t become a limiting factor
What is the purpose of a paraffin heater?
- As a paraffin heater burns, it makes carbon dioxide as a waste product
- This is used to increase the level of carbon dioxide in the greenhouse
