2. Photosynthesis Flashcards
Reason for boiling the leaf in water ;
This kills the leaf by stopping all chemical reactions
Boiling the leaf in ethanol
This removes the green pigment from the leaf so any colour change can be seen clearly
Leaf dipped in water
Placing the leaf in alcohol results in the leaf becoming brittle - this softens the leaf again
Iodine added
Iodine detects starch. If starch is present with the iodine will change from yellow / brown to blue / black
Describe the three ways that food can be used in photosynthesis
- conversion into other useful substances like cellulose (for cell walls), chlorophyll and protein for growth
- storage - in many plants glucose is converted into oils and starch for storage
- respiration to release energy for cellular processes
When the processes balance, this is called ;
The compensation point when there is no net gas exchange
If temperature was very low describe what would happen to the rate of photosynthesis
The rate would be low because the molecules have less kinetic energy and therefore collide less frequently
Factors affecting the rate of photosynthesis
Carbon dioxide concentration
Light intensity
Temperature
Affecting photosynthesis - carbon dioxide
The greater the concentration of CO2 the faster the rate will be. The more CO2 present in the atmosphere, the more sugar can be made
Affecting photosynthesis - light
The more light there is the faster the rate will be. In low light conditions not enough energy is supplied to the reactant molecules to allow them to react.
Affecting photosynthesis - temperature
The rate will increase with temperature. The higher temperatures increase the kinetic energy of the reacting molecules. This is only true up to a certain point which the enzymes in the leaf will become denatured
Which indicator is used to monitor carbon dioxide concentrations ?
Bicarbonate indicator
Colour change : decreased carbon dioxide causes the indicator to turn …
Purple
Normal carbon dioxide concentration of the air (0.04%) the indicator is ..
Red/orange
Increased carbon dioxide levels cause the indicator to turn ….
Yellow
Which plant can be used to prove the production of oxygen?
Canadian Pondweed (Elodea)
When there is bright light and photosynthesis and respiration are occurring, the indicator is …
Purple
Excess oxygen will diffuse out of the leaves through the …
Stomata
Use of glucose for growth
Can be converted into protein for growth
Cellulose for cell walls
Chlorophyll
A movement of carbon dioxide into and out of plants can be determined using
A hydrogen carbonate indicator
In normal atmosphere carbon dioxide levels are
Red
Increased carbonate dioxide levels turn the indicator
Yellow
Decreased carbon dioxide levels turn the indicator
Purple
What’s the nemonic word for the indicator colours?
M Y R E D L I P
How is a leaf adapted for photosynthesis ? (6)
- The cuticle is the waxy transparent layer that reduces evaporation but allows light through to photosynthesising cells
- the palisade mesophyll layer contains closely compacted cells, which therefore can absorb the maximum amount of light
- Guard cells surround the stoma and control the size of the stomata in order to reduce water loss
- spongy mesophyll have a large surface area and intercellular spaces, which allow diffusion of gases through the leaf
- the leaf itself is thin and flat with a large surface area which allows for easy diffusion
- The short distance between the upper and lower surfaces which allows all the cells to receive light
Chemical equation for photosynthesis
6CO2 + 6H2O —> C6H12O6 + 6O2
What is a heat shield?
When you place an outside source around a substance to reflect, absorb or dissipate the heat. It is used in experiments to ensure that the heat produced by the light onto the water does not affect the results as well as the light intensity which would cause inaccurate results
How would you change the CO2 concentration?
- Add sodium hydrogen carbonate to increase CO2
- Add soda lime to absorb CO2
What type of reaction is photosynthesis and why?
Endothermic as it absorbs energy (light energy) from its surroundings
Why must the test for starch in a leaf be carried out in a water bath?
Ethanol is flammable and must not be exposed to direct flame
Importance of destarching
- This will ensure that any starch already in the leaves will either be used by the plant cells or removed and stored elsewhere in the plant
- If the starch test at the end of the experiment is positive, it shows that starch has been produced during the period of the experiment
What chemical will absorb carbon dioxide from the air surrounding the leaf ?
Sodium hydroxide
Why is it important for farmers to understand limiting factors ? (3)
- For photosynthesis to take placed at its maximum rate, all of these environmental factors must be present at optimum levels
- If one or more factor is in short supply, the rate of photosynthesis will be limited
- Farmers need to understand how photosynthesis affects their crops as reducing the effects of limiting factors will increase the growth of a crop
How is gas exchange maximised in a leaf ?(3)
- Intercellular air spaces in the spongy mesophyll which allow carbon dioxide to enter and oxygen to leave the photosynthesising cells
- Stomata allow CO2 and oxygen to enter and leave the leaf
- Each stoma is surrounded by two guard cells that regulate the opening and closing of the stoma
