Topic 4 - Bioenergetics (photosynthesis) Flashcards
Pages 57 58 59 60
What happens in photosynthesis?
energy is used to change carbon dioxide and water into glucose and oxygen
Where does photosynthesis take place and why?
- In the chloroplasts of green plant cells
- contain pigments like chlorophyl that absorb light
How is energy transferred to the chloroplasts?
from the environment by light
Is photosynthesis exothermic or endothermic?
- endothermic (energy is transferred from the environment)
What is the word equation for photosynthesis?
carbon dioxide + water —light—> glucose and oxygen
What is the balanced symbol equation for photosynthesis?
6CO2 + 6H2O —–> C6H12O6 + 6O2
State the 5 main ways plants use glucose?
1) for respiration
2) making cellulose
3) making amino acids
4) stored as oils or fats
5) stored as starch
Why do plants use glucose for respiration?
- this transfers energy from glucose
- enables the plant to convert the rest of the glucose into other useful substances
Why do plants use glucose to make cellulose?
cellulose makes strong plant cell walls
Why do plants use glucose to make amino acids?
-glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins
Why do plants store glucose as fats and oils?
glucose is turned into lipids for storage in seeds
Why do plants store glucose 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 better for storing than glucose - a cell with lots of glucose would draw in loads of water and swell up
What three factors can limit the rate of photosynthesis?
- intensity of light
- concentration of CO2
- temperature
What is a limiting factor?
a factor that is stopping photosynthesis from happening any faster
What effects what is the limiting factor?
environmental conditions
What is often the limiting factor at night?
light
What is often the limiting factor in the winter?
temperature
What is often the limiting factor in warm and bright conditions?
amount of carbon dioxide
REMEMBER:
all environmental factors have a combined effect on the rate of photosynthesis
What non-environmental factor can effect the rate of photosynthesis?
the amount of chlorophyl in a plant
What can effect the amount of chlorophyl in a plant?
What are the effects of these?
- disease (e.g. infection with tobacco mosaic virus)
- environmental stress (like lack of nutrients)
- chloroplasts become damages and not able to make enough chlorophyl
- rate of photosynthesis is reduced because they can’t absorb as much light
Why is light intensity important to photosynthesis?
light provides the energy needed for photosynthesis
What happens to the rate of photosynthesis as the light intensity is raised?
- the rate of photosynthesis increases steadily - but only up to a certain point
Why will increasing light intensity only increase the rate up to a certain point?
- the rate will no longer increase because either temperature or CO2 level has become the limiting factor, not light
How can you change light intensity in a lab?
by moving a lamp closer or further away from your plant (see required practical)
When you plot a graph with “distance of lamp from the plant”, you get a weird shape. How do you overcome this?
- either measure the light intensity at the plant using a light meter
- or calculate the light intensity
Why does % level of CO2 effect the rate of photosynthesis?
carbon dioxide is one of the raw materials needed for photosynthesis
What effects does increasing levels of CO2 have on the rate of photosynthesis?
- the rate will increase up to a certain point
Why can increasing levels of CO2 only effect the rate up to a certain point?
- the graph will flatten out even if the amount of CO2 continues to increase because CO2 is no longer a limiting factor
If light and CO2 are in plentiful supply, what is likely to be the limiting factor for photosynthesis?
temperature
Why is temperature usually a limiting factor?
- because it is too low
- enzymes needed for photosynthesis work more slowly at lower temperatures (collision theory)
What happens when the plant gets too hot?
enzymes needed for reactions in the plant like photosynthesis become damaged (or denatured)
At what temperature are enzymes in plants usually denatured?
- about 45 degrees C
(this is pretty hot for outdoors, although greenhouses can get that hot if you’re not careful)
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
What can be given off to show the rate of photosynthesis?
Oxygen production
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
What plant may you use in this reaction?
Canadian pondweed (particularly an aquatic plant)
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
The rate at which the plant produces oxygen corresponds to what?
The rate at which its photosynthesising
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
The faster the rate of oxygen production, the faster …
the rate of photosynthesis
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
What are two control variables?
- temperature
- time that the pondweed is allowed to photosynthesise
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
What is the independent variable?
- the distance between the pondweed and the light source (light intensity)
REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis:
What is the dependent variable?
- the volume of oxygen produced
What is the purpose of a greenhouse?
to artificially create the ideal environment for plants to grow
How do greenhouses create the best conditions for plants to grow?
They trap the sun’s heat to make sure temperature doesn’t become the limiting factor
How can the temperature of a greenhouse be prevented from getting too hot or cold?
In the winter- a farmer may use a heater as well to keep the temperature at the ideal level
In the summer- it could get too hot, they might use shades and ventilation to cool hings down
What do commercial farmers often do to control the level of light intensity on their plants?
They often supply artificial light especially after the sun goes down to give their plant more quality photosynthesis time
How can farmers and gardeners increase the level of carbon dioxide in their greenhouse?
They may use a paraffin heater to heat the greenhouse
As the paraffin burns, it makes carbon dioxide as a by-product
What are two other benefits of a greenhouse?
- easier to keep plants free from pests and diseases
- fertilisers can also be added to the soil, to provide all the minerals needed for healthy grown
Why is it important that a farmer supplies their plants with everything in the right amount?
- changing the conditions cost money
- just right conditions will lead to a faster-growing, better crop which can be sold and harvested more often
- supplying the plants with more light or heat than they need would be wasting money
