B4 - Bioenergetics Flashcards
What is the source of energy for plants?
What is the name of reaction used by plants to trap this energy?
Is this reaction endothermic or exothermic?
Light from the sun is used in the reaction called photosynthesis which is an endothermic reaction as energy is taken in from the surroundings.
Where does Photosynthesis take place and why?
Photosynthesis takes place in the leaves of a plant as they contain the green chemical chlorophyll.
What does Chlorophyll do ?
The light energy required is absorbed by a green pigment called chlorophyll in the leaves. Chlorophyll is located in chloroplasts in plant cells, particularly the palisade and spongy mesophyll cells.
What is the word equation for Photosynthesis?
What is the symbol equation for Photosynthesis?
Where do the Reactants for photosynthesis come from?
What are the products of photosynthesis used for?
What are the factors that affect the rate of photosynthesis?
- light intensity
- carbon dioxide concentration
- temperature
- The amount of chlorophyll also affects the rate of photosynthesis:
How can you measure the rate of photosynthesis?
There are several ways of measuring the rate of photosynthesis in the lab. These include:
- the rate of oxygen output
- the rate of carbon dioxide uptake
- the rate of carbohydrate production
These are not perfect methods as the plant will also be respiring, which will use up some oxygen and carbohydrate and increase carbon dioxide output
Explain how the temperature affects the rate of photosynthesis?
- Increasing temperature increases the kinetic energy of particles, increasing the likelihood of collisions between reactants and enzymes which results in the formation of products
- At higher temperatures, however, enzymes that control the processes of photosynthesis can be denatured (where the active site changes shape and is no longer complementary to its substrate) – this reduces the overall rate
What is a limiting factor?
A limiting factor is simply anything in short supply that prevents photosynthesis occurring at its maximum rate. If photosynthesis occurs more slowly in plant cells then a lower quantity of sugar will be produced and the quantity of chemical energy available for cell growth will be reduced.
Explain how Carbon Dioxide affects the rate of photosynthesis?
Carbon dioxide – with water – is one of the reactants in photosynthesis.
If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.
Again, at some point, a factor may become limiting.
You need to know this graph
Explain how light affects the rate of photosynthesis?
The intensity of the light available to the plant will depend on the amount of energy that it has to carry out photosynthesis
The more light a plant receives, the faster the rate of photosynthesis
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Explain how the amount of chlorophyll affects the rate of photosynthesis
- The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis
- The more chloroplasts a plant has, the faster the rate of photosynthesis
- The amount of chlorophyll can be affected by:
- diseases (such as tobacco mosaic virus)
- lack of nutrients (such as magnesium)
- loss of leaves (fewer leaves means fewer chloroplasts)
What is the Compensation point?
These graphs have been plotted with rate of photosynthesis against the factor under investigation.
If oxygen production or carbon dioxide uptake is used as a measure of photosynthetic rate, the graphs are slightly different. The line does not go through the origin. This is because oxygen production and carbon dioxide uptake are affected by respiration as well as photosynthesis. For instance, if a graph is plotted of carbon dioxide against light intensity:
The compensation point is the light intensity at which the rate of photosynthesis is equal to the rate of respiration.
A similar graph will be obtained if oxygen production is plotted against light intensity.
What does this graph tell you?
The rate of photosynthesis increases with increasing light intensity, temperature and carbon dioxide
All three experiments level off when light intensity is no longer the limiting factor.
In the top line, this has the highest temperature and concentration of carbon dioxide so the rate of photosynthesis is much higher.
In experiment 2, the concentration of carbon dioxide is the limiting factor.
In this graph, the rate of photosynthesis is controlled by carbon dioxide levels.
What is the inverse square law?
- The inverse square law shows the relationship between light intensity and distance.
- As the distance increases the light intensity decreases. This means that they are inversely proportional to each other
- Light intensity and distance are inversely proportional to each other
- This means that as the distance doubles you decrease the intensity of the light will be four times less
- This is called the inverse square law and shown by the equation below:
Calculate the light intensity when the distance of the plant is 30cm from the lamp
Use the equation:
Light intensity = 1/d^2
Fill in the values you know:
Light intensity = 1/30^2
Calculate the light intensity:
Light intensity = 0.001 au
Remember that ‘au’ stands for arbitrary units.
How can Farmers maximise the affect of photosynthesis from crops?
Exam Tip:
You should be able to use data in the exam to relate limiting factors to the cost-effectiveness of adding heat, light or carbon dioxide to greenhouses.Remember that spending money on increasing a factor above the point at which it has an effect on the rate of photosynthesis will be a waste of money.
How can Plant growers maximise the affect of photosynthesis using light?
Plant growers can:
- use greenhouses constructed from glass or alternative materials that enable maximum transmission of light
- position plants for maximum light absorption
Artificial lighting systems can be used: - with increased light intensities
- that provide optimum wavelengths of light for photosynthesis
- that lengthen a plant’s growing season so that crops can be grown in more months of the year
How can Plant growers maximise the affect of photosynthesis using CO2?
Many plants have the capacity to use additional carbon dioxide.
To increase the carbon dioxide concentration in a growing area, plant growers:
- use paraffin heaters on a small scale
- on a larger scale, use carbon dioxide wastes from industrial processes that has been cleaned up before use
- can use liquid carbon dioxide, applied through pipes, though this can be expensive
- sometimes use fungi, grown as a mycelium in bags around the greenhouse, that add carbon dioxide through their respiration
The concentration of carbon dioxide in greenhouses is often kept at around 0.1 per cent. Above one per cent, carbon dioxide changes cell pH – it makes it more acidic – and it becomes toxic.
In greenhouses at higher temperatures, photosynthetic production declines, and carbon dioxide supplements have no effect.
How can Plant growers maximise the affect of photosynthesis using Water?
Irrigation systems in greenhouses help to increase yields. Plants in greenhouses are often sprayed with water to keep the humidity high.
Growers must find a balance as high humidity will promote the growth of pathogenic fungi.
Irrigation systems are also used outdoors.
Plants are sometimes grown in liquid systems called hydroponics. Hydroponics allow the grower to optimise mineral ions given to plants. Mineral ions are required to synthesise other essential molecules from the glucose produced during photosynthesis
How can Plant growers maximise the affect of photosynthesis using Temperature?
Heat is often used in greenhouses and makes plant growth possible when the weather is cold outside.
Increased temperatures in greenhouses increase the rate of photosynthesis. Temperature regulation is important – note that cooling may also be required.
What are the uses of Glucose?
The glucose produced in photosynthesis may be:
- Used for respiration*(in the mitochondria) to release energy (both aerobic and anaerobic)
- Converted into insoluble starch for storage in the stems, leaves and roots so plants are able to respire at night.
- Used to produce fat or oil for storage (especially in seeds)
- Used to produce cellulose, which strengthens the cell wall
- Combined with nitrate ions absorbed from the soil to produce amino acids for protein synthesis
How do you test for the presence of glucose/starch in a plant?
A test to show that a plant is photosynthesising is to test the leaf for the presence of starch using iodine
This can be used to show the effect of light on photosynthesis
