Photosynthesis (AQA GCSE Biology)
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Define the term photosynthesis.
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Define the term photosynthesis.
Photosynthesis is the process by which plants use light energy to produce carbon compounds, such as carbohydrates.
What is the energy conversion that occurs during photosynthesis?
The energy conversion that occurs during photosynthesis is the conversion of light energy into chemical energy.
True or False?
Carbon dioxide is a product of photosynthesis.
False.
Carbon dioxide is a reactant in photosynthesis; it combines with water to produce glucose and oxygen.
What is a the role of chloroplasts in photosynthesis?
The role of chloroplasts is to absorb light energy during photosynthesis.
True or False?
Chlorophyll is a pigment that absorbs energy from sunlight for photosynthesis.
True.
Chlorophyll, a green pigment found inside chloroplasts, absorbs energy from sunlight for photosynthesis.
True or False?
Plants are known as producers because they produce their own food.
True.
Plants produce their own carbon compounds using light energy, water and carbon dioxide; for this reason they are known as producers.
How is glucose used inside plant cells?
Examples of ways in which plant cells can use glucose include:
Respiration
Storage, in the form of starch
The production of cellulose cell walls
Conversion into lipids and amino acids
True or False?
Without photosynthesis plants cannot produce proteins.
True.
Photosynthesis is needed for the production of proteins because it produces glucose, which can be combined with soil minerals to produce amino acids. Amino acids are used to build proteins.
What is the word equation for photosynthesis?
The word equation for photosynthesis is:
carbon dioxide + water → glucose + oxygen
What is the role of water in the photosynthesis equation?
Water is a reactant in photosynthesis. It reacts with carbon dioxide to produce glucose and oxygen.
True or False?
Light energy is a reactant in photosynthesis.
False.
Light is required for photosynthesis, but it is not a chemical substance and so is not considered to be a reactant in photosynthesis.
What are the products of photosynthesis?
The products of photosynthesis are glucose and oxygen.
What happens to oxygen in photosynthesis?
Oxygen is produced as a waste product and released from leaves via the stomata. Note that some of this oxygen may be used by the plant for respiration.
True or False?
Chlorophyll is used up in the photosynthesis reaction.
False.
Chlorophyll is not a reactant, and so is not used up during the photosynthesis reaction. The role of chlorophyll is to absorb light energy.
True or False?
The photosynthesis equation is the same as the aerobic respiration equation in reverse.
True.
The photosynthesis equation is the reverse of the equation for aerobic respiration.
What is the chemical formula for glucose?
The chemical formula for glucose is C6H12O6.
True or False?
Photosynthesis is an endothermic reaction.
True.
Photosynthesis is an endothermic reaction which means energy is transferred from the environment to the chloroplasts.
Define the term 'endothermic reaction'.
An endothermic reaction is a chemical reaction which absorbs energy from its surroundings e.g. photosynthesis absorbs light energy.
Define the term limiting factor in the context of photosynthesis.
A limiting factor is a factor that limits the rate of photosynthesis.
What are the three main factors that limit the rate of photosynthesis?
The three main limiting factors for photosynthesis are:
Temperature
Light intensity
Carbon dioxide concentration
True or False?
Water is a limiting factor in photosynthesis.
False.
Water is not considered a limiting factor in photosynthesis; this is because plants need relatively little water for photosynthesis, and a lack of water also influences a plant's ability to absorb light and carbon dioxide.
Why does the rate of photosynthesis slow down at low temperatures?
Photosynthesis occurs slowly at low temperatures because molecules (such as enzymes involved in photosynthesis) have little kinetic energy. This means that fewer successful collisions take place.
True or False?
The rate of photosynthesis increases consistently as temperature increases.
False.
Rate of photosynthesis only increases with temperature up to a certain point, after which higher temperatures lead to a decrease in the rate of photosynthesis.
Why do very high temperatures cause photosynthesis to stop?
At very high temperatures the enzymes that control photosynthesis denature, meaning that the reaction can no longer take place.
What is the effect of increasing light intensity on the rate of photosynthesis?
The higher the light intensity, the faster the rate of photosynthesis. This continues until another factor becomes limiting.
What is the effect of increasing carbon dioxide concentration on the rate of photosynthesis?
The higher the carbon dioxide concentration, the faster the rate of photosynthesis. This continues until another factor becomes limiting.
True or False?
In a graph of light intensity against the rate of photosynthesis, the part of the graph where the line is horizontal indicates a point where light intensity is the limiting factor.
(Higher Tier Only)
False.
In a graph of light intensity against rate of photosynthesis, the level part of the graph shows a point at which a factor other than light intensity is limiting, e.g. temperature or carbon dioxide concentration.
True or False?
The relationship between distance and light intensity is directly proportional.(Higher Tier Only)
False.
The relationship between light intensity and distance is inversely proportional because as the distance increases, the light intensity decreases.
What is shown by the inverse square law? (Higher Tier Only)
The inverse square law shows the relationship between light intensity and distance between the light source and the plant.
True or False?
In a graph of carbon dioxide concentration against the rate of photosynthesis, the part of the graph where the line is horizontal could indicate a point at which temperature is the limiting factor. (Higher Tier Only)
True.
In a graph of carbon dioxide concentration against rate of photosynthesis, the part of the graph where the line is horizontal is a point at which a factor other than carbon dioxide concentration is limiting. This factor could be temperature or light intensity.
How can the use of a greenhouse help to increase the yield of crop plants?
(Higher Tier Only)A greenhouse can increase the yield of crop plants because levels of carbon dioxide, water, light and temperature can be controlled more carefully whilst crops are kept free of pests. This supports an increase in the rate of photosynthesis, therefore increasing the growth of plants.
How should a farmer determine the cost-effectiveness of using greenhouses to grow their crops? (Higher Tier Only)
The farmer will need to consider the cost of setting up the greenhouses as well as the running costs involved. They would then need to calculate the potential yield increase that they would expect to receive from the setup in order to work out their income.
The farmer must ensure that they will make a profit from their crop.
What investigation can be carried out using the practical equipment below?
The equipment shown in the image can be used to investigate the effect of light intensity on the rate of photosynthesis.
What would the independent variable be in the investigation shown?
The independent variable is light intensity, which is controlled by altering the distance between the lamp and the beaker.
What would the dependent variable be in the investigation shown?
The dependent variable in this investigation is the rate of photosynthesis, which is measured by recording the volume of oxygen produced within a set time period.
Give two control variables for the investigation shown.
Control variables for this investigation would include:
maintaining the same environmental temperature
using the same species, length and age of plant in each repeat
dissolving sodium hydrogen carbonate (NaHCO3) in the water to maintain carbon dioxide levels
In an investigation into the effect of temperature on photosynthesis, why should light intensity be controlled?
Light intensity should be controlled when investigating the effect of temperature on the rate of photosynthesis as light intensity is a limiting factor and will have an effect on the dependent variable..
In an investigation into the effect of light intensity on the rate of photosynthesis in aquatic plants, what is the predicted outcome?
In an investigation into the effect of light intensity on the rate of photosynthesis, the predicted outcome is that the rate of photosynthesis will increase with light intensity. This will continue until another factor becomes limiting.
Why does bubble production decrease as distance between the light source and the aquatic plant increases in the graph shown?
The number of bubbles produced decreases as the light moves further away from the pondweed because light intensity decreases with distance; this means that rate of photosynthesis decreases and so less oxygen is produced.
What information is required to measure the rate of photosynthesis using the equipment below?
To measure the rate of photosynthesis we need to know the volume of gas collected and time period during which it has been collected.
Name three uses of glucose from photosynthesis.
Glucose may be used for:
respiration
storage by conversion into insoluble starch
production of fat or oil for storage
production of cellulose, which strengthens the cell wall
production of amino acids for protein synthesis
What mineral ion is used by plants to produce proteins?
As well as utilising the glucose produced in photosynthesis, plants require nitrate ions absorbed from the soil to produce proteins.
What test can be carried out to show the glucose content of leaves?
Benedict's solution can be used to show the presence of glucose using the following method:
Prepare a sample of leaf material (by grinding the leaf with distilled water).
Add Benedict's solution to the sample.
Heat in a water bath.
A positive result would show a colour change from blue to orange or brick red.
A student carried out an iodine test on a leaf that had been growing in full sunlight.
Suggest and explain the results of their test.
The student should see that the iodine solution turns from brown to blue/black indicating the presence of starch in the leaf.
This is because glucose produced in photosynthesis would be stored as starch within the leaf.
True or False?
Glucose is used to synthesise fats within plants.
True.
Production of fats for storage is one of the uses of glucose produced in photosynthesis.
How does glucose facilitate the uptake of mineral ions in the roots of plants?
Glucose is transported to the root hair cells where it is used in respiration to provide energy for the uptake of mineral ions by active transport.
In what form is glucose stored in plants and animals?
Glucose is stored as starch in plants and glycogen in animals.
What is the function of cellulose in plant cells?
Cellulose provides structural support to plant cells and allows them to maintain a regular shape.
Define the term 'qualitative reagent'
A qualitative reagent is a substance used to indicate the presence or absence of a substance through visible colour changes.
Examples of qualitative reagents are:
Benedict's solution
Biuret solution
Iodine solution