The process by which plants make their own food (glucose) using light , water and carbon dioxide . It is an endothermic reaction that takes place in chloroplasts , which contain the green pigment chlorophyll .

State the word equation for photosynthesis.

carbon dioxide + water → glucose + oxygen Light is required and is shown above the arrow.

State the balanced symbol equation for photosynthesis.

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Why is photosynthesis described as an endothermic reaction?

Because energy is transferred from the environment to the chloroplasts by light — energy is taken in from the surroundings.

Photosynthesis is an reaction because energy is transferred from the environment to the chloroplasts by light.

Photosynthesis is an endothermic reaction because energy is transferred from the environment to the chloroplasts by light.

Why are plants described as producers ?

Because they make their own food (glucose) by photosynthesis, rather than consuming other organisms. Most photosynthesis takes place in the mesophyll cells of the leaves, which are packed with chloroplasts .

A factor that, when in short supply , restricts the rate of a reaction — even when other factors are in plentiful supply.

Name the four factors that affect the rate of photosynthesis.

Temperature Light intensity Carbon dioxide concentration Amount of chlorophyll

Describe the effect of light intensity on the rate of photosynthesis.

The more light a plant receives, the faster the rate of photosynthesis. This continues until another factor becomes limiting, when the rate becomes constant (levels off).

Describe the effect of carbon dioxide concentration on the rate of photosynthesis.

Carbon dioxide is a raw material for photosynthesis, so the more carbon dioxide present, the faster the rate. The rate levels off once another factor becomes limiting.

Describe the effect of temperature on the rate of photosynthesis.

Increasing temperature gives particles more kinetic energy , increasing the rate. Above the optimum, the enzymes controlling photosynthesis denature , so the rate falls .

How does the amount of chlorophyll affect the rate of photosynthesis?

More chlorophyll means more light energy can be absorbed , so the rate is faster . Chlorophyll can be reduced by disease (e.g. tobacco mosaic virus), lack of magnesium, or loss of leaves.

Why is water not usually considered a limiting factor of photosynthesis?

The amount of water needed for photosynthesis is very small compared with the amount transpired (lost) by the plant, so there is almost always enough available.

Explain what is meant by limiting factors interacting . (Higher Tier Only)

At any one time, any one of temperature, light intensity or carbon dioxide concentration may be the factor that is limiting the rate of photosynthesis. The factor in shortest supply controls the rate.

On a graph, how can you decide which factor is limiting the rate of photosynthesis? (Higher Tier Only)

Where the line is still rising , the factor being changed (e.g. light intensity) is limiting. Where the line has levelled off , some other factor (e.g. temperature or carbon dioxide) has become limiting.

State the relationship between light intensity and distance from a light source. (Higher Tier Only)

Light intensity is inversely proportional to the distance squared (the inverse square law ). As distance increases, light intensity decreases . If the distance doubles , the intensity falls to a quarter .

Give the equation used to calculate relative light intensity . (Higher Tier Only)

light intensity ∝ 1/d 2 where d = distance from the light source. The answer is given in arbitrary units .

A lamp is placed 30 cm from a plant. Calculate the relative light intensity using the inverse square law. (Higher Tier Only)

light intensity ∝ 1/d 2 = 1/30 2 = 1/900 = 0.0011 arbitrary units

Why do commercial growers grow crops in greenhouses ? (Higher Tier Only)

A greenhouse lets growers control the limiting factors (light, temperature, carbon dioxide, water) to reach the maximum rate of photosynthesis . This increases crop yield and allows more frequent harvests, increasing profit.

Explain why increasing a limiting factor in a greenhouse beyond a certain point wastes money. (Higher Tier Only)

Once a factor is no longer limiting, adding more of it (e.g. extra carbon dioxide or heat) does not increase the rate of photosynthesis. The grower pays for the input but gains no extra yield , reducing profit.

What is the aim of the photosynthesis Required Practical?

To investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed (e.g. Elodea or Cabomba ).

How is the rate of photosynthesis measured in this practical?

By counting the number of oxygen bubbles released by the pondweed per minute . More accurately, a gas syringe can be used to measure the volume of oxygen produced.

Outline the method for investigating the effect of light intensity on photosynthesis rate.

Place pondweed in a beaker of water. Place a lamp a set distance from the plant. Count the bubbles produced in one minute. Repeat and calculate a mean . Repeat at different distances from the lamp.

Why is a glass tank of water placed between the lamp and the pondweed?

To absorb heat from the lamp so that temperature is kept constant and does not become an extra variable. An LED bulb , which releases little heat, can be used instead.

How is light intensity changed in this practical, and how could other factors be investigated instead?

Light intensity is changed by altering the distance of the lamp from the plant (closer = higher intensity). Carbon dioxide : add different concentrations of sodium hydrogencarbonate to the water. Temperature : change the temperature of the water in the beaker.

How is this investigation made more reliable ?

Repeat the bubble count at each distance at least twice and calculate a mean . Control variables (e.g. temperature, mass and type of pondweed) are kept constant .

What results would you expect from this photosynthesis Required Practical?

As the lamp is moved closer to the pondweed, the light intensity increases, so more oxygen bubbles are produced per minute. This shows the rate of photosynthesis increases as light intensity increases, until another factor becomes limiting.

List the five uses of glucose produced in photosynthesis.

Used in respiration to release energy. Converted to insoluble starch for storage. Used to make fats and oils for storage. Used to make cellulose for cell walls. Combined with nitrate ions to make amino acids for proteins.

Why is glucose converted into starch for storage?

Starch is insoluble , so it does not dissolve and move away, and does not affect osmosis in the cell. It is stored in the leaves, stems and roots.

What substance, made from glucose, strengthens plant cell walls ?

Cellulose — used to build strong plant cell walls .

How is glucose used for long-term energy storage in plants?

It is converted into fats and oils , which are stored — especially in seeds .

How do plants use glucose to make proteins ?

Glucose is combined with nitrate ions (absorbed from the soil) to produce amino acids . Amino acids are then joined together to synthesise proteins .

How can you test a leaf to show that photosynthesis has taken place?

Test the leaf for starch using iodine solution . If starch is present, the iodine turns from orange-brown to blue-black .

GCSEScienceAQACombined Science: TrilogyBiologyFlashcardsBioenergeticsPhotosynthesis

Photosynthesis (AQA GCSE Combined Science: Trilogy: Biology): Flashcards

Exam code: 8464

1/33

0Still learning

Know0

FrontPhotosynthetic Reaction
Photosynthesis

Was this flashcard helpful?

Cards in this collection (33)

Photosynthesis
The process by which plants make their own food (glucose) using light, water and carbon dioxide.
It is an endothermic reaction that takes place in chloroplasts, which contain the green pigment chlorophyll.
State the word equation for photosynthesis.
carbon dioxide + water → glucose + oxygen
Light is required and is shown above the arrow.
State the balanced symbol equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Why is photosynthesis described as an endothermic reaction?
Because energy is transferred from the environment to the chloroplasts by light — energy is taken in from the surroundings.
Photosynthesis is an reaction because energy is transferred from the environment to the chloroplasts by light.
Photosynthesis is an endothermic reaction because energy is transferred from the environment to the chloroplasts by light.
Why are plants described as producers?
Because they make their own food (glucose) by photosynthesis, rather than consuming other organisms.
Most photosynthesis takes place in the mesophyll cells of the leaves, which are packed with chloroplasts.
Limiting factor
A factor that, when in short supply, restricts the rate of a reaction — even when other factors are in plentiful supply.
Name the four factors that affect the rate of photosynthesis.
Temperature
Light intensity
Carbon dioxide concentration
Amount of chlorophyll
Describe the effect of light intensity on the rate of photosynthesis.
The more light a plant receives, the faster the rate of photosynthesis.
This continues until another factor becomes limiting, when the rate becomes constant (levels off).
Describe the effect of carbon dioxide concentration on the rate of photosynthesis.
Carbon dioxide is a raw material for photosynthesis, so the more carbon dioxide present, the faster the rate.
The rate levels off once another factor becomes limiting.
Describe the effect of temperature on the rate of photosynthesis.
Increasing temperature gives particles more kinetic energy, increasing the rate.
Above the optimum, the enzymes controlling photosynthesis denature, so the rate falls.
How does the amount of chlorophyll affect the rate of photosynthesis?
More chlorophyll means more light energy can be absorbed, so the rate is faster.
Chlorophyll can be reduced by disease (e.g. tobacco mosaic virus), lack of magnesium, or loss of leaves.
Why is water not usually considered a limiting factor of photosynthesis?
The amount of water needed for photosynthesis is very small compared with the amount transpired (lost) by the plant, so there is almost always enough available.
Explain what is meant by limiting factors interacting. (Higher Tier Only)
At any one time, any one of temperature, light intensity or carbon dioxide concentration may be the factor that is limiting the rate of photosynthesis.
The factor in shortest supply controls the rate.
On a graph, how can you decide which factor is limiting the rate of photosynthesis? (Higher Tier Only)
Where the line is still rising, the factor being changed (e.g. light intensity) is limiting.
Where the line has levelled off, some other factor (e.g. temperature or carbon dioxide) has become limiting.
State the relationship between light intensity and distance from a light source. (Higher Tier Only)
Light intensity is inversely proportional to the distance squared (the inverse square law).
As distance increases, light intensity decreases. If the distance doubles, the intensity falls to a quarter.
Give the equation used to calculate relative light intensity. (Higher Tier Only)
light intensity ∝ 1/d²
where d = distance from the light source. The answer is given in arbitrary units.
A lamp is placed 30 cm from a plant. Calculate the relative light intensity using the inverse square law. (Higher Tier Only)
light intensity ∝ 1/d²
= 1/30² = 1/900
= 0.0011 arbitrary units
Why do commercial growers grow crops in greenhouses? (Higher Tier Only)
A greenhouse lets growers control the limiting factors (light, temperature, carbon dioxide, water) to reach the maximum rate of photosynthesis.
This increases crop yield and allows more frequent harvests, increasing profit.
Explain why increasing a limiting factor in a greenhouse beyond a certain point wastes money. (Higher Tier Only)
Once a factor is no longer limiting, adding more of it (e.g. extra carbon dioxide or heat) does not increase the rate of photosynthesis.
The grower pays for the input but gains no extra yield, reducing profit.
What is the aim of the photosynthesis Required Practical?
To investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed (e.g. Elodea or Cabomba).
How is the rate of photosynthesis measured in this practical?
By counting the number of oxygen bubbles released by the pondweed per minute.
More accurately, a gas syringe can be used to measure the volume of oxygen produced.
Outline the method for investigating the effect of light intensity on photosynthesis rate.
1. Place pondweed in a beaker of water.
1. Place a lamp a set distance from the plant.
1. Count the bubbles produced in one minute.
1. Repeat and calculate a mean.
1. Repeat at different distances from the lamp.
Why is a glass tank of water placed between the lamp and the pondweed?
To absorb heat from the lamp so that temperature is kept constant and does not become an extra variable.
An LED bulb, which releases little heat, can be used instead.
How is light intensity changed in this practical, and how could other factors be investigated instead?
Light intensity is changed by altering the distance of the lamp from the plant (closer = higher intensity).
Carbon dioxide: add different concentrations of sodium hydrogencarbonate to the water.
Temperature: change the temperature of the water in the beaker.
How is this investigation made more reliable?
Repeat the bubble count at each distance at least twice and calculate a mean.
Control variables (e.g. temperature, mass and type of pondweed) are kept constant.
What results would you expect from this photosynthesis Required Practical?
As the lamp is moved closer to the pondweed, the light intensity increases, so more oxygen bubbles are produced per minute.
This shows the rate of photosynthesis increases as light intensity increases, until another factor becomes limiting.
List the five uses of glucose produced in photosynthesis.
1. Used in respiration to release energy.
1. Converted to insoluble starch for storage.
1. Used to make fats and oils for storage.
1. Used to make cellulose for cell walls.
1. Combined with nitrate ions to make amino acids for proteins.
Why is glucose converted into starch for storage?
Starch is insoluble, so it does not dissolve and move away, and does not affect osmosis in the cell.
It is stored in the leaves, stems and roots.
What substance, made from glucose, strengthens plant cell walls?
Cellulose — used to build strong plant cell walls.
How is glucose used for long-term energy storage in plants?
It is converted into fats and oils, which are stored — especially in seeds.
How do plants use glucose to make proteins?
Glucose is combined with nitrate ions (absorbed from the soil) to produce amino acids.
Amino acids are then joined together to synthesise proteins.
How can you test a leaf to show that photosynthesis has taken place?
Test the leaf for starch using iodine solution.
If starch is present, the iodine turns from orange-brown to blue-black.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Communicable DiseasesNext:Respiration