4. Bioenergetics (photosynthesis and limiting factors)

Question 1

What does photosynthesis use to convert carbon dioxide and water into glucose and oxygen?

Answer 1

Energy

Question 2

How does photosynthesis get light energy?

Answer 2

1. The chlorophyll absorbs sunlight
2. Energy is transferred to the chloroplasts from the environment by light
3. Photosynthesis is endothermic - this means energy is transferred from the environment in the process

Question 3

What is the symbol equation for photosynthesis?

Answer 3

Question 4

What are the 5 ways that plants use glucose?

Answer 4

• For respiriation
• Making cellulose
• Making amino acids
• Stored as starch
• Stored as oils or fats

Question 5

Why is respiration important in plants?

Answer 5

Respiration transfers energy from glucose, which enables the plants to convert the rest of the glucose into various other useful substances

Question 6

Why is making cellulose important in plants?

Answer 6

Glucose is converted into cellulose for making strong plant cell walls

Question 7

How are amino acids made in plants?

Answer 7

Glucose is combined with nitrate ions to make amino acids, which are then made into proteins

Question 8

Why is glucose turned into lipids?

Answer 8

For storing in seeds

Question 9

Why is glucose stored as starch?

Answer 9

• Glucose is turned into starch as stored in roots, stems and leaves, ready to use when photosynthesis isn’t happening, like in the winter
• Starch is insoluble, which makes it much better for storing then glucose

Question 10

What is the rate of photosynthesis affected by?

Answer 10

1. Light intensity
2. Concentration of carbon dioxide
3. Temperature
4. Chlorophyll

Question 11

What does the graph look like for light intensity and rate of photosynthesis?

Answer 11

Question 12

What kind of reaction is Photosynthesis?

Answer 12

Endothermic reaction - in which energy is transferred from the environment to the chloroplasts by light

Question 13

What are the steps for the practical: The effect of light intensity on photosynthesis?

Answer 13

1. Place a white light a specific distance from the pondweed
2. The pondweed should be placed in a tube with a bung that is connected to a capillary tube and a syringe
3. You then measure the length of the bubbles at the specific distance and time to work out the speed
4. Repeat this at different distances to the light source and analyse how distance from the light surce affects photosynthesis

Question 14

What is the inverse square law formula between light intensity and distance?

Answer 14

Light intensity = directly proportional to:
1
———————–
Distance^2

Question 15

What is the inverse square law?

Answer 15

Light intensity and distance are inversely proportional to one another. However, Light intensity decreases in proportion to the square of the distance

Question 16

How is temperature a limiting factor for photosynthesis?

Answer 16

• As temperature increases, the enzymes gain more kinetic energy so there is more frequent and successful collisions
• So more enzyme-substrate complexes are able to form
• So the rate of photosynthesis increases up to the optimum temperature (37-40 degrees)
• After exceeding the optimum temperature, the enzyme denatures
• This means that the enzymes active site changes shape
• So this means the active site is no longer specific and complementary to the substrate
• So fewer enzyme-substrate complexes can form
• So the rate of photosynthesis decreases

Question 17

How is carbon dioxide a limiting factor?

Answer 17

• As the carbon dioxide concentration increases, the rate of photosynthesis also increases
• This means it is a limiting reactant, as more carbon dioxide means more substrates so more enzyme-substrate complexes form
• As the carbon dioxide concentration continues to increases, the rate of photosynthesis stays the same/plateus
• This is because the enzymes active sites are occupied
• So the maximum rate of reaction has been reached
• So carbon dioxide is no longer the limiting reactant, another factor is limiting the rate of photosynthesis

Question 18

How is light intensity a limiting factor?

Answer 18

• As the light intensity increases, the rate of photosynthesis also increases
• This means it is a limiting factor, as more light energy means that more carbon dioxide and water can be converted into glucose and oxygen
• As the light intensity continues to increase, the rate of photosynthesis remains the same/plateaus
• This could be because there is not enough chlorophyll to absorb the sunlight
• So the maximum rate of reaction has been reached
• So light intensity is no longer the limiting reactant, another factor is limiting the rate of photosynthesis.

Question 19

How can ideal conditions for temperature be kept in a greenhouse?

Answer 19

• Temperature can be maintained in a greenhouse, greenhouses trap the sun’s heat
• Paraffin heaters
• Use shades and ventilation to cool the greenhouse down

Question 20

How can ideal conditions for carbon dioxide be kept in a greenhouse?

Answer 20

• Using a paraffin heater gives a by product of carbon dioxide
• Carbon dioxide levels can also be controlled by using computer softwares

Question 21

How can ideal conditions for light intensity be kept in a greenhouse?

Answer 21

Artificial light can be used