(Paper 1) 4.1 Bioenergetics: Photosynthesis

Question 1

What is photosynthesis?

Answer 1

A process where plants make glucose using light energy, carbon dioxide, and water.

Question 2

What type of reaction is photosynthesis?

Answer 2

An endothermic reaction – it requires energy (from light).

Question 3

What is the word equation for photosynthesis?

Answer 3

Carbon dioxide + water → glucose + oxygen

Question 4

What is the symbol equation for photosynthesis?

Answer 4

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Question 5

Where does carbon dioxide enter the leaf?

Answer 5

Through the stomata.

Question 6

How does water reach the leaves?

Answer 6

It enters via roots and travels in the xylem.

Question 7

What is the waste product of photosynthesis?

Answer 7

Oxygen – some is used for respiration, the rest is released.

Question 8

What pigment absorbs light for photosynthesis?

Answer 8

Chlorophyll

Question 9

Where is chlorophyll found?

Answer 9

In the chloroplasts of palisade and spongy mesophyll cells.

Question 10

Which part of the plant is the main site of photosynthesis?

Answer 10

The leaves, though any part exposed to light can photosynthesise.

Question 11

What is biosynthesis in plants?

Answer 11

Using glucose to build new materials for growth and life functions.

Question 12

What are some uses of glucose in plants (other than respiration)?

Answer 12

Making cellulose for cell walls

Storing as starch

Producing amino acids (with nitrates)

Making fats and oils for storage

Question 13

Name three ways to measure the rate of photosynthesis in the lab.

Answer 13

Oxygen output

Carbon dioxide uptake

Carbohydrate production

Question 14

Why are measurements of photosynthesis not perfect?

Answer 14

Because respiration occurs at the same time and can affect oxygen and carbon dioxide levels.

Question 15

What are the four main factors affecting photosynthesis?

Answer 15

Light intensity

Carbon dioxide concentration

Temperature

Chlorophyll concentration

Question 16

What is a limiting factor?

Answer 16

A factor that is in short supply, limiting the rate of photosynthesis.

Question 17

What happens to the rate of photosynthesis as light intensity increases?

Answer 17

It increases, then levels off when another factor becomes limiting.

Question 18

Do very high light intensities occur in nature?

Answer 18

No – extremely high intensities that inhibit photosynthesis do not occur naturally.

Question 19

How does carbon dioxide concentration affect photosynthesis?

Answer 19

Higher CO₂ levels increase the rate, until another factor becomes limiting.

Question 20

What is CO₂’s role in photosynthesis?

Answer 20

It is a reactant, combined with water to make glucose.

Question 21

How does temperature affect photosynthesis?

Answer 21

Low temp: fewer enzyme-substrate collisions

High temp: enzymes become denatured

Question 22

What controls the chemical reactions in photosynthesis?

Answer 22

Enzymes

Question 23

What does chlorophyll do?

Answer 23

Absorbs light for photosynthesis.

Question 24

How does chlorophyll concentration affect photosynthesis?

Answer 24

More chlorophyll means more light absorbed, increasing the rate.

Question 25

What part of the spectrum does chlorophyll absorb?

Answer 25

Red and blue light; it reflects green light.

Question 26

What is the compensation point in photosynthesis?

Answer 26

The light intensity where photosynthesis rate equals respiration rate.

Question 27

Why does the graph not go through the origin when using CO₂ uptake or O₂ production?

Answer 27

Because respiration also affects these values.

Question 28

Why is water an important factor in photosynthesis?

Answer 28

It is a reactant in photosynthesis and a solvent for chemical reactions in cells.

Question 29

Why aren’t graphs shown for water's effect on photosynthesis?

Answer 29

Because water affects many other processes in plants, not just photosynthesis.

Question 30

What is often the main limiting factor for photosynthesis in the UK?

Answer 30

Water

Question 31

How does light intensity change throughout the day?

Answer 31

It fluctuates, affecting the rate of photosynthesis depending on time of day and weather.

Question 32

How does the season affect photosynthesis in the UK?

Answer 32

Shorter days and lower light reduce the net production during winter.

Question 33

Why is carbon dioxide a limiting factor?

Answer 33

Atmospheric CO₂ is only about 0.04%, which is lower than the optimum for photosynthesis.

Question 34

Why is CO₂ concentration important in agriculture?

Answer 34

It can limit crop growth if not maintained at optimum levels.

Question 35

What is the optimum temperature range for most plants to photosynthesise?

Answer 35

Between 15°C and 40°C

Question 36

How does temperature affect photosynthesis?

Answer 36

Low temp: fewer enzyme-substrate collisions High temp: enzymes may become denatured

Question 37

What does climate change risk in terms of crop production?

Answer 37

Rising temperatures may negatively impact crop yields.

Question 38

Which crop has the highest optimum temperature for photosynthesis?

Answer 38

Rice (30–33°C)

Question 39

What is the compensation point in plants?

Answer 39

The light intensity where photosynthesis equals respiration.

Question 40

How does light adaptation affect the compensation point?

Answer 40

Shade-adapted plants have a lower compensation point Sun-adapted plants need more light before net photosynthesis occurs

Question 41

What does the law of limiting factors state?

Answer 41

The rate of photosynthesis is determined by the factor in shortest supply.

Question 42

Do limiting factors act independently?

Answer 42

No – they often interact with each other.

Question 43

What happens when light intensity increases but CO₂ is limited?

Answer 43

The rate of photosynthesis levels off once CO₂ becomes the limiting factor.

Question 44

What happens if CO₂ concentration is increased?

Answer 44

The rate increases further, until another factor becomes limiting.

Question 45

How does temperature interact with other factors?

Answer 45

Higher temperature can increase enzyme activity, further increasing the rate of photosynthesis, until it becomes too hot or another factor becomes limiting.

Question 46

What will a graph show when multiple limiting factors are considered?

Answer 46

A series of increases and plateaus, where each rise is caused by removing a limiting factor.

Question 47

In a graph showing light intensity and CO₂ interaction, what shifts the curve upward?

Answer 47

Increasing CO₂ concentration or raising temperature.

Question 48

Why does the rate eventually level off even when light is high?

Answer 48

Because another factor, like CO₂ or temperature, becomes limiting.

Question 49

What happens to light intensity as distance from a light source increases?

Answer 49

Light intensity decreases — the light spreads out over a larger area.

Question 50

What is the inverse square law for light intensity?

Answer 50

Light intensity = 1/(Distance x distance)

Question 51

What does "inversely proportional" mean?

Answer 51

As one value increases, the other decreases, specifically by the square of the increase.

Question 52

If the distance is doubled, what happens to light intensity?

Answer 52

It becomes one-quarter as strong

Question 53

What is a limiting factor in photosynthesis?

Answer 53

A factor in short supply that slows the rate of photosynthesis.

Question 54

Why is controlling limiting factors important in farming?

Answer 54

It increases crop yield, making plant growth faster and more efficient.

Question 55

How do greenhouses maximise light for photosynthesis?

Answer 55

Built with glass or transparent materials Plants positioned for maximum light absorption Use of artificial lighting with optimum intensity and wavelength

Question 56

How can artificial lighting extend growing seasons?

Answer 56

By simulating daylight, enabling year-round crop production.

Question 57

How can growers increase carbon dioxide concentration in greenhouses?

Answer 57

Paraffin heaters Recycled CO₂ from cleaned industrial waste Liquid CO₂ systems Respiring fungi (mycelium bags)

Question 58

What is a common safe CO₂ concentration in greenhouses?

Answer 58

Around 0.1% – higher levels can become toxic.

Question 59

What happens to photosynthesis at high CO₂ levels and high temperatures?

Answer 59

Rate of photosynthesis declines – CO₂ supplements become ineffective.

Question 60

How does water support photosynthesis in greenhouses?

Answer 60

Through irrigation systems and humidity control.

Question 61

What is hydroponics?

Answer 61

Growing plants in nutrient-rich liquid without soil, allowing precise mineral ion control.

Question 62

Why must humidity be carefully controlled?

Answer 62

High humidity can promote the growth of pathogenic fungi.

Question 63

How does temperature affect photosynthesis in greenhouses?

Answer 63

Warmer conditions increase enzyme activity, boosting photosynthesis.

Question 64

Why is temperature regulation important?

Answer 64

To avoid overheating, which may denature enzymes or require cooling systems.