Bioenergetics

Question 1

Is photosynthesis an endothermic or exothermic reaction?

Answer 1

Endothermic

Question 2

What is the light energy absorbed by?

Answer 2

Chlorophyll, which is a green pigment found in chloroplasts.

Question 3

Explain how the carbon dioxide and water required for photosynthesis enters the leaf.

Answer 3

The carbon dioxide comes through the air. It enters leaves through the stomata. Water enters the plants through the roots and is transported to the leaves in the Xylem.

Question 4

Name 3 ways the glucose produced by photosynthesis is used in plants.

Answer 4

1. Respiration
2. Glucose creates cellulose which is used to build / strengthen cell walls.
3. Glucose is stored as starch.

Question 5

Name the 3 factors that can affect the rate of photosynthesis.

Answer 5

1. Light intensity
2. Carbon dioxide concentration
3. Temperature

Question 6

Name the 3 ways we can measure the rate of photosynthesis in a lab.

Answer 6

1. The rate of oxygen output
2. The rate of carbon dioxide output
3. The rate of glucose production

Question 7

Why are the methods to measure the rate of photosynthesis not perfect methods?

Answer 7

The plant will also be respiring, which will use up some oxygen and glucose and increase carbon dioxide output.

Question 8

When a light intensity / photosynthesis graph levels off, what has happened?

Answer 8

Something else has become the limiting factor.

Question 9

Draw the graph for temperature/ rate of photosynthesis.

Answer 9

Relatively steep uphill and then very steep downhill.

Question 10

Draw the graph for light intensity / rate of photosynthesis.

Answer 10

Gradually goes up and then levels off and becomes horizontal.

Question 11

Draw the graph for carbon dioxide / rate of photosynthesis.

Answer 11

Same as light intensity graph.

Question 12

Why is the rate of photosynthesis slow at a low temperature?

Answer 12

At low temperatures, the rate of photosynthesis is limited by the low number of collisions between enzymes and substrates.

Question 13

Why is the rate of photosynthesis slow at a high temperature?

Answer 13

At a high temperature the enzymes have denatured and can no longer fit into their substrate.

Question 14

How does chlorophyll increase the rate of photosynthesis?

Answer 14

• Chlorophyll absorbs the light energy required to convert carbon dioxide and water into glucose.
• More chlorophyll means there is more light intensity absorbed and therefore a higher rate of reaction.

Question 15

What is the compensation point in a light intensity graph?
(This is if there is dim light)

Answer 15

The compensation point is the light intensity at which the rate of photosynthesis = the rate of respiration. There is no net output or uptake of carbon dioxide.

Question 16

When the line on the light intensity / carbon dioxide graph is below 0, what is happening?
(This is the same for if there was no light)

Answer 16

The plant is respiring but not photosynthesising as there is no light intensity. The rate of respiration is higher than the rate of photosynthesis. Therefore there is a net output of carbon dioxide.

Question 17

When the line on the light intensity / carbon dioxide graph is above 0, what is happening?
(This is the same for if there was lots of light)

Answer 17

The plant is both respiring and photosynthesising, but the rate of photosynthesis is higher so there is a net uptake of photosynthesis.

Question 18

What is often the limiting factor in photosynthesis?

Answer 18

Water

Question 19

Why is carbon dioxide often a limiting factor for photosynthesis?

Answer 19

The concentration of carbon dioxide is very low in terms of being optimum for photosynthesis.

Question 20

What happens to the compensation point for shade - adapted plants?

Answer 20

For shade-adapted plants, the compensation point is lower – their rate of photosynthesis will exceed the rate of respiration at lower light intensities than the plants adapted to sun.

Question 21

The table shows a set of results obtained by students investigating the effect of light intensity on photosynthesis.
What does the number of bubbles produced per minute equal?

Answer 21

The rate of photosynthesis

Question 22

Why is there an inversely proportional relationship between distance and light intensity?

Answer 22

• As the distance increases, the light intensity decreases.
• As the distance away from a light source increases, photons of light become spread over a wider area.

Question 23

How would we increase the light intensity in a greenhouse?

Answer 23

1. We could use greenhouses made of glass that enable maximum transmission of light.
2. We can position plants for maximum absorption.
3. We can increase the light intensity with an artificial lighting system.
4. We can provide optimum wavelengths of light for photosynthesis.

Question 24

Why would we increase the light intensity in greenhouses?

Answer 24

Because light intensity can be a limiting factor, so Increasing the light intensity in greenhouses will increase the growth of crops.

Question 25

How would we increase the concentration of carbon dioxide in a greenhouse?

Answer 25

1. Use paraffin heaters. 2. use carbon dioxide wastes from industrial processes that has been cleaned up before use.

Question 26

Why is the concentration of carbon dioxide in greenhouses often kept at around 0.1% ?

Answer 26

Above 1%, carbon dioxide changes the cell pH and makes it more acidic and it becomes toxic.

Question 27

What is irrigation?

Answer 27

The channelling of water from rivers and streams to fields in order to help crops grow.

Question 28

Why are irrigation systems used?

Answer 28

They are used in greenhouses to help increase yields. Plants in greenhouses are often sprayed with water to keep the humidity high.

Question 29

Why is heat used in greenhouses?

Answer 29

- 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

Question 30

What do nitrate ions do in plants? What happens if there is a nitrate ion deficiency?

Answer 30

1. They synthesise proteins for healthy plant growth. 2. Without nitrate ions, the amount of chlorophyll in leaves reduces. This reduces the plants ability to photosynthesise.

Question 31

What do plants use glucose for?

Answer 31

1. They use glucose for energy production through respiration. 2. They use glucose to build cellulose.

Question 32

What is the energy released from respiration used for in plants?

Answer 32

1. Active transport of mineral ions. 2. Protein synthesis 3. Growth

Question 33

What is the energy released from respiration used for in humans?

Answer 33

1. Muscle contraction for Movement 2. Maintaining body temperature. 3. Active transport of molecules

Question 34

What is photosynthesis used for in plants?

Answer 34

1. It converts light energy into substances required for survival and reproduction. 2. It supports cellular processes, development and plant structure by producing oxygen and glucose.

Question 35

What is glucose stored as in plants?

Answer 35

1. Starch 2. Cellulose.

Question 36

What is the equation for anaerobic respiration in humans?

Answer 36

Glucose -> lactic acid + energy

Question 37

What is the equation for anaerobic respiration in plants?

Answer 37

Glucose -> carbon dioxide + ethanol.

Question 38

Name 3 differences between anaerobic respiration and aerobic respiration.

Answer 38

1. Aerobic respiration requires energy, whereas anaerobic respiration doesn’t. 2. Anaerobic respiration produces lactic acid whereas aerobic respiration doesn’t. 3. Anaerobic respiration releases less energy than aerobic respiration.

Question 39

What is anaerobic respiration in microorganisms called?

Answer 39

Fermentation

Question 40

Does anaerobic or aerobic respiration release more energy?

Answer 40

Anaerobic respiration releases less energy than aerobic respiration but more quickly than aerobic respiration.