B4 Bioenergetics

Question 1

What is photosynthesis?

Answer 1

The process by which plants synthesise glucose using light energy from the Sun. Light energy is converted into chemical energy.

Question 2

Where does photosynthesis take place?

Answer 2

Within chloroplasts in leaf palisade cells. They contain chlorophyll, a pigment which absorbs light energy.

Question 3

State the equations for photosynthesis (word and symbol)

Answer 3

carbon dioxide + water → glucose + oxygen (using light energy)

6CO2 + 6H20 → C6H12O6 +602 (using light energy)

Question 4

Is photosynthesis an endothermic or exothermic reaction, and why?

Answer 4

Endothermic - energy is transferred from the environment to chloroplasts by light.

Question 5

How can you show that a plant gives off oxygen during photosynthesis?

Answer 5

Using a water plant (eg. Elodea), collect gas bubbles produced during photosynthesis. The gas wil relight a glowing splint as it contains oxygen.

Question 6

Give examples of leaf adaptations which maximise the rate of photosynthesis

Answer 6

• Broad leaves - maximise surface area.
• Thin leaves - short diffusion distance.
• Chlorophyll present - trap light energy.
• Veins - transport water to leaves via xylem, remove photosynthesis
  products via phloem.
• Air spaces - allow CO2 to enter and O2 to leave.
• Guard cells - control opening of stomata for gaseous exchange and prevent water loss.

Question 7

What are the four main factors that affect the rate of photosynthesis?

Answer 7

• Temperature
• Light intensity
• Carbon dioxide concentration
• Amount of chlorophyll

Question 8

How does temperature affect the rate of photosynthesis?

Answer 8

Increasing the temperature increases the rate of photosynthesis as the kinetic energy of particles is increased.

The rate decreases past a certain temperature as enzymes become denatured.

Question 9

How does light intensity affect the rate of photosynthesis?

Answer 9

Increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting.

Question 10

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 10

Increasing the carbon dioxide concentration increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose.

Question 11

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

Answer 11

Decreasing the amount of chlorophyll (e.g. due to a lack of magnesium) decreases the rate of photosynthesis as chlorophyll is required to absorb light energy.

Question 12

What is a limiting factor?

Answer 12

An environmental factor which can restrict the rate of photosynthesis eg. light intensity.

Question 13

Explain how you can calculate the rate of photosynthesis by measuring oxygen production

Answer 13

• Set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe).
• Oxygen gas produced causes the bubble in the capillary tube to move. The distance moved by the bubble is used to calculate the volume of oxygen produced.

Question 14

How can farmers use their knowledge of limiting factors to increase their profits?

Answer 14

They can control temperature, light intensity and CO, concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield.

Question 15

State the law which describes the relationship between the distance of a light source from a plant and light intensity

Answer 15

Inverse square law - light intensity ∝ 1/ distance^2

Question 16

State 5 uses of the glucose produced
during photosynthesis

Answer 16

• Respiration
• Starch for storage
• Cellulose for strength
• Amino acid and protein synthesis (combined with nitrates)
• Lipids for energy storage in seeds

Question 17

What is aerobic respiration?

Answer 17

An exothermic reaction in which glucose
reacts with oxygen to release energy which can be used by cells.

Question 18

What are the equations for aerobic respiration? (word and symbol)

Answer 18

Glucose + oxygen → carbon dioxide + water (+ energy)

C6H12O6 + 602 → 6CCO2 +6H20 (+ energy)

Question 19

Where does aerobic respiration take place?

Answer 19

In the mitochondria

Question 20

Why do organisms require the energy released by respiration?

Answer 20

• Synthesis of larger molecules
• Muscle contraction
• Maintenance of body temperature
• Active transport

Question 21

What is anaerobic respiration?

Answer 21

An exothermic reaction in which glucose is broken down to release energy in the absence of oxygen.

Question 22

What is the equation for anaerobic respiration?

Answer 22

Glucose → lactic acid (+ energy)

Question 23

Why is anaerobic respiration less efficient than aerobic respiration?

Answer 23

Glucose is not completely broken down, so less energy is transferred.

Question 24

Why can anaerobic respiration lead to muscle fatigue?

Answer 24

Lactic acid (product of anaerobic respiration) builds up in muscles, preventing efficient contraction.

Question 25

What is an oxygen debt?

Answer 25

The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration.

Question 26

What is fermentation?

Answer 26

A type of anaerobic respiration that occurs in yeast cells.

Question 27

What is the equation for fermentation?

Answer 27

Glucose → ethanol + carbon dioxide (+ energy)

Question 28

Why is the fermentation reaction important?
It is used in the production of bread and alcoholic drinks.

Answer 28

It is used in the production of bread and alcoholic drinks.

Question 29

What are the differences between aerobic and anaerobic respiration?

Answer 29

• Aerobic requires oxygen; anaerobic does not.
• Aerobic produces CO2 and water; anaerobic produces lactic acid or ethanol + CO2.
• Aerobic transfers a greater amount of energy.

Question 30

How do muscles store glucose?

Answer 30

As glycogen

Question 31

What changes take place when muscular activity increases in the body?

Answer 31

• Heart rate increases and arteries dilate - increases flow of oxygenated blood to muscles.
• Breathing rate increases and breathing is deeper - increases the rate of gaseous exchange.
• Stored glycogen is converted back into glucose

Question 32

How is lactic acid transported away from the muscles?

Answer 32

Blood flow through the muscles transports lactic acid to the liver, where ti is oxidised back to glucose.

Question 33

What is metabolism?

Answer 33

The sum of all the reactions that take place in a cell or an organism.

Question 34

How do cells use the energy transferred by respiration?

Answer 34

To continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules.

Question 35

Give examples of metabolic reactions

Answer 35

• Glucose into starch/glycogen/cellulose
• Glycerol and fatty acids into lipids
• Glucose and nitrate ions into amino acids
• Photosynthesis
• Respiration
• Breakdown of excess proteins into urea

Question 36

Aerobic respiration:

Answer 36

A form of respiration that uses oxygen to release energy from molecules like glucose

Question 37

Anaerobic respiration:

Answer 37

A form of respiration that releases energy from molecules like glucose without using oxygen

Question 38

Cellular respiration:

Answer 38

An exothermic reaction which is continuously occurring in living cells.

Question 39

Inverse proportion:

Answer 39

​A relationship between two values where as one value increases, the other value decreases at the same rate.

Question 40

Inverse square law:

Answer 40

​As the distance from a light source increases, the light intensity is inversely proportional to the distance squared

Question 41

Limiting factor:

Answer 41

A factor that limits the rate of a reaction when there is not enough of it.

Question 42

Metabolism:

Answer 42

The sum of all the reactions in a cell or the body.

Question 43

Oxygen debt:

Answer 43

The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.​