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

Word: carbon dioxide + water → glucose + oxygen
Symbol: 6CO2 + 6H2O → C6H12O6 + 6O2

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 will 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 (eg. 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

State 5 uses of the glucose produced

during photosynthesis

Answer 14

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

Question 15

What is aerobic respiration?

Answer 15

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

Question 16

What are the equations for aerobic

respiration? (word and symbol)

Answer 16

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

C6H12O6 + 6O2 → 6CO2 + 6H2O (+energy)

Question 17

Where does aerobic respiration take place?

Answer 17

In the mitochondria

Question 18

Why do organisms require the energy

released by respiration?

Answer 18

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

Question 19

What is anaerobic respiration?

Answer 19

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

Question 20

What is the word equation for anaerobic respiration?

Answer 20

Glucose → lactic acid (+energy)

Question 21

Why is anaerobic respiration less

efficient than aerobic respiration?

Answer 21

Glucose is not completely broken down,

so less energy is transferred.

Question 22

Why can anaerobic respiration lead to muscle

fatigue?

Answer 22

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

Question 23

What is fermentation?

Answer 23

A type of anaerobic respiration that

occurs in yeast cells.

Question 24

What is the equation for fermentation?

Answer 24

Glucose → ethanol + carbon dioxide (+energy)

Question 25

Why is the fermentation reaction important?

Answer 25

It is used in the production of bread and

alcoholic drinks.

Question 26

What are the differences between

aerobic and anaerobic respiration?

Answer 26

● 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 27

How do muscles store glucose?

Answer 27

As glycogen

Question 28

What is metabolism?

Answer 28

The sum of all the reactions that take

place in a cell or an organism.

Question 29

How do cells use the energy transferred by

respiration?

Answer 29

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

Question 30

Give examples of metabolic reactions

Answer 30

● 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