Unit 4 - 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
light
light

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

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

Answer 14

They can control temperature, light intensity
and CO2 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

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 + 6O2 → 6CO2 + 6H2O (+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?

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 it 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