Component 3 (Adaptations for gas exchange)

Question 1

How does an organism’s size relate to its
surface area to volume ratio?

Answer 1

The larger the organism, the lower the
surface area to volume ratio.

Question 2

How does surface area to volume (SA/V)
ratio affect transport of molecules?

Answer 2

The lower the SA/V ratio, the further the
distance molecules must travel to reach all
parts of the organism. Diffusion alone is not
sufficient in organisms with small SA/V ratios.

Question 3

Why do larger organisms require mass
transport and specialised gas exchange
surfaces?

Answer 3

● Small SA/V ratio
● Diffusion insufficient to provide all cells with the
required oxygen and to remove all carbon dioxide
● Large organisms more active than smaller organisms

Question 4

Name four features of an efficient gas
exchange surface.

Answer 4

● Large surface area
● Short diffusion distance
● Steep diffusion gradient
● Moist and permeable for gases

Question 5

Describe the gas exchange mechanism
in the Amoeba.

Answer 5

● Unicellular organism with a large SA/V ratio
● Thin cell membrane provides short diffusion distance
● Simple diffusion across the cell surface membrane is
sufficient to meet the demands of respiratory processes

Question 6

Describe the gas exchange mechanism
in flatworms.

Answer 6

● Multicellular organisms with a relatively small SA/V ratio (in
comparison to the Amoeba)
● However, flat structure provides a large surface area and
reduces the diffusion distance
● Simple diffusion is sufficient to meet the demands of
respiratory processes

Question 7

Describe the gas exchange mechanism
in earthworms.

Answer 7

● Cylindrical, multicellular organisms with a relatively small SA/V ratio
(in comparison to the flatworm)
● Slow moving and low metabolic rate ∴ require little oxygen
● Rely on external surface for gas exchange
● Circulatory system transports oxygen to the tissues and removes
carbon dioxide, maintaining a steep diffusion gradient

Question 8

Define ventilation.

Answer 8

The movement of fresh air into a space and
stale air out of a space to maintain a steep
concentration gradient of oxygen and
carbon dioxide.

Question 9

Name the organ of gaseous exchange
in fish.

Answer 9

Gills

Question 10

What are gill filaments?

Answer 10

● Main site of gaseous exchange in fish, over which water
flows
● They overlap to increase resistance to flowing water -
slowing it down and maximising gaseous exchange.
● Found in large stacks, known as gill plates, and have
gill lamellae which provide a large surface area and
good blood supply for exchange

Question 11

Explain the process of ventilation in
bony fish.

Answer 11

● Buccal cavity volume increases and pressure decreases to
enable water to flow in
● Contraction of the buccal cavity forces water across the gills
● Pressure in the gill cavity rises, opening the operculum.
Water leaves

Question 12

How is a steep diffusion gradient
maintained across the entire gas
exchange surface in bony fish?

Answer 12

Due to counter current flow.

Question 12

How is a steep diffusion gradient
maintained across the entire gas
exchange surface in bony fish?

Answer 12

Due to counter current flow.

Question 13

Define counter current flow.

Answer 13

Blood and water flow in opposite
directions across the gill plate.

Question 14

How does counter current flow maintain
a steep diffusion gradient? What is the
advantage of this?

Answer 14

● Water is always next to blood of a lower oxygen
concentration
● Keeps rate of diffusion constant and enables 80%
of available oxygen to be absorbed

Question 15

What type of flow is exhibited in
cartilaginous fish?

Answer 15

Parallel flow

Question 16

Define parallel flow.

Answer 16

Water and blood flow in the same
direction across the gill plate.

Question 17

Compare counter current and
parallel flow.

Answer 17

Counter current flow
* Blood and water flow in opposite directions across
the gill plate
* Steep diffusion gradient maintained, allowing
diffusion of oxygen across the whole gill plate
* High rate of diffusion
* More efficient - more oxygen absorbed into the
blood
* Found in bony fish
Parallel flow
* Water and blood flow in the same direction across
the gill plate
* Diffusion gradient not maintained ∴ diffusion of
oxygen does not occur across the whole plate
* Lower rate of diffusion
* Less efficient - less oxygen absorbed into the
blood
* Found in cartilaginous fish, e.g. sharks

Question 18

Name and describe the main features of
an insect’s gas transport system.

Answer 18

● Spiracles - small, external openings along the thorax and abdomen
through which air enters, and air and water leave the gas exchange
system
● Tracheae - large tubes extending through all body tissues, supported by
rings of chitin to prevent collapse
● Tracheoles - smaller branches dividing off the tracheae

Question 19

What is the main site of gas exchange in
insects?

Answer 19

Tracheoles

Question 20

Describe the adaptations of the insect
tracheal system to a terrestrial
environment.

Answer 20

● Spiracles can be opened or closed to regulate diffusion
● Bodily contractions speed up the movement of air through the
spiracles
● Highly branched tracheoles provide a large surface area
● Impermeable cuticle reduces water loss by evaporation

Question 21

Describe the ventilation of the tracheal
system in insects.

Answer 21

● Expansion of the abdomen opens the thorax spiracles
(through which air enters) and closes the abdominal
spiracles
● Compression of the abdomen closes the thorax spiracles
and opens the abdominal spiracles (through which air is
expelled)

Question 22

Compare the gas exchange surface of
an active and inactive amphibian.

Answer 22

● Active amphibian has simple lungs
● Inactive amphibian relies on its moist
external surface for gas exchange

Question 23

How are mammals adapted for gas
exchange?

Answer 23

Alveoli provide a large surface area and thin
diffusion pathway, maximising the volume of
oxygen absorbed from one breath. They also
have a plentiful supply of deoxygenated blood,
maintaining a steep concentration gradient.

Question 24

Describe the structure and function of
the larynx.

Answer 24

A hollow, tubular structure located at the
top of the trachea involved in breathing
and phonation.

Question 25

Describe the trachea and its function in
the mammalian gaseous exchange
system.

Answer 25

● Primary airway, carries air from the nasal cavity down into the chest
● Wide tube supported by C-shaped cartilage to keep the air passage
open during pressure changes
● Lined by ciliated epithelial cells which move mucus, produced by
goblet cells, towards the back of the throat to be swallowed. This
prevents lung infections

Question 26

Describe the structure of the bronchi.

Answer 26

● Divisions of the trachea that lead into the lungs
● Narrower than the trachea
● Supported by rings of cartilage and lined by
ciliated epithelial cells and goblet cells

Question 27

Describe the structure and function of
the bronchioles.

Answer 27

● Many small divisions of the bronchi that allow the passage
of air into the alveoli
● Contain smooth muscle to restrict airflow to the lungs but
do not have cartilage
● Lined with a thin layer of ciliated epithelial cells

Question 28

What is the primary gaseous exchange
surface in humans?

Answer 28

Alveoli

Question 29

Describe the alveoli in the mammalian
gaseous exchange system.

Answer 29

● Mini air sacs, lined with epithelial cells
● Walls one cell thick
● Good blood supply to maintain a steep diffusion gradient
● 300 million in each lung

Question 30

What are the pleural membranes?

Answer 30

Thin, moist layers of tissue surrounding
the pleural cavity that reduce friction
between the lungs and the inner chest
wall.

Question 31

Define pleural cavity.

Answer 31

The space between the pleural
membranes of the lungs and the inner
chest wall.

Question 32

Describe ventilation in humans.

Answer 32

● The movement of fresh air into the lungs
and stale air out of the lungs via
inspiration and expiration
● Via negative pressure breathing

Question 33

What are internal intercostal muscles?

Answer 33

A set of muscles found between the ribs
on the inside that are involved in forced
exhalation.

Question 34

What are external intercostal muscles?

Answer 34

A set of muscles found between the ribs
on the outside that are involved in forced
and quiet inhalation.

Question 35

Explain the process of inspiration and
the changes that occur throughout the
thorax.

Answer 35

● External intercostal muscles contract (while internal relax), raising the ribcage
● Diaphragm contracts and flattens
● Outer pleural membrane moves out, reducing pleural cavity pressure and
pulling the inner membrane out
● The alveoli expand. Alveolar pressure falls below air pressure so air moves
into the trachea

Question 36

What is surfactant?

Answer 36

A fluid lining the surface of the alveoli that
reduces surface tension and prevents
collapse of the alveoli during exhalation.

Question 37

Describe the function of the waxy cuticle.

Answer 37

Reduces water loss from the leaf
surface.

Question 38

Describe how the upper epidermis is
adapted for photosynthesis.

Answer 38

● Layer of transparent cells allow light to
strike the mesophyll tissue
● Epidermal cells also synthesise the waxy
cuticle, reducing water loss

Question 39

Where is the palisade mesophyll layer
located?

Answer 39

Directly below the upper epidermis.

Question 40

How is the palisade mesophyll layer
adapted for photosynthesis?

Answer 40

It receives the most light so contains the
greatest concentration of chloroplasts.

Question 41

How is the spongy mesophyll layer
adapted for photosynthesis?

Answer 41

● Contains air spaces that reduce the diffusion
distance for carbon dioxide to reach the
chloroplasts in the palisade layer
● Contains some chloroplasts

Question 42

What is a vascular bundle?

Answer 42

The vascular system in dicotyledonous
plants. It consists of two transport
vessels, the xylem and the phloem.

Question 43

Why are vascular bundles important in
photosynthesis?

Answer 43

They form a large network to deliver
water and nutrients to photosynthetic
tissues and remove glucose.

Question 44

Describe how the lower epidermis is
adapted for photosynthesis.

Answer 44

It contains many stomata which enable
the evaporation of water and inward
diffusion of CO2
.

Question 45

What are stomata?

Answer 45

Small holes found on leaves that can be
opened or closed by guard cells to
control gas exchange and water loss.

Question 46

Summarise the ‘malate’ theory.

Answer 46

The ‘malate’ theory states that the
accumulation or loss of malate and K+
ions
by guard cells results in changes in turgor
pressure that open or close the stomata.

Question 47

By what mechanism do K+
ions enter
guard cells?

Answer 47

Active transport

Question 48

How does the accumulation of K+
and
malate ions affect guard cells?

Answer 48

● Lowers the water potential of guard cells
● Water moves in by osmosis
● Guard cells becomes turgid, opening the
stomata

Question 49

Why is starch important for stomatal
opening?

Answer 49

Starch is converted to malate ions.