3.1 Exchange surfaces

Question 1

How is surface area to volume ratio calculated?

Answer 1

Ratio= surface area/volume

Question 2

Name 3 features of an efficient gas exchange surface

Answer 2

-Large surface area e.g root hair cells for max amount of diffusion
-Thin short distance e.g. alveoli
-Steep concentration gradient, maintained by blood supply or ventilation e.g. gills

Question 3

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

Answer 3

-Wide tube supported by C shaped cartilage to keep the air passage open during pressure changes
-Lined by ciliated epithelium cells which move mucus, produced by goblet cells, towards the throat to be swallowed, preventing lung infections
-Carries air to bronchi

Question 4

Describe the bronchi and their function in the mammalian gaseous exchange system

Answer 4

-Like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells and goblet cells
-However there are two of them, one for each lung
-Allow passage of air into the brochioles

Question 5

Describe the alveoli and their function in the mammalian gaseous exchange system

Answer 5

-Mini air sacs lined with epithelium cells, site of gas exchange
-Walls only one cell thick, covered in a network of capillaries, 300 million in each lung all of which facilliates gas diffusion

Question 5

Describe the bronchioles and their function in the mammalian gaseous exchange system

Answer 5

-Narrower than the bronchi
-Do not need to be kept open by cartilage rings, therefore only have smooth muscle and elastic fibres so that they can contract and relax easily during ventilation
-Allow passage of air into the alveoli

Question 6

what is the role of cartilage ?

Answer 6

involved in supporting the trachea and bronchi, plays an important role in preventing the lungs from collapsing in the event of pressure drop during exhalation

Question 7

what is the role of epithelium cells?

Answer 7

present in bronchi, bronchioles and trachea, involved in
moving mucus along to prevent lung infection by moving it towards the throat

Question 8

what is the role of goblet cells?

Answer 8

cells present in the trachea, bronchi and bronchioles involved in mucus
secretion to trap bacteria and dust to reduce the risk of infection with the help of
lysozyme which digests bacteria

Question 9

what is the role of elastic fibres?

Answer 9

stretch when we inhale and recoil when we exhale thus controlling
the flow of air

Question 10

What is ventilation?
What are the two stages?

Answer 10

The flow of air in and out of the alveoli, inspiration and expiration

Question 11

What muscles aid in ventilation?

Answer 11

two sets of muscles,
the intercostal muscles and diaphragm

Question 12

What happens during inspiration

Answer 12

-the external intercostal muscles contract whereas the internal ones
relax, causing the ribs to raise upwards
-the diaphragm contracts and flattens
-the intercostal muscles and diaphragm cause the volume inside the thorax to
increase, lowering the pressure
–>the difference between the pressure inside the lungs
and atmospheric pressure creates a gradient, causing the air to enter the lungs

Question 13

What happens during expiration?

Answer 13

-the internal intercostal muscles contract whereas the external ones relax –>lowering the rib cage
-the diaphragm relaxes and rises upwards–>this in
combination decrease the volume inside the thorax, increasing the pressure, forcing
the air out of the lungs

Question 14

What is a spirometer? How does it work?

Answer 14

A spirometer is a device used to measure lung volume.
-A person using a spirometer
breathes in and out of the airtight chamber, causing it to move up and down, leaving a
trace on a graph which can then be interpreted

Question 15

What is the vital capacity?

Answer 15

the maximum volume of air that can be inhaled or exhaled in a single breath–> Varies depending on gender, age, size and height

Question 16

What is the tidal volume?

Answer 16

the volume of air we breathe in and out at each breath at rest

Question 17

What is breathing rate?

Answer 17

– the number of breaths per minute, can be calculated from the spirometer
trace by counting the number of peaks or troughs in a minute

Question 18

What is the residual volume?

Answer 18

The volume of air which is always present in the lungs

Question 19

gas exchange in bony fish

Answer 19

-fish have a small surface area to volume ratio for gas exchange
-have an impermeable membrane so gases can’t diffuse through their skin therefore fish need a
specialised exchange surface
- bony fish have four pairs of gills, each gill supported by an
arch
- Along each arch there are multiple projections called gill filaments, with lamellae on
them which participate in gas exchange
-blood and water flow across the lamellae in a counter current direction meaning they flow in opposite direction

Question 20

How are the projections held apart?

Answer 20

by water flow, in the absence of water they stick
together, meaning fish cannot survive very long out of water

Question 21

Ventilation in bony fish and insects

Answer 21

Ventilation is required to maintain a continuous unidirectional flow —Ventilation begins with the fish opening its mouth followed by lowering the floor of buccal cavity,
enabling water to flow into it
- fish closes its mouth, causing the buccal cavity floor to raise, increasing the pressure
The water is forced over the gill filaments by the difference in pressure between the mouth cavity and opercular cavity. The operculum
acts as a valve and pump and lets water out and pumps it in

Question 22

Because insects do not possess a transport system, what does it mean?

Answer 22

Insects do not possess a transport system therefore oxygen needs to be transported directly
to tissues undergoing respiration. This is achieved with the help of spiracles, small
openings of tubes, either bigger trachea or smaller tracheoles, which run into the body of an
insect and supply it with the required gases. At the end of each tracheole is a small amount of
tracheal fluid which allows gasses to dissolve and then diffuse into the cells.
Spiracles can be opened and closed to avoid excessive water loss

Question 23

What is counter-current flow?

Answer 23

An adaptation for gaseous exchange in bony fish. Blood in the gill
filaments and water moving over the gills flow in opposite directions, maintaining a steep
oxygen concentration gradient.

Question 24

Gill filaments

Answer 24

The main site of gaseous exchange in fish, over which water flows. They are
found in large stacks, known as gill plates, and have gill lamellae which provide a large
surface area for exchange.

Question 25

Gill lamellae

Answer 25

The fine branches of the gill filaments. They are adapted for gaseous
exchange by having a large surface area and good blood supply.

Question 26

Gill plates

Answer 26

Large stacks of gill filaments

Question 27

Gills

Answer 27

The organs of gaseous exchange in fish. They are contained in a gill cavity and are
made up of gill lamellae, gill filaments and gill plates.

Question 28

What is the mammalian gaseous exchange system?

Answer 28

A complex system found in mammals in which
oxygen and carbon dioxide gases are exchanged

Question 29

What is Operculum?

Answer 29

A flap that covers the gills of bony fish. It protects the gills and helps to maintain
a constant stream of water over them.

Question 30

Tracheae (insects)

Answer 30

Large tubes that run from the spiracles, into and along an insect’s body.
They are supported by spirals of chitin. The tracheae divide further into smaller tracheoles.

Question 31

Tracheal fluid

Answer 31

A fluid found at the ends of the tracheoles. The amount of fluid affects the
surface area available for gaseous exchange and water loss

Question 32

Tracheoles

Answer 32

Divisions of the tracheae that run throughout the tissues of an insect, forming a
complex network. They are the main site of gas exchange and are completely permeable to
gases.