Exchange Surfaces

Question 1

Describe surface area to volume ratio

Answer 1

Smaller organisms (such as amoeba) have large SA in comparison to V, this means that there is a shorter distance from the outside of the organism to the middle of it which means simple diffusion meets the exchange needs for small organisms
The larger an organism is, the smaller the ratio which means the larger the distance from the middle to the outside, they also have higher metabolic rates (require more oxygen) therefore have adaptations to make exchange across their surface more efficient

Question 2

Three factors which affect the rate of diffusion

Answer 2

Surface area
Concentration gradient
Length of diffusion pathway

Question 3

Examples of adaptations which increase the rate of diffusion

Answer 3

Surface area- projections on root hair cells/folded membranes
Concentration gradient- ventilation, good blood supply and countercurrent flow mechanism
Length of diffusion pathway- Alveoli wall is one in layer of squamous epithelial cells

Question 4

Features of the mammalian gas exchange system

Answer 4

Trachea
Bronchi and bronchioles
Alveoli

Question 5

Structure of the trachea

Answer 5

C shaped rings of cartilage for support
Cilliated epithelium with goblet cells
Smooth muscle is within the walls of the trachea, the muscle contracts if there are harmful substances detected which makes the lumen constrict which reduces airflow into the lungs. When smooth muscle relaxes, the lumen dilates. This stretch and recoil of the lumen is due to elastic fibres in the tracheal wall

Question 6

Structure of the bronchi and bronchioles

Answer 6

The trachea splits into two tubes (bronchi) which connect to the lungs.
These split into smaller tubes to create a network of bronchioles
They both have cartilage within their walls for structural support and to keep the tubes open

Question 7

Structure of alveoli

Answer 7

At the end of bronchioles, site of gas exchange
Large surface area (large number of alveoli)
Short diffusion distance (very thin walls made up of squamous epithelial cells)
Maintains a concentration gradient (surrounded by a network of capillaries to remove exchanged gases)
Oxygen diffuses from alveoli into the blood in capillaries and carbon dioxide diffuses from the blood in capillaries to the alveoli

Question 8

What is ventilation and why do we need it

Answer 8

Ventilation is the mechanism of breathing which involves the diaphragm and antagonistic interactions between the external and internal intercostal muscles which brings about pressure changes in the thorax
Ventilation maintains the concentration gradient for gas exchange in the alveoli

Question 9

Describe the process of ventilation (inspiration and expiration)

Answer 9

(Inspiration)
Diaphragm contracts (goes flatter)
External intercostal muscles contract
Internal intercostal muscles relaxes
Rib cage pulled up and out
Increased volume of the thorax leading to reduced air pressure.
Leads to air flowing into the lungs

(Expiration)
Diaphragm relaxes (dome shape)
External intercostal muscles relax
Internal intercostal muscles contract
Rib cage is pulled inwards and down
Decreased volume of the thorax leading to increased air pressure.
Leads to air bring forced out of the lungs

Question 10

How can you measure the volume of air inhaled and exhaled

Answer 10

Using a spirometer

Question 11

What is vital capacity

Answer 11

The maximum volume of air and individual can inhale and exhale during a deep breath

Question 12

What is tidal volume

Answer 12

The volume of air inhaled (peaks) and exhaled (troughs) when resting

Question 13

What is residual volume

Answer 13

The volume of air that always remains in the lungs so they don’t collapse

Question 14

What is the breathing rate

Answer 14

Number of breaths taken per minute
(can be calculated looking at a graph by looking at number of full leaks and troughs there are per minute)

Question 15

What is ventilation rate

Answer 15

Volume of air inhaled per minute

Question 16

How to calculate ventilation rate

Answer 16

Tidal volume x breathing rate

Question 17

Describe ventilation in fish

Answer 17

Fish swim with mouth open so water flows over gills
Fish lower their buccal cavity and open their mouth which increases volume of the buccal cavity and decreases pressure. Water flows into buccal cavity
The operculum valve will shut and operculum cavity (where the gills are) will expand, this causes an increase in the volume of the operculum cavity and a decrease in pressure.
The fish will then raise the floor of the buccal cavity forcing the water from the buccal cavity over the gills within the operculum cavity
Finally fish closes its mouth and opens the operculum (bony flap that covers gills) which increases the pressure and forces water over the gills and out of the side of the fishes head.
This ventilation ensures there is a constant flow of water over the gills for gas exchange

Question 18

Describe gas exchange in the fish

Answer 18

Occurs across their gills
There are four layers of gills on each side of their head (made of gill filaments and gill lamellae (plates))
Large surface area- Many gill filaments and lamellae which are stacked at right angles to eachother
Short diffusion distance- Gill lamellae and filaments are both thin and contain a capillary network
Maintain concentration gradient- Countercurrent mechanism

Question 19

Describe the counter current flow mechanism

Answer 19

Water has a lower dissolved oxygen concentration than the concentration of oxygen in the atmosphere
Fish use the counter current flow mechanism to maintain the concentration gradient required for diffusion
Water flows over the gill lamellae in the opposite direction to the flow of blood in the capillaries, this ensures that a diffusion gradient is maintained across the entire length of the gill lamellae

Question 20

Describe gas exchange in insects

Answer 20

Involves a tracheal system (made up of spiracles and trachea)
Spiracles are valve like structures that run along the side of the abdomen (they are
like the stomata of the plant (they can open and close to help gases go in and out and to prevent water loss))
Spiracles are attached to trachea which branch out to the site of gas exchange (tracheoles)
Insects contract and relax their abdominal muscles to move gases into and out of spiracles to the trachea
Large surface area- many branching tracheoles
Short diffusion distance- Many branching tracheoles reach muscle and thin walled
Concentration gradient- maintained by cells respiring and abdominal muscle contracting pumps air
When insects are in flight, cells anaerobically respire to produce lactate, water potential is lowered and water moves from tracheoles into cells by osmosis which decreases volume of liquid in tracheoles and causes more air from the atmosphere to move in.