Gas Exchange

Question 1

Fish Gills Structure and Adaptations

Answer 1

Filaments: Each gill arch is attached to two stacks of filaments. On the surface of each filament, there are rows of lamellae

Gill Lamellae: lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries

Operculum: a flap of tissue covering the gills

Question 2

Fish Process of Gas Exchange

Answer 2

Fish opens mouth increasing volume of buccal cavity and decreasing the pressure within it so water flows in.
Fish closes mouth increasing pressure in buccal cavity so water flows into gill cavity down a pressure gradient.
Water passes over the lamellae and oxygen diffuses into the blood, and CO2 diffuses out and water is then pushed out as the operculum opens.

Question 3

Countercurrent Exchange

Answer 3

The flow of water in the lamellae is opposite to the flow of blood.
This maintains a steep oxygen concentration gradient as water is always next to blood with a lower concentration of oxygen so that oxygen diffuses into the blood for the full length of the gill.

Question 4

Insects Gas Exchange System

Answer 4

Spiracles: an opening in the exoskeleton of an insect which has valves, allows gases to enter and exit

Tracheae: tubes within the insect respiratory system which lead to tracheoles. Rigid rings of chitin that keep the tracheae open

Tracheoles: narrower tubes that run between cells and into the muscle fibres - the site of gas exchange

Question 5

Insects Process of Gas Exchange

Answer 5

Gases move in and out of the tracheae through the spiracles. The gases move in to the tracheoles where oxygen diffuses into the body tissue and CO2 diffuses out.
Flying insects:
Contraction of abdominal muscles creates mass flow of air into the tracheal system, and fluid around the tracheoles moves in to the respiring muscle reducing the diffusion distance, increasing gas exchange

Question 6

Terrestrial Insects

Answer 6

Can close their spiracles to prevent water loss.
Have hairs around their spiracles to decrease the water potential gradient between inside the tracheae and the environment, reducing water loss.
Have a waxy cuticle which is waterproof

Question 7

Plants Leaf Adaptation

Answer 7

Thin and flat: short diffusion pathway and large surface area to volume ratio
Stomata allow oxygen to enter easily
Mesophyll contains large air spaces for movement of gases around the leaf

Question 8

Plants Limiting Water Loss

Answer 8

Stomata located on the underside of the leaf, less water loss as less sunlight for evaporation and less wind, and are regulated by guard cells.
High concentration of water, guard cells are turgid, stomata are open.
Low concentration, guard cells flaccid, stomata closed.

Question 9

Xerophytic Plants

Answer 9

Fewer stomata
Curled leaves to protect the stomata from wind
Waxy cuticle which is waterproof
Hairs which trap moist air reducing the water potential gradient between the inside of the leaves and the outside reducing water loss.

Question 10

Mammals Gas Exchange System

Answer 10

Nasal Cavity: High blood supply. Moistens the air Contains goblet cells which produce mucus which traps bacteria

Trachea: Wide tube. Supported by cartilage to keep it open during pressure changes. Lined with ciliated epithelial cells that move mucus to throat

Bronchi: Supported by rings of cartilage and lined with ciliated epithelial cells. Narrower than the trachea

Bronchioles: Narrower than bronchi. No cartilage, only muscle and elastic fibres, enabling contraction and relaxation during ventilation

Alveoli: Large number of alveoli. Site of gas exchange. High blood supply due to large network of capillaries, walls are one cell thick to increase rate of diffusion into blood

Question 11

Inhalation

Answer 11

External intercostal muscles contract
Internal Intercostal muscles relax
Pulls ribs up and out
Diaphragm contracts and flattens
Volume of thorax increases
Pressure of air inside the lungs decreases and is lower than outside
Air enters the lungs down a pressure gradient

Question 12

Exhalation

Answer 12

External intercostal muscles relax
Internal Intercostal muscles contract
Brings ribs down and in
Diaphragm relaxes and domes upwards
Volume of thorax decreases
Pressure of air inside the lungs increases and is higher than outside
Air leaves the lungs down a pressure gradient

Question 13

Tidal Volume

Answer 13

Volume of air breathed in and out during each breath at rest

Question 14

Breathing Rate

Answer 14

Number of breaths per minute

Question 15

Pulmonary Ventilation Rate

Answer 15

Tidal volume x breathing rate
Measured using a spirometer