Component 3 - Animal Gas Exchange

Question 1

What determines how much oxygen an organism needs

Answer 1

It’s Volume

Question 2

What determines the rate that oxygen is absorbed at

Answer 2

The surface area available for gas exchange

Question 3

What does the surface area to volume ratio of an organism affect

Answer 3

• the surface adapted for use for gas exchange
• the level of activity of the organism

Question 4

Why can’t insects use their external surface for gas exchange

Answer 4

they are covered in an impermeable cuticle to reduce water loss by evaporation

Question 5

How does air travel through the inect gas exchange system

Answer 5

1. Pairs of spiracles on segments of the thorax
   and abdomen
2. These holes lead to tubes called tracheae
   leading to tracheoles
3. Tracheoles enter muscle cells directly. They have fluid at the end for dissolving and diffusion of oxygen
4. During flight, fluid in tracheoles decreases to shorten diffusion path and whole-body contractions ventilate the tracheal system by speeding up air flow through spiracles.

Question 6

Why do fish require a specialised gas exchange surface

Answer 6

• they have a smaller surface area to volume ratio
• they are relatively active and so have high metabolic rates making oxygen requirements high
• they require a ventilation mechanism to maintain concentration gradients for gas exchange

Question 7

When fish are removed from water what happens to their fish gill filaments

Answer 7

The gill filaments to collapse, stick together and the gas exchange surface becomes too small for survival

Question 8

How do fish ventilate their gills

Answer 8

1. Mouth opens, floor of buccal cavity lowers so volume increases, pressure decreases and water rushes in
2. Mouth closes, floor of buccal cavity raises, increasing pressure pushing water over the gills
3. Pressure in gill cavity increases and water forces operculum open and leaves through it

Question 9

What is the exchange surface in the gills

Answer 9

The gills have gill filaments made of gill plates/lamellae (the gas exchange surface across which the water flows)

Question 10

What do the gill rakers do

Answer 10

Gill rakers prevent large particulates entering and blocking the gills

Question 11

What are the 5 features of a gas exchange surface

Answer 11

• moist in terrestrial animals
• thin (short diffusion pathway)
• have a large surface area
• be permeable to gases
• have a good blood supply to maintain concentration gradients (larger organisms only)

Question 12

Why is outercurrent flow better than continuous flow

Answer 12

Counter current flow
* The concentration gradient is maintained and oxygen diffuses into the blood across the entire gill plate

Continuous flow
* equilibrium is reached and oxygen diffusion
reaches no net movement halfway across the
gill plate

Question 13

How is an Amoeba adapted to gas exchange

Answer 13

• Single cell
• Large surface area to volume ratio
• Rate of oxygen diffusion through external surface meets demand
• A low metabolic rate means oxygen demand is low
• There is a short diffusion distance to the middle of the cell

Question 14

How is a Flatworm adapted for gas exchange

Answer 14

• Multicellular
• Smaller surface area to volume ratio
• Flattened body to reduce diffusion distance so rate of oxygen diffusion through body surface meets demand

Question 15

How is an Earthworm adapted for gas exchange

Answer 15

• Multicellular
• Even smaller surface area to volume ratio
• Body surface still used for gas exchange but circulatory system needed to distribute oxygen. Blood vessels are close
  to skin surface and blood has haemoglobin with a high affinity for oxygen.
• Mucus secreted to moisten surface and slow moving to reduce oxygen demand

Question 16

How do the human lungs inspirate

Answer 16

1. External intercostal muscles contract and pull the rib cage up and out
2. Outer pleural membrane is pulled out. This reduces pressure in the pleural cavity and the inner pleural membrane is pulled outward.
3. This pulls on the surface of the lungs and causes an increase in the volume of the alveoli.
4. Alveolar pressure decreases to below atmospheric pressure and air is drawn into the lungs.

Question 17

How does gas exchange in amphibia happen

Answer 17

Amphibia have aquatic tadpoles that have feathery gills. They don’t ventilate like fish but movement of the gills through water maintains a concentration gradient.

Tadpoles develop into adults. Adult amphibia live on land and in water but must return to the water to mate and lay eggs. Amphibia have soft, moist skin and exchange gases over their surface at rest. Oxygen and carbon dioxide circulate through a closed circulation system containing haemoglobin. When active, movements of the buccal cavity ventilate lungs, which are simple with few alveoli

Question 18

What tissue forms the alvoli

Answer 18

Squamous epithelia

Question 19

What do the external intercostal muscles do

Answer 19

contract to pull the ribcage up and out, increasing thoracic volume and causing air to enter the lungs (inspiration)

Question 20

What do internal entercostal muscles do

Answer 20

contract to pull the ribcage in and down, decreasing thoracic volume and causing air to leave the lungs (expiration).