PAPER 3: REQUIREMENTS FOR LIFE BLURT PROMPTS ANSWERS
Year 1 Chapter 8: Adaptations for gas exchange
What are the essential features of exchange surfaces for rapid diffusion of gases?
- Must have a large enough surface area to volume ratio so gas exchange can satisfy metabolism
- Be thin – short diffusion pathways
- Be permeable – respiratory gases diffuse easily
- Have a mechanism to provide steep concentration gradient across the surface
What do the above features allow?
Increase in body size and metabolic rate
Why can unicellular organisms such as Amoeba use their surface for gas exchange?
- Large SA:Vol ratio
- Cell membrane is thin – rapid diffusion
- Single cell is thin itself – distances inside cell are short
Why is there an upper limit to the size of a cell?
Diffusing molecules change direction every time they collide. If the pathway is too long the molecules
change direction too often so that it would take too long to supply enough oxygen or remove enough
carbon dioxide for the cell to function.
Compare the gas exchange systems of flatworms and earthworms
Flat worms have a much larger surface area than a spherical organism of the same volume. Their large
SA:Vol ratio means they’ve overcome the problem of size increase and diffusion pathways are kept
short.
Earthworms respiratory surface is their skin, so they keep it moist with mucus. They have low oxygen
requirements as they are slow moving and have a low metabolic rate. Enough oxygen diffuses across
the skin and into the capillaries underneath. Haemoglobin is in its blood and blood vessels maintain the
concentration gradient. Carbon dioxide also diffuses out across the skin.
What are the special features of multicellular animals in comparison to unicellular organisms?
- Higher metabolic rate
- Increase in size and specialisation creates interdependent systems
- Actively maintain concentration gradients (ventilatory mechanisms)
- Respiratory surfaces must be thin but not fragile (internal systems)
What are the major problems for gas exchange in terrestrial organisms?
- Water evaporates from surfaces causing dehydration
- Surfaces must be thin enough for gases, but this means they are also thin enough for water to
diffuse across – subsequently organisms lose water
- Heat loss
What are the three main types of respiratory surface in animals?
Gills, Lungs, and Tracheae
What special features might the most advanced multi-cellular organisms have for gas exchange?
- Ventilation mechanism
- Internal transport system
- Respiratory pigments
How does gas exchange occur in amphibians?
Through the moist and permeable skin, capillary network just below the skin. When animal is active gas
exchange also occurs through the lungs.
How does gas exchange occur in reptiles?
Lungs (more complex than lungs in amphibians)
, How does gas exchange occur in birds?
Lots of oxygen is required for flight. Do not have a diaphragm but flight muscles ventilate lungs more
efficiently than other vertebrates.
Draw and label the structure of a fish gill
Compare parallel and counter-current flow
Parallel flow (same direction) – diffusion only continues until gradients are equal blood oxygen
concentration is limited to 50% its possible maximum.
Counter-current (opposite directions) – water always has higher oxygen concentration than the blood,
so oxygen diffuses into the blood along the entire length of the lamellae. Generally get to 80%
saturation.
What is the ventilation mechanism in bony fish?
To take water in:
1. Mouth opens
2. Operculum closes
3. Mouth floor is lowered
4. Volume inside mouth cavity increases
5. Pressure inside mouth cavity decreases
6. Water flows in along pressure gradient
To force water out over the gills:
1. Mouth closes
2. Operculum opens
3. Mouth floor is raised
4. Volume inside mouth cavity decreases
5. Pressure inside mouth cavity increases
6. Water flows along pressure gradient out over the gills
Why do fish die when they are out of water for a long time?
Gill lamellae stick together out of water causing the gills to collapse. This reduces the surface area for
gas exchange.
Draw and label the structure of the human breathing system
, What is the mechanism for inspiration in humans?
1. External Intercostal Muscles contract + raise the ribcage
2. Outer pleural membranes pulled out
3. Pressure in pleural cavity decreases and inner membrane moves outwards
4. Diaphragm muscles contract = flattens
5. Pulls on the lungs + alveoli expand increasing thorax volume
6. Alveolar pressure decreases below atmospheric pressure
7. Air is drawn into the lungs
8. Surfactant reduces surface tension and prevents the alveoli collapsing during exhalation
What is the mechanism for expiration in humans?
1. External intercostal muscles relax + lower the ribcage
2. Outer pleural membranes pulled in
3. Pressure in pleural cavity increases and inner membrane
moves inwards
4. Diaphragm relaxes = domes upwards
5. Decreasing thorax volume
6. Pressure in lungs is greater than atmospheric pressure so
air is forces out of the lungs
What are the essential features of the alveoli? + Draw and
label a diagram
- They provide a large surface area
- Surfactant allows gases to dissolve
- Alveoli made of squamous epithelium (one cell thick =
short diffusion path)
- Extensive capillary network – maintains diffusion gradients
- Capillary walls also one cell thick
How does gas exchange occur in insects? Draw and label a diagram
Year 1 Chapter 8: Adaptations for gas exchange
What are the essential features of exchange surfaces for rapid diffusion of gases?
- Must have a large enough surface area to volume ratio so gas exchange can satisfy metabolism
- Be thin – short diffusion pathways
- Be permeable – respiratory gases diffuse easily
- Have a mechanism to provide steep concentration gradient across the surface
What do the above features allow?
Increase in body size and metabolic rate
Why can unicellular organisms such as Amoeba use their surface for gas exchange?
- Large SA:Vol ratio
- Cell membrane is thin – rapid diffusion
- Single cell is thin itself – distances inside cell are short
Why is there an upper limit to the size of a cell?
Diffusing molecules change direction every time they collide. If the pathway is too long the molecules
change direction too often so that it would take too long to supply enough oxygen or remove enough
carbon dioxide for the cell to function.
Compare the gas exchange systems of flatworms and earthworms
Flat worms have a much larger surface area than a spherical organism of the same volume. Their large
SA:Vol ratio means they’ve overcome the problem of size increase and diffusion pathways are kept
short.
Earthworms respiratory surface is their skin, so they keep it moist with mucus. They have low oxygen
requirements as they are slow moving and have a low metabolic rate. Enough oxygen diffuses across
the skin and into the capillaries underneath. Haemoglobin is in its blood and blood vessels maintain the
concentration gradient. Carbon dioxide also diffuses out across the skin.
What are the special features of multicellular animals in comparison to unicellular organisms?
- Higher metabolic rate
- Increase in size and specialisation creates interdependent systems
- Actively maintain concentration gradients (ventilatory mechanisms)
- Respiratory surfaces must be thin but not fragile (internal systems)
What are the major problems for gas exchange in terrestrial organisms?
- Water evaporates from surfaces causing dehydration
- Surfaces must be thin enough for gases, but this means they are also thin enough for water to
diffuse across – subsequently organisms lose water
- Heat loss
What are the three main types of respiratory surface in animals?
Gills, Lungs, and Tracheae
What special features might the most advanced multi-cellular organisms have for gas exchange?
- Ventilation mechanism
- Internal transport system
- Respiratory pigments
How does gas exchange occur in amphibians?
Through the moist and permeable skin, capillary network just below the skin. When animal is active gas
exchange also occurs through the lungs.
How does gas exchange occur in reptiles?
Lungs (more complex than lungs in amphibians)
, How does gas exchange occur in birds?
Lots of oxygen is required for flight. Do not have a diaphragm but flight muscles ventilate lungs more
efficiently than other vertebrates.
Draw and label the structure of a fish gill
Compare parallel and counter-current flow
Parallel flow (same direction) – diffusion only continues until gradients are equal blood oxygen
concentration is limited to 50% its possible maximum.
Counter-current (opposite directions) – water always has higher oxygen concentration than the blood,
so oxygen diffuses into the blood along the entire length of the lamellae. Generally get to 80%
saturation.
What is the ventilation mechanism in bony fish?
To take water in:
1. Mouth opens
2. Operculum closes
3. Mouth floor is lowered
4. Volume inside mouth cavity increases
5. Pressure inside mouth cavity decreases
6. Water flows in along pressure gradient
To force water out over the gills:
1. Mouth closes
2. Operculum opens
3. Mouth floor is raised
4. Volume inside mouth cavity decreases
5. Pressure inside mouth cavity increases
6. Water flows along pressure gradient out over the gills
Why do fish die when they are out of water for a long time?
Gill lamellae stick together out of water causing the gills to collapse. This reduces the surface area for
gas exchange.
Draw and label the structure of the human breathing system
, What is the mechanism for inspiration in humans?
1. External Intercostal Muscles contract + raise the ribcage
2. Outer pleural membranes pulled out
3. Pressure in pleural cavity decreases and inner membrane moves outwards
4. Diaphragm muscles contract = flattens
5. Pulls on the lungs + alveoli expand increasing thorax volume
6. Alveolar pressure decreases below atmospheric pressure
7. Air is drawn into the lungs
8. Surfactant reduces surface tension and prevents the alveoli collapsing during exhalation
What is the mechanism for expiration in humans?
1. External intercostal muscles relax + lower the ribcage
2. Outer pleural membranes pulled in
3. Pressure in pleural cavity increases and inner membrane
moves inwards
4. Diaphragm relaxes = domes upwards
5. Decreasing thorax volume
6. Pressure in lungs is greater than atmospheric pressure so
air is forces out of the lungs
What are the essential features of the alveoli? + Draw and
label a diagram
- They provide a large surface area
- Surfactant allows gases to dissolve
- Alveoli made of squamous epithelium (one cell thick =
short diffusion path)
- Extensive capillary network – maintains diffusion gradients
- Capillary walls also one cell thick
How does gas exchange occur in insects? Draw and label a diagram
