3.3.2 Gas exchange Flashcards
What are the adaptations of gas exchange surfaces in single-celled organisms?
Single-celled organisms have a large surface area to volume ratio a thin surface for a short diffusion pathway and gas exchange occurs directly across the body surface by diffusion.
Describe the tracheal system of an insect and how it facilitates gas exchange.
Insects have a tracheal system consisting of tracheae which branch into smaller tracheoles that extend to all body tissues. Oxygen enters through spiracles and diffuses directly into cells. Tracheoles have thin walls for a short diffusion pathway and rhythmic abdominal movements ventilate the system.
What are the adaptations of fish gills for efficient gas exchange?
Fish gills have gill filaments covered in lamellae to increase surface area. Lamellae have a thin epithelium for a short diffusion pathway and the counter-current principle ensures a steep concentration gradient is maintained along the entire length of the gill.
Explain the counter-current principle in fish gills.
In fish gills water flows over the lamellae in the opposite direction to blood flow. This maintains a steep concentration gradient along the entire length of the gill as water with a high oxygen concentration always meets blood with a lower oxygen concentration.
How do dicotyledonous plants facilitate gas exchange in their leaves?
Dicotyledonous plants have a large surface area provided by mesophyll cells which are thin for a short diffusion pathway. Stomata control gas exchange opening to allow CO2 in and O2 out. Air spaces in the mesophyll increase the surface area for diffusion.
How do terrestrial insects balance efficient gas exchange with water loss?
Terrestrial insects have spiracles that can open and close to reduce water loss. A waterproof waxy cuticle and small surface area to volume ratio also minimize water loss while allowing sufficient gas exchange.
What adaptations do xerophytic plants have to limit water loss while maintaining gas exchange?
Xerophytic plants have thick waxy cuticles to reduce evaporation rolled leaves to trap moist air and reduce the water potential gradient sunken stomata to trap humid air and fewer stomata to minimize water loss. Some also have hairs on leaves to reduce air movement.
What is the gross structure of the human gas exchange system?
The human gas exchange system includes the trachea bronchi bronchioles alveoli and lungs.
What are the essential features of the alveolar epithelium for gas exchange?
The alveolar epithelium is one cell thick providing a short diffusion pathway and is surrounded by a dense capillary network to maintain a steep concentration gradient.
Describe the mechanism of breathing during inspiration.
During inspiration the diaphragm contracts and flattens while the external intercostal muscles contract moving the ribcage upwards and outwards. This increases the volume of the thoracic cavity reducing the pressure below atmospheric pressure and drawing air into the lungs.
Describe the mechanism of breathing during expiration.
During expiration the diaphragm relaxes and moves upwards while the internal intercostal muscles contract moving the ribcage downwards and inwards. This decreases the volume of the thoracic cavity increasing the pressure above atmospheric pressure and forcing air out of the lungs.
How does antagonistic interaction between intercostal muscles aid ventilation?
External intercostal muscles contract during inspiration while internal intercostal muscles relax and vice versa during expiration. This antagonistic interaction changes the thoracic cavity’s volume and pressure to facilitate air movement.
Plants – explain why stomata open due to increase in light intensity (1)
allowing carbon dioxide to enter for photosynthesis;
Or
for gas exchange allowing photosynthesis
Plants -Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (4)
- (Carbon dioxide enters) via stomata; Reject stroma
- (Stomata opened by) guard cells; 3. Diffuses through air spaces;
- Down diffusion gradient;
Plants – describe & explain an advantage and disadvantage to having a higher stomatal density
Advantage:
1. More carbon dioxide uptake;
2. More photosynthesis so faster/more growth;
Disadvantage:
3. More water loss/transpiration Accept plant wilts for ‘more water loss’
4. Less photosynthesis so slower/less growth;
Plants - Adaptations to desert plants (6)
- Hairs so ‘trap’ water vapour and water potential gradient decreased;
- Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
- Thick (cuticle/waxy) layer so increases diffusion distance;
- Waxy layer/cuticle so reduces evaporation/transpiration;
- Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased;
- Spines/needles so reduces surface area to volume ratio;
fish - counter-current mechanism (3)
- Water and blood flow in opposite directions;
- Blood always passing water with a higher oxygen concentration;
- Diffusion/concentration gradient (maintained) along (length of) lamella/filament;
Fish - Explain two ways in which the structure of fish gills is adapted for efficient gas exchange. (2)
- Many lamellae / filaments so large surface area;
- Thin (surface) so short diffusion pathway;
Insects - Describe & explain how the structure of the insect gas exchange system provides cells with sufficient oxygen
- Spiracles (lead) to tracheae (that lead) to tracheoles;
- Open spiracles allow diffusion of oxygen from air OR Oxygen diffusion through tracheae/tracheoles;
- Tracheoles are highly branched so large surface area (for exchange);
- Tracheole (walls) thin so short diffusion distance (to cells)
OR
Highly branched tracheoles so short diffusion distance (to cells)
OR
Tracheoles push into cells so short diffusion distance; - Tracheole walls are permeable to oxygen;
Insects - Describe & explain how the structure of the insect gas exchange system: limits water loss.(2)
- Cuticle/chitin in tracheae impermeable so reduce water loss;
- Spiracles close (eg.during inactivity) preventing water loss;
Insects - Abdominal Pumping (3)
- Abdominal pumping/pressure in tubes linked to carbon dioxide release;
- (Abdominal) pumping raises pressure in body;
- Air/carbon dioxide pushed out of body /air/carbon dioxide moves down pressure gradient (to atmosphere)
Insects - Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.
- Tracheoles have thin walls so short diffusion distance to cells;
- Highly branched / large number of tracheoles so short diffusion distance to cells;
- Highly branched / large number of tracheoles so large surface area (for gas exchange);
- Tracheae provide tubes full of air so fast diffusion (into insect tissues);
- Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
OR
Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange); - Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
Lungs - Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange.
Mark in pairs
- Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane Accept thin cells
Accept ‘one cell thick’ - Reduces diffusion distance/pathway;
- Permeable;
- Allows diffusion of oxygen/carbon dioxide;
- moist
- Increase rate of diffusion
Lungs – describe and explain inhaling (4)
- Diaphragm (muscle) contracts and external intercostal muscles contract; Ignore ribs move up and out
- (Causes volume increase and) pressure decrease;
- Air moves down a pressure gradient Ignore along
OR
Air enters from higher atmospheric pressure;
Lungs - Describe the pathway taken by an oxygen molecule from an alveolus to the blood. (2)
- (Across) alveolar epithelium;
- Endothelium of capillary;
Lungs - Explain how one feature of an alveolus allows efficient gas exchange to occur.
- (The alveolar epithelium) is one cell thick; Reject thin membrane
- Creating a short diffusion pathway / reduces the diffusion distance;
Lungs - Describe the gross structure of the human gas exchange system (1)
- Named structures – trachea, bronchi, bronchioles, alveoli;
Lungs – Describe how we breathe in and out.(4)
- Breathing in – diaphragm contracts and external intercostal muscles contract;
- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
For thoracic cavity accept ‘lungs’ or ‘thorax’.
Reference to ‘thoracic cavity’ only required once.
- Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).
- (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
Describe and explain one feature of the alveolar epithelium that makes the
epithelium well adapted as a surface for gas exchange.
Do not refer to
surface area or moisture in your answer. (2)
- Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane
Accept thin cells
Accept ‘one cell thick’ - Reduces diffusion distance/pathway;
- Permeable;
- Allows diffusion of oxygen/carbon dioxide;
Ignore gas exchange
Explain how the counter-current principle allows efficient oxygen uptake in
the fish gas exchange system. (2)
- Blood and water flow in opposite directions;
- Diffusion/concentration gradient (maintained) along
(length of) lamella/filament;
Accept for 2 marks, suitably labelled diagram
Describe and explain the mechanism that causes lungs to fill with air. (3)
- Diaphragm (muscle) contracts and external intercostal muscles
contract;
Ignore ribs move up and out
- (Causes volume increase and) pressure decrease;
- Air moves down a pressure gradient
Ignore along
Explain why death of alveolar epithelium cells reduces gas exchange in
human lungs. (3)
- Reduced surface area;
- Increased distance for diffusion;
Accept description of efficient gas exchange in
healthy alveolar epithelium as long as reference
made to the damaged tissue changing this.
- Reduced rate of gas exchange;
Describe and explain the advantage of the counter-current principle in gas
exchange across a fish gill. (3)
- Water and blood flow in opposite directions;
- Maintains diffusion/concentration gradient of oxygen
Accept: converse for carbon dioxide
Accept: equilibrium not reached
OR
Oxygen concentration always higher (in water);
- (Diffusion) along length of lamellae/filament/gill/capillary;
Accept: all/whole of lamellae/filament//gill/capillary
Use your knowledge of gas exchange in leaves to explain why plants
grown in soil with very little water grow only slowly. (2)
- Stomata close;
- Less carbon dioxide (uptake) for less photosynthesis/glucose
production;
Describe the pathway taken by an oxygen molecule from an alveolus to the
blood. (2)
- (Across) alveolar epithelium;
- Endothelium / epithelium of capillary;
Explain how one feature of an alveolus allows efficient gas exchange to
occur. (2)
- (The alveolar epithelium) is one cell thick;
Reject thin membrane
- Creating a short diffusion pathway / reduces the diffusion distance;
Describe the gross structure of the human gas exchange system and how
we breathe in and out. (6)
- Named structures – trachea, bronchi, bronchioles, alveoli;
Reject mp1 if structures from other physiological
systems are named but award mp2 if the correct
structures are in the correct order.
- Above structures named in correct order
OR
Above structures labelled in correct positions on a diagram;
Reject mp1 if structures from other physiological
systems are named but award mp2 if the correct
structures are in the correct order.
- Breathing in – diaphragm contracts and external intercostal muscles
contract; - (Causes) volume increase and pressure decrease in thoracic cavity
(to below atmospheric, resulting in air moving in);
For thoracic cavity accept ‘lungs’ or ‘thorax’.
Reference to ‘thoracic cavity’ only required once.
- Breathing out - Diaphragm relaxes and internal intercostal muscles
contract; - (Causes) volume decrease and pressure increase in thoracic cavity
(to above atmospheric, resulting in air moving out);
Explain ways in which an insect’s tracheal system is adapted for
efficient gas exchange.
- Tracheoles have thin walls so short diffusion distance to cells;
- Highly branched / large number of tracheoles so short diffusion
distance to cells; - Highly branched / large number of tracheoles so large surface
area (for gas exchange); - Tracheae provide tubes full of air so fast diffusion (into insect
tissues); - Fluid in the end of the tracheoles that moves out (into tissues)
during exercise so faster diffusion through the air to the gas
exchange surface;
OR
Fluid in the end of the tracheoles that moves out (into tissues)
during exercise so larger surface area (for gas exchange); - Body can be moved (by muscles) to move air so maintains
diffusion / concentration gradient for oxygen / carbon dioxide;
Explain two ways in which the structure of fish gills is adapted for efficient
gas exchange. (2)
- Many lamellae / filaments so large surface area;
- Thin (surface) so short diffusion pathway;
1 & 2 must each have a feature and a consequence
Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the
gills. (3)
- Water and blood flow in opposite directions;
Allow diagram showing counter-flow - Blood always passing water with a higher oxygen concentration;
- Diffusion gradient maintained throughout length (of gill)
Explain why damage to alveolar epithelium cells reduces gas exchange in the lungs.
reduced surface area
increases the diffusion distance
reduces the rate of gas exchange
An oxygen concentration gradient is maintained between the alveoli and the lung capillaries.
Describe how ventilation helps to maintain this concentration gradient.
(ventilation) brings in air containing a higher oxygen concentration into the alveoli
(ventilation) removes air with a lower oxygen concentration from the alveoli
Larger organisms, such as humans, need specialised systems that allow the uptake of oxygen.
Explain why
larger organisms have a smaller surface area to volume ratio
specialised exchange systems overcome the long diffusion pathway
