Pack 7 - Exchange Flashcards
In what two ways can substance be exchanged between the internal and external environment of an organism?
- Diffusion
* Active transport
Why do animals with a higher metabolic rate require larger SA:V ratio?
They need to exchange substances at a higher rate.
Which has a higher SA to volume ratio - a bacterium or a mouse?
The bacterium
Why do large organisms need a specialised exchange surfaces?
They have a lower SA:V ratio. Substances (such as gases) need to supply and be transported to all cells. Therefore exchange surfaces increase the SA for this to take place.
What two ways have organisms adapted to supply all their cells with substances?
- Flattened shape
* Specialised exchange surface
What are 5 features of specialised exchange surfaces?
- Large SA
- Thin
- Selectively permeable
- Movement of the external medium to maintain CG (e.g. ventilation)
- Movement of the internal medium (e.g. blood)
Describe the structure of insect gas exchange systems.
- Spiracles (pores)
- Tracheae
- Tracheoles
- Body tissue
What is the importance of tracheoles in insects?
It means that each cell is a very short distance from a tracheal and therefore there is a short diffusion pathway for gases.
At rest, how does oxygen reach respiring insect cells?
Diffusion gradient - Oxygen diffuses along tracheoles down a concentration gradient as oxygen his used up an CO₂ diffuses out of cells.
How can insects increase the speed of gas exchange?
Mass transport - the contraction of muscles squeezes the tracheae enabling mass movement of air in and out.
Describe what happens to the tracheoles during periods of activity in insects and how this increases the rate of gas exchange?
- Anerobic respiration
- Lactate produced (soluble in cells)
- Decreases the ψ of the cell.
- Water at the ends of the tracheoles moves into the cells.
- Draws air in.
- Increased surface area for diffusion.
- Diffusion is after in a gas than in liquid.
Why is there water at the ends of tracheoles during rest in insects? What is the payoff of this?
- Decreases water loss
* It decreases the rate of diffusion of gases.
How can insects actively control water loss? What is the disadvantage of doing this?
- Closing the spiracles
* Gases can’t diffuse in and out
Why would the tracheal system not work for larger organisms?
It relies on diffusion and therefore the diffusion pathway must be short.
Name the process by which CO₂ is removed from single-celled organisms.
Diffusion
Why do fish need a specialised gas exchange surface?
Small SA:V ratio
Describe the structure of a gill.
- Gill filaments attached to a gill bar.
* Gill lamellae on the filaments are at right angles.
Which way does water flow over the gills in comparison to the direction of blood flow? What is this called?
- Opposite direction
* Counter current flow
Describe how the countercurrent flow system means more oxygen can absorbed than with parallel flow.
- Water with its highest oxygen concentration meets blood that already has a high concentration of oxygen.
- Water with the least oxygen concentration meets blood with little oxygen.
What is the maximum % of the oxygen in water that could be absorbed using parallel flow?
50%
Roughly how much of the water’s oxygen can diffuse into the blood using countercurrent flow?
80%
Why does water only flow one way through a fishes gills?
Water is much denser than air so would require a lot of effort to flow in and out.
How does the fish force water over its gills?
By decreasing the volume of its mouth and therefore increasing the pressure.
What happens to most of the oxygen produced by photosynthesis in plants?
It diffuses out of the leaf (some is used for respiration)
Do plants have a specialised gas exchange system? Why (not)?
No, since there is a shot fast diffusion pathway for gases in the external air to all living cells.
Where does most gaseous exchange occur in a plant?
The leaves
What three adaptation do leaves have for rapid diffusion of gases?
- Stomata (no cell is far from any stomata)
- Connected airspaces through the mesophyll.
- Large surface area of mesophyll cells.
- Flat - short diffusion distance to any one cell.
Where are most stomata cells found?
The underside of the leaves.
What is the name of the cells the surround the stomata?
Guard cells
How is the rate of gaseous exchange controlled by plants? What conflict does this create?
- Guard cells can open or close stomata.
* water loss
How is water loss controlled by guard cells?
Guard cells can open or close stomata.
In what three ways have insects evolved to reduce water loss?
- Small SA:V ratio
- Waterproof coverings
- Spiracles can close
What is the disadvantage of an effective gas exchange system (e.g. large surface area)?
Increased water loss.
How do ALL plants reduce water loss? (Two ways)
- Guard cells can open or close stomata.
* Waterproof coating
What is a xerophyte?
Plants with a restricted supply of water.
Give 5 ways in which xerophytes reduce water loss. (That other plants don’t have)
- Thick cuticle
- Rolling up leaves - traps still air with a high ψ and reduces ψ gradient.
- Hairy leaves - traps moist air next to the leaf - reduces ψ gradient
- Stomata in pits or grooves - trap moist still air - reduces ψ gradient
- reduced SA:V ratio
Why is the volume of oxygen absorbed by mammals relatively high? (2 reasons)
- Large organisms
* Maintain a high body temperature and high metabolic rate
Describe the parts of the respiratory system in order.
- mouth
- trachea
- (lungs)
- bronchi
- bronchioles
- alveoli
How and why is the trachea supported?
- Cartilage rings
* To keep it open
What do the trachea and bronchi produces to trap dirt particles? What structure moves the particles towards the throat?
Mucus
Cilia
Why are bronchiole walls made of muscle?
So they can restrict the flow of air
Why do alveoli have elastic fibres?
To stretch when inhaling and spring back to expel CO₂ when exhaling.
What is the process of moving air in and out of the lungs called?
Breathing/ventilation
Describe how inspiration takes place. (6 steps)
- External intercostal muscles contract.
- Ribs move up and out.
- Diaphragm contracts and flattens.
- Thorax volume increases.
- Pressure decreases to less than atmospheric.
- Air moves in
Describe how expiration takes place. (6 steps)
- Internal intercostal muscles contract.
- Ribs move down and in.
- Diaphragm relaxes and flattens.
- Thorax volume decreases.
- Pressure increases to more than atmospheric.
- Air moves out
State an equation for pulmonary ventilation. (give units)
pulmonary ventilation (dm³min⁻ⁱ) = tidal volume (dm³) x breathing rate (min⁻ⁱ)
What is tidal volume?
The volume of air normally breathed in in one breath.
Where is the site of gas exchange in mammals?
The epithelial cells of the alveoli.
Describe the structure of alveoli epithelial cells.
Flat
How many cells thick is the wall of an alveolus
1
Describe the movement of an oxygen molecule from the alveoli air sac to the red blood cell.
- The epithelial cells of the alveoli.
- The endothelial cells of the capillaries.
- Blood plasma
- Red blood cell
What is the advantage of having red blood cells be squeezed through the small capillaries? (2)
- Slows their movement - more time for diffusion
* Shorter diffusion distance
How is a concentration gradient maintained in the human gas exchange?
- Movement of blood
* Movement of air - ventilation
