3.2 - Gas Exchange Flashcards
- Complete the equation of Fick’s law:
Rate of diffusion = (Surface area x Concentration Gradient )/Length of diffusion pathway
- How does gas exchange take place in single-celled organisms and small thin organisms such as flat worms?
Simple diffusion
- Small organisms obtain enough oxygen without a specialised gas-exchange system. Why is this possible?
Why do larger organisms need a gas-exchange and transport system?
Small organisms have large surface/volume ratio;
All cells are close to the gas exchange surface
So diffusion/exchange can take place over the whole body surface/skin;
(short diffusion pathway)
But cells of larger organisms are a long way from gas exchange surface;
and because diffusion is a slow process;
gases (and other substances) must be supplied by transport system/circulatory system/blood;
- What are spiracles?
A pore on the surface of an insect that leads to trachioles, and serves as an entrance/exit for the movement of gases into and out of the insect.
Spiracles can be opened and closed, dependent on respiratory need and environmental changes
- What are tracheae in an insect?
The vessels connecting the spiracles to the tracheoles.
- Describe how an insect obtains oxygen and reduces water loss
1 Air enters through (open) spiracles;
2 Through tracheae;
3 Diffusion gradient is established between trachioles and trachea, so oxygen diffuses down conc grad into trachioles
4 trachioles associated with all cells/closely associated with cells;
5 Oxygen diffuses into cells;
6 Ventilation replacing air in tracheae;
7 Body covered with (waterproof) waxy layer/cuticle;
8 Spiracles are able to close
- How is an insect’s tracheal system adapted for efficient gas exchange?
- Short diffusion pathway due to
a. thin walls of tracheoles
b. lots of tracheoles so no cell is far away from a tracheole - large surface area
a. lots of tracheoles which are highly branched
b. fluid from the end of the tracheoles is absorbed into muscles - high concentration gradient for carbon dioxide and oxygen maintained by
a. movement of abdomen (ventilation) which brings in oxygen rich and carbon dioxide poor air - the fluid from tracheoles is absorbed into muscle tissue so that diffusion can happen faster through the air than it would through liquid
- Explain how the gills of a fish are adapted for efficient gas exchange (use mark scheme from June 2009, Q8a)
1 Large surface area provided by lamellae/filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions / counter current;
5 the counter current maintains an oxygen concentration gradient along the entire gill filament so equilibrium is not reached;
6 As water always next to blood with lower concentration
of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);
- Label this diagram of the lungs with the key parts
Check notes
- What makes the alveoli well adapted for gas exchange (diffusion)
- Many alveoli provide a large surface area
- Many capillaries provide a large surface area
- Alveoli and capillary walls are thin
- This is due to the squamous (flattened) epithelial cells
- So there is a short diffusion pathway between the alveoli and the blood
- Ventilation brings fresh air into the lungs containing a high concentration of oxygen (oxygen-rich air) and removes air with a low concentration of oxygen (oxygen-poor air)
- Circulation keeps the blood moving so there is deoxygenated blood in contact with the alveoli (there is always a lower concentration of oxygen in the blood compared to the alveoli)
- This maintains a concentration gradient (of oxygen) between the alveoli and the blood
- So high rate of diffusion
Describe the gas%webreatre in and out
Inhaled Air (%)Exhaled Air (%)Reason for difference
Oxygen 21 18 Enters the blood by diffusion and used in respiration
Carbon dioxide 0.04 4 Enters the alveolus by diffusion and used in respiration
Nitrogen 78 78
Water vapour Variable Variable but more than inhaled
Water vapour diffuses from moist surface
- Describe the path that oxygen takes from the alveoli to the blood
(HINT: Don’t forget “epi” and “endo”)
Through the alveolar epithelium
Through the capillary endothelium to the blood
- Write the equation for pulmonary ventilation and rearrange it to calculate tidal volume and ventilation rate (include units)
Pulmonary ventilation = breathing rate x tidal volume
dm3min-1 pv min-1 br
dm3. tv
- How can breathing rate be calculated if you know time taken for one breath?
Breathing rate = 60 seconds / time taken for one breath (in seconds)
Intercostal muscle
Inhaling -
* Externals contract
* Internals relax
Exhaling-
* Externals relax
* Internals relax (unless vigorous exercise, in which case the internal intercostal muscles contract)
Diaphragm muscle
Inhalation -
Contracts and flattens
Exhalation -
Relax and becomes dome- shaped
What happens to lung tissue when exhaling?
It is elastic so alveoli are able to recoil
What happens to volume when inhaling?
Increases
What happens to volume when exhaling ?
Decreases
What happens to pressure when inhaling?
Decreases
What happens to pressure when exhaling ?
Increases
