3.2- Gas Exchamge Insects Fish Flashcards
- Complete the equation of Fick’s law:
Rate of diffusion Surface area x Concentration Gradient
Thickness 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;
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 in trachea
4 Tracheae 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 markscheme 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 / countercurrent;
5 the countercurrent maintains a 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);
- What are xerophytic plants and where would you find them?
- Xerophytic plants are adapted to live in dry conditions where water availability is limited
- You would find them in hot, dry places (like deserts) and also in areas where this is lots of salt (such as by the sea or in salt marshes).
- Complete this table about the structural adaptations of a xerophytic plant to reduce water loss and still allow efficient gas exchange
Adaptation How it helps
sunken stomata
(sometimes with hairs around them)
(Jan 2010 5c) • Water vapour accumulates next to the stomata
• This increases the humidity next to the stomata
• So the water potential/diffusion gradient decreases
stomata mainly on the underside of leaves
Reduces water loss by evaporation because the top of the leaves receive more radiation from the sun waxy cuticle The waxy cuticle is impermeable so reduces water loss by evaporation as it cannot pass through leaves reduced in size (e.g. in a cactus they are reduced to thorns) • Reduced surface area so reduced surface area to volume ratio • fewer stomata • so less loss of water vapour by diffusion stomata open at night Allows diffusion of carbon dioxide into the plant, but less water vapour is lost by diffusion at night because it is cooler
- 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 and removes air with a low concentration of oxygen
- Circulation keeps the blood moving so there is deoxygenated blood in contact with the alveoli
- This maintains a concentration gradient between the alveoli and the blood
• So fast rate of diffusion
- 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 min-1 dm3
- How can breathing rate be calculated if you know time taken for one breath?
Breathing rate = 60 / time taken for one breath
- Complete this table:
Intercostal muscles Diaphragm Lung Tissue Volume Pressure Air moves…
• Externals contract
• Internals relax Contracts and flattens N/A Increases Decreases In
• Externals relax
• Internals relax (unless vigorous exercise, in which case the internal intercostal muscles contract) Relax and becomes dome shaped
Is elastic
So alveoli recoils
Decreases Increases out
