1. Gas Exchange

2. The Significance of Surface Area to Volume Ratio
When a cell increases in size the diffusion pathway gets longer, as diffusion from the outer cell surface to the centre of the cell is slow. When the cell becomes very large, diffusion will not meet the cell’s needs , i.e.
to supply nutrients:
and to remove waste:
For an organism to become larger, a number of cells must come together - multicellular.
Name the organisms and state whether unicellular or multicellular
___________ ___________
Which organism has the largest surface area:volume ratio?

3. Surface area to volume ratio 4
Organism
Surface Area (cm2)
Volume
(cm3)
Surface Area: Volume Ratio 1 2 3 4
Complete the above table
Which size /shape represents
small mammal large mammal
amoeba earthworm

4. Gas Exchange - the process by which oxygen reaches cells and carbon dioxide is removed from them. Unicellular (Single Celled ) Organisms e.g. Amoeba Simple Multicellular Organisms e.g. Flatworm
Features of an
amoeba
Features and adaptations of a flatworm

5. Earthworms

6. Larger and more advanced multicellular animals
Why do multicellular organisms require a specialised gas exchange surface?

7. Specialised Gas Exchange Surfaces
Many animals and ________ have evolved specialised gas exchange surfaces so that ______________ of gases into and out of cells can take place rapidly and efficiently.
Gas exchange surfaces include :
in fish
in the lungs of a mammal
of insects
In order to achieve the maximum rate of diffusion, all respiratory surfaces must be:
What additional feature increases the efficiency of gas exchange in organisms which possess a circulatory system and respiratory pigment?

8. Vertebrate group adaptations for gas exchange
The vertebrates include five classes: amphibia, reptiles, birds, fish and mammals. Life is thought to have evolved in water with animals adapting in order to colonise the land. This section looks at how terrestrial (land living) animals are adapted for gas exchange.
 Amphibians
 The amphibians include , and .
In amphibians, the larvae (tadpoles) live in water and have __________ for gas exchange
The adult amphibians live on_______, .
Gas exchange in adults:
when inactive (at rest) -
when active (e.g. mating) -

9. Reptiles These include:
Pairs of ribs project from the vertebrae (backbone)
Give 2 functions of the reptile ribs
How does the structure of reptile lungs differ from that of amphibian lungs

10. Birds
The lungs of birds have an internal structure similar to______________.
Why do birds need large volumes of oxygen?
Lung ventilation in birds is far more efficient than in other _____________.
Ventilation is assisted by a system of _______ sacs connected to the lungs. The air sacs function as bellows. In birds, breathing in fills the lungs with completely fresh air. The air passes through the bird’s respiratory system in one direction only, bringing the fresh air firstly into the _____________ air sacs and then into the lungs. Finally the air flows into the ____________ air sacs before it exits through the ______________.
Ventilation is brought about by the movement of the ________.
During flight the action of flight____________ ventilates the lungs.

11. Insects
Insects fly, which requires lots of__________ and so they need a good supply of ________ for respiration. The gas exchange system is different from other land animals, because they do not use _________ to transport gases. Air diffuses into the insect through paired holes called ___________ running along each side of the body. The spiracles lead to a system of branched chitin lined air tubes called ___________. The spiracles can open and close like valves. Why is this important?
At rest, simple diffusion of gases meets the needs of the insect.
During periods of activity e.g. flight, movements of the ____________ ventilate the tracheae.

12. The Gas Exchange Surface of Insects
The tracheae branch repeatedly until they end as very fine, thin-walled tracheoles. Oxygen diffuses directly from the end of the tracheoles into the cells, __________ __________diffuses out.
What structural feature ensures that the tracheae remain open?
Why are the gas exchange organs retained inside the body of terrestrial (land living) organisms?
Prevents _______ loss
Protection - by the ________ or ___________ in insects

13. Fish Cartilaginous Fish Bony Fish
What problems are caused by living in water ?
How do fish overcome these?
Cartilaginous Fish
Bony Fish

14. Fish Anatomy
Head of a bony fish with operculum pulled back to reveal gills. There are usually ___ gills on each side
Horizontal section through the pharynx and gill region of a bony fish. Water is taken in through the mouth, passes over the gills and is expelled via the operculum. Movements of the buccal cavity floor and operculum allow a one-way current of water to flow through the gills for exchange of gases.

15. Ventilation mechanism in fish
Water flows in
Water flows out
Mouth
Operculum
Floor of buccal cavity
Volume
Pressure

16. The structure of the gills of bony fish
Along each gill arch there are many thin lamellae and on these are the gill_____________. The gill lamellae therefore have a large __________ ___________ for gas exchange. Blood circulates through the gill plates - oxygen diffuses through the gill plates into the capillaries and ______________ _____________ diffuses out into the water.
Counter Current Flow
Water flows between the gill plates in the _____________ direction to the blood flow.

17. Gas Exchange in the Gills: Counter current v. Parallel flow
Counter current flow

18. Human Respiratory System

19. Ventilation of the human lungs
Inspiration
Expiration
Ribs
External intercostal muscles
Diaphragm
Volume of thorax
Pressure in thorax
Outside air (atmospheric) pressure
Inspiration Expiration

20. Gas Exchange in Alveoli
The alveoli are suitable as a gas exchange surface because:
Surfactant
A chemical substance which covers the surface of the alveoli. Surfactant reduces ______________ _______________ and prevents the alveoli from sticking together and collapsing when breathing out.

21. Structure Function These move the ribs to expand the thorax
Bronchi branch into these smaller tubes where some gas exchange takes place
Box shaped structure above trachea, contains vocal cords.
Main site of gas exchange, have a large surface area
Trachea splits in two of these
This prevents the alveoli from sticking together and collapsing, it also reduces surface tension
Tube held open by rings of cartilage
These bones are moved by the intercostal muscles and alter the size of the chest cavity
This dome shaped muscle relaxes and contracts altering the volume of the chest cavity
Contains pleural fluid which acts a lubricant to reduce friction during ventilation
Flap of skin that stops food entering the trachea when swallowing
Acts as a lubricant allowing friction free movement against the inner wall of the thorax

22. Summary of Gas Exchange
Ventilation is the movement of a ______________ medium over the respiratory ______________ and maintains a diffusion gradient.
Internal Transport System (blood circulation) moves gases between _________________ cells and the respiratory _____________
Respiratory Pigment increases the ____________ carrying capacity of the blood, e.g. Haemoglobin
Organism
Respiratory medium
Gas exchange surface
Ventilation
Blood Circulation
Respiratory
Pigment
Amoeba
Flatworm
Earthworm
Fish
Amphibian
Reptile
Bird
Insect
Mammal

23. Gas exchange in plants Transverse section through a Leaf
One of the functions of leaves is gaseous exchange.
How are they are adapted for this function ?

24. The leaf is also adapted for photosynthesis in the following ways :-
Large ______ _______
Leaves can orientate themselves towards the _________
___________ to allow _________ to penetrate lower layers
Cuticle and epidermis are ______________
______________ cells are elongated and densely packed together and contain many _________________
_______________ can rotate and move within the mesophyll cells
Intercellular air spaces allow __________ ___________ to diffuse into the cells , ________ and ______________vapour to diffuse away.

25. Stomata Draw stomata in T.S. and surface view
Where in the leaf are stomata found?
What is their role?
How many guard cells surround each stoma (pore)?
What is unusual about guard cells?
they contain _________________
they have unevenly thickened cell____________.

26. Stomatal opening and closing
Turgid cells Flaccid cells
The inner cell wall is thick and the outer wall thin, so that if the guard cells become turgid the pore __________ and if the guard cells become flaccid the pore___________.
The mechanism for stomatal opening:
Why are stomata usually open during the day and closed at night?

27. Mechanism of stomatal opening/closing - Summary
Feature
Day (opens)
Night (closes)
Potassium pump
Carbon dioxide concentration
pH levels
Enzyme activity
Guard cells contain? WP
Guard cells become?
Size of pore (stoma)