Insects 6.2

How does single celled organisms exchange gases ?

Single cell organisms are small and therefore have a large surface area to volume ratio.

Oxygen is absorbed by diffusion across their body surface ,which is covered only be a cell surface membrane.

In the same way carbon dioxide from respiration diffuses out across their body surface .

Terrestrial insects what do they have?

Insects have an exoskeleton made of hard fibrous material for protein and a lipid layer to prevent water loss.

Insects do not have lungs and instead have a tracheal system

How do they limit water loss?3

1)Insects have a small surface area to volume ration where water can evaporate from

2)Insects have a waterproof exoskeleton

3)Spirarcles where gases Enter and water can evaporate from can open and close to reduce water loss

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What are the components in the Insect tracheal system ?

Trachea ,tracheoles and spiracles

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1)Spiracles are round valve like openings ,running along the length of the abdomen .oxygen and carbon dioxide enter and leave via the spiracles .the trachea attach to these openings .

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2)The @@trachea@@ is a network of internal tubes .

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3)The trachea tubes have rings within them to strengthen the tubs and to keep them open.

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4)The trachea branch into smaller tubes deeper into the abdomen of the insects called tracheoles .these extended throughout all the tissues in the insect ti deliver oxygen to respiring cells. %%This is an advantage because oxygen is taken directly to respiring tissues, hence the diffusion pathway is short%%

What are the 3 methods of moving gases in the tracheal system ?

1)Gas exchange by diffusion as when cells respire they use up oxygen so its concentration towards the ends of tracheoles falls.

This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells

and produce carbon dioxide during respiration ,creating a concentration gradient in the opposite direction ,thus causes gaseous carbon to diffuse along the the tracheoles and trachea from cells to atomsoojere .

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2) gas exchange in mass transport ,in which insect contracts and relaxes their abdominals rings of muscles to move gases on mass .==This contraction of muscle in insects squees the trachea, enabling mass movements of air in and out.==

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3) when the insect is in flight the muscles start to respire anaerobically to produce lactase .this lowers the wp of the cells and therefore water moves from the tracheoles into the cells by osmosis .this decreases the volume in the tracheoles and as a result more air from the atmosphere is draw in .

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Carbon dioxide can diffuse from the cells into the tracheoles and oxygen diffuses from the tracheoles into the body cells .

Explain how the tracheal system limits the size of insects ?

Because it relies on diffusion to bring oxygen to the respiratory tissues .if insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs .

Explain why there is a conflict in terrestrial insects between as exchange and conserving water ?

Gas exchange requires a thin permeable surface with large sa.conserving water requires thick waterproof surfaces with a small area

What are the conditions when spriacles are open or closed ?

If conditions are dry /insect is inactive the spiracles will remain closed or partially open

If thr conditions are relatively moist or insect is active the spiracles remain open .

What are the positive and negative consequence of the tracheoles ends filling with water?

Positive

%%increased rate at which air is moved into the tracheoles%%

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negative

-leads to greater water evaporation.

Describe and explain how a terrestrial insect is adapted to reduce water loss?

4 marks

1) waterproof cuticle

2)cuticle supports trachea and is impermeable to gases

3)spiracles close during the day

4)hairs around spiracles reduce evaporation

Describe and explain how an insect’s tracheal system is adapted for efficient gas exchange ?

6 marks

1. tracheoles have thin walls +short distance between spiracles and tracheoles =so short diffusion pathway.

2)tracheoles are branched /large number of tracheoles so large surface area.

3) The trachea provides lots of oxygen so rapid diffusion into cells.

4)movement if insect causes fluid at the end of tracheoles to move out so faster diffusion.through air to gas exchange surface.

5) The body can be moved by muscles to move air so a concentration gradient is maintained.