Cricket Tracheal System
Concept 7: Overview of the Cricket Tracheal System
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I can briefly describe the ecological niche of crickets.
You need to be able to identify that crickets are terrestrial animals living on land for key requirements 2 in the rubric to get Achieved.
You need to be able to identify that air is the source of oxygen for crickets, and that in air, the oxygen availability is 21% for key requirement 3 in the rubric to get Achieved.
I can describe ventilation and gas exchange in the cricket tracheal system.
A brief description of ventilation may apply to key requirement 6 in the rubric to get Achieved if you link ventilation to an adaptation.
May apply to key requirement 7 to get Merit if you explain in-depth how ventilation helps maintain a high concentration gradient across the respiratory surface.
May apply to key requirement 8 to get Excellence if you compare ventilation across the three taxonomic groups.
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Do Now in your books:
Compare adaptations for SA : V between humans and snapper. What are their similarities and differences?
Watch these videos to broaden your understanding.
Ecological Niche of Crickets (Insect)
CRICKETS belong to the insect taxonomic group. They are TERRESTRIAL animals which means they live on land and their source of oxygen is air, which is 21% oxygen. Air is dry so they are susceptible to desiccation or drying out. As a matter of fact, because insects are so small compared to mammals, they have a higher surface area to volume ratio, they’re susceptible to drying out faster than mammals. Air also contains debris, which may block or clog the airways.
Crickets have high metabolic demands, which means they need a lot of energy to carry out necessary activities to survive - like flying away from predators. Flying is a vigorous activity that needs a lot of energy. Also, to make those distinctive mating calls that crickets are notorious for, male crickets stroke their wings against each other to attract females. This wing stroke behaviour requires a lot of energy.
What are the parts of the cricket tracheal system?
The tracheal system consists of the following structures: spiracles, tracheal tubes, tracheoles, and air sacs.
Insects take in air through spiracles along the sides of their body. Spiracles are pores on the exoskeleton, or the outside skin or shell of the cricket. Spiracles are lined by small hairs, and can open and close to control ventilation or air flow into the tracheal system. They are directly connected to relatively wide tubes called the tracheae. Unlike mammals that just have one trachea, insects have a network of tracheae - tracheae is the plural of trachea.
The tracheae then branch off into many tracheoles, that further branch off into narrower and narrower tracheoles. These tracheoles extend to all the tissues of the cricket’s body. The very tips of these tracheoles are the specialised respiratory surface of the tracheal system, where gas exchange occurs directly between inhaled air and the body cell. This extensive branching of airways is so that oxygen can reach all tissues and cells of the body.
Unlike mammals and fish, insects don’t have a closed circulatory system to pump oxygenated blood around the body.
Instead, the tracheal system takes oxygen directly into the cells of the body.
What's the journey of air in and out of the tracheal system like?
Usually, air flows into and out of the cricket’s body through open spiracles by diffusion. This air flow is regulated by small muscles that operate valves within each spiracle. The muscles contract to close the spiracles or the muscles relax to open the spiracles. From the spiracles, air diffuses along the tracheae, then the tracheoles. No new air can flow into the tracheal system when spiracles are closed.
Air sacs increase the volume of air that can be taken in by the cricket, which become useful when the spiracles are closed and there is no new air flow.
To increase the rate of ventilation during high activities such as flying, crickets can make rhythmic body movements to help actively ventilate their respiratory surface.
Rhythmic body movements compress and expand the air sacs like bellows (see picture to the left).
These rhythmic body movements help to draw more air into the tracheae and tracheoles at a faster rate. This increased ventilation only happens when crickets make rhythmic body movements during high energy activities. In all other times, ventilation happens via simple diffusion.
Concept 8: Tracheal System Adaptations & Limitations
I can explain how specific adaptations of the tracheal system enable snapper to survive in their terrestrial niche.
I can discuss the advantages and limitations of the cricket tracheal system.
Do Now in your books:
List all of the tracheal system structures you would expect to see with the naked eye.
Ms. Adviento's Video on Concept 8: Cricket Tracheal System Adaptations & LimitationsClick here to subscribe and stay updated with 12BIO videos: https://www.youtube.com/channel/UCw3WszDC9IWy4KNKzunutMw/
Watch these videos to broaden your understanding.
Overview of Tracheal System Adaptations
The cricket tracheal system needs to make sure it possesses the 4 characteristics of an efficient gas exchange system, to be able to keep up with the high metabolic demands of this flying insect.
There are adaptations for:
Maximise the SA : V of tracheoles.
Preventing damage to the tracheae and tracheoles.
Retaining moisture and keeping tracheoles moist.
Minimise the diffusion distance across tracheoles(thin).
Maximise the concentration gradient across tracheoles.
Adaptations for a Large SA : V
1) Extensive branching of tracheoles
2) Small hairs lining the spiracles
Adaptations for Moisture
1) Internal tracheal system
2) Spiracles and hairs
Adaptations for a Short Diffusion Distance (Thin)
Adaptations for Maintaining a Steep Concentration Gradient
1) Rhythmic Body Movements
2) Chitin Rings
Limitations of the Tracheal System
There are 4 limitations of the tracheal system:
1) Incompatibility with water
The tracheal system cannot be used to "breathe under water". The tracheal system is incompatible with water for two reasons.
First, is that water is too dense/viscous to be ventilated by passive diffusion in and out of the spiracles, and water is too dense to be ventilated by rhythmic body movements. Without ventilation, gas exchange would stop because a concentration gradient of oxygen and carbon dioxide would not be maintained across the tracheoles - there would be nothing driving the diffusion of oxygen and carbon dioxide.
Second, is that the tracheoles would not be able to exchange gases efficiently enough with water to meet the oxygen demands of aerobic respiration, and sustain life. This is because the SA : V of tracheoles is not large enough to absorb enough oxygen from the 1% of oxygen available in water. The SA : V of the tracheal system is not compatible with the extremely low oxygen availability in water; it can only efficiently carry out gas exchange with air, which has 21% oxygen availability.
2) Limited to a small size
The cricket tracheal system is only efficient if the organism is small. This means that the cricket’s tracheal system limits the size these insects can grow to, because if they grow any larger, the tracheal system would not be efficient enough to meet their metabolic demands. This is for 2 reasons.
First, is that crickets do not have a closed circulatory system to pump oxygenated blood around the body. They rely on diffusion alone to move inhaled air through the networks of tracheae and tracheoles to reach all tissues and cells of the body. Because of this, insects are limited by the size to which they can grow. If crickets were to grow larger then the diffusion distance from spiracles to the body cells would be far greater, reducing the rate of diffusion. As a result, body cells may not get the O2 they need to meet metabolic demands fast enough.
The second reason is that the chitin rings that surround the tracheae are relatively heavy, especially when you consider the fact that a large proportion of the insect’s mass is taken up by the tracheal gas exchange system. If the cricket increases in size, the number and length of tracheae containing chitin would increase significantly, and the cricket won’t be able to move or fly due to the weight and physical restrictions of the chitin.