The Cricket Tracheal System (+ cricket dissection)

Navigate the knowledge tree: 🌿 Biology ➡ NCEA Level 2 Biology ➡ 2.3 Plant & Animal Adaptations

Learning Intentions

By the end of this topic, you should be able to:

Explain aspects of the cricket ecological niche, that is relevant to gas exchange.
Describe the parts of the cricket tracheal system and where gas exchange takes place.
Explain how the cricket tracheal system is ventilated.

Glossary

Key terms and definitions.

air sacs: Pockets of air that extend from the tracheae and increase the volume of air taken in, in flying insects.

breathing / ventilation: Movement of air / water in and out of the gas exchange system.

chitin rings: Rigid ring structures that prevent the tracheae from collapsing during ventilation and rhythmic body movements.

cricket: Example of an with a tracheal system for gas exchange.

desiccation: Drying out

ecological niche: The functional position of an organism in its environment (the environment being the habitat and the resources available in this habitat).

exoskeleton: Hard, waterproof external covering that supports and protects the body of insects.

rhythmic body movements: The process of compressing and expanding the air sacs to increase the rate of ventilation.

spiracles: Openings in the exoskeleton of insects that connect to the tracheal tubes.

terrestrial: To live on land.

trachea (insect): A network of airways that connect the spiracles to the tracheoles.

tracheoles: Many narrow, highly-branched airways that connect the tracheae and all cells of the body; their tips are the site of gas exchange in insects.

volume: The amount of three dimensional space a substance takes up.

Ecological Niche of Crickets (Insect)

Insects are a taxonomic group characterised by a tracheal gas exchange system (among other things). One example of an insect isresources

(Remember: ecological niche includes where animals live (their Crickets and the resources that are obtained from that hterrestriale their source of oxygen)).

Crickets arand their sourceimals 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. As a matter of fact, because insects are so small compared to mammals, their bodies have a higher surface area to volume ratio, they’re susceptible to desiccation 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, network of trachea, tracheoles, and air sacs. 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.

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.

Below, you can clearly see stripes, or rings around the trachea - these rings are called chitin rings. They prevent the tracheae from collapsing.

And finally there are air sacs, which are air bag extensions of the tracheae. Flying insects like crickets have these air sacs to increase the volume of air taken in.

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 the picture above). 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.

More on The Cricket Tracheal System

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