3.1.1g Gas Exchange in Insects

Question 1

Why do insects need an effective gaseous exchange system

Answer 1

Many insects are very active during parts of their life cycles. They are mainly land-dwelling animals with relatively high oxygen requirements.

Question 2

What is the issue with insects and gas exchange

Answer 2

• They have a tough exoskeleton through which little or no gaseous exchange can take place
• They do not usually have blood pigments that can carry oxygen

They need a diff way of exchanging gases

Question 3

The gaseous exchange system of insects has evolved to…

Answer 3

…deliver the oxygen directly to the cells and to remove the CO2 in the same way

Question 4

What are spiracles

Answer 4

Along the thorax and abdomen of most insects are small openings known as spiracles. Air enters and leaves through the spiracles, but water is also lost

Question 5

What do mammals and insects need to ensure their exchange system does

Answer 5

Just like mammals, insects need to maximise the efficiency of gaseous exchange, but minimise the loss of water

Question 6

What are sphincters

Answer 6

The spiracles can be opened and closes by sphincters. The spiracle sphincters are kept closed as much as possible to minimise water loss

Question 7

When are the spiracles in insects usually closed

Answer 7

When an insect is inactive and oxygen demands are very low, the spiracles will all be closed most of the time

Question 8

When are the spiracles in insects usually opened

Answer 8

When the oxygen demand is raised or the CO2 levels build up, more of the spiracles open

Question 9

What are the tracheae

Answer 9

• Leading away from the spiracles are the tracheae.
• These are the largest tubes of the insect respiratory system, up to 1mm in diameter, & they carry air into the body.
• They run both into & along the body of the insect. The tubes are lined by spirals of chitin (which keep them open if they are bent or pressed)

Question 10

What is significant about the tracheae being lined with chitin

Answer 10

Chitin is the material that makes up the cuticle. It is relatively impermeable to gases & so little gaseous exchange takes place in the trachea

Question 11

What are the tracheoles

Answer 11

• The tracheae branch to form narrower tubes until they divide into the tracheoles - minute tubes of diameter 0.6-0.8pm.
• Each tracheole is a single, greatly elongated cell w NO chitin lining so they are freely permeable to gases
• Bc of their very small size they spread throughout the tissues of the insect, running between individual cells. This is where most of the gaseous exchange takes place between the air & the respiring cells

Question 12

By what process does air reach all tissue in insects

Answer 12

Air moves along the tracheae and tracheoles by diffusion alone, reaching all the tissues

Question 13

Features of tracheoles that make them effective exchange surfaces

Answer 13

• The vast no. of tiny tracheoles give a very large SA for gaseous exchange.
• Moist walls of the tracheoles causes oxygen to dissolve into the walls and diffuse into the surrounding cells
• Towards the end of tracheoles, there is tracheal fluid, which limits the penetration of air for diffusion

Question 14

What happens when oxygen demands build up in insects

Answer 14

When oxygen demands build up - when the insect is flying for eg, a lactic acid build up in the tissues results in water moving out of the tracheoles by osmosis. This exposes more SA for gaseous exchange

Question 15

How is all the oxygen needed by the cells of an insect supplied to them

Answer 15

all the oxygen needed by the cells of an insect is supplied to them by the tracheal system

Question 16

What controls the extent of gas exchange in most insects

Answer 16

The extent of gas exchange in most insects is controlled by the opening and closing of the spiracles

Question 17

Alternative methods of increasing the level of gaseous exchange INTRODUCTION

Answer 17

Some insects (eg, larger beetles, locusts, grasshoppers, bees, wasps, flies) have very high energy demands. To supply the extra oxygen they ned, these insects have alternative methods of increasing levels of gaseous exchange

Question 18

Alternative methods of increasing the level of gaseous exchange: Mechanical ventilation of the tracheal system

Answer 18

Air is actively pumped into the system by muscular pumping movements of the thorax & abdomen. These movements change the volume of the body & this changes the pressure in the tracheae & tracheoles. Air is drawn into the tracheae & tracheoles, or forced out, as the pressure changes

Question 19

Alternative methods of increasing the level of gaseous exchange: Collapsible enlarged tracheae or air sacs

Answer 19

Collapsible enlarged tracheae or air sacs, whcih act as air reservoirs - these are used to increase the amount of air moved through the gas exchange system. They are usually inflated & deflated by the ventilating movements of the thorax & abdomen

Question 20

Exam Q: Outline structures of the insect gaseous exchange system (6)

Answer 20

SPIRACLES:
- open & close by sphincters, to allow gas in and out
- pores on the tough exoskeleton (impermeable) to allow gas exchange

TRACHEAE:
- leads away from the spiracles into the body cavity
- lined with chitin, creating rigid structure, preventing collapse

TRACHEOLES:
- many branches - increased SA
- highly permeable
- tracheal fluid