L5 and 6 Exoskeleton, ventilation, circulation

Question 1

What 6 layers form the integument?

Answer 1

Waxy layer
Epicuticle
Exocuticle, 
Endocuticle
Epidermis - only cellular layer
Basement membrane

Question 2

What function does the waxy layer have?

Answer 2

Waterproofs cuticle - prevents dehydration

Contains sex pheromones for sex recognition

Question 3

Describe the structure of the cuticle

Answer 3

Chitin formed of polysaccharide chain, sugar and nitrogen
bundles of chains form microfibrils, many microfibrils form strands which are flexible and strong and arranged in sheets .
Sheets stacked on top of each other to form helicoid structure (each sheet rotated slightly).
Protein chains twist between layers of microfibrils and held together by sulfide bonds.

Question 4

What does it mean if the cuticle is sclerotized?

Answer 4

Proteins between microfibril layers are much more rigid with Sulfide bonds locked closer together.
Loses flexibility and darker in colour.

Question 5

Which of the cuticle layers are sclerotised?

Answer 5

Exocuticle and Epicuticle are, Endocuticle is not.

Question 6

What 3 features can be found on the exoskeleton?

Answer 6

Pores run through layers of cuticle to allow pheromones out
Microtrichiae - hairlike ridges, can be formed of just cuticle or epidermal cells as well. Irregularly scattered
Macrotrichiae - sensory hairs, dendrite detects rate, direction and extent of mvt of hair. Attached to tormogen and trichogen cells

Question 7

What is chaetotaxy?

Answer 7

Study of arrangement of hairs and bristles. Important in insect ID.

Question 8

What 4 sclerites form the exoskeleton and what joins them?

Answer 8

Tergum - dorsal
Sternum - ventral
2 x Pleuron - Lateral
Plates are joined by unsclerotized cuticle called the aticular membrane

Question 9

Describe the intersegmental membrane.

Answer 9

Joins sclerotized plates between segments.
Tucked under scletotized plates for protection.
Many other different protective mechanisms

Question 10

How does muscle attach to cuticle?

Answer 10

At apodemes - internal folds of cuticle, anchor points of muscle attachment.

Question 11

fancy name for moulting

Answer 11

ecdysis

Question 12

What structure aids moulting?

Answer 12

Air sac in the head inflates to put pressure on the cuticle

Question 13

How does the exoskeleton constrain size in terrestrial environments?

Answer 13

If larger would be too heavy to move around

Marine crustaceans can grow larger but are supported by water.

Question 14

What hormones are involved in moulting and what organs produce them?

Answer 14

Neurosecretory cells in brain and along ventral nerve cord - neurohormones [master regulators]
Corpus cardiacum in brain - Store and release neurohormones
Corpus allatum in brain - Produces juvenile hormone [metamorphosis and egg development]
Prothoracic gland - produces ecdysteroids. eg ecdysone induces moulting.

Question 15

describe a study which shows that neurohormones are released in the brain

Answer 15

5 caterpillars development observed

1. Intact, pupates after 16 days
2. Ligated at 7 days - front pupates, back half stays larval
3. Ligated at 9 days - both halves pupate
4. Debrained at 7 days - remains larval
5. Debrained at 10 days - pupates

Question 16

What relative amounts of Ecdysteroids and JH result in:
Larval/larval
Larva/pupal
Pupal/larval development

Answer 16

Less E, More JH - larval/larval
equal - larval/pupal
Less E, More JH - pupal/larval

Question 17

When is JH produced?

Answer 17

Once the adult emerges, JH is produced to initiate moulting.

Question 18

What are the two steps in moulting?

Answer 18

Apolysis and Ecdysis

Question 19

What occurs during apolysis?

Answer 19

Cuticle lifts off epidermis, creating a subcuticular space.
Epidermis becomes very metabolically active and divides. Excretes inactive ‘moulting gel’ which is released into the sub-cuticular space.

Question 20

What follows apolysis?

Answer 20

New epicuticle forms on top of the epidermis for protection.
Then new layers of procuticle start to form. Moulting gel becomes active and degrades the old endocuticle, remnants of the old cuticle are reabsorbed into the body.
When only the exo and epicuticle are left, ecdysis can begin.

Question 21

What are the steps involved in ecdysis?

Answer 21

Insect expands body by taking in more air and water, and increasing blood turgor. Cuticle splits and breaks out. Muscle attachments and nerves are lost.
Insect is immobile and soft.
Once insect gets out of old cuticle, wings unfurl and sclerotization of the new cuticle occurs.
New muscle attachments form and sclerotize.

Question 22

describe insect blood

Answer 22

hemolymph, moves around inside the hemocoel.
can be 20-40% of body weight
Composed of water, inorganic salts and inorganic compounds.

Question 23

6 functions of the blood

Answer 23

1. Transports hormones
2. Removes waste from excretory organs
3. Vitellins transported to ovaries
4. Blood pressure changes are important for moulting, mvt, ventilation
5. Water reserve
6. Distributes nutrients from gut to fat body.

Question 24

activity of hemocytes

Answer 24

phagocytosis
encapsulation of foreign body to suffocate it
Coagulation - plug damage to cuticle

Question 25

What is the difference to vertebrate blood?

Answer 25

hemolymph does not contain any respiratory pigment

Question 26

Describe a family of diptera with distinctive hemolymph

Answer 26

Chironomidae - some species have bright red larvae due to Hb analouge. ‘Bloodworms’.

Question 27

Describe a genus of diptera with a distinctive respiratory pigment

Answer 27

Gasterophilus - parasitic, Larvae hook onti stomach lining of horses. Very hostile, hot and acidic environment. Eggs laid on host surface, maggots licked and ingested, hook onto stomach lining. Excreted out when fully mature. Use respiratory pigment to get as much O2 as possible in this hostile environment.

Question 28

4 parts of a spiracle

Answer 28

Filter apparatus - Blocks large particles entering atrium
Valve - Behind atrium, can close the opening of spiracle. made of unsclerotized cuticle.
Taenidium - spiral of thickened cuticle which lines the trachea and atrium, is shed upon moulting. Spiral can be stretched lengthways but has resistance to being squashed laterally.
Peritreme - sclerotised plate on cuticle surface containing spiracle.

Question 29

Describe the trachea and the tracheoles

Answer 29

Trachea - penetrates into the body and branches to form tracheoles.
Tracheoles are blind ending and very fine, fluid filled at the tip where gas exchange occurs.

Question 30

Why are tracheoles not lined with cuticle?

Answer 30

So insect can still breathe during ecdysis.

Question 31

What are 3 methods of gas exchange?

Answer 31

1. Passive diffusion
2. Suction ventilation
3. Active ventilation

Question 32

Which method of gas exchange is the least efficient

Answer 32

O2 concentration gradient is maintained at 2%. Relatively inefficient and constrains insect size.
Paleozoic dragonfly like insect was huge, due to 35% O2 conc in the air so diffusion was much more efficient.

Question 33

Which method prevents water loss?

Answer 33

Close spiracular valves and use up O2 in tracheoles and trachea. Pressure falls to form slight vaccum [taenidium prevents collapse]. Air sacs are flexible and can callapse but are used as a reservoir of air.
CO2 is produced but stored as bicarbonate. When valves open, CO2 released, O2 rushes in.

Question 34

Describe active ventilation.

Answer 34

Thoracic spiracle valves open, abdominal ones closed,

Contractions as air is forced through body. Sternum moves up and down, forcing ventilation.

Question 35

How does aquatic insects ventilation differ to terrestrial?

Answer 35

Aquatic is a closed system with gills in place of spiracles.
Some so have 2 posterior spiracles eg mosquito larvae make contact with the surface. Some have lobes to close posterior spiracles when underwater.

Question 36

Example of an aquatic larvae

Answer 36

Rat tailed maggot - larvae of Drone fly, elongated posterior siphon

Question 37

Describe the pathway hemolymph takes when circulating round the body

Answer 37

Abdominal dorsal heart runs lengthways down the abdomen,sucks blood in through ostia (1 way valves, one per body segment) when the dorsal vessel is relaxed.
Blood from the ventral ‘Perineual sinus’ moves upwards to the dorsal ‘pericordial sinus’. Aided by ventral and dorsal diaphragms.
Peristalsic muscular contractions move blood towards head through dorsal vessel. Branches off main dorsal vessel circulate around wings.
At head end, released into hemocoel.
Accessory pulsatile organs are muscular pumps at base of antenna, wings and legs. Use changes in pressure to move blood to other organs.