ENT201 - Exam 1 - Where Are the Bones?

Structural advantage hollow tube design in insect exoskeletons

A metal tube or cylinder provides greater structural strength against bending compared to a solid rod of equal weight

Inelasticity of hardened exoskeleton

Once an insect’s exoskeleton completely hardens and tans, it cannot stretch or expand further.

Can’t get bigger

Basement membrane function

A non-cellular layer that separates the internal body cavity (hemolymph) from the epidermal cells

Three main layers of insect cuticle from innermost to outermost

Endocuticle —> exocuticle —> epicuticle

Endocuticle composition and mechanical properties

• Soft, flexible

• Non-tanned matrix of chitin and protein

• Flexible but non-stretching

Exocuticle composition and sclerotin formation

• Hardened, rigid layer

• Formed when protein, chitin, and phenolics cross-link into sclerotin

Primary function of epicuticle

• Prevents water loss by forming a thin, waterproof layer of protein, wax and cement

The primary reason insects require a waterproof epicuticle

• Due to their high surface-area-to-volume ratio

• Body water is their most precious and easily lost resource

Resilin

An extraordinarily elastic, rubbery protein found in joints, wing hinges, and jumping mechanisms

Setae function in bees

Branched hair like sturcutres that catch and hold pollen grains during foraging

Defensive adaptation of setae in certain caterpillars

Hiding stinging or venomous spines under setae to deter predators

Chitin chemical definition

a large natural sugar (polysaccharide) polymer that forms the structural backbone of insect cuticles

Chemical resistance of chitin

Highly resistant to degradation by dilute acids and alkalis

Three advantages of an exoskeleton

1. Prevents water loss

2. Physical protection against predators/pathogens

3. High strength-to-weight ratio

Three major disadvantages of an exoskeleton

1. Limits the ultimate physical body size

2. Decreases flexibility/freedom of movement

3. Requires a dangerous molting process

Reason molting poses a extreme danger to insects

• Shedding the old exoskeleton leaves the insect soft, immobile and defenseless against predators

Most abundant biogenic organic polymer on Earth

Cellulose

Biological role of cellulose in plants

Provides structural support for plant cell walls and stems

Presence of an exoskeleton in internal insect structures

• Cuticle lines interval invaginations, including the foregut, hindgut, and tracheal respiratory tubes

Sclerotin

A rigid, tanned protein complex formed by cross-linking proteins, chitin, and phenolics in the exocuticle

Wax layer location and function within epicuticle

• Situated in the epicuticle

• Serves as the primary barrier preventing evaporative water loss

Physical reason exoskeletons constrain maximum insect body size

As body size increases, exoskeleton weight increases exponentially, becoming too heavy for interval muscles to move on land