Gas exchange in insects, fish and plants

Gas exchange in insects

Specialised structures:

• Insects have a waterproof exoskeleton for protection and to reduce water loss.

• Gas exchange occurs via a network of tracheae that deliver air directly to cells.

• Spiracles (openings in the exoskeleton) lead to tracheae that branch into smaller tracheoles.

• Tracheoles:

  • Thin walls provide a short diffusion distance.

  • Highly branched, increasing surface area.

  • Penetrate deep into tissues for direct oxygen delivery.

The insect gas exchange system.

Process:

• Oxygen diffuses through the spiracles, down the tracheae, down the trachioles and into body tissues (such as muscle cells) at the end of the trachioloes.

• Carbon dioxide diffuses in the opposite direction.

Ventilation:

• Some insects actively compress and expand sacs connected to the tracheae to ventilate the system.

Water Conservation:

• Spiracles can close to minimize water loss, but this limits oxygen intake, so it happens during rest.

Gas exchange in fish

The flow of water over fish gills.

Specialised Structures:

• Fish use gills for gas exchange, which consist of:

  • Gill filaments attached to gill arches.

  • Each filament has dozens of semi-circular lamellae on each surface, giving a large surface area.

  • Lamellae have thin walls with blood capillaries directly beneath the epithelial cells to ensure a short diffusion distance.

Structure of a fish gill.

Process:

• Water flows over the gills, allowing oxygen to diffuse into the blood capillaries found and carbon dioxide to diffuse out.

• Countercurrent Flow: Blood flows in the opposite direction to water which maintains a constant diffusion gradient along the entire gill.

Countercurrent flow of water and blood in fish gills.

Gas exchange in plants

Specialised structures:

• Gas exchange occurs mainly in the leaves through stomata:

  • Guard cells control stomatal opening to regulate gas exchange.

  • Spongy mesophyll:

    • Loosely packed cells create large air spaces for gas exchange.

    • Large surface area for efficient diffusion.

  • Palisade mesophyll:

    • Packed with chloroplasts to optimize light absorption for photosynthesis.

Water conservation:

• Water vapor escapes through stomata, but plants minimize loss via:

  • Waxy cuticle on the leaf surface.

  • Stomatal closure during dry conditions.

Xerophytes (plants in dry environments) have additional adaptations:

• Stomata in deep pits to trap moisture.

• Rolled leaves to reduce surface area.

• Leaf hairs to create a humid microenvironment.

• Fewer stomata to minimize water loss.

Internal structure of a leaf.

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