Adaptations for gas exchange

What is gas exchange

Oxygen and carbon dioxide diffusing across a suitable body surface in respiring organisms

What is the rate of gas exchange effected by?

Area available for diffusion, length of diffusion pathway, concentration gradient across gas exchange surface and speed that molecules move through membranes

What characteristics do efficient gas exchange surfaces have?

Large surface area to volume ratio, thin, mechanisms for maintaining steep concentration gradient across themselves, permeable to gases

What affects the nature of the gas exchange surface?

The environment the organisms lives, the thickness of the organisms other surface, organism rate of respiration and size of organism

What effect does lipid solubility have on rate of diffusion

Increases rate because the molecules can diffuse through the phospholipid membrane

What is an organisms 0₂ requirement proportional to?

It’s total volume

What is an organisms absorption of O₂ proportional to?

The surface area of the organism

Amoebas adaptations to gas exchange

The cell membrane is the gas exchange surface (single-celled organism)

Large surface area to volume ratio

Thin, moist membrane

Short diffusion pathway

Flatworms adaptations for gas exchange

Increased surface area to volume ratio (flattened shape)

Short diffusion pathway

Earthworms adaptions to gas exchange

Elongated shape provides large surface area to volume ratio

Keeps its skin moist by secreting mucus

Do simple organisms or larger organisms have a faster metabolic rate?

Larger organisms

What does a faster metabolic rate require?

More energy and oxygen supply

What else do larger organisms need?

Ventilation to maintain the concentration gradient

Gill structure

Covered by the operculum which contains 4 gills supported by bony gill arches, each gill has many feathery gill filaments which each have many gill lamellae

Gills adaptations

Large surface area from many gill filaments and lamellae

Short diffusion pathway (one squamous epithelial cell)

Good blood supply

Counter current flow

Why do gills have a counter current flow?

The blood and water moved in opposite directions because it maintains the concentration gradient across the whole gill lamellae which allows more oxygen to diffuse out of the water

Step 1 of ventilation in fish

Mouth opens lowering buccal cavity floor, increasing volume so water rushes in down pressure gradient

Step 2 of ventilation in fish

Operculur cavity expands raising the buccal cavity floor, increasing pressure which moves water over the gills from the buccal cavity into the operculur cavity

Step 3 of ventilation in fish

Mouth closed, opening operculum, sides of opercular cavity move inwards increasing pressure causing water to rush out of fish through the operculum

why do gills not function effectively on land?

when gills dry out they can no longer dissolve oxygen on their surface, also they may collapse, decreasing the surface area

inspiration

External intercostal muscles contract, ribs move up and out, diaphragm flattens, decreasing pressure pulling air in

expiration

External intercostal muscles expand, ribs move down and in, diaphragm relaxes to dome shape, pressure increases pushing air out

What do pleural membranes do?

Found between the ribs and lungs and also the thorax, they are filled with pleural fluid which prevents friction between lungs and ribs as the lung inflates and deflates

Adaptations of alveoli

Large surface area, short diffusion pathway, good blood supply, moist and surfactant (dosn’t collapse)

gas exchange in insects

air enters the trachea through an opening called a spiracle (found on thorax and abdomen), trachea branches into many tracheoles where it diffuses into body cells

why are spiracles closed for long periods?

to reduce water loss

what is the advantage of having internal lungs for gas exchange?

reduces water loss and mainiants moist gas exchange surfaces

Malate hypothsis

The sun transfers energy so that ATP can be synthesised, this is then used for active transport of potassium ions into the guard cell which triggers the conversion of starch into soluble malate, this decreases the water potential in the guard cell, meaning water can enter by osmosis. This causes the cell to become turgid and expand unevenly due to the different cell walls, forcing them apart opening the stomatal aperture

When and why do stomata close

At night because there’s no sunlight

In dry soil to reduce water loss

In high light intensities to reduce water loss due to the high temperature

Open and closed guard cell structure

Gas exchange in amphibians

Juveniles (tadpoles) live in water and use external gills

Gas exchange in adults occurs through the skin which is moist, thin and close to capillaries

Gas exchange also occurs in the lungs when active

open circulatory system

blood is not in vessels