Gas Exchange

• Fick’s Law = diffusion rate is proportional to=(surface area x difference in concentration)/diffusion distance
• A good gas exchange surface has a large surface area, large concentration gradient and a small/thin diffusion distance.
• To limit water loss insects have a waterproof covering and a small surface area to volume ratio.
• 1)In insects the oxygen first enter the insect through spiracles and into trachea.

  2)The oxygen then diffuses through the trachea into the tracheoles

  3)Oxygen is then delivered directly to the respiring tissue (oxygen moves down the concentration gradient)
• Gas enters and exits through the spiracles that open and close deducting water loss.
• The trachea is a network of tubes supported by strengthened rings.
• Tracheoles are small tubes which extend throughout the body tissues.
• Insects have a small air sac in their trachea with muscles that contract pumping the air sacs deeper into the tracheoles.
• When a insect flies it may respire partially anaerobically producing lactic acid this lowers the water potential of the muscles cells causing water from the tracheoles into the muscle cells via osmosis.
• The gills are the organ by which gasses exchange between the fish and the water.
• Water moves through the fish mouth and out through the gills.
• The series of lines on a fish gill that project out are called gill filaments
• Water carrying oxygen travels through the fish mouth and passes through the lamellae on the gill filaments where most of the oxygen is removed from the water.
• Each gill filament has a gill lamellae
• Gill lamellae are positioned at right angles to the filaments
• Lamellae contain capillaries
• Lamellae have a thin epithelium
• Gill filaments and Many lamellae provide a large surface area for gas exchange.
• the position of the filament and lamellae means that blood and water flow happens in opposite directions this is known as countercurrent flow.
• Countercurrent flow massively increases the fish’s ability to absorb oxygen from the water as the diffusion gradient pis always maintained
• Countercurrent means that no equilibrium is reached and the concentration gradient is maintained.
• Gill lamellae are at a right angle to filaments which increases the surface area of the gills.
• Leaves are adapted in three main ways for gas exchange they are flat (for a large surface area), stomata pores allow air to move in and out of the leaf and air spaces in the leaf so there is a short diffusion distanc.
• diffusion is the movement from an area of high concentration to an area of low concentration
• At night guard cells close the stomata to prevent water loss.
• Xerophytic plants live in dry environments and have specific adaptations to reduce water los.
• Xerophytic plants have five adaptations to reduce water loss.
• Xerophytic plants have a reduced number of stomata (less surface area for water loss), stomata pits (reduced concentration gradient), hairs to trap water vapour( reduced concentration gradient), leaves reduced to spines (less surface area for water loss) and a thick waxy cuticle(increased diffusion distance)
• Gills are the gas exchange surface for fish