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Flashcards in Adaptations For Gas Exchange Deck (23)
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What is a respiratory surface?

The site of gas exchange


Examples of respiratory surfaces:

Gills of a fish

Lungs of a mammal

Tracheae of an insect


Essential features for respiratory surfaces?

Large surface area (increases area for movement of gases)

Thin membrane ((short diffusion pathway)

Permeable membrane (to allow gases through)

Moist (so gases will dissolve and diffuse faster)

Concentration gradient across a membrane


How is amoeba suited for gas exchange?

Habitat = water (moist)

Thin, permeable membrane

Oxygen will diffuse across the entire body surface (large surface area)

Has concentration gradient (what oxygen it gets, it uses)


The problem with multicellular organisms?

There has to be a limit to cell size and a point will be reached where the length of the diffusion pathway limits the efficiency of the process of diffusion.

The organism can get larger if the cells aggravate together to become multicellular

However the larger the organism the smaller the surface area to volume ratio


Why flatworm is good at gas exchange?

Habitat = water (moist)

Flattening itself has elongated the body (large surface area)


Why earthworms are good at gas exchange?

Long (large surface area)

Blood vessels carry oxygen around the body

Secretes mucus onto surface (moisture)

Habitat - terrestrial but DAMP ENVIRONMENT

low metabolic rate (rate of energy expenditure by body)

Respiratory pigment within blood


Where are the spiracles on an insect?

On the thoracic and abdominal body segments of an insect


What are spiracles?

Basically pores in the exoskeleton of the insect


What are exoskeletons and why do insects need them?

Insects have this covering (exoskeleton) to prevent them from drying out (heat) but by having the waterproof layer, they are impermeable to gases.


What do spiracles possess. And what are they lined with?

They possess valves which are responsible for opening and closing spiracles.

They are lined with hairs which reduce water loss.


Process of gas exchange when insects are at rest?

They close the spiracles to reduce water loss which helps maintain a concentration gradient.

Oxygen is reduced of cellular respiration in body, decreasing the levels of oxygen, creating a concentration gradient.

An active insect can ventilate the system through muscular movements of the abdomen. This is done by the alternate compression and expansion of the tracheal.

If it begins resourcing anaerobically, so can't ventilate quick enough, lactic acid is produced. By increasing the amount of lactic acid in the muscle, it is lower than the water potential in the fluid at end of tracheoles. This allows osmosis to occur between the high water potential in the tracheoles and respiring tissue, clearing the tracheoles of fluid and allowing more room for oxygen.


Amount of gases inspired and expired!


Inspired - 20%
Expired - 16%

Carbon dioxide

Inspired - 0.04%
Expired - 4%


Inspired - 79%
Expired - 79%

Water vapour

Inspired - variable
Expired - saturated


Amount of oxygen absorbed in mammals and fish?

Mammals 20%
Fish 80%


What are the problems that under water organisms face?

Water contains around 25x less oxygen than air

Rate of diffusion of oxygen is a lot slower in water

Water is more dense than air, so it doesn't flow easily as it is more difficult to ventilate the respiratory surfaces


Why do fish need gills?

They are very active, so require a specialist respiratory system

They have a large SA for gas exchange, created by the many folds

A specialised pumping mechanism ensures a one way current of water flows constantly over the gills

An extensive capillary network maintains diffusion gradients at the Gill surface (and fish have haemoglobin to carry oxygen)


Why do fish use the counter current?

Once equilibrium is reached, there is no net movement of oxygen into the blood, therefore, with a parallel flow blood will only be up to 60-70% saturated with oxygen

The counter current flow results in the oxygen concentration gradient between the blood in the gills and the water being maintained across the entire length of the Gill lamella


The flow of ventilating gills : (11)

1. Mouth opens

The buccal cavity floor is lowered

This increases the volume and decreases the pressure of the buccal cavity compared to outside

Water rushes into the mouth down a pressure gradient

Operculum cavity expands

The buccal cavity floor is raised

The pressure inside the buccal cavity is now higher than in the operculum cavity

Water moves from the buccal cavity, over the gills, into the operculum cavity

The mouth is now closed and the operculum opens

The sides of the operculum cavity move inwards, increasing the pressure

Water rushes out of the fish through the operculum


Rate of diffusion equation:

SA x concentration gradient
Thickness of membrane


Process when humans inspire?

External intercostal muscles contract

Ribs are pulled upwards and outwards

The diaphragm muscles contract, so it flattens

Outer pleural membrane is pulled out

thorax volume increases

Reduces pressure in the lungs

Inner pleural membrane pulled outwards. This causes 'pull on the lungs and the alveoli will expand

Atmospheric air pressure is now greater than pressure in the lungs, so air is forces into the lungs


Process when humans expire?

External intercostal muscles relax

Ribs move downwards and inwards

At the same time, the diaphragm muscles relax so it domes upwards

Outer pleural membrane pulled in

Both actions decrease the thorax volume

This increases pressure in the lungs

Inner pleural membrane pulled inwards

Air pressure in lungs is now greater than atmospheric pressure so air is forced out of the lungs


Role of surfactant?

A chemical which coats the inside layer of the alveoli

Job is to reduce surface tension and stop the alveoli from collapsing


Role of guard cells and stomata in the day:

The guard cells possess chloroplasts so photosynthesis will take pace and ATP will be synthesised

The ATP provides energy for the active transport of K+ ions into the guard cells

Starch sitting the guard cells is converted to malate

The presence of both Malate and k+ ions will lower the water potential in the guard cells. Water will enter the guard cell by osmosis

Due to differences in the thickness of the cell wall (outside thinner than inside) the presence of the water will cause the thinner wall to stretch (more than the inner walls) so a pore appears between the two guard cells

Stoma opens