BY2 - Adaptations for gas exchange

A large enough surface area

Be thin, so diffusion pathways are short

Be pemeable so respiratory gases diffuse easily

Have a mechanism to produce a steep concentration gradient

They have a large surface area to volume ratio

Cell membrane is thin, rapid diffusion

Single cell is thin, diffusion distance short

They can absorb enough O2 across cell membrane

They can remove CO2 fast enough to prevent building up a high concentration

It's cylindrical, surface area to volume smaller than a flatworm's

Skin is respiratory surface, its moist by secreting mucus

Low oxygen requirement because it is slow moving, low metabolic rate

Haemoglobin present in its blood

Carbon dioxide carried in blood

Frogs, toads, newts

Skin is moist and permeable, with a well-developed capillary network just below the surface

Gas exchange takes place through skin, and in the lungs

Crocodiles, lizards, snakes

Lungs have a more complex internal structure

Increases surface area for gas exchange

Their ribs and flight muscles ventilate their lungs more efficiently than the methods used by other vertebrates

One-way current of water, kept flowing by a specialised ventilation mechanism

Many folds to provide large surface area

A large surface area maintained as density of water prevents gills from collapsing

They have gill pouches

Don't have a special mechanism to force water over gills, must keep swimming

Parallel flow - blood and water travel in same direction, bloods oxygen concentration is limited to 50% of its possible maximum value

Gas exchnage in parallel flow doesn't occur across whole gill lamella

Gills are covered with a flap called the operculum

Counter-current flow, water moves in different direction to blood. Water always has a higher oxygen concentration

Water forced over gill filaments by pressure differences

To take in water:

1) mouth opens

2) operculum closes

3) floor of mouth is lowered

4) volume inside mouth increases

5) pressure inside mouth decreases

6) water flows in as external pressure higher than internal pressure

Each gill is supported by a gill arch

Along each gill arch are gill filaments

On gill filaments are gas exchange surfaces, the gill lamellae, provide a large surface area for gas exchange

Lungs are in an airtight compartment, the thorax

Pleural membranes line the thorax, cover each lung. Fluid between them prevents friction between lungs and chest cavity

Base of thorax is the diaphragm, separates thorax from abdomen

Ribs surround thorax

Intercostal muscles are between ribs

Trachea is a flexible airway, brings air to lungs

Two bronchi are branches of trachea

Lungs consist of branching network, bronchioles, arise from bronchi

At ends of bronchioles are air sacs, alveoli

1) external intercostal muscles contract

2) ribs are pulled upwards and outwards

3) diaphragm muscles contract, it flattens

4) both actions increase thorax volume

5) reduces pressure in lungs

6) atmospheric pressure greater than pressure in lungs, air forced in

It is elastic, it recoils and regains original shape when not being expanded

Feature plays a large part in pushing air out of lungs

They provide a large surface area to volume ratio

Gases dissolve in surfactant moisture lining the alveoli

Have walls made of squamous epithelium, only one cell thik, diffusion pathway is short

Extensive capillary network surrounding alveoli, maintains diffusion gradient as CO2 is rapidly brought to alveoli, oxygen is rapidly carried away

Capillary walls are one cell thick, cotrinbutes to short diffusion pathway

Deoxygenated blood enters capillaries surrounding alveoli

Oxygen diffused out of air, in the alveoli into the red blood cells in the capillary

Carbon dioxide diffuses out of the plasma in the capillary, into the air in the alveoli, from where it is exhaled

It occurs through paired holes, spiracles

Spiracles lead into a system of branched, chitin-lined air-tubes called tracheae, which branch into smaller tubes called tracheoles

They can open and close so gas exchange can take place

Hairs covering spiracles contribute to water loss prevention, prevent solid particles getting in

When resting they rely on diffusion, when moving the ends of the tracheoles are fluid-filled and close to muscle fibres, oxygen dissolves in the fluid and diffuses into muscle cells, no respiratory pigment or blood circulation needed. Carbon dioxide out by reverse.

Gases diffuse through stomata, down a concentration gradient

Once inside leaf, gases in the sub-stomatal air chambers diffuse through intercellular spaces between spongy mesophyll cells and into cells

Small pores that are bounded by two guard cells

Width of stomata can change, so they control exchange of gases between atmosphere and the internal tissues of the leaf.

If water enters, they become turgid and swell, opening a pore

If water leaves, they become flaccid and pore closes

1) Chloroplasts in guard cells photosynthesise to produce ATP

2) ATP provides energy for active transport of K+ into guard cells

3) Stored starch is conerted to malate

4) Malate and K+ lower water potential in guard cells, water enters by osmosis

5) Cell walls of guard cells are thinner in some places than other, and guard cells expand and a pore appears.

reverse process for closing

At night to prevent water loss due to insufficient light

In bright light as it would increase evaporation

If there is excessive water loss