Biology 2.2 Gas Exchange

Respiratory surfaces

where gases are exchanged with the environment

4 features of a respiratory surface

Thin

Permeable

Moist

Large surface area

How are all gases exchanged

Diffusion

SA:Volume in amoeba

large

SA:Volume in large organisms

small

How are large organisms adapted for gas exchange

specialised respiratory surfaces

circulatory systems

blood pigments

metabolic rate

The rate of energy expenditure by the body

respiratory surface in bony fish

gills

Why must water be forced over gill filaments

Water is dense with low oxygen content

How does the density of water prevent gills from collapsing

By maintaining a large surface area

How is water forced over the gills

A ventilating mechanism - the water flows in one way

How is ventilation achieved in fish

pressure changes in the buccal and opercular cavities

Stage 1 of ventilation mechanism in bony fish

The mouth opens and the floor of the buccal cavity is lowered.

Volume of the buccal cavity increases and pressure decreases.

The operculum remains closed.

Water is pulled into the buccal cavity from the outside due to the change in pressure

Stage 2 of ventilation mechanism in bony fish

The mouth closes and the buccal cavity contracts, raising the floor of the buccal cavity.

Water is forced across the gills

Stage 3 of ventilation mechanism in bony fish

Pressure in the gill cavity increases and forces the operculum open

Water leaves via the operculum

How is efficient diffusion of oxygen maintained in bony fish

The gills have an extensive network of capillaries

How is oxygen carried through bony fish

haemoglobin and a circulatory system

Counter current flow in bony fish

Water flows between the gill plates in the opposite direction to the blood flow in the gill capillaries

How does counter current flow increase the efficiency of diffusion

By maintaining a steep concentration gradient across the whole gill filament

What do inactive amphibians use for gas exchange

its moist skin

What do active amphibians use for gas exchange

simple lungs

Frogs lungs

a pair of hollow sacs

highly folded surface increases surface area

What do reptiles use for gas exchange

exclusively lungs

Reptile lungs

sac-like and have more complex folding than amphibian lungs

how is ventilation aided in amphibians

movement of the ribs by the intercostal muscles

why is efficient gas exchange essential in birds

warm-blooded

high respiration rate

birds lungs

small and compact, composed of numerous branching air tubes called bronchi

where does gas exchange take place in birds lungs

parabronchi as they have an extensive blood capillary network

what is at the end on the parabronchi

large, thin walled air sacs which help in ventilation

How is ventilation of the lungs brought about in birds

movement of the ribs

during flight the action of the wing muscles ventilates the lung

How does gas exchange occur in insects

paired holes called spiracles
running along the side of the body

What do spiracles lead into

a system of branched, chitin lined airtubes called tracheae

Why do spiracles open and close like valves

allows gas exchange to take place and reduces water loss

How does ventilation happen in insects during periods of activity, such as during flight

movements of the abdomen ventilate the tracheae

What are the ends of the tracheae called

tracheoles

gas exchange takes place here

oxygen passes directly into cells rapidly

thorax

An airtight compartment where the human lungs are enclosed

site of gas exchange in humans

alveoli

how do humans ventilate their lungs

forcing air into the lungs

What happens during inspiration

intercostal muscles contract, raising the ribcage upwards and outwards

diaphragm contracts and flattens

volume of the thorax increases and the pressure decreases

Air enters the lungs and the lungs expand

What happens during expiration

intercostal muscles relax which moves the ribcage inward and downward

diaphragm relaxes and curves upwards

volume of the thorax decreases and the pressure increases.

air is forced out of the lungs

How are alveoli adapted for efficient gas exchange

large, moist surface area

thin walls provide a short diffusion pathway

extensive capillary network

maintain a steep concentration gradient

what prevents the alveoli collapsing when breathing out

A surfactant

angiosperm

flowering plants

equation for photosynthesis

carbon dioxide + water = glucose and oxygen

function of photosynthesis

synthesis glucose for respiration

when does photosynthesis occur

daylight

where does respiration occur

night time

equation for respiration

glucose + oxygen = carbon dioxide + water + ATP

function of xylem

transport of water and minerals

function of phloem

transport of sucrose

function of stoma

regulates transpiration

allows gas exchange

function of palisade mesophyll layer

contains chloroplasts for photosynthesis

function of cuticle

waterproof layer that reduces water loss

function of vascular bundle

contains xylem and phloem

function of guard cells

allow gasses to diffuse easily through the leaf

change shape to allow stomata to open and close

Malate theory

1. ATP produced in photosynthesis

2. K+ ions actively transported into the cell

3. Stored starch converted to malate

4. Malate and K+ lower the water potential

5. Water moves in via osmosis cell becomes turgid

6. Thin outer cell walls expand

7. Stomata opens

Stomal opening

Turgid cell = open pore

Flaccid cell = closed pore