4- Gas Exchange

Why does the volume affect the rate of gas production or use?

• Smaller vol= less cells= less respiration= less O2 needed= less CO2 produced

• Larger vol= more/bigger cells= increased respiration= more O2 used= more CO2 produced

What is surface area always presented to in SA:vol ratio?

1

Describe the relationship between size and SA:vol ratio

as size increases, SA:vol ratio decreases

How does the shape affect the SA:vol ratio?

enlongating/ flattening will increase ratio

Explain why very small organisms such as amoeba can meet all its gas exchange requirements by diffusion through its cell surface membrane only

(common question)

Large SA:vol ratio so gas can penetrate to all parts easily. Diffusion pathway is short

Explain why larger organisms such as fish and mammals need specialised gas exchange systems

(common question)

Smaller SA:vol ratio so not enough SA to supply their needs by diffusion (too slow). Also length of diffusion pathway is too long

What is metabolic rate?

rate at which all chemical reactions in body occur (respiration)

Why do smaller mammals need a higher metabolic rate?

have a larger SA:vol ratio so lose heat faster

• production of heat will be related to the mass/ volume of organism

• rate of heat loss determined by SA

What is the equation for aerobic respiration

glucose + oxygen —> carbon dioxide + water + energy

C6H12O6 + 6O2—> 6CO2 + 6H2O + ATP

How do we get the most efficient gas exchange? (Fick’s law)

• provide large SA

• maintain high conc gradient

• thin exchange surface

How do single-celled organisms exchange gas?

diffusion across outer surface membrane

• due to large SA:vol ratio and short diffusion pathway

What are the levels of O2 and CO2 inside a single-celled organism?

• low 02 conc

• high CO2 conc

What are the levels of O2 and CO2 outside a single-celled organism?

• high O2 conc

• low CO2 conc

Where are gas exchange structures found in a fish?

buccal cavity (mouth) and operculum

How is a larger SA created in fish for gas exchange?

• many gill filaments covered with lamellae which protrude off gill filaments

How is a short diffusion pathway created in fish for gas exchange?

• many capillaries with single layer of endothelium (1 cell thick) close to thin- walled lamellae (makes pathway shorter between blood + water)

What are epithelium cells?

in contact with substances from outside environment

What are endothelium cells?

in contact with substances from an internal source/ environment (line blood vessels)

How is a concentration gradient created in fish for gas exchange?

• continuous flow of blood through capillaries= oxygenated blood replaced with deoxygenated blood quickly

• water flows over gill plates in the opposite direction to blood flow to create a counter current mechanism

Why is a counter current mechanism an improvement over parallel flows?

• water and blood flow in opposite directions

• blood always meets water with lower conc of O2

• a conc gradient is maintained along whole length of lamellae

• constant diffusion of 02 can occur across whole length of lamellae

What does a ventilation mechanism ensure in a fish?

that water enters the fish’s mouth and flows over the gills so a constant flow of water over the gills

Explain why a constant flow of water over the gills is essential for gas exchange to occur efficiently

to maintain a conc gradient by ensuring water with a higher O2 conc continuously moves over gills (and water with a lower O2 conc is removed)

Describe how a fish is adapted for effective diffusion (large surface area)

• provided by gill filaments and lamellae

Describe how a fish is adapted for effective diffusion (large conc gradient)

• continuous blood flow and removal of high O2 conc blood

• ventilation mechanism

• counter current flow

Describe how a fish is adapted for effective diffusion (thin exchange surface)

• thin walled lamellae/ filaments

• blood capillaries close to gill surface

• walls of capillaries 1 cell thick

What is the body if an insect protected by?

exoskeleton made from chitin

• waxy + waterproof= minimises water loss but pevents gas exchange across surface

What system do insects have for gas exchange?

tracheal system= air filled tubes (tracheae) that open to outside though small holes called spiracles

What happens to larger tracheal tubes of an insect?

subdivide into smaller tubes (tracheoles) that penetrate into the insects cells

What are the sites of gas exchange in insects?

tracheoles

What does a large number of tracheoles do in an insect?

give large SA with thin walls, extensive branching and close proximity to cells provide a short diffusion pathway

What is the order of the tracheal system in insects?

1. exoskeleton

2. spiracles

3. trachea

4. tracheoles

5. body cells

What happens with gas exchange when the insect is inactive?

• have a shorter diffusion pathway

• so can rely on just diffusion down a conc gradient that is maintained due to cellular respiration

What happens with gas exchange when the insect is active (abdominal pumping)?

• flight requires more ATP for increased muscle contraction

• ventilation by contraction can force air in + out of spiracles and tracheae to maintain greater air flow and steeper conc gradients for fast diffusion

• insects can also remove fluid from ends of tracheoles to increase diffusion rates (gas diffuses quicker in air than liquid)

How does removal of water help insects with gas exchange when active?

• lactic acid is in the cells as it anaerobically respires, so cell has a lower water potential

• water moves from high water potential in fluid to low water potential in cells

• this means the fluid is now gone so more air can fill space where fluid was= increases diffusion

Describe how insects are adapted to minimise water loss?

1. waterproof, waxy cuticle all over body

2. spiracles may be guarded by valves which can close spiracles

3. spiracles surrounded by hairs which trap a layer of moist air around the spiracle to minimise water loss

Describe how an insect is adapted for effective diffusion (large SA)

• large number of branching tracheoles (site of gas exchange)

Describe how an insect is adapted for effective diffusion (large conc gradients)

• use of O2 in cells by respiration maintains lower O2 conc in cells

• in larger, more active species, abdominal pumping increases air flow= ventilation mechanism

Describe how an insect is adapted for effective diffusion (thin exchange surface)

• tracheoles thin walled

• tracheoles very close to body cells

Where does gas exchange occur in plants?

spongy mesophyll layer of leaf (large air spaces and thin walled cells)

Why will there be steep concentration gradients for gases in plant spongy mesophyll layers?

• CO2 will be low in leaf by day (light available) as it is used in photosynthesis. Reverse for O2

• At night O2 conc will be low in leaf as it is used by cells for respiration (no light for photosynthesis). Reverse for CO2

Name the process that occurs in the leaf cells throughout both the day and night and the gases it uses and produces

PROCESS= respiration

USES= oxygen

PRODUCES= carbon dioxide

Name the process that only occurs in the leaf cells throughout daylight hours and the gases it uses and produces

PROCESS= photosynthesis

USES= carbon dioxide

PRODUCES= oxygen

How does the leaf minimise water loss while still maintaining effective diffusion?

• stomata open/ close at different points in the day + at different temps

• stomata mainly on underside of leaf as cooler

• thicker waxy cuticle on upper epidermis

Describe how a plant is adapted for effective diffusion (large SA)

• large number of stomata

• flat, thin leaves

• air spaces in spongy mesophyll layer

Describe how a plant is adapted for effective diffusion (large conc gradient)

• by day, photosynthesis is faster than respiration so CO2 is used and O2 is produces

• at night only respiration occurs so 02 is used and CO2 is produced

Describe how a plant is adapted for effective diffusion (thin exchange surface)

• flat, thin leaves so a short diffusion pathway

• spongy cells have thin cell walls

Explain the role of the cilia and mucus in the human gas exchange system

• Mucus= traps micro-organisms and debris, helping keep airways clear

• Cilia= beat repeatedly to move micro-organisms and dust particles along with the mucus

Describe the structure of the human gas exchange system

1. trachea

2. bronchi

3. bronchioles

4. alveoli

What is alveoli made from and how does this help with gas exchange in humans?

elastic tissue= short diffusion distance

Describe how a human is adapted for effective diffusion (large SA)

• millions of alveoli and large SA of blood capillaries

Describe how a human is adapted for effective diffusion (large conc gradients)

• blood circulates through capillaries, removing blood with a high O2 conc and delivering blood with low O2 conc

• ventilation ensures air with high O2 conc taken in and air with low O2 conc is removed

Describe how a human is adapted for effective diffusion (thin exchange surface)

• squamous epithelium of the alveolar wall, consisting of thin flattened cells

• squamous epithelium of capillary wall is 1 cell thick

What is inspiration?

taking air into the thorax

What is expiration?

moving air out of the thorax

What do both inspiration + expiration require?

• breathing movements to alter the volume of the thorax= creates pressure differences

Why is air forced out of the lungs? (in terms of preesure)

when pressure in the thorax is greater than pressure in the atmosphere

How does air move? (gradient)

from area of higher pressure to lower pressure down a pressure gradient

What is meant by “pressure is inversely proportional to volume”?

when volume increases, pressure decreases and vice versa

During inspiration what happens to volume and pressure?

volume= increases

pressure= decreases

During expiration what happens to volume and pressure?

volume= decreases

pressure= increases

What is the term used to describe intercostal muscles?

antagonistic

Explain the term antagonistic muscles

a pair of muscles which, on contraction, produce opposite effects to each other

Describe how the intercostal muscles and diaphragm muscles bring out during inspiration

• external intercostal muscles contract

• ribcage moves up and out

• diaphragm muscles contract and diaphragm flattens

• elastic tissue stretches

• volume increases in thorax

• pressure decreases below that atmosphere

• air enters down a pressure gradient

Describe how the intercostal muscles and diaphragm muscles bring out during expiration

• external intercostal muscles relax

• intercostal muscles contract

• ribcage moves in and down

• diaphragm muscles relax

• diaphragm returns to dome shaped

• elastic tissue recoils

• volume of thorax/ lungs decreases

• pressure increases above atmospheric

• air is forced out down a pressure gradient

Why is forced expiration not passive?

external intercostal muscles relax and the internal intercostal muscles contract which pulls the ribcage further down and in

What is the role of elastic tissue in breathing?

• during inspiration the elastic tissue in lungs stretches to allow the lungs to inflate

• during expiration the elastic tissue recoils

What is tidal volume?

the volume of air breathed in or out of the lungs in a normal resting breath

What is ventilation rate?

the number of breaths in and out per minute

What is pulmonary ventilation?

the total volume of air that is moved into the lungs in 1 minute

What is the formula for calculating pulmonary ventilation

pulmonary ventilation= tidal wave x ventilation rate