3.1-3.2-Gas exchange and SA:V

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

bigger volume- more/bigger cells and therefore increases use of oxygen and production of carbon dioxide in respiration

what is the relationship between size and sa:v?

as size increases, the sa:v ratio decreases

negative correlation

why do very small organisms meet its gas exchange requirements by diffusion thru its cell surface membrane?

large sa:v

gases penetrate easily

why do larger organisms need specialised gas exchange systems?

have smaller sa:v ratio

otherwise diffusion pathway would be too long or rate of diffusion would be too slow

why do small animals lost heat faster?

larger sa:v ratio

need higher metabolic rate as they respire faster and so replace the heat lost

what are the three adaptations of a gas exchange surface with most efficient rate of diffusion?

provide large surface area

maintain high concentration gradient

exchange surface as thin as possible

what are the features of a single celled organisms

rely on simple diffusion of gases across their outer surface membrane

small size- larger sa:v ratio

short diffusion pathway

continuous aerobic respiration- maintain conc. gradient for O2 and CO2

how do fish have a larger surface area?

each gill consist of many thin walled filaments each covered in many lamellae

how do fish have a short diffusion pathway?

gills have a very rich blood supply

many capillaries- with single layer of thin epithelium- close to thin walled lamellae

many blood capillaries increase surface area

thin epithelium ensures short diffusion pathway between blood and water

how do fish maintain a conc. gradient?

continuous flow of blood through capillaries ensure blood saturated in oxygen is quickly removed from gills

water flows over gills in the opposite direction to the flow of blood in the capillaries

what is this system of opposite flow called?

counter current mechanism

why is a counter current mechanism an improvement over one of parallel flow?

gas exchange takes place over entire gill- oxygen never requires equilibrium

blood always meets water with higher conc. of O2- gradient is maintained along whole line length of lamellae

constant diffusion is occurring

what does a ventilation mechanism ensure?

water enters the fish mouth and flows over the gills, leaving via the operculum

constant flow of water over the gills

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

maintain a steep diffusion gradient, ensuring oxygen rich water is always in contact with the blood rich lamellae

why do the larger trachae of insects have rings of chitin?

keep airways open when pressure inside them decreases/when body moves

what do the trachea subdivide into?

tracheoles- sites of gas exchange

how do insects have a large surface area for diffusion?

larger number of small, branched tracheoles

how do insects have a short diffusion pathway?

thin walls of tracheoles

close proximity of tracheoles to cells

how is the conc. gradient maintained in an insect?

diffusion down a conc. gradient that is maintained in the tracheal system due to cellular respiration in the insects tissues

why the O2 requirements of muscles increase during flight?

increases muscle contraction which requires ATP

increased rate of respiration- more O2 needed to maintain high rate of respiration

what is abdominal pumping?

ventilation by contraction of the muscles of the abdomen can force air in and out of the spiracles and trachea to maintain a greater air flow and maintain steeper conc. gradient for faster diffusion

how are insects minimised to water loss?

exoskeleton- made of chitin, makes it waterproof and waxy

small sa:v ratio- reduces area over which water is lost

spiracles can open and close- reduce water lost

spiracles- hairy- trap layer of moist air

how do plants have a large surface area?

spongy mesophyll layer- loosely packed- creates air spaces

flat thin leaves

large number of stomata

how do plants have a short diffusion pathway?

spongy cells have thin walls and are in direct contact with air

flat thin leaves

how is the conc. gradient maintained in plants?

co2 low in the leaf by day as its used in photosynthesis- vice versa for o2

o2 low in the leaf at night as its used in respirationn- vice versa for co2

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

day- photosynthesis- uses co2 and produces o2

respiration- uses o2 and produces co2

what is the process that only occurs in leaves during daylight hours and the gases it uses and produces?

photosynthesis- uses co2 and produces o2

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

stomata mainly on underside only

thick waxy cuticle on upper and lower epidermis

guard cells can close stomata/reduce stomatal diameter e.g when temp is too high

why do we need to carry out gas exchange?

for aerobic respiration- release ATP

otherwise pH would be dangerously low

why must the the volume of gases that are exchanged be large in mammals?

high rate of respiration- maintain constant body temp.

what is the role of mucus?

traps micro organisms and debris, helping to keep airways clear

what is the role of cilia?

beat regularly to move micro organisms and dust particles along with the mucus

how do lungs have a large surface area?

millions of alveoli

(large sa of capillaries)

how do lungs have a short diffusion pathway?

only 2 layers of cells between air in alveoli and blood in capillary

squamous epithelium of alveolar wall (thin flattened cells)

squamous endothelium of capillary wall

alveroli + capllary walls are one cell thick only

how do lungs maintain a large conc. gradient?

blood continuously circulates through capillaries, removing blood with high o2 and delivering blood with low o2

ventilation ensures air with high o2 conc taken in with air and low o2 conc is removed

what is the path oxygen takes to diffuse into the blood?

epithelium of alveoli

endothelium of blood capilaries into the blood

what do the elastic tissues allow?

allows elastic recoil- force co2 out of lungs

why is air forced out of the lungs, in terms of pressure?

pressure in the thorax is greater than pressure in the atmosphere

air moves from an area of higher pressure to one of lower pressure down a pressure gradient

what are antagonistic muscles?

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

what is metabolic rate?

rate at which chemical reactions in body occur e.g respiration

what occurs during inspiration?

diaphragm contracts, causing it to flatten

intercostal muscles contract

ribs move up and out

volume increases in thorax

pressure decreases in thorax- air drawn in

what occurs during expiration?

diaphragm relaxes, returning to dome shape

intercostal msucles relax

ribs moves down and in

volume decreases in thorax

pressure increases in thorax- air drawn out

what is the role of the external and internal muscles in forced expiration?

external intercostal muscles relax

internal intercostal muscles contract

pulls ribcage down and in

what is the role of elastic tissue in breathing?

inspiration- elastic tissues in lungs stretches to allow lungs to inflate

expiration- recoils

what is pulmonary ventilation and what is the equation for it?

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

tidal volume x ventilation rate

what is tidal volume?

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

what is ventilation rate?

number of breaths in and out per minute

what does causally linked mean?

one variables causes another to occur