OCR A Level Bio. 3.1.1 Exchange Surfaces

what are the (2) roles of exchange surfaces?

supply cells, remove metabolic waste from cells

what substances are exchanged in organisms? (in, excreted)

oxygen, waste products from metabolic activity - CO2, urea (NOT faeces)

true or false: single-celled organisms have low SA:V so need exchange systems

false - they have high SA:V so don't need exchange surfaces

what does the need for exchange systems depend on?

surface area (SA):volume (V) ratio

how do single-celled organisms exchange substances?

the substances diffuse directly into/out of the cell

do multicellular organisms need exchange systems? why (x3)?

yes - cells can be deep within the organism (high diffusion distance); low SA:V; high metabolic rate

REMEMBER SA:V = SA/V

REMEMBER SA:V = SA/V

volume of a cylinder

πr²h

surface area of a cylinder

2πr² + 2πrh

volume of a sphere

4/3πr³

surface area of a sphere

4πr²

how would you find the SA:V of a rod-shaped bacillus?

1) split the bacillus into 2 hemispheres and an cylinder

2) find the SA and V of the hemispheres and cylinder

3) do SA:V

what are the 3 features of an efficient exchange surface? & example/s of each?

• large SA - root hair cells

• thin exchange surface - alveoli, capillary wall

• good blood supply/ventilation - gills, alveoli

what is the effect of exchange surface having a large SA?

more space for exchange/diffusion => increased diffusion rate

what is the effect of exchange surface having a thin exchange surface?

decreased diffusion distance => increased diffusion rate/efficiency

what is the effect of exchange surface having a good blood supply/ventilation?

maintains conc.n gradient => increased diffusion rate

what tissues make up the mammalian gaseous exchange system?

trachea, bronchi, bronchioles, alveoli

goblet cell function

secrete mucus

ciliated epithelial cells function

beat mucus from goblet cells towards throat [get rid of dust & microorganisms, prevent lung infections]

where are goblet cells found?

trachea, bronchi, large bronchioles

where are ciliated epithelial cells found?

trachea, bronchi, large & small bronchioles

elastic fibres function (explain)

aid gas exchange -

• stretch when breathe in

• recoil when breathe out (help push air out)

where are elastic fibres found?

walls of: trachea, bronchi, all bronchioles, alveoli

smooth muscle function

controls airway diameter - propels substances along airways

where is smooth muscle found?

trachea, bronchi, large bronchioles

how does smooth muscle appear in the trachea?

on one side

how does smooth muscle appear in bronchi?

small pieces - interspersed w/ cartilage

how does smooth muscle appear in bronchioles?

in the walls/ outside layer

cartilage function

support - prevents collapsing when breathe in

where is cartilage found?

trachea, bronchi

how does cartilage appear in the trachea?

large 'C' shape around most of the diameter

how does cartilage appear in bronchi?

small pieces - interspersed w/ smooth muscle

what is ventilation?

movement of air into (inspiration) and out of (expiration) the lungs

what tissues control ventilation in mammals?

diaphragm, intercostal muscles (internal & external), ribcage

what happens during inspiration? (x5 steps)

1) i.c. muscles & diaphragm contract

2) ribcage goes upwards & outwards

3) thorax volume increases

4) thorax pressure decreases

5) air moves into the lungs (down conc.n grad. from outside -> inside)

what happens to the diaphragm when it contracts?

flattens

is inspiration active or passive?

active

what happens during expiration? (x5 steps)

1) i.c. muscles & diaphragm relax

2) ribcage goes downwards & inwards

3) thorax volume decreases

4) thorax pressure increases

5) air moves out of lungs (down conc.n grad. inside -> outside)

tidal volume (& average)

volume of air [in & out] each breath (0.4dm3)

vital capacity (& average range)

max. volume air that can be breathed out after a deep breath in (2.5-5dm3)

what (4) factors affect vital capacity?

size, age, gender, amount of regular exercise

breathing rate

number of breaths per unit time (usually /min)

oxygen uptake (& units)

volume of O2 consumed by body per min (dm3/min)

what machine can be used to investigate breathing?

spirometer

how does a spirometer work? (x3 points)

1) person breathes through mouthpiece - wearing a nose clip so only breathe using machine

2) breaths move chamber lid => moves pen to draw trace

• has soda lime to absorb expired CO2 => gas level decreases over time

label tidal volume on a spirometer trace

label vital capacity on a spirometer trace

how do you find breathing rate from a spirometer trace?

count no. peaks per min. (count full waves)

how do you find oxygen uptake from a spirometer trace?

find gradient between 2 points on trace (rise/run) (dm3s-1)

residual volume (& average)

volume of air remaining in lungs after maximum exhalation (1.5dm3)

why do we have residual volume?

airways & alveoli remain open constantly to prevent the lungs collapsing

label residual volume on a spirometer trace

what structures do bony fish use for gas exchange

gills - covered by the operculum

how many gills do fish have?

5 pairs

what is the (basic) structure of gills?

gill arch w/ gill filaments(/1ary lamellae) protruding; gill plates(/2ary lamellae) = grooves in gill filaments

gill arch

a cartilage skeletal element that supports the gills; contains blood vessels to carry blood to/from gills

gill filaments/primary lamellae

thin plates protruding from gill arch; increase SA so increase gas exchange; covered in grooves

gill plates/secondary lamellae

grooves on gill filaments; increase exchange SA; contain blood vessels to maintain conc.n grad.; thin so decrease diffusion distance } increase gas exchange rate

counter-current system

blood and water flow in opposite directions in gills

why do fish have counter-current systems?

maintains (O2) conc.n gradient - H2O w/ relatively high O2 conc.n always runs next to blood w/ relatively low O2 conc.n - maximise gas exchange

how do fish ventilate their gills? (x4 steps)

1) open mouth - lower buccal cavity floor - increase b.c. vol. & decrease pressure

2) water goes into b.c.

3) close mouth - raise b.c. floor - decrease b.c. vol. & increase pressure

4) water forced out through gills & operculum

how do you dissect a bony fish gaseous exchange system? (x4 steps)

1) find operculum

2) lift operculum & observe gills

3) cut 1 operculum away to view gills - note gill slits & space between gills

4) cut out 1 gill - note gill arch & gill filaments - draw gill

similarities between mammalian & bony fish gaseous exchange systems (x3)

• large SA - alveoli; gill filaments & plates

• good blood supply

• thin exchange surface - alveoli; gill filaments & plates

difference between mammalian & bony fish gaseous exchange systems

only fish have counter-current system

true or false: insects don't have a transport system

true - they have an open circulatory system

what system do insects use for gas exchange?

tracheal system

how does an insect tracheal system work (O2)? (x1 point) (x3 steps)

• insects have multiple tracheae

1) air moves into tracheae through pores - spiracles

2) tracheae branch into tracheoles

3) tracheoles go to individual cells & contain tissue fluid that dissolves O2 (air diffuses out of tracheoles, into cells)

how does CO2 leave an insect? (x3 steps)

1) diffuses into tracheole from cell

2) moves to trachea

3) diffuses out of insect through spiracle

how are tracheoles adapted for efficient gas exchange? (x2)

• thin - decrease diffusion distance for gases

• go to individual cells - decrease diffusion distance

how do insects generally ventilate themselves?

• sections of the tracheal system have flexible walls - expansion & contraction of these air sacs are controlled by flight action

• wings control thorax vol. - increase/decrease pressure

how do large insects ventilate themselves?

they can change their abdominal vol. - increasing ab. vol. = opens front spiracles = air in; decreasing ab. vol. = opens back spiracles = air out