3.1.1- Exchange Surfaces

3.1.3- Exchange Surfaces

what is an exchange surface

area adapted for efficient movement of molecules from one side to another

why do some organisms need specialised exchange surfaces

• larger organisms have lower SA:V meaning less SA for nutrient absorption and too high of a diffusion distance

• also have a higher metabolic demand as they are larger and so have more cells and move more

• warm blooded animals have higher demand as they need more energy etc to thermoregulate so need more ATP and respiration

why don’t single-celled organisms need specialised exchange surfaces

they have a high SA:V, meaning they can get everything they need through simple diffusion as the diffusion distance is low and SA is high

what is metabolic rate

energy expended by an organisms in a given time

do larger or smaller organisms have a higher metabolic demand

• larger organisms do in general as they have more respiring cells which need ATP and O2 etc

• however per unit of mass, the metabolic rate of smaller organisms is higher as they have higher heat loss as they have a larger surface area

what are the four adaptations of SES and why are they good

1. thin layers= lower diffusion distance so higher rate of diffusion

2. good blood supply= keeps concentration gradient high as taking away O2 and CO2 quickly

3. ventilation= maintains diffusion gradient by bringing in fresh things to be diffused and getting rid of waste

4. higher SA= provides larger area for exchange so more exchange can occur at one time

what are the key parts of the mammalian gas exchange system

• trachea

• bronchi

• bronchioles

• alveoli

formal name for the lung cavity

thorax

trachea- types of tissue

• lined with ciliated epithelial

• goblet cells

• elastic fibres

• smooth muscle

• C-shaped cartilage rings to prevent walls collapsing during inhalation

  • C shaped so doesn’t rub against oesophagus

bronchi- types of tissue

• similar to trachea but thinner walls and smaller diameter

• cartilage (full rings; not C)

• goblet

• ciliated epithelial

• elastic fibres

• smooth muscle

bronchioles- types of tissue

• larger bronchiole walls supported by cartilage but not all

• smooth muscle

• lined with ciliated epithelial but not usually goblet cells

• vary in size, smaller closer to alveoli

alveoli- types of tissue

• elastic fibres

• squamous epithelial

function of goblet cells

produce and secrete mucus which traps dust and microorganisms, which is then digested by stomach enzymes

function of ciliated epithelial cells

have projections of cilia; waft mucus to throat so pathogens cannot enter

function of elastic fibres

allow contraction and recoil of lungs and is what makes expiration passive; means it doesn’t break and returns to original shape

function of smooth muscle

when relaxes, the lumen widens so more air is able to get in and vice versa; regulates air flow into and out of the lungs

function of squamous epithelial tissue

provides structure while being very thin for alveoli walls

where are alveoli located and what is their role

• located in groups at the ends of bronchioles

• site of gas exchange; specialised exchange surface

adaptations of alveoli to make it a sufficient SES

• thin layer; walls are one cell thick and capillary walks are also one cell thick; means short diffusion distance

• good blood supply= network of capillaries surround the alveoli which helps keep concentration gradient steep

• ventilation= constantly inhaling and exhaling brings new O2 into the lungs and removes waste CO2 to keep concentration gradient high

• high SA through its bulging shape so more diffusion can occur at once

what is Boyles law

pressure and volume are indirectly proportional; as pressure increases, volume decreases and vice versa

muscles involved in inspiration and expiration

• diaphragm

• intercostal muscles (internal and external)

inspiration process

1. diaphragm contracts out and down, increasing volume

2. external intercostal muscles contract up and out, forcing the ribcage out, further increasing volume of the thorax

3. volume has increased so pressure decreases to less than the atmosphere so air enters

is inspiration active or passive

active because muscles are contracting, which requires ATP

expiration process

1. diaphragm relaxes and moves up and in, decreasing volume

2. ribcage moves down and external intercostal muscles relax, causing movement down and inwards

3. volume has now decreased so pressure has increased to higher than the atmosphere so air exits, including CO2

is expiration active or passive

passive as muscles are relaxing, unless its forced expiration

what happens during forced expiration

• internal intercostal muscles contract, pulling the ribs down and in further, decreasing the volume more

• therefore forces more air out of the lungs at a faster rate

• active process as muscle contraction that requires ATP

• when exercising etc

what is a spirometer

device used to measure breathing rate and volume of breaths

how does a float spirometer work

• airtight chamber with O2 inside it floats on water

• when you breath in, less air inside so the chamber goes downwards

• when you breath out, more air so the chamber moves upwards

• this is attached to a pen which can draw a graph onto a rotating drum of paper

• soda lime inside reacts with CO2 to remove it and keep it safe

three precautions to make when using a spirometer

• wear a nose clip so no other breathing

• ensure to not use it for too long as the CO2 in the drum increases and can cause the subject to not have enough air

• clean the mouthpiece after use

on a spirometer, are the peaks breathing out or breathing in and why

breathing out; this is because the y axis is spirometer volume and when breathing in, the volume of the spirometer decreases as the subject is taking air out of it, meaning that a trough is formed (the opposite is the case for if the y axis has lung volume)

what is tidal volume on a graph

• the normal resting breath capacity from peak to trough

• on the graph, is the regular breaths that a subject takes

what is vital capacity on a graph

• the largest volume of air breathed in and out at once

• measured from the largest peak to the largest trough

what is residual volume on a graph

• air still left in the lungs after full exhalation

• keeps the lungs working; cannot have no air inside

• is from the bottom of the lowest trough to 0 on the y-axis

what is inspiratory capacity on a graph

• the maximum inhalation

• from the tidal volume trough to the maximum peak

what is expiratory capacity on a graph

• the maximum exhalation

• from the tidal volume peak to the lowest trough

what is total lung capacity on a graph

• the sum of vital and residual volume; the total air in the lungs

• from the bottom of the graph (0 on the y-axis) to the highest peak

what is inspiratory reserve volume on a graph

• the difference from the peak of the tidal volume to the peak of the largest inhalation

what is expiratory reserve volume on a graph

from tidal wave trough to max exhalation trough

what are the three calculations that can be made from a spirometry trace

• breathing rate

• ventilation rate

• O2 consumption

how to calculate breathing rate and its unit

• number of complete breaths in one minute

• number breaths/time

• breaths min-1

how to calculate ventilation rate and unit

• breath rate/tidal vol

• dm3min-1

how to calculate O2 consumption and unit

• volume O2 consumed/time

• subtract from the highest peak to the lowest trough

• mm3min-1

what does a spirometry trace look like that makes it different from a lung capacity graph

it slowly slopes downwards because the soda lime reacts and human doesn’t breathe in all the air

how do fish ventilate

• fish mouth opens, which lowers the floor of the bucchal cavity and water enters

  • increases volume, decreases pressure which allows it to enter down conc grad

• mouth then closes, decreasing the volume and increasing the pressure, forcing the operculum to open and water into the opercular cavity

• here the water then moves over the gills

what is counter-current exchange

• where blood and water flow in opposite directions, with deoxygenated blood closer to deoxygenated water

why is counter-current exchange beneficial for the fish

• means there is a low and constant concentration gradient for max O2 uptake rather than concurrent where the concentration gradient gets lost and only 50% oxygen

why do fish need a gas exchange system

• low SA:V ratio

• high metabolic demand

• scaly surface impermeable to simple diffusion

• O2 concentration in water less than that in air

describe the structure of the gills

• few gill arches, from which gill filaments branch

• gill filaments come in pairs and extend out from the gill arch

• gill rakers on the inside of gill filaments

• lamellae cover the surface of gill filaments

what is the purpose of gill filaments

• increase the resistance of water flow

• slows it down, allowing more time for GE to occur

• also move (not rigid) to allow water to flow all over for max O2 uptake

what are lamellae and how are the adapted for efficient gas exchange

• microscopic and cover gill filaments and are the site of GE

• short diffusion distance into bloodstream

• capillary network so good blood supply to keep conc grad high

• ventilated b lots of water entering

• lots of them to increase SA

what do gill rakers do

filter out particles

what do gill arches do

hold gill filaments together and out

why do insects need a gas exchange system

• have a high SA:V ratio so seems like it shouldn’t need one

• but exoskeleton is impermeable so gases cannot diffuse straight in

• also increased metabolic demand when flying

describe the gas exchange system of insects

• spiracles allow gases to enter

• then enters tracheae

• then enters tracheoles which are the same as above but smaller

• tracheoles go directly into tissues and muscle fibres and diffusion occurs directly into them

what are spiracles

openings in the exoskeleton that allow gases to enter

how are tracheae held open

rings of chitin hold them open

how are the tracheole ends adapted for gas exchange

• very thin so short diffusion distance

• large number of them so large SA for GE

what ventilation mechanisms do insects have

• when flying and moving, the insects muscles relax and contract which pump gases in and out faster to help make demand

• when flying they can respire anaerobically which produces lactic acid inside cells

what does anaerobic respiration do that helps to meet the demand of gases

• lactic acid inside the cells decreases the water potential inside them

• this causes tracheal fluid at the ends of the tracheoles to enter the cells

• less means lower diffusion distance as closer to the cells, meaning that diffusion rate increases

how do insects store gas for later use

in air sacs in their body