Module 2

Exchange & Transport

Special Exchange Surfaces• Living organisms must be able to take in

or remove substances

• To do this they need specialised exchange surfaces

Organisms must take in:

Substance for

Organisms must remove:

Substance source

Exchange surfaces in living organisms

Organ exchange surface substances exchanged

Exchange surface characteristics:

Organisms must take in:

• Substance:• Oxygen• Glucose• Amino acids• Lipids• Mineral ions• Water

• For:• Aerobic respiration• Respiration/energy source• To make proteins for growth & repair• Make membranes and store energy• Various• solvent

Organisms must remove:• Substance:

• Carbon dioxide

• Oxygen

• Urea/ammonia

• From:

• A waste product of cell respiration

• A waste product of plant cell photosynthesis

• Nitrogenous waste from breakdown of protein

Organs & exchange surfaces

• Lungs• Alveoli• Small intestine• Villi• Kidney • Kidney tubules• Roots• Root hair cells• Leaves• Mesophyll cells• Fungi mycelium• Hyphae

Exchange surface characteristics

• Large surface area• Thin barrier for faster diffusion• Moist to allow molecules to dissolve so they can

diffuse• Maintain a steep concentration gradient across the

barrier• To do this ensure fresh supply of molecules arrives

and removal of the molecule on the other side.This means exchange surfaces often have a good blood supply

• Sometimes Active transport proteins in the membranes to pump materials across

Surface area/Volume ratio: cube animalsCube size(cm) Surface area (cm2) Cube volume (cm3) Surface

area/volume ratio

1

2

3

4

5

1. Plot a graph of this data2. What pattern is shown?3. How does this information link to the need for a specialised exchange surfaces

and transport systems in organisms?

Surface area/Volume ratio

Proof is in the pudding

• You will get 3 squares of jelly• 1 of them you will keep whole• 1 of them you will cut in half• The last you will need to cut into quartersWith each one you will need to drop into to a beaker containing 50ml of just boiled

water

Make a note of how long it takes each one to dissolve

What are your conclusions about the rates of reaction?

Examples of specialised exchange surfaces

• Single celled organisms

• Their exchange surface is their outer membrane

• They have a large surface area/volume ratio

• This allows materials to enter and leave by diffusion

• Small organisms

• Such as jellyfish, flatworms and true worms

• They also have large SA/V ratios and can still exchange some materials through their outer skin

• Large Organisms

• As animals and plants get larger their SA / V ratio gets smaller and they can no longer rely on diffusion through their outside layer

• They will need specialised organs as exchange surfaces

Specialised exchange surfaces in larger

organisms• Lungs, gills for gaseous exchange

• Small intestines for exchange of nutrients with the blood

• Roots of plants for exchange of water & minerals

• Hyphae of fungi for absorbing nutrients

• Liver for exchange of glucose and other nutrients with the blood

• Kidney for reabsorption of useful molecules back into the blood

The Gaseous exchange system

Airways• Trachea• Leads from the throat to the

lungs• Lined with ciliated epithelium• Glands in the wall also

secrete mucus• Protected from collapse &

supported by C shaped cartilage rings

• Cartilage is a tough ,hard tissue as well as being slightly flexible

Trachea Section

Loose tissue

Trachea Section

Trachea Section

Ciliated epithelium• Much of the airways are lined with

this tissue• May look like several layers,but

each reaches the basement membrane.

• (Pseudostratified epithelium)• In goblet cells the end nearest

the membrane is thin,and widens at the top like a goblet

• The top part is full of mucus secreted by the cell

• Mucus is a slimy solution of mucin ,contains glyocoprotein & carbohydrate.

• It is sticky and traps particles (bacteria, pollen, dust etc)

• It keeps the surface moist

Basement membrane

Goblet cell

Pseudostratified epithelium

Ciliated epithelium• In between the goblet

cells are columnar ciliated epithelial cells

• The cilia beat carrying a carpet of mucus upwards

• Speed about 1cm/minute• At the top of the trachea

the mucus is swallowed and destroyed by the stomach acid along with any pathogens

Ciliated epithelium

• Bronchi• At the base of the trachea

are 2 bronchi,one leading to each lung

• They subdivide and branch forming the bronchial tree.

• Lined with ciliated epithelium,but less goblet cells

• Cartilage is in irregular blocks not rings so allowing more flexibility

• Also contains elastic fibres and smooth muscle

• Bronchioles• The bronchi divide into smaller and smaller tubes:• Bronchiole -terminal bronchioles – respiratory bronchiole – alveolar duct• No cartilage, no goblet cells• Walls contains smooth muscle which can contract to narrow the airway

(lack of cartilage allows this)• This can reduce flow of air to alveoli and is a reflex action to protect against

harmful substances in the air• Allergic reactions, asthma etc• When the smooth muscle relaxes airway widens due to recoil of elastic

tissues

Alveoli Structure & Function

Alveolus wall- very thin for easy exchange of gases

Alveolus-millions give large surface area

Blood capillary- good blood supply removes O2 and brings CO2

Air moved in and out by breathing(ventilation)

Alveoli• Gaseous exchange surface in mammals• Moist lining to dissolve gases• Very thin single cell thick lining of epithelial cells• Surrounded by very thin blood capillaries walls one cell thick.• low blood pressure so very slow flow of RBCs• RBCs only just fit through and are pressed against the

capillary wall to lower diffusion distance• Blood removes oxygen from and brings carbon dioxide to the

alveoli, maintaining a steep concentration gradient• Very short distance from blood to alveoli(2-4µm)• Total surface area 70m2

• All leads to rapid and efficient diffusion of CO2 & O2

• Contain elastic fibres so alveoli can stretch when inhaling (increase area more), recoil after , and push air out

• Surfactant chemical lowers surface tension and stops alveoli collapsing

http://fantastrid.googlepages.com/Alveole01-full.jpg/Alveole01-full-full.jpg

Lung Section

Gaseous Exchange surfaces

• Produce a set of powerpoint slides to:• Explain the characteristics of an exchange

surface• A slide each on how this is achieved in the

following organisms:• Bony fish• Land snail• Insect• Plant

Measuring Fitness

Breathing rate & depthPulse rate

Blood pressure

Breathing

• Breathing or ventilation renews the air inside the alveoli(bringing fresh O2 and removing CO2

• Maintains a concentration gradient so oxygen and carbon dioxide can diffuse in and out of the blood

• At rest need to ventilate 6.0dm3/minute of air into the lungs

• Only about 1/7th of air in the alveoli is changed with each breath

• This means composition of gases in the alveoli stays constant and aids gaseous exchange

Breathing rate• The depth and rate of breathing varies

with our level of activity

• The rate of breathing is called the ventilation rate

• Depth of breathing is the amount of air taken in with each breath

• These can be measured using a spirometer.

Spirometer

Using the spirometer• The air in the air chamber is breathed in and out• This causes the float to rise up(expiring) and down(inspiring)• This movement can be recorded by a pen on a kymograph drum or by

computer sensors• The kymograph paper can be calibrated for time and volume • Sterile mouthpiece must be used• Nose clip ensures breathing through mouth only• The air chamber can be used with normal air for a limited time• For longer use it must be filled with medical grade oxygen and a carbon

dioxide absorber such as soda lime used(why?)

Spirometer Trace

• Tidal volume• The volume of air breathed in (or out) in one breath • Breathing rate• Number of breaths /minute• Ventilation rate• Total volume of air breathed in and out in one minute• Vital capacity• The largest volume of air you can breathe in and out in one breath• Inspiratory reserve volume• Extra air above the tidal volume you breathe in when deeply filling

your lungs• Expiratory reserve volume• Extra air you breathe out when emptying your lunmgs• Residual capacity• Air that you cannot empty from your lungs• Total capacity• Equals VC + RC

Measuring oxygen consumption• Use soda lime to absorb the exhaled CO2

• The trace will gradually fall as the breathed air volume in the chamber reduces

• Measure how much the trace drops in a set time

• Work out the volume of O2 consumed/minute

Trace drops 0.5dm3 in 55s500cm3 in 55s500/55 = 9.1cm3/s9.1 x 60 = 546cm3/min