Module 3: Section 1 - Exchange Surfaces


Terms in this set (...)

Why do we need to exchange substances with their environment?
- cells need to take in things like oxygen and glucose for aerobic respiration and other metabolic reactions

- secrete waste products from these reactions (CO2 and Urea)
Smaller animals have a HIGH surface area to volume ratio
Why do Multicellular Organisms need exchange surfaces?
- diffusion across the outer membrane is too slow:

- some cells are deep within body = big distance between them and outside environment

- large animals have a low surface area to volume ratio - it is difficult to exchange enough substances to supply a large volume of animal through a relaitvely small outer surface

- a higher metabolic rate than single celled organisms, so they use up oxygen and glucose faster

- multicellular animals need specialised exchange surfaces - like the alveoli in the lungs
Exchange in Single Celled Organisms
- substances can diffuse directly into/out of the cel across the cell surface membrane

- diffusion rate is quick because of the small distances the substances have to travel
How to Increase Exchange of Substances
- Large Surface Area

- Thin

- Good Blood Supply

- Ventilation
Example of Large SA increasing Diffusion
- Root Hair Cells

- cells on plant roots grown into long 'hairs' which stick out into the soil
Example of Thin Diffusion Distance
- in lung

- each alveolus is made from a single layer of thin, flat cells = Alveolar Epithelium

- O2 diffuses out into blood

- CO2 diffuses in opposite direction

- decreases diffusion distance

- increases rate of diffusion
Example of Good Blood Supplies
- alveoli

- surrounded by a large capillary network, so each alveolus its own blood supply

blood takes O2 away and brings more CO2 in

- the lungs are ventilated, so the air in the alveolus is constantly replaced

- good blood supply maintains concentration gradients of O2 and CO2
Examples of Ventilation
- Fish Gills

- the gills are the gas exchange surface in fish

- in the gills, O2 and CO2 are exchanged between the fish's blood and the surrounding water

- fish gills contain large network of capillaries (well supplied with blood)

- well ventilated as fresh water constantly passes over them

- maintain concentration gradient of O2
increasing rate at which O2 diffuses into blood
What happens in Lungs?
1. when you breathe in, air enters the trachea

2. trachea splits into 2 bronchi

3. 1 bronchus leads to each lung

4. each bronchus branches into bronchioles

5. bronchioles end in alveoli

6. the rib cage, intercostal muscles and diaphragm all work together to move air in and out
Goblet Cells
- line airways

- secrete mucus

- mucus traps microorganisms and dust particles in the inhaled air

- stop particles from reaching alveoli
- on surface of cells lining airways

- beat the mucus

- moves mucus and trapped organisms upward away from the alveoli towards the throat where it is swallowed

- prevents lung infection
Elastic Fibres
- in the walls of the trachea, bronchi, bronchioles and alveoli

- help process of breathing out

- breathing in = lungs inflate and elastic fibres are stretches

- fibres RECOIL to help push air out when exhaling
Smooth Muscle
- in walls of the trachea, bronchi and bronchioles

- allows their diameter to be controlled

- during exercise the smooth muscle relaxes, making the tubes wider

- less resistance to airflow and air can move in and out of lungs more easily
Rings of Cartilage
- in the walls of the trachea and bronchi

- they provide support

- it's strong but flexible

- stops the trachea and bronchi collapsing when you breathe in and pressure drops
Shape of Cartilage in Trachea
C Shaped Cartilage Pieces
Shape of Cartilage in Bronchi
Shape of Cartilage in Larger Bronchiole
Shape of Cartilage in Smaller Bronchiole
Shape of Cartilage in Smallest Bronchiole
Components of Trachea
- Smooth muscle

- Elastic Fibres

- Goblet Cells

- Ciliated Epithelial
Components of Bronchi
- Smooth muscle

- Elastic Fibres

- Goblet Cells

- Ciliated Epithelial
Components of larger Bronchiole
- Smooth muscle

- Elastic Fibres

- Goblet Cells

- Ciliated Epithelial
Components of Smaller Bronchiole
- Smooth muscle

- Elastic Fibres

- NO Goblet Cells

- Ciliated Epithelial
Components of Smallest Bronchiole
- NO Smooth muscle

- Elastic Fibres

- NO Goblet Cells

- NO cilia
Shape of Cartilage Pieces in Alveoli
Components of Alveoli
- NO Smooth muscle

- Elastic Fibres

- NO Goblet Cells

- NO cilia
Breathing In and Out
- consists of inspiration and expiration

- controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage
1. external intercostal and diaphragm muscles contract

2. this causes the ribcage to move upwards and outwards

3. diaphragm flattens, increasing the volume of the thorax (where lungs are)

4. as the volume of thorax increases, the lung pressure decreases (to below atmospheric pressure)

5. causes air to flow into the lungs

6. inspiration is an active process (energy is required)
1. external intercostal and diaphragm muscles relax

2. ribcage moves downwards and inwards and the diaphragm becomes curved again

3. the thorax volume decreases, causing the air pressure to increase (to above atmospheric pressure)

4. air is forced out of lungs

5. normal expiration is a passive process (no energy required)

6. expiration can be forced through

7. during forced expiration, the intercostal muscles contract, to pull the ribcage down and in
Tidal Volume (TV)
is the volume of air in each breath (usually about 0.4 dm3)
Vital Capacity
the maximum volume of air that can be breathed in or out
Breathing Rate
how many breaths are taken in a certain amount of time
Oxygen Consumption / Uptake
the rate at which an organism uses up oxygen
a machine that can give readings of tidal volume, vital capacity, breathing rate and oxygen uptake
How does a Spirometer work?
1. oxygen filled chamber with movable lid

2. the person breathes through a tube connected to the oxygen chamber

3. as the person breathes in and out, the lid of the chamber moves up and down

4. these movements can be recorded by a pen attached to the lid of the chamber
this writes on a rotating drum, creating a spirometer trace

- or the spirometer can be hooked up to a motion sensor - which uses movements to produce electronic signals, which can be picked up by a data logger

5. The soda lime in the tube the subject breathes into, absorbs carbon dioxide
Why does the total volume of gas in the chamber decreases over time in a Spirometer?
- because the air that's breathed out is a mixture of oxygen and carbon dioxide

- the CO2 is absorbed by the soda lime, so there's only O2 in the chamber which the subject inhales from

- O2 gets used up by respiration, so the total volume decreases
What is the function of the soda lime in the spirometer?
the CO2 is absorbed by the soda lime, so there's only O2 in the chamber whcih the subject inhales from
How to Calculate the Breathing Rate?
number of peaks per minute
How to calculate Tidal Volume?
difference in one peak
How to calculate Vital Capacity?
highest peak - lowest peak
How to calculate Oxygen Consumption?
decrease in volume of gas = work out gradient
What system do fish use for gas exchange?
a counter - current system
Concentrations of Oxygen in Water
lower concentration of oxygen in water than in air
How does a Counter Current System work in Fish?
1. water containing oxygen enters the fish through its mouth and passes out through gills

2. each gill is made of lots of thin branches called Gill Filaments or Primary Lamellae

-- big surface area for gas exchange

-- covered in gill plates / secondary lamellae, which increases SA further

-- each gill supported by gill arch

3. the gill plates have lots of blood capillaries and a thin surface layer of cells

4. blood flows through the gill plates in one direction and water flows over in opposite direction = Counter-Current System
maintains a large concentration gradient between water and blood

-- concentration of O2 is always higher than in the blood, so as much oxygen as possible diffuses from the water into the blood
Ventilation of Fish Gills
1. fish opens mouth, which lowers the floor of the buccal cavity (space inside mouth)

2. volume of buccal cavity increases, decreasing pressure inside cavity

3. water sucked in to cavity

4. when fish closes its mouth, the floor of the buccal cavity is raised again

5. volume inside the the cavity decreases, the pressure increases and water is forced out of the cavity across the gill filaments

6. each gill covered by a bony flap (operculum, which protects the gill)

7. increase in pressure forces the operculum on each side of the head to open, allowing water to leave gills
How to Dissect Fish Gill
1. Wear apron, lab coat and gloves

2. Place fish in dissection tray / cutting board

3. Push back operculum and use scissors to carefully remove gills

4. Cut each gill arch through the bone at the top and bottom

5. Look at gill filaments
Gas Exchange in Insects
1. Insects have microscopic air filled pipes called tracheae, which they use for gas exchange

2. Air moves into tracheae through spiracles (pores on insect's surface)

3. Oxygen travels down concentration gradient towards cells

4. CO2 from cells moves down its own concentration gradient towards spiracles to be released into the atmosphere

5. Trachea branch off into smaller tracheoles which have thin, permeable walls andgo to individual cells

6. Tracheoles also contain fluid, which oxygen dissolves in

7. Oxygen diffuses from this fluid into body cells

8. CO2 diffuses in opposite directions

9. Insects use rhythmic abdominal movements to change volume of their bodies and move air in and out of the spiraces

10. When larger insects are flying, they use their wing movement to pump their thoraxes too
Dissecting the Gaseous Exchange System in Insects
1. Fix insect to dissecting board (dissecting pins)

2. Examine trachea - carefully cut and remove piece of exoskeleton (outer shell) from along the length of the insect's abdomen

3. Use syringe to fill the abdomen with saline solution

4. Look at network of very thin silver - grey tubes (trachea)

-- Silver - as they are filled with air

5. Examine trachea under light microscope using a wet mount slide

-- Grey / silver trachea

-- Rings of chitin in trachea walls (support)
Why are the trachea silver in insects?
as they are filled with air