3.1.1 - Exchange and Transport Flashcards
Factors affecting exchange system
Size
SA:V ratio
Metabolic activity
How does size affect the need for an exchange system
In single-celled organisms, the cytoplasm is very close to its environment. Diffusion will supply enough O2 and nutrients to keep the cells alive and active
In multicellular organisms have several layers of cells, so there’s a longer diffusion pathway. Diffusion is too slow to enable a sufficient supply to the innermost cells
How does SA:V affect the need for an exchange system
When organisms have a large SA:V their SA is large enough to supply all the cells with sufficient O2
V increases more quickly than SA so the SA:V is smaller in larger organisms so a specialised exchange surface is needed
How does metabolic activity affect the need for an exchange system
Metabolically active organisms need good supplies of O2 and nutrients to supply energy for movement and warmth so the exchange of substances need to be efficient
Features of a good exchange surface
Large surface area - achieved by folding walls and membranes
Thin, permeable barrier - shorter diffusion distance
Good blood supply - maintain steep concentration gradient (brings molecules to supply side and removes from demand side)
How are lungs adapted
Many alveoli - large SA:V
Thin barrier - short diffusion pathway
Good blood supply (capillaries) to carry dissolved gases to and from alveoli
Ventilation refreshes air in alveoli
Elastic tissue to stretch/ recoil to help expel air
Function of goblet cells
Produce mucus
Function of cartilage
Prevent collapse of airways
Why do the walls of alveoli contain elastic fibres
Expand (inhalation) to increase lung volume
Prevent alveoli bursting
Elastic fibres recoil
Inspiration
Diaphragm contracts to move down and become flat. Displaces digestive organs downwards
External intercostal muscles contract moving the ribs outward and upward
Volume of thorax increases
Pressure in thorax < atmospheric pressure
Air is drawn in through the nasal passages, trachea, bronchi and bronchioles into lungs
Thorax
Chest cavity
Lined with pleural membranes - space between these membranes is the pleural cavity - usually filled with lubricating fluid
Expiration
Diaphragm relaxes and is pushed up by displaced organs underneath
External intercostal muscles relax and ribs fall
Volume of thorax decreases
Pressure in thorax > atmospheric pressure
Air is moved out of the lungs
What does the alveoli consist of
Thin, flattened epithelial cells alone with some collagen and elastic fibres
Elastic recoil
When the elastic fibres in the alveoli return to their resting size, they help squeeze the air out
What is the inner surface of the alveoli covered in
A thin layer of solution of water, salts and lung surfactant
When O2 diffuses out of the alveoli, it first dissolves in the water before diffusing into the blood. Water can also evaporate into the air in the alveoli
Lung surfactant
Phospholipid that coats the surfaces of the lungs
Without it, watery lining of alveoli would have surface tension —> collapse
Collagen in alveoli
Ensures alveoli aren’t deformed as they stretch (support)
Distribution and function of capillaries
Over surface of alveoli
To provide a large surface area for exchange
Distribution and function of cartilage
In walls of bronchi and trachea
To hold the airways open and provide structural support
Distribution and function of goblet cells
In ciliated epithelium
To produce and release mucus
Distribution and function of smooth muscle
In walls of airways
Contracts to constrict or narrow the airways
Loose tissue
Contains elastic fibres, glands and blood vessels
Peak flow meter
Simple device that measures how much air can move out of (and therefore into) the lungs
Spirometer
Device that measures the movement of air in and out of the lungs as the person breathes
Also measures oxygen consumption as the chamber of soda lime absorbs carbon dioxide
Vital capacity
Maximum volume of air that can be moved by the lungs in one breath
Measured by taking a deep breath and expiring all the air possible from the lungs
Usually in the region or 2.5-5.0 dm^3
What does vital capacity depend on
The size of the person (particularly their height)
Their age and gender
Their level of regular exercise
Tidal volume
Volume of air moved in and out with each breath
Usually measured at rest (0.5 dm^3) - sufficient to supply all the oxygen
Increases when exercising
Residual volume
Volume of air that remains in the lungs even after forced expiration
Air remains in airways and alveoli
Approx. 1.5 dm^3
Total lung capacity
Sum of vital capacity and residual volume
Precautions to take when using a spirometer
Subject should be healthy and free from asthma
Wear a nose clip
Sterilise mouthpiece
No air leaks in apparatus - invalid/ inaccurate results
Don’t overfill water chamber - water may enter air tubes
How do we know the volume of oxygen absorbed by the blood
We can assume that the volume of carbon dioxide released and absorbed by the soda lime is equal to the volume of O2
How is breathing rate calculated
Counting the number of peaks in one minute
Calculating oxygen uptake
Divide the difference between the first peak and last peak by the time (s)
What will increases oxygen uptake result from
Exercise (more O2 and less CO2)
Deeper breaths
Why do insects require a gas exchange system
Very active in life cycle
Tough exoskeleton through which little/ no gas exchange takes place
Spiracles
Air opening in each segment of the insect
Allows air to enter inside the insect
Why do insects frequently close their spiracles
To minimise water loss
Insect tracheae
Leads away from the spiracles
Run both along and into the body of the insect
Carry air into the body
What are insect tracheae lined with
Spirals of chitin which keeps them open if they are bent or pressed
Why does little gas exchange take place in insect tracheae
Chitin is mostly impermeable to gases
Tracheoles
Further branches of the tracheae
Vast number gives a large surface area
Some oxygen dissolves in moisture in the walls of the tube and diffuses into the surrounding cells
Where is tracheole fluid found
In the ends of tracheoles
Why do insects frequently close spiracles
To reduce water loss
How do larger insects ventilate their tracheal system
Sections of the tracheal system can be expanded and contacted by flight muscles
Movement of wings can alter volume of the thorax
Abdomen volume can also be expanded then reduced
Oxygen conc. in water is
Typically lower than that in air
Operculum
Covers and protects the gills and is active in maintaining a flow of water over the gills
Gill arch
Bony structure with two rows of gill filaments (primary lamellae) coming off it
Gill filaments
Very thin and their surface is folded into many secondary lamellae
Where does gas exchange take place in bony fish
Secondary lamellae - blood capillaries carry deoxygenated blood close to the surface
Advantages of counter current flow
Absorbs maximum amount of oxygen from the water
Ensures steeper conc. gradients are maintained vs a parallel system
Bony fish can remove approx. 80% of O2 from the water
Ram-ventilation
Only occurs when fish are moving
Fish open their mouths and operculums to keep a current of water flowing over their gills
Buccal - opercular pump
Used when fish aren’t moving
How does the buccal-opercular pump work
Base of mouth moves downward, lowering pressure in buccal cavity - water is drawn in
Mouth then closes, pressure of buccal cavity increases - pushing water through gills
At the same time, operculum opens, reducing pressure in opercular cavity helping water flow over gills
Inspiratory capacity
The maximum volume of air that can be breathed in
Function of ciliated epithelial
Move mucus
Function of squamous epthelial
Provide a short dffusion distance
Features of nasal cavity
Large SA w/ good blood supply - warms air to body temp
Hairy lining - secretes mucus to protect lung tissue from infection
Moist surfaces - Increase humidity of incoming air, reducing evaporation
Bronchus
Division of trachea
Also has supporting rings of cartilage but much smaller
Ciliated cells but v. little goblet cells
Bronchiole
No cartilage
Walls contain smooth muscle, contracts to constrict bronchioles, changes amount of air reaching lungs
Lined w/ thin layer of flattened epithelium
Adaptations of gills
Large SA for diffusion
Rich blood supply to maintain conc gradient
Thin layers - short diffusion distance
Tips of adjacent gill filaments overlap - increases resistance to flow of water over gill surfaces and slows down movement of water - more time for gas exchange
How is the steep conc gradient maintained in the lungs
Blood is constantly flowing through and out of lungs, bringing a fresh supply of RBC
Blood arrives in the lungs w/ a lower [O2] and a higher [CO2] than air in alveoli
