Gas Exchange Flashcards
What is the environment around the cells of multicellular organisms called?
Tissue Fluid
How have organisms developed to maximise their SA:V?
Flattened shape so no cell is ever too far from the surface
Specialised exchange surfaces with large SA to increase the SA:V eg. Lungs or gills
What are 5 characteristics of specialised exchange surfaces?
A large SA:V
Thin
Selectively permeable to allow certain materials to cross
Movement of the environmental medium to maintain a diffusion gradient eg. Air
A transport system to ensure the movement of the internal medium eg. blood in order to maintain a diffusion gradient
Why single celled organisms not need a specialised gas exchange surface?
They have a high SA:V so gases can freely diffuse in and out of the organism and effectively support all cells.
How do respiratory gases move in and out of the tracheal system in insects?
Along a diffusion gradient - When cells are respiring the oxygen is used up so its concentration towards the end of the tracheoles falls. This creates a CG allowing O2 to diffuse into the trachea through the tracheoles and into the cells.
CO2 is diffused out in the same way as its concentration increases through respiration creating a CG. Insects tracheole systems are highly branched so have a large SA
Mass Transport - Contraction of insect’s muscles squeezes the trachea which enables mass movement of air in and out of the insect. Creates pressure changes leading to air movement.
Ends of tracheoles are filled with water - During periods of major activity the muscle cells around the tracheoles respire anaerobically. This produces a soluble lactate which therefore lowers the water potential of the muscle cells therefore, water moves from the tracheoles into the muscle cells by osmosis. This decreases the volume and as a result the pressure decreases in the tracheoles and therefore air moves in.
This final diffusion pathway is gas rather than liquid and therefore diffusion is more rapid.
However, this does lead to greater water evaporation.
How does gas enter and leave the tracheae?
Through spiracles on the body surface.
These can be opened and closed by a valve.
When they are open water evaporation occurs
How do insects limit water loss through their spiracles?
They can open and close
They have small external hairs that catch water and limit the diffusion gradient
Waxy covering that’s impermeable to water
What is a negative about the tracheal system in insects?
As it relies mostly on diffusion of gases the diffusion pathways need to be short and as a result it limits the insects size.
Why have fish evolved a specialised gas exchange system?
They have a relatively small SA:V
They have a waterproof and gas tight outer covering which would limit diffusion.
Describe the structure of gills in fish?
Made up of gill filaments which are stacked up in a pile
Perpendicular to the filaments are the lamellae which increases SA
The water moves through the fish in one direction - through the mouth and is forced out through the gills
The flow of water is in a opposite direction to the flow of blood - this is known as a countercurrent flow.
How does a counter current flow maximise gas exchange in fish?
Maintains the concentration gradient across the whole lamellae.
The water always has a higher O2 concentration than the blood flowing next to it so diffusion can always occur
As most diffusion occurs in the leaves of plants how are they adapated for rapid gas exchange?
Many stomata so no cell is far from one so the diffusion pathway is short.
Numerous interconnecting air spaces throughout the mesophyll so gases can readily come into contact with the mesophyll cells.
Large SA of mesophyll cells for rapid diffusion
How do insects make structural compromises when maintaining efficient gas exchange while limiting water loss?
Small SA:V
Waterproof coverings - rigid outer skeleton of chitin surrounded by a waterproof cuticle
Spiracles open and close
How do plants limit water loss?
Waterproof waxy cuticle
Ability to close stomata
What is a xerophyte?
A plant with restricted water supply that has made adaptations to limit transpiration
How have xerophytes adapted?
Thick cuticle - less water can escape due to this waterproof barrier
Rolled up leaves - Protects the lower epidermis (where the stomata are located), this area becomes saturated with water potential which leads to a very high water potential so evaporation of water doesn’t occur.
Hairy leaves - Captures moisture so the water potential gradient is reduced around the stomata. Limits diffusion.
Stomata in pits or grooves - traps moist air ^^^
Smaller SA:V in leaves eg. spikes - less diffusion can occur
Why does a large volume of oxygen have to be absorbed and a large volume of CO2 have to be removed in animals?
Large organisms with a large volume of living cells
Maintain high body temperatures so they have high metabolic and respiratory rates
Why are the lungs located inside the body?
Air is not dense enough to support and protect the delicate structure
The body would loose lots of water otherwise
What is the trachea surrounded by?
Why?
What’s it lined with?
Rings of cartilage
Prevents trachea collapsing and the air pressure falling
Lined with ciliated epithelium and goblet cells
Why are there elastic fibers between alveoli?
There are elastic fibers allow the alveoli which allow them to stretch as they fill and then recoil to expel CO2.
How are the alveoli adapted for efficient gas exchange?
Folded and lots of alveoli - Increases SA
Epithelial cells are flattened to one cell thick to minimise diffusion distance
Descbribe the process of inspiration
External intercostal muscles contract while internal ICMs relax - this pulls the ribs up and out.
Diaphragm contracts and flattens.
Volume in thorax increases
Therefore, pressure in lungs decrease
Atmospheric pressure is greater than pulmonary pressure so air is force into the lungs.
Inspiration is an active process
Describe the process of expiration
Internal intercostal muscles contract while the external ICMs relax - this moves the ribs downwards and inwards.
Diaphragm relaxes and moves back up
This decreases the volume of the thorax and therefore increases the pressure inside the lungs.
Pulmonary pressure is greater than atmospheric pressure so the air is forced out the lungs.
Expiration is a largely passive process
Pulmonary ventilation rate = ?
Tidal volume x breathing rate
