💙 3.3.2 Gas Exchange In Insects, Fish And Plants Flashcards
What is ficks law?
Rate of diffusion (is directly proportional to) surface area x concentration gradient/length of diffusion pathway
How is an insect breathing system (tracheal system) adapted to gaseous exchange?
1) there are many, highly branched tracheoles over which gas exchange can take place.
2) the walls of the tracheoles are thin so there is a short diffusion pathway for oxygen to reach the muscle cells
3) the many tracheoles are highly branched so there is a short diffusion pathway
4) contraction of air sac to maintain or increase concentration gradient of oxygen
5) fluid in the tracheoles moves into the muscle cells during increased activity so oxygen can freely (move quickly) diffuse to the muscle cells.
Exam tip: what must you do if there is an explain adaptation question?
You must link the adaptation to the ficks law component by the connective ‘so’
How does gas exchange occur in single celled organisms?
They absorb and release gases by diffusion through their cell surface membranes.
Why do single celled organisms not require a specialised gas exchange system?
They have a relatively large surface area to volume ratio, a thin surface and a short diffusion pathway.
How do fish have a large surface area?
Fish have many gil filaments with many Lamellae over which gas exchange can take place.
How do fish have a relatively short diffusion pathway between the water and the blood of the fish?
The lamellae are thin wall so there is a short diffusion pathway between the water and the blood of the fish
What is the counter current system in fish?
In the gills of a fish, blood flows through the lamellae in one direction and water flows over them in the opposite direction this is called a counter current system
How does the counter current system ensure as much oxygen is kept inside the blood ?
The counter current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen. This intern means that a steep concentration gradient is maintained between the water and the blood – so as much oxygen as possible diffuses from the water into the blood.
Where does the counter current system occur ?
Across the full length of the gill
What is maintained across the full length of the gill ?
The concentration gradient
How does gas exchange occur in plants?
1) carbon dioxide diffuses into the leaf due to a diffusion/concentration gradient being produced by photosynthesis, reducing the carbon dioxide concentration.
2) carbon dioxide diffuses in through the stomata. Guard cells surrounding them become turgid on humid days (especially) allowing carbon dioxide to enter the leaf.
3) carbon dioxide diffuses through the spongy mesophyll and into the palisade mesophyll, where it dissolves in the chloroplasts stroma (the chloroplasts are situated at the edge of the palisade cells to decrease the length of the diffusion pathway). Once this occurs, it takes part in the light dependent stage of photosynthesis.
What is a xerophytic plant?
Plants which are adapted to dry conditions
How can xerophytic plants reduce water loss?
By trying to reduce the rate of diffusion of water particles using the components of ficks law.
What are some adaptations xerophytic plants have to reduce water loss whilst still exchanging gases?
1) small leaves
2) thick cuticles
3) sunken stomata/hairs
How does having small leaves reduce water loss in xerophytic plants?
So smaller surface area to lose water
How does thick cuticles reduce water loss in xerophytic plants?
So longer diffusion pathway (as they are thick) to reduce water loss. Waxy cuticles also reduce evaporation from leaves.
How does sunken stomata/hairs reduce water loss in xerophytic plants?
Hair around stomata to reduce water potential, gradually trapping moist air. Sunken stomata also traps water vapour, reducing the concentration gradient of water between the leaf and the air. This reduces evaporation of water from the leaf.
What problem do insects face which is similar to plants?
Water loss
What are some adaptations insects have evolved to reduce water loss?
1) thick exoskeleton
2) opening and closing of spiracles
3) sunken spiracles/hairs around spiracles
How does having a thick exoskeleton reduce water loss?
It increases the diffusion pathway for water particles. Waxy exoskeleton also reduces evaporation.
How does opening and closing of spiracles reduce water loss?
It reduces surface area for water loss
How does sunken spiracles and hairs around spiracles reduce water loss?
The hairs around the spiracles trap moist air and therefore reduce the water potential gradient. The sunken spiracles also trap water vapour, reducing the concentration gradient of water between the leaf and the air. This reduces evaporation of water from the leaf.
