ORGANISMS EXCHANGE SUBSTANCES WITH THEIR ENVIRONMENT TOPIC 3 (Exchange- Chapter 6) Flashcards
What is the surface area of a sphere :
4 x pi x r^2
What is the volume of a sphere ?
4/3 x pi x r^3
In microscopic organisms (like amoeba), the organism can exchange all the substances it needs directly through the cell membrane. What are the 2 reasons?
1) Microscopic organisms have a relatively low rate of respiration , not very active organisms
2) The surface area of the cell membrane of an amoeba is relatively large, compared to volume of the cell. SA:V ratio
How do you calculate the surface area to volume ratio ?
SA:V = surface area / volume
How do you calculate volume ?
Length x width x height
How to calculate surface area?
Area of a face x number of faces
What type of SA:V ratio do small animals have, and what does this mean?
Small animals have a large SA:Vol ratio. This means very small animals can exchange gases with environment using their external surface
What is the happens to diffusion in large surface area: volume ratios ?
Organisms like the tapeworm, which have a large surface area to volume ratio, can use the process of diffusion efficiently (to sustain life). It is able to take all of the oxygen that it needs across the body surface by diffusion. Diffusion is sufficient to supply their cells with enough oxygen to allow them to continue to carry out aerobic respiration and to generate ATP.
What type of SA:V ratio do large organisms have, and what does this mean?
Larger organisms, like humans, have a smaller surface area to volume ratio, so cannot use diffusion alone to survive.
This is because diffusion over this greater distance will not occur fast enough to meet the demands of the cells of the body
Larger organisms have evolved 2 specialised systems to compensate :
1) Specialised gas exchange with a very large SA. e.g. gills in fish, lungs in mammals
2) They have a specialised transport system to carry molecules around their body. E.g. blood
What three things to gas exchange surfaces have ?
1) Large SA
2) short diffusion pathway (Thin)
3) Steep concentration gradient
How do you calculate the rate of diffusion ?
Rate of diffusion = surface area x concentration gradient / diffusion pathway distance
Gas exchange in single-celled organisms + insects
Info about terrestrial insects (land-born animal /insect) :
- insects have an exoskeleton made of hard, fibrous material for protection and a lipid layer to prevent water loss
- insects do not have lungs, and instead have a tracheal system
What does limiting water loss insects mean ?
Organisms that live on land have to balance being able to exchange gases with reducing the amount of water loss
What does water have to do with insects (in limiting water loss) ?
Water evaporates off the surface of terrestrial insects, and the adaptations of gas exchange surfaces provide ideal conditions for evaporation
What are the insect adaptations to reduce water loss?
1) Insects have a small surface area to volume ratio where water can evaporate from
2) Insects have a waterproof exoskeleton
3) Spiracles, where gases enter + water can evaporate from, can open and close to reduce water loss
Gas exchange in insects involves a tracheal system.
What are spiracles and what do they do?
Spiracles are round, valve like opening, running along the length of the abdomen (on the surface of the exoskeleton).
Spiracles allow gases: oxygen + carbon dioxide to diffuse into the body of the insect (gases also diffuse out via spiracles).
The trachea attach to these openings
What is the trachea, and what do they have?
The trachea is a network of internal tubes, are wider tubes, they extend down and alone the insect’s body.
The walls of trachea are reinforced with spirals of chitin. This chitin prevents the trachea from collapsing (e.g. when insects move).
The trachea tubes have rings within them to strengthen the tubes and to keep them open.
What are the tracheoles, and what do they do?
The trachea branch into smaller tubes, deeper into the abdomen of the insect called tracheoles.
These extend throughout all of the body tissues, so the diffusion pathway is very short, so oxygen from the air is brought directly to respiring tissues, Oxygen is needed for aerobic respiration, producing CO2.
The huge number of tracheoles provides a very large surface area for gas exchange. This allows insects to maintain a very rapid rate of aerobic respiration. E.g. during flight.
How do insects achieve efficient gas exchange ?
- Diffusion gradient
- Mass transport
- The ends of the tracheoles are full of water
How does an insect’s diffusion gradient achieve gas exchange ?
The concentration of oxygen decreases (CO2 increases), at the ends of the tracheoles because it is used up in respiration.
This creates a diffusion gradient so oxygen diffuses from the air into the tracheole, a diffusion gradient for CO2 works in the opposite direction.
How does an insect’s mass transport achieve efficient gas exchange ?
Muscles contract (when insects contract + relax their abdominal muscles) to squeeze the trachea.
Allows mass movements of air in + out so gas exchange is faster.
The ends of the tracheoles are full of water in an insect, how does this achieve efficient gas exchange ?
- When the insect is in flight (if the activity is strenuous (a lot), the muscle cells around the tracheoles will start to respire anaerobically, producing lactate.
- [This is soluble], so lowers the water potential of the cells, therefore water moves from the tracheoles into the muscle cells by osmosis [from an area of high water potential to an area of low water potential down the water potential gradient]
- This decreases the volume of water in the ends of the tracheoles and as a result, more air from the atmosphere draws in, this leads to greater water evaporation
What is the significance of more air from the atmosphere being drawn in , into the tracheoles?
But how do this cause a potential problem ?
Means the final part of the diffusion pathway of gas, not liquid. This means diffusion happens faster (in gas, than liquid).
Causes a potential problem : increases the amount of evaporation
Why are insects small ?
The tracheal system limits the size of insects
~> gas exchange relies upon diffusion, so the pathway needs to be short
What are insect’s adaptations for efficient diffusion ?
- Large number of fine tracheoles - large surface area
- Walls of tracheoles are thin + short distance
- Use of oxygen and production of carbon dioxide sets up steep diffusion gradient
Gas exchange in fish
Why do fish require a gas exchange surface : in the gills ?
Fish are waterproof, and have a small surface area to volume ratio.
Fish obtain oxygen from the water, but there is 30 times less O2 in water than air, so they have a special adaptation to maintain the concentration gradient to enable diffusion to occur
What is Fick’s law equation (how to calculate rate of diffusion ) ?
Rate of diffusion = SA x difference in concentration / length of diffusion path
How many layers of gills do fishes have on both sides of their head
4 layers of gills
What are gills made up of ?
Stacks of gill filaments
What is are gill filaments ?
These are stacked in a pile and supported by a bone or cartilage gill bar /arch
What is gill lamellae?
Each filament is covered in gill lamellae
Lamellae are positioned at right angles to the filament, creating a large surface area : this is the site of gas exchange
What happens when fish open their mouth ?
Water rushes in and over the gills and then out through a hole in the sides of the head
Where does diffusion only happen in fish ?
In the lamellae
What are the 3 adaptations for efficient gas exchange in fish ?
1) Large surface area to volume ratio created by many gill filaments covered in many gill lamellae
2) Short diffusion distance due to a capillary network in every lamellae and very thin gill lamellae
3) Maintaining concentration gradient ~> countercurrent flow mechanism
What is the counter current exchange principle ?
- this is when water flows over the gills in the opposite direction to the flow of blood in the capillaries
What does counter current flow ensure, that makes diffusion occur?
It ensures equilibrium is never reached , ensuring that a diffusion gradient is maintained across the entire length of the gill lamellae ; so diffusion occurs.
There is a diffusion gradient favouring the diffusion of oxygen from water into the blood all the way across the gill lamellae. Almost all the oxygen from the water diffuses into the blood
What is parallel flow, why is it bad ?
Blood and water move in the same direction, equilibrium is reached, so no diffusion.
There is a diffusion gradient favouring the diffusion gradient of oxygen from water to blood for only part of the way across the gill lamellae.
Only 50% of the oxygen from the water diffuses into the blood.
Why can’t fish breathe air ?
- they lack structural support ; they would collapse
- Use in air results in too much water loss by evaporation
Gas exchange in leaf of a plant
Why is a leaf similar to an insect?
Both have a short diffusion pathway + rapid diffusion
How is a leaf adapted to achieve efficient gas exchange ?
- large surface area
- diffusion distances are small
- concentration gradient
How does a leaf having a large surface area achieve efficient gas exchange ?
-Large surface area ~> many mesophyll cells (keep moist to aid diffusion - gases can dissolve into the water layer )
How does the diffusion distances in a leaf (they are small) achieve efficient gas exchange ?
Leaves are thin - so CO2 and O2 molecules only have to travel from an air space across a single cell wall to get to the cytoplasm in the cell
How does a leaf having a concentration gradient achieve efficient gas exchange ?
Concentration gradient is maintained by constant diffusion of O2 + CO2 in and out of the cells (through the stomata)
How does a leaf achieve gas exchange in the stomata ?
Stomata : small openings that allow O2 + CO2 in and out of the cell
(O2 diffuses out of the stomata, CO2 diffuses into the stomata)
Surrounded by 2 guard cells, controlling the opening +closing
This controls diffusion of gasses + water vapour
They have a thicker inner wall, thinner outer wall
How does the stomata reduce water loss by evaporation ?
Stomata close at night when photosynthesis wouldn’t be occurring
How does stomata open + close ?
When cells absorb water, the cell wall expands and becomes turgid. The thinner outer wall bends more than the thicker, inner wall, so stomata will open.
What are the 3 factors which influence the stomata to open ?
1) Light intensity
2) Water availability
3) CO2 concentration
How do insects limit water loss ?
-small surface area, less SA to lose water from
- waterproof covering -chitin outer skeleton has a waterproof cuticle
- spiracles can close
What causes a problem for water loss, and what is the solution ?
- large SA needed for photosynthesis, causes problem for water loss
Solution :
1) waterproof : waxy cuticle
2) Stomata can close
3) Xerophytes
What are xerophytes ?
A plant which is able to survive in an environment with little availability of water or moisture
What is an example of a xerophyte ?
Marram grass : found at sand dunes
What are the 5 adaptations to reduce water loss in xerophytes ?
1) Thick waxy cuticle
2) Reduced SA:V ratio
3) Hairy leaves
4) Sunken stomata
5) Rolled leaves
How does a thick waxy cuticle reduce water loss in xerophytes ?
Impermeable to water.
Reduces evaporation.
Increase in diffusion + distance/ slower rate of diffusion
How does a reduced SA:V ratio in xerophytes reduce water loss?
E.g. Pine needles.
Pine trees live in conditions where water is inaccessible due to freezing temperatures, so have a small, rounded leaves / needles
So reduces SA:V ratio
How does having ‘hairy leaves’ in xerophytes reduce water loss?
E.g Trichomes
The hairs trap a layer of saturated air. This means the water potential gradient between inside + outside of the leaves is reduced, so less water loss by evaporation
How does having a sunken stomata in xerophytes reduce water loss ?
The pits above the stomata become saturated.
Air is trapped reducing air movement. Increasing the water vapour around the stomata reduces the water potential gradient, so slows down water loss.
How do rolled leaves in xerophytes reduce water loss?
Keeps the stomata on the inside + reduces the area exposed to the air - the rolling traps still air within the leaf, so increases water vapour inside the roll.
This means there isn’t a water potential gradient between inside + outside of the leaf : so no water is lost
