3.3 Chapter 6- Exchange Flashcards
(50 cards)
1
Q
What must organisms do to survive and why?
A
- To survive, organisms transfer and materials across environments by exchange at exchange surfaces.
- This ensures that each cell is supplied with substances for respiration e.g. oxygen and that damaging waste products are removed from cells.
2
Q
What enables exchange?
A
The internal environment of the cell or organism is different from its external environment.
3
Q
How does exchange occur?
A
- Exchange of substances between the internal and external environments takes place at exchange surfaces.
- To truly enter or leave an organism, most substances must cross cell plasma membranes.
4
Q
What is the environment around cells in large multicellular organisms and hwy is it hard to maintain.?
A
- In large multicellular organisms, tissue fluid is the immediate environment around cells.
- Most cells are too far away from exchange surfaces, and from each other, for simple diffusion alone to maintain the composition of tissue fluid within a suitable metabolic range
5
Q
Why are mass transport systems needed in multi-cellular organisms to maintain a constant environment and what do they work with?
A
- Most cells in multicellular organisms are too far away from the outer exchange surface (e.g. the skin) for simple diffusion to supply tissue fluid with materials to keep its composition constant (within a certain metabolic range).
- So, in multicellular organisms, exchange surfaces are associated with mass transport systems that carry substances between exchange surfaces, cells, and between parts of the body. This helps to maintain a diffusion gradient and a stable tissue fluid environment.
6
Q
What are mass transport systems used to do?
A
- Once absorbed, materials are rapidly distributed and waste products are returned to exchange surfaces for removal.
- This requires a mass transport system to maintain a final diffusion gradient that bring substances to and from the cell membranes of individual cells.
7
Q
What affects the rate of exchange and how is this reflected?
A
- The size and metabolic rate of organisms.
- E.g. organisms with a high metabolic rate exchange more and need a higher surface area to volume ratio.
- This is reflected by evolved exchange surfaces and transport systems specific to each organism.
8
Q
What substances do cells need to exchange?
A
- Absorb oxygen for aerobic respiration.
- Excrete waste products (e.g. urea, CO2)
- Absorb CO2 for photosynthesis.
- Absorb nutrients (e.g. glucose, fatty acids, minerals)
- Exchange heat
9
Q
What types of exchange are there and what does this not apply to?
A
- Passive- no metabolic energy- diffusion and osmosis.
- Active- metabolic energy required- active transport
- Doesn’t apply to heat exchange
10
Q
Where are surfaces and volume located in organisms?
A
- Surfaces- where exchange happens
- Volume- made up of substances within the organism
11
Q
What key factor affects how quickly substances are exchanged and describe.
A
- An organism’s surface area to volume ratio.
- An organism’s surface area must be large compared to its volume for maximum exchange to occur.
12
Q
Describe the surface area to volume ratio of large organisms and how this impacts them.
A
- There is a relationship between the size of an organism or structure and its surface area to volume ratio.
- You should appreciate the relationship between surface area to volume ratio and metabolic rate.
- **As size increases, ratio of surface area to volume decreases. **
- Larger cells have a smaller surface area to volume ratio- takes longer for gases to diffuse- diffusion pathway is longer- so larger cells are often close to the cell-surface membrane.
- Larger organisms have a smaller surface area to volume ratio, so simple diffusion only facilitates inactive organisms. Larger organisms have evolved specialised systems which facilitate oxygen uptake to **overcome the long diffusion pathway and enable faster diffusion. **
- The large size of multicellular organisms means that it would take too long for substances to reach cells deep within the body with just simple diffusion from the outer environment as the distance is too great.
- This makes it harder for them to lose heat so they have a lower metabolic rate.
- Multicellular organisms have evolved to mitigate this.
13
Q
When asked to calculate surface area to volume ratio, what must you assume?
A
- You may be given the dimensions of cells with different shapes to calculate the surface area to volume ratio of these cells.
- Assume the organism has a uniform shape, e.g. a cube/ sphere
14
Q
How do you calculate the surface area and volume of a cube or a cuboid?
A
- Remember, a cube or a rectangle has six sides for the surface area.
- The volume is equal to the base times the width times the height
15
Q
How do you calculate the surface area and volume of a cylinder?
A
Use the circumference of a circle (πd) multiplied by the height to find the surface area of the curvy bit. Then find the area of the two circles using πr 2
For the volume multiply the area of one circle by the height.
16
Q
How do you calculate the surface area and volume of a sphere?
A
Use the formula for volume 4/3 πr3
Use the formula for surface area 4πr2
17
Q
How can you investigate the effects of surface area to volume ratio on diffusion.
A
- Using agar blocks containing indicator to determine the effect of surface area to volume ratio and concentration gradient on the diffusion of an acid or alkali- not a required practical but could be an example:
- The effect of changing surface area to volume ratio can be investigated timing the diffusion of ions through cubes of agar of different sizes.
18
Q
Describe the method used to investigate diffusion in agar blocks.
A
- Coloured agar is made up and cut into cubes of required dimensions. The agar can include dilute acids/ alkalis and universal indicator, or universal indicator only.
- The surface area, volume and SA: V of the cubes is calculated and recorded.
- The cubes are placed into boiling tubes containing a diffusion solution- such as a dilute acid- same volume should be used each time.
- Measurements can be taken of the time taken for the acid to completely change the colour of the indicator in the agar blocks or the distance travelled into the block by the acid- shown by the change in colour of the indicator in a given time.
- If the time taken for the acid to completely change the colour of the indicator is recorded, the times can be converted into rates and a graph can be drawn to show how the rate of diffusion changes with SA:V. Greater SA:V= faster rate of diffusion.
19
Q
How have organisms adapted to aid exchange.
A
- Changes to body shape and development of systems in larger organisms have developed as adaptions to facilitate exchange as the ratio reduces.
- You need to be able to relate surface are to volume ratio to metabolic rate.
- You may need to point out these adaptions in different organisms- always remember to say how it helps simple diffusion.
- **Remember to state how organisms with higher metabolic/ respiratory rate use more oxygen over time for aerobic respiration- need more efficient exchange surfaces. **
20
Q
What surface area to volume ratio do small organisms have and how does this impact them?
A
Smaller organisms have a larger surface area to volume ratio, so they need a high metabolic rate as they loose heat quickly.
21
Q
How does the compactness of animals affect the surface area to volume ratio and how is this acted upon?
A
- Animals with a compactor shape have a smaller surface area to volume ratio, reducing exchange.
- Animals with a less compact shape have a larger surface area to volume ratio.
- The shape is acted upon by evolution to create adaptions.
22
Q
What have large organisms evolved to mitigate small surface area to volume ratio?
A
- Larger animals with a less compact shape have a larger surface area to volume ratio.
- The shape is acted upon by evolution to create adaptions.
- Multicellular organisms have evolved to mitigate issues with a small surface area to volume ratio:
- A flattened shape so cells aren’t far away from the surface.
- Specialised exchange services with large surface areas.
- Hard to lose heat so lower metabolic rate
23
Q
What physiological and behavioural adaptations aid and mitigate exchange (give specific e.g.s)?
Hint: 7 points
A
- Body shape and size- **thin body shape and small so short diffusion pathway. **
- Higher surface area to volume ratio increases exchange- **flat body shape- increases surface area to volume ratio. **
- Higher surface area to volume ratio- causes more water loss. Small animals produce less urine from kidneys to compensate.
- Higher metabolic rate means small animals need to eat large amounts of high energy food every day e.g. seeds/ nuts
- Thick layers of fur and hibernation for cold weather
- Elephants have large ears to increase their surface area to lose more heat.
- Hippos live in water helping them to lose heat.
- Organisms with higher metabolic activity often have a higher lung volume to provide **more oxygen for respiration. **
24
Q
How does gas exchange occur and why is it important?
A
- Occurs at gas exchange surfaces at the boundary between the outside and internal environment of an organism
- Important for the quick exchange of respiratory gases e.g. oxygen.
- Gas exchange is usually a passive process involving diffusion of carbon dioxide or oxygen.
25
How are gas exchange surfaces adapted to maximise diffusion?
* Steep concentration gradient to increase the rate of diffusion.
* Large surface area to volume ratio to increase the rate of exchange.
* **Thin- short diffusion pathway for rapid diffusion at the gas exchange surface.**
* Selectively permeable
* Movement of environmental medium to maintain a diffusion gradient
* A transport system to ensure movement to maintain a diffusion gradient.
26
How are exchange surfaces adapted for effective transfer of material?
| Hint: 5 points
* Large surface area to volume ratio to increase the rate of exchange.
* Thin- short diffusion distance for rapid crossing.
* Selectively permeable
* Movement of environmental medium to maintain a diffusion gradient
* A transport system to ensure movement to maintain a diffusion gradient.
27
What is the equation for the relationship of diffusion?
Diffusion is proportional to:
Surface Area X difference in concentration/ Length of diffusion path
28
Why are exchange services located inside the body?
They are easily dehydrated and damaged.
29
What must an organism do because exchange services are inside the body?
Organisms need to move external medium over the internal surface by ventilating.
30
What creates body heat and what is important about this?
Metabolic activity creates heat. The organism needs to carefully maintain their temperature.
31
What affects the ability to exchange heat, how is this acted upon and give an e.g.?
| Hint: 3 detailed points
* Body size- larger organisms have a small surface area to volume so they can’t lose heat easily. Small organisms have a **larger surface area to volume ratio,** so they **lose more heat faster and need a higher metabolic/ respiration rate to generate heat.**
* Body shape- compact body shape- small surface area to volume ratio to lowers heat loss. Not compact body shape- higher surface area to volume ratio- larger heat loss.
* The temperature of an environment is acted on by evolution creating adaptions so the organism can suit it’s environment e.g. round faced foxes- colder climate- more compact- lower surface area. Narrow faced foxes- warmer climate- less compact- higher surface area.
32
What must you remember when intepreting graphs comparing gas exchange systems in different species.
Read carefully and remember to compare- difference greater than, more, less etc.
33
What is hte difference between epithelial and endothelial cells.
* Exchange systems often contain epithelial cells- cover both internal and external surfaces of the body,, and endothelial cells- which line the inner surfaces of the circulatory system.
34
What are the adaptions of gas exchange shown by?
* Gas exchange across the body surface of a single-celled organism.
* Gas exchange in the tracheal system of an insect (tracheae, tracheoles and spiracles)
* Gas exchange across the gills of fish (gill lamellae and filaments including the counter-current principle)
* Gas exchange by the leaves of dicotyledonous plants (mesophyll and stomata).
35
How does exchange occur in single-celled organisms?
* Substances e.g. CO2, Oxygen diffuse across the cell surface membrane in and out of the cell
* There is only one cell-surface membrane for substances to cross
* Substances such as oxygen can take part in reactions as soon as they enter the cell.
* No need for specialised exchange systems
* The cell wall is not a barrier for diffusion
36
Why is exchange quick in single celled organisms?
Diffusion is quick because:
* Large surface area to volume ratio due to small size.
* Short diffusion distances
* Thin surfaces.
37
Describe the features of exchange in multicellular organisms and why they exist?
* Diffusion across membranes is too slow, as some cells are deep within the body creating a long distance.
* Large size means lower surface area to volume ration- hard to supply volume with small outer surfaces
* Require specialised exchange surfaces/ organs
* Requires an efficient mass transport system to carry substances e.g. circulatory system, xylem, phloem
38
What are insects?
Terrestrial organisms hence called terrestrial insects.
39
What conflicts regarding exchange within insects?
Conservation of water versus mechanism for gas exchange.
40
What adaptations do insects have for gas exchange?
* Insects can’t use body to diffuse respiratory gases like a single celled organism- have trachea- internal network of tissues to carry air to tissues.
* Trachae
* Tracheoles
* Muscle contractions
* Water movement
* Spriacles
41
Describe trachea.
A network of microscopic air filled pipes to perform gas exchange.
42
What adaptions do trachea have?
* Prevented from collapsing by strengthening rings.
* Muscles that contract to squeeze gases
43
What do trachea branch into and describe them?
Smaller tubes called tracheoles that go throughout the insect's tissue and have an end.
44
What adaptions do tracheoles have and what does this enable them to do?
* Have dead ends.
* **Thin permeable walls- short diffusion distance to cells.**
* **Highly branched- large numbers of tracheoles- short diffusion distance to cells. **
* **Highly branched- large number of tracheoles- large surface area for gas exchange.**
* **Tubes full of air- fast diffusion.**
* Close to cells throughout tissue
* Brings air straight to respiratory tissues with a short diffusion pathway.
* Gases diffuse directly into cells- no transport required
* Mass transport occurs when** body can be moved when muscles contract** in rhythmic abdominal movements and squeeze the trachea. This creates **movement of air** to **maintain diffusion gradient for oxygen and CO2** to speed up gas exchange.
* **The ends of tracheoles are filled with fluid**. **During exercise**/ high activity, muscles around the tracheoles anaerobically respire, producing lactate, which is soluble and lowers the water potential in the cells. Water then **moves out of the tracheoles into tissues, increasing the surface area for gas exchange and enabling faster diffusion through the air to gas exchange surfaces** as more gas diffusion over liquid diffusion occurs, which is faster. Increases gas exchange but also water loss
45
How are respiratory gases moved within tracheoles?
| Hint: 3 big points
* Gases move through trachea along a diffusion gradient down the concentration gradient. Oxygen used up in respiration causes a fall in concentration at the end of the tracheos, creating a diffusion gradient from the atmosphere to the cells. Large concentrations of CO2 produces a diffusion gradient in the opposite direction from the cells to the atmosphere. Diffusion in the air is quick compared to the diffusion in water.
* Mass transport occurs when muscles contract in rhythmic abdominal movements and squeeze the trachea. This creates mass movement of air to speed up a gas exchange.
* The ends of tracheoles are filled with water. During high activity, muscles around the tracheoles anaerobically respire, producing lactate, which is soluble and lowers the water potential in the cells. Water then moves into cells from the tracheoles, increasing the volume of air. More gas diffusion over liquid diffusion occurs, which is faster. increases gas exchange but also water loss
46
How do gases enter in these the trachea and describe the behaviour of these structures?
* Through pores called spiracles
* Open and close by a valve.
* Once open water evaporates so mostly left closed.
* Only open periodically to allow gas exchange
47
What are the limitations of gas exchange in insects?
* Relies mostly on diffusion
* Need short diffusion distance
* Insects can only be a small size.
48
Describe why specialised gas exchange systems are needed in fish and name the structure?
* Gills are the specialised gas exchange system of fish.
* * Fish- waterproof- skin impermeable to gas.
* Large- small SA:V- surface area not enough for gas exchange so have specialised internal gas exchange surface- gills- aid gas exchange as water has a lower concentration of oxygen than air.
49
Describe and draw the structure of fish gills.
* Need to be able to label the structure of fish gills- see revision card.
* Gills- located behind the head of the fish- water enters through the fish mouth in an opening each side of the body and passes out through the gills.
50
How are gills adapted to aid exchange?
* Gills are made of gill **filaments** attached to a gill arch- thin plates stacked in a pile- create a **large surface area** for gas exchange- increase the rate of diffusion.
* Gill filaments are covered in tiny **secondary** gill **lamellae** at right angles- further increases **large surface area. **
* Lamellae have lots of capillaries and a t**hin surface layer of cells- short diffusion pathway** to speed up the diffusion between water and blood.
* The flow of water over the lamellae and the flow of blood between them are in opposite directions- counter current flow.
* **Gills are on the outside of the body**, as opposed to lungs on the inside, as **water is denser than air, so it supports the gills.** **Water has a lower partial pressure of oxygen so the system reduces the diffusion distance.**
