3.3 Chapter 6- Exchange

Question 1

What must organisms do to survive and why?

Answer 1

• 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.

Question 2

What enables exchange?

Answer 2

The internal environment of the cell or organism is different from its external environment.

Question 3

How does exchange occur?

Answer 3

Exchange occurs by crossing cell plasma membranes.

Question 4

What is the environment around cells in large multicellular organisms?

Answer 4

Tissue fluid.

Question 5

Why are mass transport systems needed in multi-cellular organisms to maintain a constant environment and what do they work with?

Answer 5

• 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.

Question 6

What are mass transport systems used to do?

Answer 6

• 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.

Question 7

What affects the rate of exchange and how is this acted upon?

Answer 7

• 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.

Question 8

What substances do cells need to exchange?

Answer 8

• Respiratory gases for aerobic respiration (oxygen and carbon dioxide)
• Nutrients (e.g. glucose, fatty acids, minerals)
• Waste products for excretion (e.g. urea)
• Heat

Question 9

What types of exchange are there and what does this not apply to?

Answer 9

• Passive- no metabolic energy- diffusion and osmosis
• Active- metabolic energy required- active transport
• Doesn’t apply to heat exchange

Question 10

Where are surfaces and volume located in organisms?

Answer 10

• Surfaces- where exchange happens
• Volume- made up of substances within the organism

Question 11

What key factor affects how quickly substances are exchanged and describe.

Answer 11

• 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.

Question 12

Describe the surface area to volume ratio of large organisms and how this impacts them.

Answer 12

• Larger organisms have a smaller surface area to volume ratio, so simple diffusion only facilitates inactive organisms.
• 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.
• Makes harder for them to lose heat so they have a lower metabolic rate.
• Multicellular organisms have evolved to mitigate this.

Question 13

What have large organisms evolved to mitigate small surface area to volume ratio?

Answer 13

• 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

Question 14

What surface area to volume ratio do small organisms have and how does this impact them?

Answer 14

Smaller organisms have a larger surface area to volume ratio, so they need a high metabolic rate as they loose heat quickly.

Question 15

How does the compactness of animals affect the surface area to volume ratio and how is this acted upon?

Answer 15

• 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.

Question 16

When asked to calculate surface area to volume ratio, what must you assume?

Answer 16

That the organism has a uniform shape, e.g. a cube/ sphere

Question 17

How do you calculate the surface area and volume of a cube or a cuboid?

Answer 17

• 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

Question 18

How do you calculate the surface area and volume of a cylinder?

Answer 18

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.

Question 19

How do you calculate the surface area and volume of a sphere?

Answer 19

Use the formula for volume 4/3 πr³
Use the formula for surface area 4πr²

Question 20

How does gas exchange occur and why is it important?

Answer 20

• 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.

Question 21

How are gas exchange surfaces adapted?

Answer 21

• Large surface area
• Thin to provide a short diffusion pathway across the gas exchange surface
• Steep concentration gradient to increase the rate of diffusion.

Question 22

How are exchange surfaces adapted for effective transfer of material?

Hint: 5 points

Answer 22

• 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.

Question 23

What is the equation for the relationship of diffusion?

Answer 23

Diffusion is proportional to:
Surface Area X difference in concentration/ Length of diffusion path

Question 24

Why are exchange services located inside the body?

Answer 24

They are easily dehydrated and damaged.

Question 25

What must an organism do because exchange services are inside the body?

Answer 25

Organisms need to move external medium over the internal surface by ventilating.

Question 26

What creates body heat and what is important about this?

Answer 26

Metabolic activity creates heat. The organism needs to carefully maintain their temperature.

Question 27

What affects the ability to exchange heat, how is this acted upon and give an e.g.?

Hint: 3 detailed points

Answer 27

• Body size- larger organisms have a small surface area. so they can’t lose heat easily. Small organisms have a large surface area, so they lose heat more easily and need a higher metabolic 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 ares

Question 28

What physiological and behavioural adaptations aid and mitigate exchange (give specific e.g.s)?

Hint: 7 points

Answer 28

• Body shape and size
• Higher surface area to volume ratio increases exchange.
• Higher surface area to volume ratio- causes more water loss. Small animlas 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.

Question 29

How does exchange occur in single-celled organisms?

Answer 29

• 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

Question 30

Why is exchange quick in single celled organisms?

Answer 30

Diffusion is quick because:
* Large surface area to volume ratio due to small size.
* Short diffusion distances
* Thin surfaces.

Question 31

Describe the features of exchange in multicellular organisms and why they exist?

Answer 31

• 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

Question 32

What are insects?

Answer 32

Terrestrial organisms hence called terrestrial insects.

Question 33

What conflicts regarding exchange within insects?

Answer 33

Conservation of water versus mechanism for gas exchange.

Question 34

What adaptations do insects have for gas exchange?

Answer 34

• Trachae
• Tracheoles
• Muscle contractions
• Water movement
• Spriacles

Question 35

Describe trachea.

Answer 35

A network of microscopic air filled pipes to perform gas exchange.

Question 36

What adaptions do trachea have?

Answer 36

• Prevented from collapsing by strengthening rings.
• Muscles that contract to squeeze gases

Question 37

What do trachea branch into and describe them?

Answer 37

Smaller tubes called tracheoles that go throughout the insect’s tissue and have an end.

Question 38

What adaptions do tracheoles have and what does this enable them to do?

Answer 38

• Thin permeable walls.
• Close to cells throughout tissue
• Brings air straight to respiratory tissues with a short diffusion pathway.
• That has diffused directly into cells- no transport required

Question 39

How are respiratory gases moved within tracheoles?

Hint: 3 big points

Answer 39

• Move 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

Question 40

How do gases enter in these the trachea and describe the behaviour of these structures?

Answer 40

• 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

Question 41

What are the limitations of gas exchange in insects?

Answer 41

• Relies mostly on diffusion
• Need short diffusion distance
• Insects can only be a small size.