⭐️Exchange: Exchange Between Organisms And Their Environment

Question 1

What is tissue fluid?

Answer 1

The environment around the cells of multicellular organisms

Question 2

Give 4 examples that need to be interchanged between an organism and its environment

Answer 2

Respiratory gases, nutrients, excretory products and heat

Question 3

Except from heat, how can the exchanges between the body and its environment take place?

Answer 3

• Passively (diffusion and osmosis )

- actively (active transport)

Question 4

What features have organisms that rely on diffusion to exchange substances with the environment evolved? Give examples for each

Answer 4

• a flattened shape so that no cell is far from the surface e.g. flatworms or leaves
• specialised exchange surfaces with large areas to increase the SA:V e.g. lungs in mammals or gills in fish

Question 5

What’s the formula for the surface area of a sphere?

Answer 5

4 πr^2

Question 6

What’s the formula for the volume of a sphere?

Answer 6

4/3 πr^2

Question 7

Give 5 features of specialised exchange surfaces

Answer 7

• they have a large surface area to volume ratio of the organism to increase the rate of exchange
• they are very thin so diffusion distance is short allowing materials to cross the exchange surface rapidly
• they are selectively permeable to allow selected materials to cross
• they have a moving environmental medium (e.g. air) to maintain a concentration gradient
• they have a transport system to ensure the movement of the internal medium (e.g. blood) to maintain a diffusion gradient

Question 8

What does ficks law state?

Answer 8

Diffusion is directly proportional to:

(Surface area x difference in concentration)/length of diffusion path

Question 9

What is the gas exchange system of insects composed of and describe each one

Answer 9

• tracheae, an internal network of tubes held open by rings of chitin to prevent them collapsing
• traheoles, divisions of the tracheae which are dead end tubes which extend throughout the body tissue of the insect and so carry air with oxygen towards respiring tissue. There’s a short diffusion pathway between the tracheae and the cells
• spiracles, tiny pores on the side of the body surface through which gases enter and leave and can be closed and opened by valves

Question 10

How do gases move in and out of the tracheal system along a diffusion gradient?

Answer 10

1. When cells are respiring, oxygen is used up so it’s concentration towards the ends of the tracheoles falls
2. This creates a diffusion gradient that causes oxygen to diffuse from the atmosphere, along the tracheae and tracheoles into cells
3. CO2 is produced by cells during respiration creating a diffusion gradient in the opposite direction
4. This causes gaseous co2 to diffuse along the tracheoles and tracheae from the cells and to the atmosphere allowing respiratory gases to be exchanged quickly because diffusion in air is more rapid than in water

Question 11

How are respiratory gases moved in and out of the tracheal system by mass transport?

Answer 11

As the contraction of muscles in insects squeeze the trachea allowing mass movement of air in and out, further speeding up the exchange of respiratory gases

Question 12

How are respiratory gases moved in and out of the tracheal system by the ends of the tracheoles being filled with water?

Answer 12

1. During periods of major activity like flying, muscle cells around the tracheoles carry out anaerobic respiration
2. This produces lactate which lowers the water potential of the muscle cells causing water to move into the cells from the tracheoles by osmosis
3. The water in the ends of the tracheoles decreases in volume and on doing so draws air further into them
4. This means the final diffusion pathway is in a gas rather than in a liquid phase hence diffusion is more rapid increasing the rate at which air is moved into the tracheoles however this leads to greater water evaporation

Question 13

Give a limitation of the tracheal system in insects

Answer 13

It relies mostly on diffusion to exchange gases between the environment and the cells and to be effective, the diffusion pathways needs to be short hence why insects are small. This means the diffusion pathway limits the size insects can attain

Question 14

Give an overview of the process of water movement in the gills of a fish

Answer 14

1. Water is taken in through the mouth and forced over the gills and out through an opening behind the gills
2. Oxygen dissolved in the water is absorbed by the gills
3. The movements of the mouth, floor and operculum are coordinated to produce a stream of water that goes in through the mouth, over the gills and out through the operculum
4. The water is kept moving over the gills by a ventilation system

Question 15

Give the structures of the gills and what they each do

Answer 15

• gill arc: supports the gills and the associated blood vessels
• gill filaments: increase the surface area of the gills
• gill lamellae: positioned at right angles to the gill filaments, further increase surface area and are the site of gas exchange

Question 16

What system does the gas exchange in fish follow and what does this mean?

Answer 16

It follows a counter current exchange system which means that blood and water flow over the gill lamellae in opposite directions

Question 17

Give the points that would give maximum marks in the exam that explain why countercurrent flow in fish is useful.

Answer 17

1. Water and blood flow in opposite directions
2. SO blood is always meeting water with a higher oxygen concentration
3. This means a concentration gradient is maintained over the whole length of the gill
4. Therefore diffusion of oxygen into the blood can occur across the whole length of the gill
5. This ensures maximum possible gas exchange is achieved

Question 18

Why would parallel flow in fish be bad?

Answer 18

Because water and blood would flow in the same direction which means half way across the gill, equilibrium would be reached causing diffusion of oxygen into the blood to stop

Question 19

What are the products of photosynthesis?

Answer 19

Glucose and oxygen

Question 20

What are the products of respiration?

Answer 20

Carbon dioxide and water (and a transfer of energy)

Question 21

What are the relative rates of photosynthesis and respiration when there is a net co2 uptake in a plant?

Answer 21

When the rate of photosynthesis is greater than that of respiration

Question 22

What happens to the relative rates of photosynthesis and respiration to plants at night?

Answer 22

No photosynthesis is occurring, only respiration so rate of respiration is much higher hence CO2 is only being produced

Question 23

In a plant, when would all the glucose and carbon dioxide made by photosynthesis be used by respiration?

Answer 23

When the rate of photosynthesis and respiration are equal so the plant wouldn’t grow

Question 24

Give 2 ways gas exchange in plants is similar to insects

Answer 24

• no living cell is far from the external air hence a source of oxygen and carbon dioxide
• diffusion takes place in the gas phase which makes it more rapid than if it were in water

Question 25

Give 4 adaptations of the gas exchange surfaces in leaves

Answer 25

• diffusion occurs in air which is more rapid than in water
• diffusion distances are short as no living cells are far from a source of air due to the air spaces
• the leaf is thin, flat and only a few cells thick with large SA:V of the mesophyll cells for rapid diffusion
• the stomata on the lower surface mostly ensure air inside the leaf exchanges with the air outside

Question 26

Where are stomata found and why?

Answer 26

On the underside of the leaf as it’s more shady and so exposed less to direct sunlight hence reducing unnecessary water loss

Question 27

What happens when water enters the guard cells?

Answer 27

They swell opening the stomata due to the uneven thickness of the guard cell wall (this happens in sunlight)

Question 28

Where does most gas diffusion occur through in plants and why?

Answer 28

Through the stomata because the epidermis layers are waterproofed by a waxy cuticle

Question 29

What is a xerophyte?

Answer 29

Plants adapted to live in areas where water is limited by means of mechanisms to prevent water loss through transpiration, or store available water

Question 30

Give two adaptations insects have evolved to reduce water loss and how each one does so.

Answer 30

• they have waterproof coverings over their bodies made of chitin that’s covered with a waterproof cuticle
• they have spiracles which can be opened and closed to reduce water loss however this conflicts with the need for oxygen so occurs largely when the insect is at rests

Question 31

Cactuses are xerophytes

Describe and explain how they are adapted to be so

Answer 31

Describe: they have a swollen stem for photosynthesis and the leaves are spikes
Explain: the stem means they can store water in succulents and leaves reduce water loss due to them having a lower SA:V

Question 32

Labs ears leaves are part of xerophytes

Describe and explain how they are adapted to be so

Answer 32

Describe: they have hairy leaves
Explain: this traps moist air next to the leaf surface and so water vapour is closer to the stomata reducing the water vapour diffusion gradient so less water loss

Question 33

Holly leaves are xerophytes

Describe and explain how they are adapted to be so

Answer 33

Describe: they have a thick waxy cuticle
Explain: this increases the waterproof barrier and so reduces water loss by evapotranspiration

Question 34

Marram grass is a xerophyte

Describe and explain how they are adapted to be so

Answer 34

Describe: it has rolled up leaves
Explain: this allows the leaves to trap water vapour inside the rolls so there’s no diffusion gradient between the inside and outside of the leaf

Question 35

Pine leaves are xerophytes

Describe and explain how they are adapted to be so and give a consequence of this adaptation

Answer 35

Describe: they have a reduced surface area to volume ratio
Explain: this slows the rate of diffusion of water into the atmosphere however a consequence of this is that gas exchange is also reduced

Question 36

What causes the “lub” sound of the heart beat?

Answer 36

The closing of the atrioventricular valves

Question 37

What adaptations do insects have to limit water loss?

Answer 37

• have a small surface area: volume where water can evaporate from
• they have a waterproof exoskeleton
• the spiracles can open and close to reduce water loss