6.1- EXCHANGE BETWEEN ORGANISMS AND THEIR ENVIRONMENT

Question 1

Is the internal and external environment of organism the same?

Answer 1

no

Question 2

What does an organism transfer and between where to survive?

Answer 2

transfer materials between two environments (internal + external)

Question 3

Where does the exchange of materials from internal + external environments of organism happen?

Answer 3

at exchange surfaces

Question 4

What does exchanging materials between the two environments involve for an organism?

Answer 4

crossing cell plasma membranes

Question 5

What is the environment around the cells of a multicellular organism called?

Answer 5

tissue fluid

Question 6

What is tissue fluid?

Answer 6

environment around cells of multicellular organisms

Question 7

What is the problem with majority of cells in an organism being too far from exchange surfaces?

Answer 7

diffusion alone cannot supply or remove their tissue fluid with the various materials needed to keep its composition relatively constant

Question 8

What happens to materials once absorbed into an organism?

Answer 8

rapidly distributed to tissue fluid + waste products returned to exchange surface for removal

Question 9

What does the process of materials distributed to tissue fluid + waste being removed involved?

Answer 9

mass transport system

Question 10

What does the mass transport system maintain?

Answer 10

diffusion gradients that bring materials to + from cell-surface membranes

Question 11

What can affect the amount of each material that is exchanged ? (2)

Answer 11

size

metabolic rate of organism

Question 12

What does an organism with a high metabolic rate require?

Answer 12

larger surface area to volume ratio

Question 13

Why does an organism with a high metabolic rate require a larger SA:V?

Answer 13

exchanges more materials

Question 14

Examples of things that need to be interchanged between an organism and its environment (5)

Answer 14

respiratory gases (oxygen + CO2)

nutrients (glucose, fatty acids, amino acids, vitamins, minerals)

excretory products (urea + CO2)

heat

Question 15

Except for heat, how can exchange of the 4 substances take place? (2)

Answer 15

passively- diffusion or osmosis

actively- by active transport

Question 16

What is meant by passive exchange?

Answer 16

no metabolic energy required

Question 17

What is meant by active exchange?

Answer 17

metabolic energy required

Question 18

Where does exchange take place in an organism?

Answer 18

surface of an organism

Question 19

What is the materials absorbed by an organism used by?

Answer 19

cells that mostly make up its volume

Question 20

For exchange to be effective, what must the exchange surface(s) of an organism be like?

Answer 20

must be large compared with its volume

Question 21

What do small organism have? (hint: SA)

Answer 21

SA large enough, compared with their volume

Question 22

What does small organisms having a SA large enough compared with their volume allow?

Answer 22

efficient gas exchange across their body surface

Question 23

What happens to volume as organisms become larger in comparison to SA?

Answer 23

volume increases at faster rate than their SA

Question 24

What happens as organisms are larger and volume increases at a faster rate than their SA?

Answer 24

simple diffusion of substances across outer surface can only meet needs of relatively inactive organisms

Question 25

Even if the outer surface could supply enough of a substance in a larger organism, why is this still not good enough?

Answer 25

still take too long for it to reach middle of organism if diffusion along was method of transport

Question 26

Organisms have developed one or more of the following features for exchange (2)

Answer 26

flattened shape so no cell ever far from surface (e.g. flatworm or leaf)

specialised exchange surfaced with large areas to increase SA:V (e.g. lungs in mammals, gills in fish)

Question 27

What features do exchange surfaces show to allow effective transfer of materials across specialised exchange surfaces by diffusion/ active transport? (5)

Answer 27

large SA relative to volume of organism

very thin

selectively permeable

movement of environmental medium

transport system

Question 28

What does the exchange surface having a large SA relative to volume of organism do?

Answer 28

increases rate of exchange

Question 29

What does the exchange surface being very thin do?

Answer 29

diffusion distance short so materials cross exchange surface rapidly

Question 30

What does exchange surface being selectively permeable do?

Answer 30

allow selected materials to cross

Question 31

What does movement of environmental medium e.g. air do for exchange?

Answer 31

maintain diffusion gradient

Question 32

What does a transport system do for exchange?

Answer 32

ensure movement of internal medium e.g. blood to maintain diffusion gradient

Question 33

What is Fick’s law equation?

Answer 33

diffusion ∝

length of diffusion path

Question 34

As specialised exchange surfaces are thin, what can easily happen to them? (2)

Answer 34

easily damaged + dehydrated

Question 35

As specialised exchange surfaces are easily damaged + dehydrated, where are they often located?

Answer 35

often located inside organism

Question 36

Where an exchange surface is located inside the body, what must the organism need to have?

Answer 36

means of moving external medium over surface

Question 37

What is an example of an organism have a means of moving external medium over the surface?

Answer 37

means of ventilating lungs in mammal