3. Organisms Exchange Substances With Their Environment

Question 1

What plays a significant role in the types of adaptations an organism will have?

Answer 1

The relationship between the size of an organism or structure and its surface area to volume ratio

Question 2

What do adaptations on exchange surfaces do?

Answer 2

Makes transport across the surface more efficient

Question 3

Small organisms… (in regards to surface area:volume ratio)

Answer 3

• have a very large surface area in comparison to their volume
• e.g. amoeba

Question 4

What does it mean by a large surface area:volume ratio for small organisms?

Answer 4

• big surface for the exchange of substances
• smaller distance from the outside of the organism to the middle

Question 5

How do very small organisms exchange substances across its surfaces?

Answer 5

Very small organisms can simply exchange substances across its surface by diffusion

Question 6

Larger organisms… (in regards to surface area:volume ratio)

Answer 6

• have a smaller surface area compared to its volume, therefore a smaller surface area:volume ratio
• and therefore larger the distance from the middle to the outside

Question 7

What does it mean by a smaller surface area:volume ratio for larger organisms?

Answer 7

They have adaptations that help make their exchange across surfaces more efficient

Question 8

Why do single cell organisms need to be small?

Answer 8

Because they need a larger surface area to volume ratio to diffuse across its surfaces

Question 9

As organisms get bigger… (in regards to surface area:volume ratio)

Answer 9

Surface area:volume ratio gets smaller as their dimensions do not increase proportionally

Question 10

The greater the diameter of a single-cell organism… (in regards to surface area:volume ratio)

Answer 10

The less surface area it has relative to its volume

Question 11

Features of good exchange surfaces: (4)

Answer 11

• large surface area
• thin surface
• steep diffusion gradient
• a system that moves the substances to maintain the diffusion gradient

Question 12

Why is a large surface area good for exchange surfaces?

Answer 12

• makes the surface area:volume ratio greater
• more molecules can cross the surface unit per time

Question 13

Why is a thin surface good for exchange surfaces?

Answer 13

• shorter distance to travel
• more molecules can cross the surface per unit time

Question 14

Why is a steep diffusion gradient good for exchange surfaces?

Answer 14

• greater difference in concentration increases rate of diffusion
• more molecules can cross the surface per unit time

Question 15

What are some examples of adaptations to the exchange surfaces for larger organisms? (6)

Answer 15

• villi and microvilli
• alveoli and bronchioles
• spiracles and tracheoles
• gill filaments and lamellae
• thin wide leaves

Question 16

Villi and microvilli allow for…

Answer 16

Efficient absorption of digested food

Question 17

Alveoli and bronchioles allow for…

Answer 17

Efficient gas exchange in mammals

Question 18

Spiracles and tracheoles allow for…

Answer 18

Efficient gas exchange in terrestrial insects

Question 19

Gill filament and lamellae allow for…

Answer 19

Efficient gas exchange in fish

Question 20

Thin wide leaves allow for…

Answer 20

Efficient gas exchange in plants

Question 21

How does an organism’s surface area:volume ratio relate to their metabolic rate?

Answer 21

Per unit of body mass metabolic rate is actually higher in small animals compared to larger ones

Question 22

How might a large organism adapt to compensate for its small surface area:volume ratio?

Answer 22

Changes that increase surface area, e.g. folding; body parts become larger–> e.g. elephants’ ears; elongating shape; developing a specialised gas exchange surface

Question 23

Why do multicellular organisms require specialized gas exchange surfaces?

Answer 23

Their smaller surface area:volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in single-celled organism