7.1 - Specialised exchange surfaces

Question 1

Why do single-celled organisms rely solely on diffusion for exchange of substances?

Answer 1

1. Their metabolic activity is low, so oxygen demands and carbon dioxide production are minimal.
2. They have a large surface area to volume (SA:V) ratio, allowing efficient diffusion across the cell membrane.
3. The distances for diffusion are very small, so substances can easily reach all parts of the cell.

Question 2

Why is diffusion alone insufficient for larger, multicellular organisms?

Answer 2

1. Their metabolic activity is high, leading to increased oxygen demands and carbon dioxide production.
2. The distance between cells and the oxygen supply is too great for efficient diffusion.
3. Larger organisms have a smaller SA:V ratio, meaning less surface area is available for exchange relative to their volume.

Question 3

Why do more active organisms have a greater demand for Oxygen and Glucose?

Answer 3

1. more energy is required for more movement
2. more ATP must be produced
3. more aerobic respiration must occur
4. more reactants (glucose and oxygen) is required

Question 4

Why do smaller animals have higher metabolic rates per unit of body mass?

Answer 4

Smaller animals lose heat more quickly due to their higher SA:V ratio. To maintain body temperature, they must generate more energy, resulting in a higher metabolic rate.

Question 5

How does the surface area to volume ratio (SA:V) change as organisms get larger? What does this lead to?

Answer 5

1. As organisms get larger, the volume increases faster than surface area.
2. This leads to a smaller SA:V ratio, meaning less surface area is available per unit of volume for exchange processes.

Question 6

As organisms get larger, what happens to the size of the diffusion distance?

Answer 6

It increases

Question 7

As organisms get larger, what happens to the size of the surface area?

Answer 7

It increases

Question 8

As organisms get larger, what happens to the size of volume?

Answer 8

It increases

Question 9

As organisms get larger, what happens to the size of the SA:V?

Answer 9

It decreases

Question 10

What is the formula for calculating the surface area of a sphere?

Answer 10

Surface Area:
4𝜋𝑟^2

Question 11

What is the formula for calculating the volume of a sphere?

Answer 11

Volume:
(4/3)𝜋𝑟^3

Question 12

How does the SA:V ratio differ between small and large organisms? Use the example values:
1. sphere 1 radius = 2
2. sphere 2 radius = 6

Answer 12

Larger organisms have a smaller SA:V ratio, meaning less surface area is available for exchange relative to their volume. To meet their high metabolic demands, they require specialized exchange surfaces to ensure efficient gas and nutrient exchange.

Small sphere (radius =2):
Surface area = 16𝜋
Volume = 32/3𝜋
SA:V ratio = 1.5:1

Larger sphere (radius = 6):
Surface area = 144𝜋
Volume = 288𝜋
SA:V Ratio = 0.5:1

Question 13

Why do larger organisms need specialized exchange surfaces?

Answer 13

1. Their small SA:V ratio limits the surface area available for diffusion relative to their size.
2. Substances like oxygen cannot reach all cells quickly enough via diffusion alone due to larger diffusion distances.
3. Their higher metabolic activity requires efficient gas and nutrient exchange.

Question 14

What are the four main features of efficient exchange surfaces?

Answer 14

1. Increased Surface Area
2. Thin Layers
3. Good Blood Supply
4. Ventilation

Question 15

How does an increased surface area increase the effectiveness of exchange surfaces? Give examples.

Answer 15

Provides a larger area for diffusion to occur, overcoming the SA:V ratio limitation of larger organisms.

(e.g., root hair cells in plants, villi in the small intestine of mammals).

Question 16

How does an increased surface area affect the root hair cells, and alveoli?

Answer 16

Root hair cells: Absorb water and minerals from soil.

Alveoli: Facilitate oxygen and carbon dioxide exchange.

Question 17

How do thin layers increase the effectiveness of exchange surfaces? Give examples.

Answer 17

Reduces diffusion distance, making the process faster and more efficient

(e.g., alveoli in lungs, villi in the small intestine).

Question 18

How do thin layers affect the alveoli?

Answer 18

Alveolar walls are one cell thick, minimizing the distance oxygen and carbon dioxide travel during gas exchange.

Question 19

How does a good blood supply increase the effectiveness of exchange surfaces? Give examples.

Answer 19

Maintains a steep concentration gradient by constantly delivering and removing substances
–> steeper the gradient = faster the diffusion rate

(e.g., alveoli in the lungs, gills in fish, villi in the small intestine).

Question 20

How does ventilation increase the effectiveness of exchange surfaces? Give examples.

Answer 20

maintains a diffusion gradient
–> Ensures a continuous flow of gases to maintain diffusion gradients

(e.g., alveoli in the lungs, fish gills).

Question 21

How do thin layers enhance the efficiency of exchange surfaces?

Answer 21

Thin layers minimize the distance substances must diffuse, increasing the rate of diffusion and ensuring efficiency (e.g., the single-cell thick alveolar walls).

Question 22

How does a good blood supply improve exchange surfaces?

Answer 22

A good blood supply maintains a steep concentration gradient by:

1. Delivering oxygen or nutrients to the exchange surface.
2. Removing waste products like carbon dioxide.
   –> This enhances diffusion efficiency (e.g., alveoli, gills).

Question 23

Why is ventilation important for gaseous exchange surfaces?

Answer 23

1. Fresh air (or water in aquatic organisms) is constantly supplied to the exchange surface.
2. Concentration gradients for oxygen and carbon dioxide are maintained, enabling efficient diffusion.
   –> Examples include alveoli in lungs and gills in fish.

Question 24

What are some examples of specialized systems in large multicellular organisms?

Answer 24

1. Gas exchange systems (e.g., lungs in mammals).
2. Circulatory systems (e.g., the heart and blood vessels).
3. Urinary systems (e.g., kidneys for waste removal).
4. Vascular systems in plants (e.g., xylem and phloem for water and nutrient transport).