3.3.1 Surface area to volume ratio

Question 1

Why do organisms need to exchange materials with their environment ?

Answer 1

1. Oxygen and nutrients are needed to be taken up by cells for metabolism.
2. Waste products of metabolism like carbon dioxide and urea need to be excreted
   from the body.
3. There is a need to maintain the body temperature of animals as it is crucial to
   their survival. Because of this, there is a need for exchange of heat between the
   body and the environment.

Question 2

Define surface area

Answer 2

refers to the area exposed to the external environment.

Question 3

Define volume

Answer 3

refers to the amount of space inside of the object.

Question 4

What happens as size of an organism increases ?

Answer 4

The surface area to volume ratio decreases

Question 5

What are ways to increase the SA:V ratio ?

Answer 5

• Folding in the surface of the cell membrane to increase the surface area
• Developing into long, thin, or elongated shaped cells
• Presence of large vacuoles inside the cell that pushes the other organelles to the side
  of the cell for easier diffusion of materials.

Question 6

What does the small size mean for unicellular organisms ?

Answer 6

Large SA:V ratio which means its easier for materials to move in and out via diffusion and active transport

Question 7

What are developments in multicellular organisms for material exchange ?

Answer 7

1. Exchange organs - Organs in charge of exchanging material from the outside
   environment to inside of the body. Examples lungs and kidneys.
2. Mass transport system - System by which materials can be transported from the
   exchange organs to the all the cells in the body. The transport system is also the ones
   used by the body to transport materials to be eliminated from the cells to the exchange
   organs, eventually to the outside environment. (Examples blood vessels, circulatory
   system, xylem and phloem in plants)

Question 8

What are the two main factors that influence heat exchange ?

Answer 8

1)Size: Larger organisms have a smaller surface area relative to their volume, making heat loss harder; smaller organisms have a higher surface area relative to their volume, leading to higher heat loss and requiring a higher metabolic rate to stay warm.
2)Shape: Compact-shaped animals have a smaller surface area, reducing heat loss and minimizing the need for a high metabolic rate; less compact-shaped animals have a higher surface area, increasing heat loss and necessitating a higher metabolic rate to maintain body temperature.

Question 9

What are the behavioral and physiological adaptations to facilitate exchange ?

Answer 9

Small desert mammals have high SA:V ratio which makes loss of water fast. To control loss
of water, they develop smaller kidneys to produce less urine. On the other hand, the big SA:V
ratio of an elephant is very low which makes them hard to cool down during the hot months.
Because of this, they develop to have large ears to increase their surface area. In the cold
region, small mammals like squirrels tend to store nuts as a source of high energy food that
they need to support their high metabolic rates.