Exchanges of substances

Question 1

What is surface area to volume ratio?

Answer 1

• The ratio of an organisms surface area compared to its volume
• influences the efficiency of substance exchange

Question 2

How does size affect surface area to volume ratio?

Answer 2

as organism increases in size, its surface area to volume ratio decreases

Question 3

Why do small organisms rely on diffusion for exchange?

Answer 3

• They have a large surface area to volume ratio and short diffusion distances
• allowing efficient diffusion of substances

Question 4

Why do large organisms need specialized exchange surface?

Answer 4

• They have a small surface area to volume ratio
• This increases diffusion distances
• So requires adaptations for efficient exchange

Question 5

Calculation for surface area of a cube

Answer 5

area of one face x 6

Question 6

Calculation for volume of a cube

Answer 6

length x width x height

Question 7

What happens to the surface area to volume ratio when the size of a cube doubles?

Answer 7

decreases
because surface area increases at a slower rate than volume

Question 8

What are the adaptations for exchange surface

Answer 8

• Large surface area - more space for diffusion (villi, alveoli)
• Thin barriers - short diffusion distance
• Good blood supply or ventilation - maintains concentration gradients (capillaries, gills)

Question 9

How do villi and microvilli improve exchange?

Answer 9

increase surface area in the small intestine for efficient absorption of nutrients

Question 10

What features make alveoli efficient for gas exchange?

Answer 10

• Large surface area
• Thin walls
• Rich blood supply
• Moist surface

Question 11

Why do large organisms need efficient exchange surfaces?

Answer 11

Their surface area to volume ratio is too small for diffusion alone to meet metabolic demands

Question 12

Why cant large organisms rely on diffusion alone for exchange?

Answer 12

Diffusion becomes too slow due to increased diffusion distance

Question 13

How do organisms overcome diffusion limitations without specialized exchange systems?

Answer 13

By having a flattened shape (e.g flatworms) - reduces diffusion distances and increases surface area

Question 14

How do desert animals adapt their surface area to volume ratio?

Answer 14

Many have large ears to increase surface area for heat loss

Question 15

Why do fish need a specialized gas system?

Answer 15

fish have scales, which make them waterproof and a small surface rea to volume ratio, so they cannot rely on diffusion alone

Question 16

What is the gas exchange surface in fish

Answer 16

gills - allowing oxygen uptake from water

Question 17

Why is extracting oxygen from water more difficult than from air?

Answer 17

water contains 30 times less oxygen than air

Question 18

How are fish gills adapted for a large surface area?

Answer 18

• fish have four sets of gill filaments on each side of the head
• each filament has many thin gill lamellae at right angles to increase surface area

Question 19

How do fish gills provide a short diffusion distance?

Answer 19

• gill lamellae are very thin
• dense capillary network in each lamellae brings blood close to the surface for gas exchange

Question 20

What adaptation in fish gills maintains a high oxygen concentration gradient?

Answer 20

The countercurrent exchange principle ensures continuous diffusion

Question 21

What happens in countercurrent flow?

Answer 21

• water flows over the gills in the opposite direction to blood in the capillaries
• ensuring blood always meats water in a high oxygen concentration, maintaining diffusion gradient along the entire lamellae

Question 22

Why is countercurrent flow more efficient than concurrent flow?

Answer 22

• in countercurrent flow, equilibrium is never reached so oxygen diffuses along the entire length of the lamellae
• in concurrent flow, equilibrium will be reached at 50% oxygen saturation, stopping further diffusion

Question 23

What must you mention in an exam question about countercurrent flow?

Answer 23

1. water and blood flow in opposite directions
2. equilibrium is never reached, so diffusion continues
3. a diffusion gradient is maintained across the entire lamellae

Question 24

Why can single celled organisms rely on diffusion only?

Answer 24

They have a large surface area to volume ratio, allowing oxygen and carbon dioxide to diffuse directly across the cell membrane

Question 25

What are the main gases exchanged in single celled organisms?

Answer 25

• oxygen diffuses in for respiration
• carbon dioxide diffuses out

Question 26

Why do multicellular organisms need a transport system?

Answer 26

• small surface area to volume ratio
• need specialized circulatory system

Question 27

What is the main challenge insects face for gas exchange?

Answer 27

They must balance gas exchange with the need to conserve water in dry environments

Question 28

What is the specialized gas exchange system in insects called?

Answer 28

The tracheal system - a network of internal air-filled tubes

Question 29

what are the key components of the tracheal system?

Answer 29

• Trachea - large air tubes supported by rings
• Tracheoles - smaller tubes that extend into body tissues, delivering oxygen directly
• Spiracles - pores that control gas entry and water loss

Question 30

What are the three ways gases move in and out of the tracheal system?

Answer 30

1. Diffusion gradient - oxygen moves in and it is used up and co2 moves out
2. Ventilation (mass transport) - muscle contractions speed up airflow
3. Water movement in tracheoles - lactate lowers water potential, drawing water into muscle cells, reducing diffusion distance in liquid phase

Question 31

How does an insect reduce water loss through spiracles?

Answer 31

Spiracles can open and close using valves to minimize water loss when gas exchange isn’t needed

Question 32

What is the main limitation of the insect tracheal system?

Answer 32

Insects must be small as diffusion must cover short distances for efficient exchange

Question 33

How do multicellular animals overcome diffusion limitations?

Answer 33

They use a specialized circulatory system to transport substances efficiently

Question 34

What are the three main components of a circulatory system?

Answer 34

• A heart - to pump the transport fluid
• Vessels - to direct fluid flow
• A transport fluid - to carry substances (eg blood, haemolymph)

Question 35

What is an open circulatory system?

Answer 35

• found in insects
• haemolymph is pumped into a body cavity where it bathes organs directly
• ostia (pores) allows haemolymph to be sucked back into the heart

Question 36

What is a closed circulatory system?

Answer 36

• found in vertebrates and some invertebrates
• blood remains enclosed in vessels at all times
• blood is pumped through a series of vessels, allowing efficient transport