Module 3 - Chapter 8

Question 1

Why are specialised transport systems required?

Answer 1

• metabolic demands (high metabolic rate)
• decreased surface area to volume ratio
• transport of molecules

Question 2

Why are do metabolic demands of multicellular organisms result in specialised transport systems being required?

Answer 2

metabolic demands of most multicellular organisms are high so diffusion alone isn’t adequate to supply quantities required.

Question 3

Why are does decreased surface area to volume ratio in multicellular organisms result in specialised transport systems being required?

Answer 3

surface area to volume ratio decreases as size of multicellular organisms increases, so diffusion distance increases and rate of diffusion decreases. SA available to absorb or remove substances becomes relatively smaller.

Question 4

Why are specialised transport systems required for the transport of molecules?

Answer 4

• enzymes and hormones made in glands but transported to organs in circulatory system
• food digested in one organ system but must be transported to all cells for use in respiration and other parts of cell metabolism
• waste products need to be removed from cells and transported to excretory organs.

Question 5

what is the relationship between the rate of diffusion and the square of the distance it has to travel?

Answer 5

the rate of diffusion increases with the square of the distance it has to travel

Question 6

How is oxygen distributed throughout cells?

Answer 6

by cytoplasmic streaming

Question 7

Describe cytoplasmic streaming

Answer 7

• the cytoskeleton supports cells with fibres from the cell surface membrane to the nucleus
• the cytoskeleton pushes the cytoplasm to the centre of the cell from the cell surface membrane in currents.
• the currents help move oxygen to the centre of the cell and stop the boundary effect of oxygen only being on the outer edge of the cell.
• this increases the concentration gradient across the membrane so the rate of diffusion increases

Question 8

what do circulatory systems comprise of?

Answer 8

a liquid transport medium (fluid) which circulates the body, vessels through which the transport medium can flow, and a pumping mechanism to move the fluid around the system (heart)

Question 9

what is a mass transport system?

Answer 9

when substances are transported in a mass of fluid with a mechanism for moving the fluid around the body

Question 10

what does an open circulatory system consist of?

Answer 10

• a transport medium being pumped straight from the heart into the body cavity of an animal.
• the body cavity is the haemocoel
• the haemocoel is under low pressure and comes into direct contact with the tissues and cells, where diffusion and exchange takes place
• the transport medium returns to the heart through open-ended vessels called ostia.

Question 11

describe the open circulatory system in insects.

Answer 11

• the transport medium is haemolymph
• gas exchange takes place in the tracheal system
• haemolymph transports food, nitrogenous waste products and cells involved in the immune response, but not carbon dioxide or oxygen.
• haemolymph moves around the haemocoel due to the movement of the organism. the haemolymph circulates but steep diffusion gradients cannot be maintained for efficient diffusion

Question 12

describe closed circulatory systems

Answer 12

blood is fully enclosed in blood vessels at all times and doesn’t come into direct contact with body cells.