6.2 Single Celled Organisms

Question 1

True or False single celled organisms have a small surface area to volume ratio?

Answer 1

False, they have large surface area to volume ratio’s.

Question 2

How does oxygen enter into and carbon dioxide leave single celled organisms?

Answer 2

By diffusion.

Question 3

Why can single celled organisms give off CO2 and take in O2 by diffusion?

Answer 3

Because their body is only covered by a single cell-surface membrane so it is easier and quicker for diffusion to occur.

Question 4

Why do insects find it hard to conserve water?

Answer 4

Because of their large surface area to volume ratio needed for efficient diffusion of gases in and out of the body.

Question 5

What is the internal network of tubes called in insects that helps them transport gases?

Answer 5

Tracheae

Question 6

What are the structures called that keep the tracheae open?

Answer 6

Cartilage

Question 7

What are the three ways in which gases can move through the tracheal system?

Answer 7

1. Mass transport
2. Along a diffusion gradient
3. Ends of tracheoles filled with water.

Question 8

When cells respire, what happens to their oxygen concentration?

Answer 8

It falls/reduces.

Question 9

Explain what a diffusion gradient is?

Answer 9

A difference in concentration of a gas/liquid/solution between two different areas causing there to be a net movement of the particles from an area of high concentration of the particles, to an area of low concentration of the particles.

Question 10

What gaseous substance is produced when cells respire?

Answer 10

Carbon dioxide

Question 11

Which is faster, diffusion in air or diffusion in water?

Answer 11

Diffusion in air.

Question 12

Explain how a diffusion gradient is useful in transporting substances between the cells of an insect and the atmosphere.

Answer 12

1. Cells respire and oxygen is used up. Carbon dioxide is also made.
2. A gradient is made between the cell and the atmosphere.
3. Oxygen diffuses from the atmosphere down its concentration gradient to the respiring cell via the tracheae and tracheoles.
4. Carbon dioxide also diffuses down its concentration gradient from the cell to the atmosphere via the trachea and tracheoles.

Question 13

Explain how mass transport helps move gases in and out of an insect.

Answer 13

The insects muscles contract squeezing the trachea and helping to move air in and out. This speeds up the exchange of respiratory gases between the insect and atmosphere.

Question 14

Explain how the ends of the tracheoles being filled with water help with the exchange of respiratory gases?

Answer 14

The cells respire anaerobically producing lactate that lowers the cells water potential. Water, from the tracheal ends, then enter the cells by osmosis due to the water potential gradient made. By water moving into the cell, it causes air to be drawn into the trachea. So the final diffusion is in a gaseous state not liquid state.

Question 15

Why is it good that the final diffusion is in a gaseous state and not in liquid state when the insect exchanges gases by using it’s tracheoles filled with water?

Answer 15

Because diffusion is faster in air than liquids.

Question 16

What is a disadvantage of exchanging respiratory gases using the method of the tracheoles filled with air?

Answer 16

It increases the rate of water being evaporated.

Question 17

What are the pores called on the surface of an insect?

Answer 17

Spiracles.

Question 18

Majority of the time, spiracles on an insect are closed, why?

Answer 18

To reduce the rate of water loss.

Question 19

List three ways in which insects are adapted to allow for efficient gas exchange:

Answer 19

1. Small surface area to volume ratio
2. Small, so short diffusion pathway
3. Can maintain a diffusion gradient

Question 20

When spiracles are closed what happens to the carbon dioxide and oxygen concentrations in the trachea?

Answer 20

Oxygen concentrations fall,

Carbon dioxide concentrations rise.