Gas Exchange

Question 1

How does gas exchange in small organisms work?

Answer 1

-The nutrients they need can diffuse directly into the cell
-The diffusion distance is very small
-Large surface area to volume ratio
-Low metabolic demands

Question 2

How does gas exchange in large organisms work?

Answer 2

-Evolved to have specialised systems e.g. gills, lungs, tracheal system etc.
-Distance for nutrients to diffuse would be too far
-Have a higher metabolic rate than smaller organisms

Question 3

What are factors affecting the rate of diffusion?

Answer 3

-The surface area
-The concentration gradient of the particles diffusing
-The distance over which diffusion is taking place

Question 4

What are the features of an effective gas exchange system?

Answer 4

-Large surface area
-Thin layers
-A rich blood supply to respiratory surfaces
-Moist surfaces
-Permeable surfaces

Question 5

Adaptations of alveoli

Answer 5

-Very large surface area to volume ratio
-Short diffusion distance, one cell thick
-Steep concentration gradient, blood constantly flowing through the capillaries

Question 6

What are the 3 components of a gas exchange system in insects?

Answer 6

-Spiracles
-Tracheae
-Tracheoles

Question 7

Spiracles

Answer 7

-Found along thorax and abdomen of most insects
-Site of entry and exit for respiratory gases
-Can be opened or closed my sphincters which can control water loss

Question 8

Tracheae

Answer 8

-Largest tubes of insect respiratory system
-Carry air directly into the body for gas exchange with the cells
-Supported by spirals of chitin to hold it open if it is squashed or deformed but makes gases relatively impermeable to gases so little gas exchange takes place here

Question 9

Tracheoles

Answer 9

-Minute tubes
-Each one is a single elongated cell with no chitin lining
-Freely permeable to gases
-Most gas exchange takes place here

Question 10

What is mechanical ventilation?

Answer 10

-Air actively being pumped into the tracheal system
-Ventilating movements change volume and pressure inside the body, drawing air in and out

Question 11

What are collapsible tracheae or air sacs that act as air reservoirs?

Answer 11

-Increase volume of air moved through the respiratory system
-The ventilating movements inflate and deflate them

Question 12

What is the operculum?

Answer 12

-A protective bony flap covering the gills
-Important in maintaining a flow of water over the gills

Question 13

What is a countercurrent exchange system?

Answer 13

-The blood in gill filaments and the water moving over the gills flow in opposite directions
-Creates a steep concentration gradient for diffusion to happen efficiently

Question 14

Overlapping gill filaments

Answer 14

-Slows the water down to give more time for diffusion to take place
-The overlapping adjacent gill filaments increase resistance to the flow of water

Question 15

What gives plants a large surface area?

Answer 15

-The leaves
-Gas exchange surfaces of spongy mesophyll cells which have irregular shapes and are arranged with large air spaces between them

Question 16

Adaptations of a plant

Answer 16

-Large surface area
-Moist surfaces for diffusion (e.g. spongy mesophyll cells)
-Waxy cuticle acting as a barrier to diffusion of gases and evaporation of water
-Stomata to control water loss

Question 17

How are stomata controlled?

Answer 17

-The stomata control water loss in a plant
-Molecules (potassium ions) moves into the guard cells by active transport
-Water then moves into guard cells for, surrounding cells by osmosis causing the guard cells to swell and turbot pressure to increase
-This results in the opening of the stomata
-In less favourable conditions for photosynthesis, the water leaves the cell by osmosis reducing the turgor pressure
-This causes the guard cells to become flaccid resulting in the closing of the stomata

Question 18

What are lenticels?

Answer 18

-Lenticels are special spongy areas which are made up of loosely arranged cells with many air spaces
-They link inner tissues of the trunk of woody stem to the outside world so gas exchange can take place
-They also form on roots so they can exchange gases with air in the soil