Topic 4.2 Gas exchange

Question 1

Factors affecting the rate of diffusion

Answer 1

-Surface area
-Concentration gradient
-Diffusion distance
-Amount of energy

Question 2

Rate of diffusion equation

Answer 2

(surface area x steepness of concentration gradient) / thickness of membrane

Question 3

Effective gas exchange surfaces

Answer 3

-Large surface area
-Thin layers to minimise diffusion pathway
-Moist surfaces as the gases can dissolve and diffuse faster
-(Semi) permeable surfaces that allow gases to pass through

Question 4

Safe dissection

Answer 4

-Wear gloves
-Not cutting frozen parts (may slip)
-Use a chopping board
-Cut downwards and away
-Use scissors

Question 5

Where does most of the gas exchange happen?

Answer 5

In the chest within the lungs (not the passages that takes gases in and out).

Question 6

Why do the passages have linings to secrete mucus and are lined with cilia?

Answer 6

The external air is filtered of dust and pathogens before entering the lungs.

Question 7

Adaptations of alveoli

Answer 7

-Walls are one cell thick
-Surrounding capillaries are one cell thick
-Elastic tissue holds capillary to alveoli (helps to force the air in/out)
-Lung surfactant coats the alveoli, prevents them from collapsing.

Question 8

Inhalation

Answer 8

Active process (uses energy)
-Diaphragm contracts and flattens
-Intercostal muscles contact and move the ribs up and out
-Increased volume and decreased pressure
-Air rushes in to equalise pressure

Question 9

Exhalation

Answer 9

-Diaphragm relaxes and moves up
-Intercostal muscles contract and move ribs down and in
-Decreased volume and increased pressure
-Air rushes out to equalise the pressure

Question 10

Forced exhalation

Answer 10

You can force air out of your lungs by contracting your intercostal muscles. Ribs move down and in and the diaphragm moves up.

Question 11

What is the fluid for in between the pleural membranes?

Answer 11

The serous fluid continuously lubricates the pleural surface and makes it easy for them to slide over each other during lung inflation and deflation.

Question 12

Gas exchange in fish

Answer 12

1. Water flows in through the mouth
2. Water flows over the gills
3. Water flows out the operculum

(Fish without operculum have to continuously move)

Question 13

Why don’t fish have lungs?

Answer 13

Water contains very little dissolved oxygen, lungs would therefore not work efficiently as it would take too much energy to move water in and out.

Question 14

How are fish adapted for efficient gas exchange?

Answer 14

-Gills are made up of overlapping gill filaments which are covered in lamellae
-Lamellae + gills have a good blood supply (where gas exchange takes place)
-Overlap of filaments can slow down flow of water
-Lamellae have a large surface area
-The water moving over the gills moves in the opposite direction to the blood in the blood vessels- this is called countercurrent exchange.

Question 15

How are lamellae adapted?

Answer 15

-Lamellae have a good blood supply and this is where gas exchange takes place
-Lamellae have a large surface area

Question 16

Countercurrent exchange (equilibrium)

Answer 16

Countercurrent flow ensures that equilibrium is not reached.
This maintains a (steep) diffusion gradient across the entire length of the gill lamellae
(The counter current mechanism maintains the concentration gradient allowing diffusion of oxygen into the blood)
-Water always has more oxygen than the blood to maintain the diffusion gradient
(Diffusion happens along the length of the lamellae)

Question 17

Gas exchange in insects

Answer 17

-Insects have high oxygen requirements and have evolved to deliver oxygen straight to their cells and to remove carbon dioxide
-Made up of the main parts- spiracles, tracheae and tracheoles.

Question 18

Tracheae

Answer 18

Largest tubes and carry air directly into the body, they run into and along the body.
They are supported by chitin spirals which holds them open.
Chitin makes these vessels impermeable, so no gas exchange happens here.
(Air moves through the tracheae and tracheoles by diffusion).

Question 19

Tracheoles

Answer 19

Single elongated cells with no chitin, therefore are permeable to gases. They spread throughout the insect tissues providing a large surface area.
(Air moves through the tracheae and tracheoles by diffusion).

Question 20

Spiracles

Answer 20

-Entry/exit point (on outside of body).
-Can be opened and closed.
-Controls the rate of gas exchange- mainly to prevent water loss.

Question 21

Gas exchange in plants

Answer 21

Plants need to exchange gases for photosynthesis and respiration
-So the net movement of gases can change
-Need to balance their gas exchange with minimising water loss
-CO2 moves out during the night, but during the day more CO2 needs to be taken in
-Plants need water to evaporate from the leaves as this pulls water up throughout the plant to be used in chemical reactions, this requires stomata to open.

Question 22

Opening and closing the stomata

Answer 22

-Guard cells have an uneven distribution of cellulose in their walls
-Driven by turgor pressure
-Guard cells respond to levels of CO2 in the leaf
-When conditions for photosynthesis are favourable

Question 23

Stomata opening sequence

Answer 23

1. Solutes (mainly potassium ions) are moved into guard cells by active transport
2. Water then moves into the guard cells from surrounding cells by osmosis
3. Guard cells swell and increases turgor pressure
4. Stomata then open due to uneven bending, caused by the cellulose distribution.

Question 24

How are insects adapted for gas exchange?

Answer 24

-Spiracles can be opened and closed to regulate diffusion
-Muscles in the trachea allow mass movement of air in and out
-Tracheoles highly branched to provide large surface area.

Question 25

Name and describe the main features of a fish’s gas exchange system

Answer 25

Gills- made of filaments and supported by arches.
Lamella- folds that cover the filaments. Water passes over them due to pressure from the floor of the mouth.

Question 26

How are plant leaves adapted for gas exchange?

Answer 26

-Spongey mesophyll layer provides large surface area
-Waxy cuticle is impermeable to gas, preventing excessive water loss
-Lenticels (loosely arranged cells) allow gases to enter and leave.

Question 27

Fick’s law

Answer 27

Rate of diffusion= (surface area x difference in concentration gradient) / thickness of surface

Question 28

Mechanical pumping (in locusts/insects)

Answer 28

Insect moves its thorax in a muscular pumping motion which draws air in and out of the spiracles.
(Collapsible trachea act as reservoirs. Movement of the thorax can inflate or deflate them).