Gas Exchange

Question 1

For gas exchange to be effective the SA:V ratio must be…

Answer 1

Large

Question 2

The larger the organism gets….

Answer 2

…the SA to volume ration decreases

Question 3

How do you calculate SA:V ratio

Answer 3

Calculate surface area by length x width
Calculate volume length x width x height
Do surface area divided by volume

Question 4

What is Fick’s law

Answer 4

Rate of diffusion = surface area x concentration gradient
———————————————————-
Diffusion distance

Question 5

What makes a good exchange surface

Answer 5

Large surface area
Large concentration gradient
Thin exchange surface

Question 6

To limit water loss insects may have….

Answer 6

Waterproof covering
Small surface area to volume ratio to minimise area over which water is lost

Question 7

Describe the movement of oxygen through the insect

Answer 7

Oxygen enters the insect through spiracles and into the tracheae. Sporades close
Oxygen diffuses through the tracheae into the tracheoles down a conc gradient
Oxygen is delivered directly to the respiring tissues

Question 8

Why is it good that spiracles can open and close

Answer 8

To control any water loss by evaporation

Question 9

When do spiracles open

Answer 9

When CO2 level increase

Question 10

What are tracheae

Answer 10

Network of tubes supported by strengthened rings
Provide tubes full of air so that diffusion is fast

Question 11

Tracheoles

Answer 11

Small tubes with THIN walls so that the diffusion distance is reduced
Highly branched so that there is a large surface area

Question 12

Gas exchange in fish

Answer 12

Each fish has 4 gills each side of its head
Water moves in through the mouth and out through the gills
Gills have finger like projections called gill filaments
Each filament has many lamellae at 90 degrees to increase surface area

Question 13

Structure of a leaf

Answer 13

Cuticle
Upper epidermis cells
Palisade mesophyll cells
Spongy mesophyll cells
Stomata air space
Lower epidermis cell
Guard cell
Stoma

Question 14

Adaptations of leaf for gaseous exchange

Answer 14

Flat - gives larger surface area to volume ratio
Many stomata - pores to allow air to move in and out of leaf
Air spaces in leaf so short distance between mesophyll cells and air

Question 15

Adaptations of plants to reduce water loss

Answer 15

Guards cells close the stomata at night to reduce water loss
Less co2 required due to lack of sunlight for photosynthesis

Upper and lower surfaces have a waxy cuticle

Question 16

Adaptions of xerophytic plants to reduce water loss

Answer 16

Reduced amount of stomata - less surface area for water loss
Stomata in pits - reduced conc grad
Hairs to trap water vapour - reduced conc grad
Rolled leaves - reduced conc grad
Leaves reduced to spines - less surface area for water loss
Thick waxy cuticles - increased diffusion distance

Question 17

How does oxygen move through the insect?

Answer 17

1. Oxygen diffuses in through the spiracles;
2. Spiracle closes;
3. Oxygen moves through the trachea into the tracheoles;
4. Oxygen delivered directly to the respiring tissues;

Question 18

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

Answer 18

1. Tracheoles have thin walls so short diffusion distance to cells
2. Highly branched tracheoles so short diffusion distance to cells
3. Highly branched tracheoles so large surface area
   4.Tracheae provide tubes full of air so fast diffusion

Question 19

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

Answer 19

1. Water and blood flow in opposite directions;
2. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
3. (Diffusion) along length of lamellae/filament/gill/capillary

Question 20

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.

Answer 20

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);

Question 21

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Answer 21

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order OR Above structures labelled in correct positions on a diagram;
3. Breathing in – diaphragm contracts and external intercostal muscles contract;
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

Question 22

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf. (4)

Answer 22

1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 23

Explain why plants grown in soil with very little water grow only slowly

Answer 23

1. Stomata close;
2. Less carbon dioxide (uptake) for less photosynthesis/glucose production;

Question 24

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake

Answer 24

Larger organisms have a smaller surface area to volume ratio
Overcomes long diffusion pathways

Question 25

How do lungs provide an efficient gas exchange surface in human

Answer 25

They have short diffusion distance and a large surface area

Question 26

What is the trachea

Answer 26

Tube like structure that carries air from the mouth to the lungs

Question 27

Bronchi

Answer 27

The trachea spilts into two bronchi as it enters the lungs, which allows air to travel to the left and right lung

Question 28

Bronchioles

Answer 28

Bronchi further divide into smaller branches called bronchioles. These then supply the alveoli with air

Question 29

How are alveoli adapted for good gas exchange

Answer 29

Many alveoli so Large surface area
Rich blood supply so maintains a large concentration gradient
Alveolar squamous epithelium is one cell thick so thin diffusion distance

Question 30

Mechanism of breathing when inhaling

Answer 30

External intercostal muscles contract
Pulls the rib cage up and out
Diaphragm contracts and pulls down
Volume increases
Pressure in lungs is LOWER than atmospheric pressure
Air moves into the lungs DOWN a pressure gradient

Question 31

Mechanism of breathing when exhaling

Answer 31

Internal intercostal muscles contract
Diaphragm relaxes and moves up
Volume decreases
Pressure increases
Air movies out of the lungs down a pressure gradient

Question 32

How does the oxygen get into the red blood cells

Answer 32

Oxygen passes through the squamous epithelial cell of alveoli
Then through the endothelial cell of the capillary
And then combines with red blood cell