Gas Exchange

Question 1

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

Answer 1

1. Tracheoles have thin walls so short diffusion distance to cells;
2. large number of tracheoles so short diffusion distance to cells;
3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
   4.Tracheae provide tubes full of air so fast diffusion (into insect tissues);
4. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
5. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;

Question 2

How does oxygen move through the insect?

Answer 2

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 3

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

Answer 3

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

Question 4

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

Answer 4

1 Large surface area provided by many lamellae over many gill filaments;
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 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs (4)

Answer 8

Trachea bronchi and bronchioles
Down pressure gradient
Down the diffusion gradient
Across alveolar epithelium

Question 9

Explain 1 features of how an alveolus
Allows efficient gas exchange to occur (2)

Answer 9

Alveolus epithelium is 1 cell thick creating shirt diffusion distance

Question 10

Describe the pathways taken by an oxygen molecule from an alveolus to the blood (2)

Answer 10

Across alveolar epithelium
Endothelium of capillary
(Correct order fir 2 marks )

Question 11

Explain how uptake of oxygen is a measure of the metabolic rate in organisms

Answer 11

Oxygen used in respiration which is a metabolic reaction

Question 12

Adaptation of xerophytic plants (4)

Answer 12

1.Reduced number of stomata so less surfaces are for water loss
2.Stomata in pits reduce concentration gradient
3.Thick waxy cuticles increase diffusion distance
4.Leaves reduced to spines less surface area for water loss

Question 13

Adaptations of leaf for gaseous exchange (2)

Answer 13

Flat - large surface area to volume ration
Many stomata pores allows air to move in and out of the leaf
Air spaces in leaf so short diffusion distance

Question 14

Adaptation of inspects that help limit water loss (1)

Answer 14

Waterproof covering - smaller surface area to volume ration to minimise area over which water can be lost

Question 15

1 way in which student could ensure first 3 bettors are kept at 25•C throught out the experiment

Answer 15

Check the temp at regular intervals

Question 16

Describe adaptation of lead that allow efficient gas exchange (3)

Answer 16

Thin and flat to produce short diffusion distance and large s.a. To vol. ratio
Air spaces in mesophyll allows gases to move around lead - short d.d.
Many stomata - pores to allows gasses to move in and out

Question 17

What is tidal volume

Answer 17

Natural breathing volume (at rest)

Question 18

What is inspiratory/expiratory reserve

Answer 18

Extra volume required for a deep breath

Question 19

What is vital capacity

Answer 19

Maximum volume of air a person can expel from the lungs

Question 20

Breathing out as hard as you can is called expiration
Describe and explain the mechanism that causes forced expiration (4)

Answer 20

a) 1. Contraction of internal intercostal muscles;
2. Relaxation of diaphragm muscles OR Relaxation of external intercostal muscles;
3. Causes decrease in volume of chest / thoracic cavity;
4. Air pushed down pressure gradient.

Question 21

Describe a method student could have used to monitor the temp of the water in each tube

Answer 21

(Take) readings (during the experiment) using a (digital) thermometer / temperature sensor;

Question 22

How to calc percentage increase

Answer 22

Final - initial / initial x 100

Question 23

explain why plant that live in a desert have sunken stomata or stomata surrounded by hair 2

Answer 23

help trap moisture
reduce concentration gradient from leaf to air which reduces water loss

Question 24

explain 2 ways in which lungs are specialised for efficient gas exchange 2

Answer 24

many alveoli so large surface area
alveoli epithelium is one cell thick so short diffusion distance
alveoli surrounded by many capillaries so maintains steep conc of O2 and CO2 between alveoli and blood

Question 25

what is tidal volume

Answer 25

The volume of air inspired per breath when at rest is the tidal volume

Question 26

what is the breathing rate
also known as ?

Answer 26

the number of breaths taken per minute
aka ventilation rate

Question 27

what is vital capacity

Answer 27

VC maximum number of air it is possible to breathe forcefully out of the lungs after a deep breath in

Question 28

Calculating the Pulmonary Ventilation Rate

Answer 28

PVR = tidal volume (dm) x breathing rate

Question 29

what is residual volume,

Answer 29

e residual volume, this is the volume of air left in the lungs after as much air has been breathed out as possible.

Question 30

An individual’s pulmonary ventilation rate at rest was found to be 7.4 dm3 min-1. They took 12 breaths in one minute. Calculate their tidal volume.

Answer 30

tidal volume = 7.4 ÷ 12 = 0.6166

Tidal volume = 0.62 dm3

Question 31

name a lung disease and describe or explain its symptoms

Answer 31

pulmonary tuberculosis TB
coughing up blood and mucus shortness of breath
gasseous exchange surface damage so reduce tidal volume so less air can be inhaled in each breath so to make up required oxygen have to breath faster (increasing ventilation rate)

Question 32

Small physical exertion such as walking 100 yards becomes difficult with fibrosis because

Answer 32

Less CO2 is removed and less O2 is inhaled/taken in/absorbed; [1 mark]
So there is less aerobic respiration; [1 mark]
So there is less ATP produced which is required for muscle contraction/muscle fatigue develops sooner; [1 mark]
[Total: 3 marks]

Question 33

if graph showing a correlation why cant we say one variable caused the other
eg smoking decreased mortality due to lung cancer decreased

Answer 33

correlation not mean causation
as other variable causing the trend
smokign decrease
rate mortality for cancer decrease
however the rate of cases lung cancer may have increased but due to medical advances more people surviving (so less death due to lung cancer)

Question 34

if graph gives us risk factors for a disease against mortality rates and asks us to describe (2/3) and conclude (1) what general things to keep in mind

Answer 34

describe state when starts to increase and when decreasing the peak points with vlues from graph and say risk factor and mortality follow same pattern
conclude: correlation/link between risk factor and mortality rate NOT CAUSE