Exchange

Question 1

In large mammals, why is the volume of oxygen absorbed high and the volume of carbon dioxide removed large?

Answer 1

1. They are relatively large organisms with a large volume of living cells
2. They maintain a high body temperature which is related to them having high metabolic and respiratory rates.

Question 2

why are lungs located inside the body?

Answer 2

1. Air is not dense enough to protect these delicate structures.
2. The body as a whole would lose a great deal of water and dry out

Question 3

why does the trachea not collapse as the air pressure falls when breathing in?

Answer 3

The rings of cartilage support the trachea making it a flexible airway.

Question 4

what are bronchi?

Answer 4

They are the two sub-divisions of the trachea each leading to one lung

Question 5

What is the role of bronchi?

Answer 5

They produce mucus to trap dirt particles in the cillia that move the dirt laden mucus up the throat

Question 6

What does the muscle in walls of the bronchioles allow?

Answer 6

The bronchioles can constrict and so they can control the air in and out of the alveoli

Question 7

Between the alveoli, there is collagen and elastic fibre and the alveoli is lined with epithelium. What do the elastic fibres do?

Answer 7

They stretch as they fill with the air when breathing in. They spring out when breathing out to expel carbon dioxide and they fill the air when breathing in. This is because it is the mammals GAS EXCHANGE SURFACE

Question 8

what is ventilation?

Answer 8

Air is constantly circulated
e.g. to maintain the diffusion of gases across the alveolar epithelium, air is constantly moved in and out of the lungs.

Question 9

Inspiration ? ( only under strenuous conditions)

Answer 9

Active process
ANTAGONISTIC INTERACTION - External intercostal muscles contract and internal relax
Ribs pulled upwards and outwards, increasing the volume of the thorax
This results in reduction of pressure in lungs
Atmospheric pressure is greater than pulmonary therefore air is forced into the lungs

Question 10

Expiration ? ( only under strenuous conditions)

Answer 10

Passive process
Internal intercostal muscles contract and external relax
Ribs pulled downwards and inwards, decreasing the volume of the thorax
This results in increase of pressure in lungs
Atmospheric pressure is lower than pulmonary therefore air is forced out the lungs

Question 11

How does normal breathing occur?

Answer 11

Recoil of elastic tissue in the lungs is the main reason for air being forced out of the lungs.

Question 12

What is pulmonary ventilation rate?

Answer 12

The total volume of air that moves out of the lungs in a minute.
PVR= TV x BR
Tidal volume = volume of air normally taken in at each breath at rest
Breathing (ventilation) rate = number of breaths taken in a minute

Question 13

How do you maintain a constant diffusion gradient

Answer 13

There has to be movement of both environmental medium ( e.g air) and internal medium (e.g blood)

Question 14

Adaptations of alveolus?

Answer 14

1. constant supply of oxygen - diffusion gradient
2. Exchange surfaces are partially permeable - gases can move
3. thin - diffusion distance -(THEY HAVE TO BE LOCATED INSIDE FOR PROTECTION)

Question 15

DIFFUSION PATHWAY OF ALVEOLI?

Answer 15

red blood cells are slowed as they enter pulmonary capillaries
the distance between the alveolar air and rbc is reduced as rbc are flattened as they enter the capillary.
The walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very small
alveoli and pulmonary capillaries have a large total surface area
Breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these can ensure that a steep conc gradient of gases to be exchanged is maintained
Blood flow through the pulmonary capillaries maintains conc gradient

Question 16

Describe the difference in the composition of gases inhaled and exhaled in air. Explain how these differences are caused.

Answer 16

1. Inhaled air contains more oxygen than exhaled air.
2. Inhaled air contains less water vapour.
3. Relative amount or percentage of nitrogen also changes
4. Oxygen enter blood and carbon dioxide leaves the blood in the alveoli .
5. Water vapour diffuses from a moist surface

Question 17

Monocotyledenous and di

Answer 17

Plant embryo that will have one / two embryonic leaf/ leaves

Question 18

Gas exchange in plants

Answer 18

Types of gases exchanged vary depending on the rate of the plant’s respiration or photosynthesis.
- small organism

Question 19

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (5)

Answer 19

1 Many alveoli / alveoli walls folded provide a large surface area;
2 Many capillaries provide a large surface area;
3 (So) fast diffusion;
4 Alveoli or capillary walls / epithelium / lining are thin / short distance between alveoli and blood;
5 Flattened / squamous epithelium;
6 (So) short diffusion distance / pathway;
7 (So) fast diffusion;

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 lamellae/filaments;
Q Candidates are required to refer to lamellae or filaments. Do not penalise for confusion between two

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;
5 Not enough to say gives steep concentration gradient

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);
6-8 Accept answers relating to carbon dioxide

Question 21

Describe how the structure of xylem is related to its function.

Answer 21

Vessels;
Have no end walls / hollow / no cytoplasm; Allows unrestricted flow of water. Lignification;
Provides support / strength / impermeability; Pits allow lateral transport;
Tracheids with porous end walls.

Question 22

Describe a method you could use to find the surface area of a leaf.

Answer 22

Either
1. Draw around leaf on graph paper;
Mark as a trio − MP1, MP2 and MP3 OR MP4, MP5 and MP6. Do not mix and match.
Both aspects needed for mark − drawing and type of paper.

2. Count squares (however described);
   There is no reward for additional detail e.g. dealing with part squares.
3. Multiply by 2 (for upper and lower leaf surface); OR
4. Draw around a leaf on paper of known mass (per unit area);
   Both aspects needed for mark − drawing and mass of paper.
5. Cut out and weigh;
6. Multiply by 2 (for upper and lower leaf surface).