3.1.1 - Exchange Surfaces

Question 1

How does an organism’s surface area to volume ratio change as their size changes?

Answer 1

The larger the organism’s size the smaller its surface area to volume ratio

Question 2

How does the rate of diffusion change as the surface area to volume ratio changes?

Answer 2

The rate of diffusion into and out of an organism increases with surface area to volume ratio

Question 3

Why do small organisms not need exchange systems?

Answer 3

The surface area to volume ratio is very large and there is a shorter distance from the outside of the organism to the middle so simple diffusion is adequate for substance exchange

Question 4

Why do larger organisms need exchange systems?

Answer 4

They have a higher metabolic rate, smaller surface area to volume ratio and there is a longer distance from the outside of the organism to the middle of it so they require adaptations to increase the efficiency of exchange across their surface

Question 5

Which 3 structural factors affect the rate of diffusion?

Answer 5

• Surface area
• Concentration gradient
• Length of diffusion pathway

Question 6

What are the 3 features of an efficient exchange surface?

Answer 6

• Increased surface area - root hair cells in plants have protrusions to absorb water and the lungs have numerous alveoli that allow oxygen to diffuse across the surface rapidly
• Thin layer - alveoli walls and capillary walls are only one cell thick to provide a short diffusion pathway
• Maintain a good concentration gradient - rich blood supply and ventilation in the gills and alveoli

Question 7

What is the structure of the human gas exchange system?

Answer 7

Air is drawn into the lungs through the trachea. The trachea divides into 2 bronchi which further divide into bronchioles until they terminate in millions of alveoli

Question 8

What is the structure of the trachea?

Answer 8

• Supported by C shaped cartilage to keep it open
• Lined with ciliated epithelial cells and goblet cells which produce mucus and move it up the trachea until it can be swallowed
• Smooth muscle within the walls which contracts if there are harmful substances detected in the air. This results in the lumen of the trachea constricting and reducing airflow into the lungs. When the smooth muscle relaxes the lumen dilates which is possible due to the elastic fibres within the tracheal wall

Question 9

What is the structure of the bronchi and bronchioles?

Answer 9

• Both have cartilage within their walls for structural support and to keep the tubes open
• Both have smooth muscle and elastic tissue

Question 10

What is the structure of the alveoli?

Question 11

What is ventilation?

Answer 11

The mechanism of breathing which involves the diaphragm and antagonistic interactions between the external and internal intercostal muscles bringing about pressure changes in the thoracic cavity.

Question 12

What happens during the process of inspiration?

Answer 12

• Air moves into the lungs
• Diaphragm contracts and flattens
• External intercostal muscles contract moving ribs up
• Volume of lungs increases
• Thorax volume increases and thoracic pressure decreases

Question 13

What happens during the process of expiration?

Answer 13

• Air moves out of the lungs
• Diaphragm relaxes and moves up
• External intercostal muscles relax moving ribs down and when exercising internal intercostal muscles contract
• Volume of lungs decreases
• Thorax volume decreases and thoracic pressure increases

Question 14

What does a spirometer do?

Answer 14

Measure the volume and function of the lungs and oxygen uptake

Question 15

How does a spirometer work?

Answer 15

• Inhalation and exhalation move the lid of the spirometer which is recorded by the datalogger
• Carbon dioxide from exhaled air is absorbed by soda lime so that the volume of oxygen used can be measured

Question 16

What is tidal volume?

Answer 16

Normal volume of air displaced by the lungs at rest per breath (dm³)

Question 17

What is breathing rate?

Answer 17

The number of breaths taken per minute (breaths per minute)

Question 18

What is vital capacity?

Answer 18

Maximum volume of air that can be exhaled after a maximum inhalation (dm³)

Question 19

What is residual volume?

Answer 19

The volume of air remaining in the lungs after maximum exhalation

Question 20

What is the formula for ventilation rate?

Answer 20

Ventilation rate = tidal volume x breathing rate

Question 21

How does ventilation occur in fish?

Answer 21

• The fish opens its mouth, lowering the floor and increasing the volume of the buccal cavity
• This lowers the pressure inside the buccal cavity which forces water into it
• The operculum is shut
• The fish closes its mouth reducing the volume in the buccal cavity
• Pressure inside the buccal cavity increases forcing the water across the gill filaments
• The operculum opens and the water flows out of the gills

Question 22

What are the adaptations of the gills?

Answer 22

• Large surface area as there are many gill filaments and lamellae which are stacked at right angles to each other
• Short diffusion distance as the gill lamellae and filaments are both thin and contain a capillary network
• Maintain concentration gradient due to countercurrent mechanism

Question 23

What is the countercurrent principle?

Answer 23

Blood in the capillaries flows in the opposite direction to the water flowing over them so the oxygen concentration in the water is always higher than the oxygen concentration in the blood along the whole gill. This maximises the gas exchange compared with a parallel system as it maintains a concentration gradient for the whole length of the gill lamellae.

Question 24

How does ventilation occur in insects?

Answer 24

• Many insects have spiracles along their thorax and abdomen
• They use the movement of the thorax and abdomen to change body volume and move air in and out
• They contract and relax their abdominal muscles to move gases on mass into and out of the spiracles to the trachea
• When the insect is in flight the muscle cells start to respire anaerobically to produce lactate. This lowers the water potential of the cells and therefore water moves from the tracheoles (tracheal fluid) into the cells by osmosis. This decreases the volume of liquid in the tracheoles and causes more air from the atmosphere to move in

Question 25

What are the tracheoles lined with?

Answer 25

Tracheal fluid

Question 26

How does gas exchange occur in insects?

Answer 26

Oxygen and carbon dioxide dissolve in the tracheal fluid and diffuse through the thin walls of the tracheoles and into the body cells

Question 27

What are the adaptations of the gas exchange system in insects?

Answer 27

• Large surface areas as many branching tracheoles
• Short diffusion distance as many branching tracheoles reach muscle and thin walled tracheoles
• Maintain a concentration gradient as when the cells respire they use up oxygen and produce carbon dioxide and abdominal muscles contract to pump air