3.1 Exchange Surfaces

Question 1

What are the features of an efficient exchange surface?

Answer 1

Large surface area to provide more space for molecules to pass through - e.g root hairs in plants

Thin barrier to reduce diffusion distance - e.g alveoli in lungs

Good blood supply to maintain steep concentration gradient so diffusion can occur rapidly - e.g gills in fish

Question 2

Why is ventilation important?

Answer 2

It ensures that the concentration of the oxygen in the air of the alveolus remains higher than that in the blood

The concentration of carbon dioxide in the alveoli remains lower than that in the blood

Maintaining a steep concentration gradient necessary for efficient diffusion

Question 3

What is the process of inspiration?

Answer 3

The diaphragm contracts to move downwards and flatten

The intercostal muscles contract to raise the ribs

The volume of the thorax increases and pressure drops below atmospheric pressure

Air is moved into the lungs

(Alveolus contains elastic fibres that stretch during inspiration and recoil to help push air out during expiration)

Question 4

What is the process of expiration?

Answer 4

The diaphragm relaxed and moves upwards

The intercostal muscles relax and the ribs fall - can contract to push air out more forcefully (sneezing, coughing)

The volume of thorax decreases and is above atmospheric pressure

Air is moved out of lungs

Question 5

What are the functions of the mammalian lung features?

Answer 5

Large surface area to provide more space for molecules to pass through

Thin barrier to exchange which is permeable to oxygen and carbon dioxide - one cell thick, capillary is close to alveolus walls, squamous cells

Good blood supply to maintain steep concentration gradient

Question 6

How are the trachea and bronchi adapted to be effective?

Answer 6

Allow the passage of air into the lungs and out again

Lined by ciliated epithelium - goblet cells secrete mucus which traps pathogens and cilia move mucus to the top of he airway where it is swallowed

Supported by rings of cartilage - prevents collapse during inspiration

C shaped cartilage - flexibility and space for food to pass down oesophagus

Question 7

What is the structure of bronchioles?

Answer 7

The bronchioles are much narrower than bronchi

Larger ones may have cartilage but smaller ones don’t

Wall is comprised mostly of smooth muscle and elastic fibres

Question 8

What is the function of smooth muscle and elastic tissue?

Answer 8

Smooth muscle can connect to constrict the airway making the lumen narrower - restricts flow of air to and from alveoli

• controlling movement of air - harmful substances in air?
• involuntary action - allergic reaction?

Smooth muscle is elongated again by elastic fibres - as muscle contracts, it deforms elastic fibres/as muscle relaxes, they recoil back to shape

…….acts to dilate the airway

Question 9

What is a spirometer?

Answer 9

A device that measures the movement of air in and out of the lungs as a person breathes

Question 10

What is a float-chamber spirometer?

Answer 10

Consists of a chamber of air or medical grade oxygen floating on a tank of water

During inspiration, air is drawn from the chamber so the lid moves down

During expiration, air returns to the chamber so the lid raises up

These movements are recorded on a data logger

Question 11

What allows the measure of oxygen consumption?

Answer 11

The carbon dioxide rich air exhaled is passed through a chamber of soda lime which absorbs carbon dioxide

Question 12

What are the precautions that should be taken when using a spirometer?

Answer 12

The subject should be healthy and free from asthma

Soda lime should be fresh and functioning

No air leaks in the apparatus

Mouthpiece should be sterilised

Water chamber must not be overfilled or water may enter air tubes

Question 13

What is vital capacity?

Answer 13

The greatest volume of air that can be moved by lungs in one breath - measured by taking a deep breath and exhaling all e air possible from lungs

Vital capacity depends on a number of factors:

• age and gender
• size of person
• level of regular exercise

Usually in range of 2.5 - 5 dm3

Question 14

What is the residual volume?

Answer 14

Volume of air that remains in lungs even after forced expiration that remains in airways and alveoli - usually 1.5 dm3

Question 15

What is the tidal volume?

Answer 15

The volume of air moved in and out with each breath - at rest approx. 1.5 dm3

Question 16

What is oxygen uptake?

Answer 16

The volume of oxygen absorbed by the lungs in one minute

As oxygen is taken in, carbon dioxide is released and absorbed by soda lime in the spirometer so volume in air chamber decreases

Decrease can be observed and measured in spirometer trace

Assume - volume of carbon dioxide released equals to volume of oxygen absorbed

Question 17

What are the factors that oxygen uptake depends on?

Answer 17

Breathing rate

Deeper breaths

Question 18

How can breathing rate be measured?

Answer 18

By counting the number of peaks in each minute

Question 19

Why do fish have gills?

Answer 19

To absorb oxygen and release carbon dioxide into water

Each gill consists of two rows of gill filaments (primary lamellae) attached to bony arch

Filaments are very thin and folded into many secondary lamellae (or gill plates)

This provides a very large surface area - blood capillaries carry deoxygenated blood to the surface of the secondary lamellae where exchange takes place

Question 20

What is countercurrent flow?

Answer 20

Blood flows along the gill arch and out along the secondary lamellae (gill plates)

Blood then flows through capillaries in opposite direction to flow of water over the lamellae - countercurrent flow absorbs maximum oxygen from water

Question 21

How do bony fish ventilate?

Answer 21

The buccal cavity (mouth) opens and water moves in

Mouth closes and water is pushed through gills

Movements of operculum (flap that covers gills) coordinated with mouth - water pushed from mouth, operculum moves outwards

Reducing pressure in opercular cavity (space under operculum) helping water flow through gills

Question 22

How do insects transport oxygen?

Answer 22

Insects have open circulatory system where blood and tissue fluid both act as bodily fluid

Insects posses tracheal system which supplies air directly to all respiring tissues

Air enters via a pore in each segment called the spiracle and transported through a series of tubes called trachae which divide into smaller tubes called tracheoles

Ends of tracheoles are open and filled with tracheal fluid - gaseous exchange occurs between the air in the tracheole and the tracheal fluid

Question 23

What happens when insects are very active?

Answer 23

Demand more oxygen

Tracheal fluid can be withdrawn into the body fluid to increase surface area of tracheole wall exposed to air - more oxygen can be absorbed

Question 24

How do insects ventilate?

Answer 24

Sections of tracheal system are expanded and have flexible walls which act as air sacs and can be squeezed by the action of flight muscles - repetitive expansion and contraction ventilate the tracheal system

Movements of wings alter volume of thorax

Locusts can alter volume of abdomen - as abdomen expands (contract), spiracles at the front (rear) end of the body open and air enters (leave) tracheal system

Question 25

Why do we need specialised exchange surfaces?

Answer 25

In small organisms, diffusion will supply enough oxygen and nutrients to keep the cells alive and active but multicellular organisms are too large and diffusion is too slow

Multicellular organisms have small SA:V

Metabolic activity - the more energy required, the more the demand for oxygen