Gas exchange

Question 1

How does gas exchange in small organisms work by just diffusing directly? (3)

Answer 1

• Diffusion distances from outside to innermost areas are very small
• Surface area to volume ratio is large
• Metabolic demands are low - organisms don’t regular their own temperature and cells do not use much oxygen and food or produce much CO2

Question 2

What factors affect rate of diffusion? (3)

Answer 2

• surface area: the bigger the surface area the more particles can be exchanged at the same time
• concentration gradient of particles diffusing
• distance over which diffusion is taking place

Question 3

What features make gas exchange systems effective? (5)

Answer 3

• large SA giving sufficient gas exchange to supply all needs of organism
• thin layers to minimise diffusion distance
• in animals, a rich blood supply - it’s involved in transport of respiratory gases to and from the site, helping to maintain steep concentration gradient.
• permeable surfaces that allow free passage of respiratory gases
• moist surfaces as diffusion takes place with gases in solution

Question 4

How does the rich blood supply help in the nasal cavity?

Answer 4

It raises the temperature of the air if needs be

Question 5

What is the epiglottis?

Answer 5

Flap of tissue that closes over the glottis in a reflex action when food is swallowed, preventing food from entering gas exchange system

Question 6

What is the trachea?

Answer 6

Major airway to bronchi, lined with cells. Cilia on the surface move mucus and microorganisms and dust away.

Question 7

What is the function of the incomplete rings of cartilage?

Answer 7

Prevents trachea and bronchi from collapsing but allows food to be swallowed and moved down the oesophagus.

Question 8

What do the pleural membranes do?

Answer 8

Surround the lungs and line the chest cavity.

Question 9

What is the pleural cavity?

Answer 9

Space between pleural membranes usually filled with thin layer of lubricating fluid allowing membranes to slide easily with breathing movements.

Question 10

What is the diaphragm?

Answer 10

Broad sheet of tissue forming the floor of the chest cavity, also important in breathing movements.

Question 11

What is an alveolus made of?

Answer 11

Single layer of flattened squamous epithelial cells.

Question 12

What is between the alveoli and capillaries and what does it do?

Answer 12

Elastic connective tissue holding everything together, helps to force air out of the lungs when you breathe in.

Question 13

What stops alveoli from collapsing?

Answer 13

Lung surfactant that coats the alveoli’s inner surface

Question 14

What is inside the alveolus and why?

Answer 14

Macrophage to engulf bacteria, keeping it free of bacteria.

Question 15

What happens in inhalation?

Answer 15

Muscles around diaphragm contract so it’s lowered and flattened.
Intercostal muscles contract, raising the rib cage upwards and outwards.
Volume of chest cavity increases, decreasing pressure to lower than pressure of atmospheric air outside.
Air moves in through the trachea into the lungs down a pressure gradient.

Question 16

What happens in normal exhalation?

Answer 16

Muscles surrounding diaphragm relax so it moves up into domed shape. Intercostal muscles relax so ribs move down and in, and elastic fibres around alveoli of lungs return to normal length.
Volume of chest cavity decrease, increasing pressure to higher than of outside air, so air moves out of the lungs.

Question 17

What happens in forced exhalation?

Answer 17

Internal intercostal muscles contract, pulling ribs down and in, and abdominal muscles contract forcing diaphragm upwards, increasing pressure in chest cavity, causing exhalation.

Question 18

How does the body protect when you’re breathing in pathogens?

Answer 18

Respiratory system produces mucus lining your airways that traps these particles. It’s moved up by cilia and most of it is swallowed, and the acid in your stomach and digestive enzymes digest the mucus.

Question 19

Where are spiracles found and what do they do/have?

Answer 19

Found along thorax and abdomen. Site of entry and exit of respiratory gases. They can sometimes be closed by sphincters which controls water loss.

Question 20

What are tracheae in insects and what is the structure like?

Answer 20

Large tubes carrying air directly into body for gas exchange with cells. Supported by chitin spirals, which hold the tracheae open.

Question 21

Why doesn’t much gas exchange happen in the tracheae of insects?

Answer 21

Chitin makes the tracheae relatively impermeable to gases.

Question 22

What are tracheoles like, and where are they?

Answer 22

Single elongated cells with no chitin lining, so permeable to gases. Spread throughout tissues of insect.

Question 23

Why do tracheoles contain water at the end of their length and when don’t they? How come?

Answer 23

To limit penetration of gases for diffusion.
Lactic acid builds up when very active, affecting osmotic concentration of cells so after moves out to expose additional surface area.

Question 24

How do the insects know to open or close the sphincters?

Answer 24

Respiratory centres are stimulated by increasing CO2 levels and by lactic acid building up in active tissues when there’s no oxygen.

Question 25

How do very active insects meet the high energy demands? (2 ways)

Answer 25

• Mechanical ventilation: air is actively pumped into trachea. Spiracles open and insect makes muscular pumping movements of the thorax/abdomen, changing the volume and pressure in body, drawing air in and out
• Collapsible tracheae/air sacs: increase volume of air moved through respiratory system. General body movements or ventilating movement inflate and deflate them.

Question 26

Where’s the main site for gas exchange in fish? Name two features

Answer 26

Gill lamellae. Rich blood supply and give filaments the large SA.

Question 27

How does not having an operculum affect the lifestyle of a fish?

Answer 27

It means they need to swim all the time to keep water flowing through mouths and out over gills

Question 28

What is a countercurrent exchange system?

Answer 28

System where two fluid components flow in opposite directions and some properties are exchanged between two fluids.

Question 29

How do stomata open and close?

Answer 29

When turgor in guard cells is low, asymmetric thickening of cellulose on cell walls closes the pore. When conditions are favourable for photosynthesis and it needs CO2, potassium ions are actively transported into guard cells, so water moves into guard ells from surrounding epidermal cells by osmosis and guard cells swell so turgor pressure increases, opening the pores.

Question 30

What are lenticels, what do they do and why are they needed?

Answer 30

Spongy areas in thickened stems. They are made of loosely arranged cells with many air spaces, linking inner tissues of trunk with outside world so gas exchange can take place. Needed because the thickened cork and bark are impermeable but the tissues underneath still need oxygen and need to remove CO2