3.1.1 exchange surfaces

Question 1

What are the features of efficient exchange surfaces?

Answer 1

-Increased surface area: provides area needed for exchange and overcomes limitations of SA:V in larger organisms (root hair cells).
-Thin layers: distances that substances have to diffuse are short (alveoli).
-Good blood supply: steeper the concentration gradient, the faster diffusion happens (alveoli and capillaries).
-Ventilation to maintain gradient: (gills).

Question 2

Why is there a need for specialised exchange surfaces?

Answer 2

-The metabolic activity of a single-celled organism is usually low, so the oxygen demands and carbon dioxide production of the cell is relatively slow compared to larger organisms in which a simple system would not meet the metabolic demands.
Smaller organisms also have a higher SA:V ratio and larger organisms have a smaller SA:V ratio and so diffusion would happen at a much slower rate.

Question 3

What is the structure and function of the Trachea?

Answer 3

Structure:
-incomplete rings of cartilage=>stop the trachea from collapsing.
-lined with ciliated epithelium with goblet cells=>trap any harmful bacteria, direct away from the lungs.

Question 4

What is the structure of the Bronchi?

Answer 4

-Similar structure to Trachea, with the same supporting rings of cartilage but smaller.
-Two each branching off the Trachea.

Question 5

What is the structure and function of the Bronchioles?

Answer 5

Structure:
-diameter of 1mm or less.
-no cartilage rings.
-wall of bronchioles contain smooth muscle=>when smooth muscle contracts, the bronchioles restrict (changes the amount of air going to the lungs).
-lined with thin layer of flattened epithelium=>makes gas exchange possible.

Question 6

What is the structure of Alveoli?

Answer 6

-Tiny air sacs.
-Diameter of around 200-300 micrometres.
-Consists of a layer of thin flattened epithelial cells, with some collagen and elastic fibres=>elastic tissue allows alveoli to stretch and return to original shape (elastic recoil).

Question 7

What are the main adaptations of Alveoli

Answer 7

-Large surface area.
-Thin layers- only a single epithelial cell thick so distance between capillaries and alveoli is very small.
-Good blood supply: network of around 280 capillaries.
-Good ventilation.

Question 8

What is the mechanism of inspiration in mammals?

Answer 8

-Diaphragm contracts, flattening, and lowers.
-External intercostal muscles contract, moving the ribs upwards and out.
-Volume of thorax increases so pressure is decreased.

Question 9

What is the mechanism for expiration in mammals?

Answer 9

-Diaphragm relaxes, moves up.
-External intercostal muscles relax, ribs move down and inwards.
-Increase in thorax pressure, thorax volume is decreased.

Question 10

What is Tidal volume?

Answer 10

Tidal volume is the volume of air that moves into and out of the lungs with each resting breath.

Question 11

What is Vital capacity?

Answer 11

Vital capacity is the volume of air that can be exhaled when the deepest possible intake of breath is followed by the deepest possible exhalation.

Question 12

What is Inspiratory reserve volume?

Answer 12

Inspiratory reverse volume is the maximum volume of air that you can breathe in over and above a normal inhalation.

Question 13

What is Expiratory reserve volume?

Answer 13

Expiratory reserve volume is the extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe out.

Question 14

What is residual volume?

Answer 14

Residual volume is the volume of air that is left in your lungs when you have exhaled as hard as possible.

Question 15

How can lung capacity be measured with a spirometer?

Answer 15

Person exhales as hard as possible into spirometer with a nose clip on.
Soda lime absorbs carbon dioxide from exhaled air=>stops the concentration of CO2 in the re-breathed air from getting too high (respiratory distress).
A trace is drawn.

Question 16

What is total lung capacity?

Answer 16

Total lung capacity is the sum of the vital capacity and the residual volume.

Question 17

What is the equation for ventilation rate?

Answer 17

Ventilation rate= tidal volume x breathing rate (per minute).

Question 18

Why does ‘normal’ gas exchange not happen in insects?

Answer 18

They have a tough exoskeleton-used for protection.

Question 19

What are the three parts of an insect?

Answer 19

-Head
-Thorax
-Abdomen

Question 20

What is the pathway of an insect’s gas exchange system?

Answer 20

-Spiracles
-Tracheae
-Tracheoles
-Muscle

Question 21

What are Spiracles?

Answer 21

Little circular openings on the abdomen for gas exchange.

Question 22

What do larger insects also have in their gas exchange system?

Answer 22

Air sacs.

Question 23

How are Tracheal tubes held open?

Answer 23

Tracheal tubes are held open because they are lined with spirals of chitin.

Question 24

What is the structure of a Tracheole?

Answer 24

A tracheole is a single elongated cell with no chitin lining so that they are freely permeable to gases.

Question 25

What does Tracheal fluid do?

Answer 25

Tracheal fluid limits the penetration of air for diffusion.

Question 26

What is meant by mechanical ventilation of the tracheal system?

Answer 26

Air is actively pumped into the system by muscular pumping movements of the thorax and/or the abdomen.
These movements change the volume of the body and this changes the pressure in the tracheae and tracheoles.

Question 27

How do collapsible enlarged tracheae or air sacs increase the level of gaseous exchange in insects?

Answer 27

Act as air reservoirs, used to increase the amount of air moved through the gas exchange system.

Question 28

What is the structure of gills in fish?

Answer 28

Gill lamellae: rich blood supply and large surface area (lots of them).
Gill filaments: occur in large stacks (gill plates) and need a flow of water to keep them apart, exposing the large surface area needed for gaseous exchange.
Gill arch: support structure of the gill.
Blood vessels: carry blood leaving the gills in the opposite direction to incoming water, creating a steep concentration gradient.

Question 29

What is the mechanism for blood flow in fish (gaseous exchange)?

Answer 29

The capillary system within the lamellae ensures that blood flow is in the opposite direction to the flow of water-countercurrent flow.
The countercurrent floe ensure the concentration gradient is maintained along the whole length of the capillary.
The water with the lowest oxygen concentration is found adjacent to the de-oxygenated blood.

Question 30

What are the adaptations of gills?

Answer 30

-The tips of adjacent gill filaments overlap=>increases the resistance to the flow of water over the gill surfaces and slows down the movement of the water, move time for gaseous exchange.
-The water moving over the gills and the blood flow in different directions=>ensures that steeper concentration gradients are maintained, more gaseous exchange can happen.

Question 31

What is the ventilation mechanism for fish?

Answer 31

-When fish open their mouth they lower the floor of the buccal cavity, causes the volume inside the buccal cavity to increase which causes a decrease in pressure within the cavity.
-The pressure is higher outside the mouth of the fish and so water flows into the buccal cavity.
-The fish then rises the floor of the buccal cavity to close its mouth, increasing the pressure within the buccal cavity.
-Water flows from the buccal cavity(high pressure) into the gill cavity(low pressure).
-As water enters pressure begins to build up in the gill cavity and causes the operculum to be forced open and water to exit the fish.
-The operculum is pulled shut when the floor of the buccal cavity is lowered at the start of the next cycle.