Chapter 7 Exchange surfaces and Breathing

Question 1

For amoeba (single celled organism), transporting materials into and out of the cell happens via simple diffusion. Why do larger organisms require adaptions to increase efficiency of exchange?

Answer 1

Single celled organisms have:
> A large surface area : volume - This means they have a large surface area to diffuse by to fill up a relatively smaller space.
> Lower metabolic activity - They have a lower metabolic demand for things like glucose, oxygen and water, because they have less complex systems.
> Short diffusion distance - Distance by which substances diffuse from outside of the cell to the centre inside, is small, which gives a higher diffusion rate.

Question 2

What are the features of specialised exchange surfaces?

Answer 2

> Increased surface area - Overcoming the limitations of low SA:V in larger organisms (villi in small intestine, root hair cells).
Thin layers - Thin layer; short diffusion distance; faster diffusion rate.
Good blood supply - Ensures substances are constantly diffused from blood to exchange surface; maintains a steep concentration gradient for diffusion.
Ventilation to maintain diffusion gradient- A good ventilation system means there is a constant supply of oxygen in, and constant remove of carbon dioxide to maintain concentration gradients.

Question 3

Describe the movement of air (to alveoli) in the human gas exchange system.

Answer 3

> Nose
Nasal cavity
Trachea
Bronchi
Bronchioles
Alveoli

Question 4

How is the nasal cavity adapted to taking in air?

Answer 4

> The nasal cavity has a large surface area with a good blood supply, which warms the air to body temperature.
It has a hairy lining that secretes mucus to trap dust and bacteria (protecting lung tissue from irritation and infection).

Question 5

How is the trachea in humans adapted to its function?

Answer 5

The trachea carries air from the nasal cavity to bronchi.
> The trachea is supported with C-shaped rings of cartilage, to prevents the trachea from collapsing down on itself. It is C-shaped as it allows for movement of food down the adjacent pipe, the oesophagus.
> The trachea is lined with goblet cells and ciliated epithelium. The goblet cells secretes mucus (made of glycoproteins) which traps any bacteria and pathogens in the trachea, stopping them from reaching the lungs. The cilia then sweeps this mucus back up to be coughed up.
> The tracheal walls are made of smooth muscle. The trachea is able to contract and recoil due to the elastic fibres in trachea wall. The contraction of smooth muscle reduces the size of the lumen in the trachea, possibly to reduce airflow to the lungs in the presence of harmful substances.

Question 6

How are the bronchioles adapted to its function?

Answer 6

The bronchioles carries air from the bronchi to alveoli.
> The bronchioles also contains some smooth muscles in its walls, so when it constricts, it is able to reduce airflow to the lungs.
> The walls of the bronchioles is made up of a thin layer of flattened epithelium, making some gas exchange possible.

Question 7

How are the alveoli adapted to its function?

Answer 7

The alveoli is the site of gas exchange is humans.
> The alveoli has high surface area. Each individual alveoli is very small in size, giving a high SA:V. But with millions of alveoli in the lungs, this increases the surface area greatly, giving a faster diffusion rate.
> Short diffusion distance - Each alveoli has one layer of squamous epithelial cells in its walls.
> Maintained concentration gradient- Each alveoli is surrounded by a network of capillaries, with a good blood supply that is constantly exchanging gases.
> Elastic tissues in the walls of the alveoli allows the alveoli to expand as air is drawn in (and then recoil).

Question 8

Describe the process of inspiration in humans.

Answer 8

> The diaphragm contracts and moves downwards.
External intercostal muscles contract.
Ribcage is pulled upwards and outwards.
The volume of thorax (chest cavity) increases.
The pressure in the thorax drops below atmospheric pressure.
Causes air to flow in the lungs.

Question 9

Describe the process of expiration in humans.

Answer 9

> The diaphragm relaxes.
External intercostal muscles relax.
Internal intercostal muscles can contract, if air is being pushed out forcefully (forceful expiration).
Ribcage is pulled inwards and downwards.
The volume of the thorax decreases.
The pressure in the lungs increases and rises above atmospheric pressure.
Air moves out of the lungs.

Question 10

What is the difference between normal expiration and forcefully exhaling (like during exercise, sneezing or coughing)?

Answer 10

Normal expiration is a passive process, where the internal intercostal muscles do not contract. When someone forcefully exhales, the intercostal muscles contracts which requires energy- it is not passive.

Question 11

Describe how a floating chamber spirometer works.

Answer 11

> A floating chamber spirometer consists of a chamber of air or medical grade oxygen floating on top of a tank of water.
During inspiration, air is drawn from the chamber so the lid moves down.
During expiration, air returns to the chamber, raising the lid.
These movements are recorded by a data logger.

Question 12

What precautions should be taken when using a spirometer?

Answer 12

> The subject should be healthy (free from asthma).
Soda lime should be fresh and functioning.
There should be no air leaks in the apparatus (it can give inaccurate results).
Sterilised mouthpiece.
Water chamber should not be overfilled.

Question 13

What is the purpose of soda lime in a spirometer?

Answer 13

The soda lime is absorbed by carbon dioxide, so the data logger solely gives an indication of oxygen consumption.

Question 14

What is tidal volume?

Answer 14

The air inhaled and exhaled when at rest.

Question 15

What is vital capacity?

Answer 15

A measurement of maximum volume of air an individual can breathe in after strongest possible exhalation.

Question 16

What is inspiratory reserve volume?

Answer 16

The maximum volume of air you can breathe in over and above normal inhalation.

Question 17

What is expiratory reserve volume?

Answer 17

The extra amount of air you can force out of your lungs over and above normal tidal volume of air you breathe out.

Question 18

What is residual volume?

Answer 18

The volume of air that remains in the lungs so they don’t collapse.

Question 19

What is total lung capacity?

Answer 19

This is the sum of vital capacity and residual volume.

Question 20

What is breathing rate?

Answer 20

Number of breaths taken per minute.

Question 21

What is ventilation rate?

Answer 21

This is the volume of air inhaled in one minute. It is calculated by:
Tidal volume x Breathing rate

Question 22

How is oxygen transported in the body of an insect?

Answer 22

In an insect’s body, oxygen is transported via body fluids. These body fluids acts as both blood and tissue fluid.

Question 23

Describe the movement of air through an insect.

Answer 23

Air enters through the spiracles.
The air travels to the trachea.
The air reaches the tracheoles. Near the ends of the tracheoles is where gas exchange occurs, as the end of the tracheoles are found near muscles.

Question 24

What is the function of the spiracles in an insect? How is it adapted to its function?

Answer 24

The spiracles are little holes found on the surface of the body of the insect, and it is where air enters. Gases are able to enter the insect through this, but water can also be lost. To maximise gas exchange and reduce water loss, the spiracles have adaptions where it can open and close, with the help of sphincters. So, when an insect is inactive and has a low demand for oxygen, the sphincters closes the spiracles to reduce water loss.

Question 25

In what places of the ventilation system of an insect is chitin found, and why is it found there?

Answer 25

Spirals of chitin is found in the walls of the trachea in insects, and it’s job is to hold the trachea open if it is bent or pressed. However, chitin is semi-permeable to gases (lets a bit of gas through), which is why it is not found in the tracheoles- it would prevent maximum gas exchange from occurring.

Question 26

In anaerobic respiration, what process leads to the insect in enabling it to take in more air?

Answer 26

> In anaerobic respiration, lactate is produced, which dissolves in cells to make lactic acid.
The production of lactic acid lowers the water potential in cells, so water moves from the tracheoles (tracheal fluid) into surrounding cells by osmosis.
The movement of tracheal fluid from the tracheoles decreases the volume of liquid in tracheoles, leaving space for air from the atmosphere to move in.

Question 27

What is tracheal fluid?

Answer 27

Tracheal fluid is liquid found in the tracheoles. Gaseous exchange occurs between tracheal fluid and air in tracheoles.

Question 28

Larger insects have adapted to getting an extra supply of oxygen in the body. Why may they need to do this?

Answer 28

As they are larger, they have higher metabolic demands for things like oxygen, glucose and water. They may also have more complex systems.

Question 29

What adaptions may larger insects have in order to get an extra supply of oxygen?

Answer 29

> Mechanical ventilation of tracheal system- Air is actively pumped into the system by pumping movements of thorax and/or abdomen.
Collapsible enlarged trachea or air sacs- Tracheoles and air sacs can be inflated or deflated by ventilating movements of thorax or abdomen. It increases the amount of air moving through gas exchange.

Question 30

Describe the structure of the site of gas exchange in fish.

Answer 30

> Gas exchange occurs in fish at the gills.
The fish has 4 gills on either side of its head.
Each gill is made of gill filaments at right angles to each other.
These gill filaments are made of gill plates (lamellae).
The gill arch has vessels to carry deoxygenated blood to gill filaments. After taking oxygen from the water, the oxygenated blood returns to the gill arch to the main vessel.

Question 31

What is the operculum?

Answer 31

The operculum is flaps on both sides of the fish’s head, that covers each set of gills.

Question 32

Describe the ventilation mechanism in bony fish.

Answer 32

> Fish lowers buccal cavity.
Volume in buccal cavity increases; decease in pressure compared to water outside.
Decrease in pressure results in water flowing into the buccal cavity.
At the same time, the operculum valve shuts and operculum cavity expands.
This causes an increase in pressure in the operculum cavity and a decrease in pressure.
Fish raises floor of buccal cavity, forcing water from buccal cavity over gills into operculum cavity.
Fish closes mouth and open operculum cavity. Increases in pressure in operculum cavity forces water out of the gills, out of the side of the fish’s head.

Question 33

How are the gills in fish adapted to efficient gas exchange?

Answer 33

Large surface area- Gill filaments are stacked at right angles to each other.
Short diffusion distance- Gill plates are thin and contain a network of capillaries.
Maintained concentration gradient- Counter current flow mechanism

Question 34

Why does the counter current flow mechanism in fish give a maintained concentration gradient?

Answer 34

The counter current flow mechanism is where water and blood flow in opposite directions to each other. This gives a more fast and efficient diffusion of oxygen than if the water and blood were flowing in the same direction (parallel system).

Question 35

Why do all fish in general needs adaption to their gas exchange systems?

Answer 35

There is a lower concentration of oxygen in water than in air, which is why the fish needs to be adapted to efficient gas exchange.

Question 36

How does the ventilation system in bigger fish differ to the ones in bony fish?

Answer 36

In order for fish to take in oxygen at all times, they must have a constant flow of water over the gills, and hence, they can only get this if they are constantly swimming.
In bigger fish, this is called ram ventilation- ramming water past the gills to keep a continuous flow of water.
However, in bony fish, they have adapted to use the operculum in such a way where they can have a constant flow of water at all times, even when they are not moving.