3.1 SA:VOL Ratio & 3.2 Gas Exchange

Question 1

How does an organism’s size relate to its surface area to volume ratio?

Answer 1

The larger the organism, the lower the surface area to volume ratio.

Question 2

How does an organism’s SA:VOL ratio relate to its metabolic rate?

Answer 2

The lower the surface area to volume ratio, the lower the metabolic rate.

Question 3

Adaptations for large organisms.

Answer 3

Changes that increase surface area e.g. folding; body parts become larger e.g. elephant’s ears; elongating shape; developing a specialised gas exchange surface.

Question 4

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

Their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism.

Question 5

3 features of an efficient gas exchange surface.

Answer 5

1. Large surface area, e.g. folded membranes in mitochondria.
2. Thin/short distance, e.g. wall of capillaries.
3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli.

Question 6

Why can’t insects use their bodies as an exchange surface?

Answer 6

They have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water.

Question 7

What are spiracles in an insect’s gas transport system?

Answer 7

Holes on the body’s surface which may be opened or closed by a valve for gas or water exchange.

Question 8

What are tracheae in an insect’s gas transport system?

Answer 8

Large tubes extending through all body tissues, supported by rings to prevent collapse.

Question 9

What are tracheoles in an insect’s gas transport system?

Answer 9

Smaller branches divide off the tracheae.

Question 10

How do gases move in and out of the tracheae in insects?

Answer 10

Gases move in and out of the tracheae through the spiracles.

Question 11

What allows oxygen to diffuse into insect’s body tissue?

Answer 11

A diffusion gradient.

Question 12

What happens to waste CO2 in insects during gas exchange?

Answer 12

Waste CO2 diffuses out of the body.

Question 13

What role do muscle contractions in the tracheae play in insects?

Answer 13

They allow mass movement of air in and out.

Question 14

Why can’t fish use their bodies as an exchange surface?

Answer 14

They have a waterproof, impermeable outer membrane and a small surface area to volume ratio.

Question 15

Where are fish gills located?

Answer 15

Within the body.

Question 16

What supports the gills in fish?

Answer 16

Arches

Question 17

What are the projections along the gill arches called?

Answer 17

Gill filaments

Question 18

How are lamellae oriented in relation to gill filaments?

Answer 18

At right angles

Question 19

What is the function of lamellae in fish gills?

Answer 19

To increase surface area.

Question 20

What type of exchange system do fish gills use?

Answer 20

Countercurrent exchange system.

Question 21

In the countercurrent exchange system, how do blood and water flow?

Answer 21

In opposite directions

Question 22

How do fish initiate the gas exchange process?

Answer 22

The fish opens its mouth to enable water to flow in.

Question 23

What happens after a fish closes its mouth during gas exchange?

Answer 23

The closing of the mouth increases pressure.

Question 24

Where does oxygen diffuse during the gas exchange in fish?

Answer 24

Oxygen diffuses into the bloodstream over the lamellae.

Question 25

What happens to waste carbon dioxide in the gas exchange process of fish?

Answer 25

Waste carbon dioxide diffuses into the water and flows back out of the gills.

Question 26

What is the purpose of a countercurrent exchange system?

Answer 26

Maintains a steep concentration gradient.

Question 27

How does a countercurrent exchange system affect the concentration of oxygen in blood?

Answer 27

Water is always next to blood of a lower oxygen concentration.

Question 28

What is the benefit of a countercurrent exchange system in gills?

Answer 28

Keeps the rate of diffusion constant along the whole length of the gill.

Question 29

What percentage of available oxygen can be absorbed due to the countercurrent exchange system?

Answer 29

80%

Question 30

What is the purpose of leaves being thin and flat?

Answer 30

To provide a short diffusion pathway and large surface area to volume ratio.

Question 31

What are stomata?

Answer 31

Minute pores in the underside of the leaf that allow gases to easily enter.

Question 32

What is the function of air spaces in the mesophyll of a leaf?

Answer 32

To allow gases to move around the leaf, facilitating photosynthesis.

Question 33

What regulates the opening and closing of stomata?

Answer 33

Guard cells

Question 34

Why do most stomata stay closed?

Answer 34

To prevent water loss.

Question 35

What gas do some stomata open to allow in?

Answer 35

Oxygen

Question 36

Describe the pathway of air in mammals.

Answer 36

Nasal cavity → trachea → bronchi → bronchioles → alveoli.

Question 37

Function of the nasal cavity.

Answer 37

A good blood supply warms and moistens the air entering the lungs. Goblet cells in the membrane secrete mucus, which traps dust and bacteria.

Question 38

What is the function of the trachea?

Answer 38

To carry air to the bronchi.

Question 39

What supports the trachea to keep the air passage open?

Answer 39

C-shaped cartilage.

Question 40

What type of cells line the trachea, and what is their function?

Answer 40

Ciliated epithelium cells, which move mucus towards the throat.

Question 41

How do ciliated epithelium cells in the trachea help prevent lung infections?

Answer 41

By moving mucus towards the throat to be swallowed.

Question 42

What is the function of the bronchi?

Answer 42

Allow passage of air into the bronchioles.

Question 43

What supports the bronchi?

Answer 43

Rings of cartilage.

Question 44

What type of cells line the bronchi?

Answer 44

Ciliated epithelium cells.

Question 45

How do the bronchi compare to the trachea in terms of size?

Answer 45

The bronchi are narrower than the trachea.

Question 46

How many bronchi are there?

Answer 46

Two, one for each lung.

Question 47

What are bronchioles narrower than?

Answer 47

Bronchi

Question 48

What do bronchioles primarily consist of?

Answer 48

Muscle and elastic fibres.

Question 49

Why do bronchioles not need cartilage to stay open?

Answer 49

They can contract and relax easily during ventilation.

Question 50

What is the function of bronchioles in the respiratory system?

Answer 50

Allow passage of air into the alveoli.

Question 51

What are alveoli?

Answer 51

Mini air sacs in the lungs.

Question 52

What is the primary function of alveoli?

Answer 52

Site of gas exchange.

Question 53

How thick are the walls of alveoli?

Answer 53

Walls are only one cell thick.

Question 54

What covers the walls of alveoli?

Answer 54

A network of capillaries.

Question 55

What process is facilitated by the structure of alveoli?

Answer 55

Gas diffusion.

Question 56

What happens to the external intercostal muscles during inspiration?

Answer 56

External intercostal muscles contract while internal intercostal muscles relax.

Question 57

What happens to the diaphragm during inspiration?

Answer 57

The diaphragm contracts and flattens.

Question 58

What is the effect on the volume of the thorax during inspiration?

Answer 58

The volume of the thorax increases.

Question 59

What causes air to move into the lungs during inspiration?

Answer 59

Air pressure outside the lungs is higher than the air pressure inside.

Question 60

What happens to the external intercostal muscles during expiration?

Answer 60

They relax while the internal intercostal muscles contract.

Question 61

What happens to the diaphragm during expiration?

Answer 61

The diaphragm relaxes and domes upwards.

Question 62

What change occurs in the volume of the thorax during expiration?

Answer 62

The volume of the thorax decreases.

Question 63

What is the relationship between air pressure inside the lungs and outside during expiration?

Answer 63

Air pressure inside the lungs is higher than the air pressure outside.

Question 64

What is the result of the pressure difference during expiration?

Answer 64

Air moves out of the lungs to rebalance the pressure.

Question 65

What is tidal volume?

Answer 65

The volume of air we breathe in and out during each breath at rest.

Question 66

What is breathing rate?

Answer 66

The number of breaths we take per minute.

Question 67

State the pulmonary ventilation rate calculation and how it's measured.

Answer 67

Tidal volume x breathing rate. These can be measured using a spirometer (a device which records volume changes on a graph as a person breathes).