3.1 and 3.2 SA:V and gas exchange

Question 1

How does an organisms size relate to its SA:V ratio?

Answer 1

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

Question 2

How does an organisms SA:V ratio relate to their metabolic rate?

Answer 2

The smaller the SA:V ratio, the higher the metabolic rate

Question 3

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 3

Their smaller SA:V 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 4

Name three features of an efficient gas exchange surface

Answer 4

-Large surface area
-Thin/ diffusion pathway
-Steep concentration gradient

Question 5

Why cant insects use their bodies as an exchange surface?

Answer 5

-Waterproof chitin exoskeleton making it hard for gases like oxygen or carbon dioxide to pass through
-Small SA:V ratio to conserve water

Question 6

What are the three main features of an insects gas transport system?

Answer 6

spiracles-holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
Tracheae-large tubes extending through all body tissues, supported by rings of chitin to prevent collapse
Tracheoles- smaller branches dividing off the trachea that extend very close to the cells allowing a short diffusion pathway

Question 7

Explain the gas exchange process in insects

Answer 7

-Gases move in and out of the tracheae through the spiracles
-a diffusion gradient allows oxygen to diffuse out the body tissue while waste CO2 diffuses out
-contraction of muscles in the tracheae allows mass movement of air in and out

Question 8

Why do insects have efficient gas exchange

Answer 8

-Tracheoles extend right next to cell allowing short diffusion pathway
-Huge number of tracheoles provides large surface area allowing high rate of aerobic respiration
-small size of insect decreases diffusion distance
-Much higher concentration of air externally so steep concentration gradient and flipped with C02

Question 9

How do Insects deal with water loss?

Answer 9

-The walls of the tracheoles are moist and the ends of the tracheoles contain tracheal fluid which means water vapour can diffuse out of an insect via the spiracles
-Each spiracle has a valve that can shut reducing water loss when low requirements of oxygen are required

Question 10

What is tracheal fluid

Answer 10

-During intense activity, cells around the tracheoles undergo anaerobic respiration
-Anaerobic respiration produces lactic acid which lowers the water potential of the cells which causes water in the tracheal fluid to move into the cells
-This reduces volume of tracheal fluid, drawing air down into the tracheoles.
-More tracheal surface is available for diffusion of oxygen and C02

Question 11

What is the flap either side of the head on a bony fish called?

Answer 11

-Operculum
-Behind is operculum cavity and inside is the gills

Question 12

How does oxygen enter bony fish?

Answer 12

-Oxygen rich water enters the fish through the mouth
-The water then passes over the gills
-In the gills, oxygen diffuses from the water into the blood and C02 diffuses from blood to water
-The water passes out through the opercular opening

Question 13

Structure of gills

Answer 13

-Consist of several bony gill arches
-Extending off each gill arch are large number of gill filaments
-Gill filaments are covered with numerous gill plates
-gill plates=gas exchange

Question 14

How does gas exchange take place in bony fish?

Answer 14

-Water flows between the gill lamellae where oxygen diffuses from water to bloodstream and C02 from bloodstream to water
-The oxygen is carried away maintaining steep concentration gradient

Question 15

Why are gill lamellae adapted for efficient gas exchange

Answer 15

-Massive surface area for gases to diffuse over
-Very short diffusion distance through the walls of the lamellae and into bloodstream
-Gill lamellae have an extensive network of blood capillaries

Question 16

What is the counter current exchange system in bony fish?

Answer 16

-Flow of blood is in the opposite direction to flow of water which always maintains steep concentration of oxygen

Question 17

Why is parallel flow not efficient for gas exchange in bony fish?

Answer 17

-Eventually equilibrium of oxygen in water and bloodstream is reached stopping diffusion
-This means no more than 50% of available oxygen in the water can diffuse into the blood

Question 18

Why do mammals require more energy than fish?

Answer 18

-They maintain a constant body temperature (endotherms)
-requires increased levels of aerobic respiration

Question 19

Adaptations of the trachea?

Answer 19

-The walls contain cartilage which is firm but flexible which prevents walls of trachea collapsing when we inhale
-The walls are lined with ciliated epithelia and goblet cells

Question 20

Function of goblet cells

Answer 20

Secretes mucus which traps dust particles and pathogens

Question 21

Function of ciliated epithelia?

Answer 21

Have cilia extending from the cell membrane. The beating of the cilia moves the mucus to the throat. The mucus is then swallowed and the dust and mucus are digested by the stomach enzymes.

Question 22

Where is the site of gas exchange in mammals?

Answer 22

In Alveoli (in the lungs)