Adaptions for gas exchange - Fish, Humans and Insects

Question 1

Gaseous exchange

Answer 1

The exchange of gases between an organism and its environment across a respiratory surface by the process of diffusion

Question 2

Properties of an efficient respiratory surface

Answer 2

• Large surface area to volume ratio
• Thin
• Permeable
• Moist

Question 3

Surface area : Volume

Answer 3

• The total oxygen requirement of an organism is proportional to its total volume
• The rate of absorption of oxygen is proportional to the organism’s surface area
• SA:V ratio decreases as size increases
• SA:V affects the level of activity of an organism

Question 4

Amoeba

Answer 4

• Single celled organism with large SA:V

- So diffusion is fast enough to meet oxygen demands

Question 5

Flatworms

Answer 5

• Multicellular organisms with a smaller SA:V
• But they are flattened so diffusion distance is reduced
• Therefore they can rely on external surface for gas exchange

Question 6

Earthworms

Answer 6

• Rely on external surface area for gas exchange

- But have a circulatory system to deliver oxygen to tissue

Question 7

Gaseous exchange in fish

Answer 7

They have small SA:V, so they need specialised gas exchange organs called gills.

Water has much less oxygen (0.7%) and doesn’t move as freely as air

Gill adaptions:

• Water kept flowing one-way by ventilation mechanism
• Many folds providing a large surface area over which water flows

Question 8

Ventilation in bony fish

Answer 8

Water is taken in by:

• Opening the mouth
• Closing the operculum
• Buccal cavity floor lowered
• Pressure decreases as volume increases
• Water flows into the mouth

Water forced over gills by:

• Closing the mouth
• Opening the operculum
• Buccal cavity floor raised
• Pressure increases as volume decreases
• Water forced over the gill and out of the operculum

Question 9

Counter current flow

Answer 9

Occurs at the gill lamellae:

• Water flows over the lamellae in the opposite direction to blood in the capillaries
• The concentration gradient is always maintained across entire length of lamellae
• Equilibrium is never reached
• Much more efficient than parallel flow

Question 10

Ventilation in cartilaginous fish

Answer 10

No specific mechanism of ventilation, so they must keep swimming

Question 11

Parallel flow

Answer 11

Occurs at the gill lamellae:

• Water flows over the lamellae in the same direction to blood in the capillaries
• Oxygen diffuses along a concentration gradient into the blood until the concentrations are equal
• Less efficient than counter current flow

Question 12

Human respiratory system

Answer 12

(10)

• Larynx
• Trachea
• Bronchi
• Bronchioles
• Alveoli
• Pleural membranes
• Pleural cavity
• Ribs
• External and internal intercostal muscles
• Diaphragm

Question 13

Ventilation in humans - Inhalation (8)

Answer 13

• External intercostal muscles contract
• Internal intercostal muscles relax
• Ribcage pulled upward and outward; volume increases
• Diaphragm contracts down; volume increases
• Outer pleural membrane pulled out; reduces pressure
• Causes inner pleural membrane to pull on lung surface
• Alveoli expand; alveolar pressure decreases
• Air is drawn into the lungs

Question 14

Ventilation in humans - Exhalation (7)

Answer 14

• External intercostal muscles relax
• Internal intercostal muscles contract
• Ribcage moves downward and inward; volume decreases
• Diaphragm relaxes; volume decreases
• Lung volume decreases
• Pressure increases inside lungs
• Air is forced out

Question 15

Surfactant in the alveoli

Answer 15

• Alveoli surfaces coated with a surfactant
• Surfactant comprised of phospholipids and proteins
• It reduces surface tension within alveoli and prevents them from collapsing

Question 16

Adaptions of insect tracheal system

Answer 16

To reduce water loss:

• Have an impermeable exoskeleton made of chitin to reduce water loss by evaporation
• Have a small surface area to volume ratio
• Spiracles may open or close if it is hot to conserve water

To increase gas exchange:

• Consists of 2 main tracheae supported by chitin ring to prevent collapse
• Each tracheae opens to paired holes called spiracles on each side of the insect
• Smaller tubes called tracheoles branch off the tracheae
• ->Large surface area for gas exchange
• ->Thin walls ensure short diffusion distance
• ->Have fluid on the ends which allows gases to dissolve and diffuse directly in or out of the respiring cells
• ->They also carry air into tiny air sacs which act as temporary stores

Question 17

Insects during rest

Answer 17

• Movement of gases through tracheal system occurs by diffusion at rest and in small insects
• As cells respire oxygen is used up so concentration at the respiring tissue is low
• This creates a diffusion gradient that causes oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells

Question 18

Insects during activity

Answer 18

• When insects are active and in larger insects there is more demand from cells
• The tracheal system therefore needs to be ventilated
• Ventilation ensures there is mass flow of gases which is much faster than diffusion

Mass flow process:

• Air drawn in by spiracles at thorax (head end) and pumped out by spiracles at abdomen (back end)
• So air flows in one direction which is more efficient