Gas exchange in insects/fish/plants

Question 1

Mass transport in insects

Answer 1

Muscles contract around tracheoles which squeezes them enabling gas to move.

Question 2

Diffusion gradient in insects

Answer 2

Lower O2 concn on inside as 02 used for respiration.
Higher concn outside.

Question 3

What is the order of the gas exchange system in insects?

Answer 3

Spiracles
Trachea
Tracheoles
Cells

Question 4

How does having water in the trachea in insects aid gas exchange?

Answer 4

• Anaerobic respiration caused by intense exercise increases lactic acid levels
• Decreases water potential
• water potential higher in tracheoles so H2O moves into cell (osmosis) which decreases the vol of H2O.
• Draws air in

Question 5

What is the structure of a fish gill ?

Answer 5

Gill filaments
With lots of lamellae
Increases s.a

Question 6

How does countercurrent flow aid gas exchange ?

Answer 6

• Water and blood flow in opposite directions
• Blood passes H2O with a higher O2 concn first
• maintains concn gradient along whole gill filament.

Question 7

Why is parallel flow not used in fish gas exchange?

Answer 7

• Blood and water flow in same direction
• concn gradient isn’t maintained along the whole filament.

Question 8

What is the structure of a leaf

Answer 8

Waxy cuticle
upper epidermis
palisade mesophyll
spongy mesophyll + vascular bundle
lower epidermis + guard cells + stomata

Question 9

How are leaves adapted for gas exchange?

Answer 9

• Many stomata so no cell far from stoma so short diffusion path
• Many air spaces so gas can readily come in to contact with palisade mesophyll cells
• large s.a of palisade mesophyll for rapid diffusion

Question 10

How do leaves control the rate of gas exchange?

Answer 10

They can open and close the stomata.

Question 11

What is a xerophyte?

Answer 11

Plants that are adapted to living in dry areas.

Question 12

Give 5 adaptations of xerophytes.

Answer 12

Thick waxy cuticle
Leaves rolled
Hairy leaves
Sunken stomata ( in pits)
small/ thin leaves

Question 13

How does a thick waxy cuticle limit water loss?

Answer 13

Less water can escape

Question 14

How do rolled leaves limit water loss?

Answer 14

Traps a region of air which becomes saturated with water vapour so the water potential is high so there is no water potential gradient between inside and outside of the leaf.

Question 15

How do hairy leaves limit water loss?

Answer 15

Traps water vapour so there is no water potential gradient between inside and outside of leaf.

Question 16

How do sunken stomata limit water loss?

Answer 16

H2O vapour has to travel further to exit the leaf and water vapour is trapped which reduces the H2O vapour gradient

Question 17

How do small/ thin leaves limit water loss?

Answer 17

Reduced SA:V

Question 18

What is the relationship between SA:V and size?

Answer 18

As size increases SA:V decreases

Question 19

What is the relationship between SA:V and metabolic rate?

Answer 19

High metabolic rate = higher SA:V

Question 20

How to calculate SA:V of a cube?

Answer 20

area of one side x 6 = S.A
length x width x height = V

Question 21

How have larger organisms evolved to increase SA:V?

Answer 21

A flattened shape so cells are close to the surface
Specialised exchange surfaces .

Question 22

What are the features of specialised exchange surfaces?

Answer 22

• large SA
• Very thin so short diffusion path
• selectively permeable
• Movement of the environmental medium to maintain diffusion gradient
• transport system for movement of internal medium.