3 - Gas exchange

Question 1

Describe how humans breathe in

Answer 1

1 - Diaphragm muscles contract and flattens
2 - external intercostal muscles contract and ribcage pulled out
3 - Volume increase and pressure decrease in thoracic cavity

Question 2

Describe how humans breathe out

Answer 2

1 - Diaphragm relaxes and curves upwards
2 - external intercostal muscles relax and ribcage moves downwards
3 - Volume decrease and pressure increase

Question 3

How many layers of gills does a fish have on each side of the head and what are these covered in

Answer 3

There are four layers of gills on both sides of the head. The gills are made up of stacks of gill filaments which are covered in gill lamellae. Every lamellae has a capillary network

Question 4

Describe the counter current mechanism

Answer 4

• Water and blood flow in opposite directions
• Water always has a higher concentration of oxygen than blood
  -Maintains a diffusion gradient across the whole length of the lamellae
• more diffusion of oxygen into the blood occurs

Question 5

Structural adaptation in mammals

Answer 5

• Large SA
  . many small alveoli
  . Alveoli surrounded by branching
  capillaries
• Short diffusion pathway
  . Alveoli and capillaries are made up of
  single layer of flattened epithelial cell

Question 6

Structural adaptation in fish

Answer 6

-Large SA
.Gills have long filaments
. Each filament contains many small
lamellae
. Lamellae surrounded by many small branching capillaries

-Short diffusion pathway
. Lamellae and capillaries are made up of a single layer of flattened epithelial cells

Question 7

Structural adaptation in plants

Answer 7

-Large SA
. Lots of mesophyll cells lining the intercellular air spaces in leaf
-Short diffusion pathway
. Thin leaves
. Gases diffuse across cell wall and cell membrane of mesophyll cells which are thin

Question 8

Explain the adaptations of xerophytes

Answer 8

-Thick waterproof cuticle- reduces evaporation
- Sunken stomata- lowers water gradient between leaf and air - reduces evaporation from stomata
- Few stomata - reduces evaporation
- Leaves reduced to spines - surface area lowered so less evaporation
- Hairy leaves -reduces water pot grad - less evaporation
- Leaves rolled inwards- water withing rolled up space - reduces water pot grad - reduces evaporation

Question 9

How do insects prevent water loss

Answer 9

• Tough waterproof exoskeleton
• Waterproof, waxy cuticle all over body
• Hairs around spiracles - reduce evaporation
• Close spiracles

Question 10

Structural adaptation in insects

Answer 10

-Large SA
.Trachea branch into many, small
tracheoles
-Short diffusion pathway
.Tracheole walls are thin
. Trachea branch into many, small tracheoles which reduce diffusion distance to muscle cells