6- Exchange

Question 1

Single-cell organisms- Adaptations for gas exchange (3)

Answer 1

• Large SA> V = increases rate of gas exchange
• Can increase their SA (by making themselves wide, flat or fold)
• Cell membrane= Short diffusion distance (to exchange)

Question 2

Insects- Adaptations for gas exchange (5)

Answer 2

1) Thin surface for gas exchange
2) Increased SA for gas exchange
3) fluid-filled ends
4) Ventilation by muscles
5) Opening & closing of spiracles (to control air & slow loss of water)

Question 3

What are spiracles?

Answer 3

openings along insect bodies

• O2 diffuses through them into tracheoles, CO2 diffuses out of them

Question 4

Fish- Adaptations for gas exchange- GILLS (2)

Answer 4

-highly branched & folded filaments of 
thin tissue (creates large SA)

• gills covered in lamellae (increases SA)

Question 5

Fish- Adaptations for gas exchange- counter-current system (outline+explain)

Answer 5

• B flows through lamellae in OPPOSITE direction of w flow through gills
• This ensures a STEEP conc gradient between the w & the b
• O2 can diffuse from w> b because of CC system

Question 6

Dicotyledonous Plants- Leaves adaptations for gas exchange (3)???

Answer 6

Large SA of mesophyll cells (for rapid exchange)
Stomata= pores
Guard cells= can open & close stomata to control water loss

Question 7

Compromises between opposing needs for efficient gas exchange and the limitation of water loss

(in insects ) (3)

Answer 7

1. spiracles= can close to prevent water loss.
2. spiracles have hairs > decrease WP gradient between I T& E (decreases rate of D)

3.waxy cuticle= waterproof so prevents water loss

Question 8

Compromises between opposing needs for efficient gas exchange and the limitation of water loss

(in XEROPHYTIC plants ) (5)

Answer 8

• Fewer stomata (to avoid dehydration)
• Sunken stomata (trap moist air, this decreases rate of water loss)
• Hairs (trap moist air & decrease rate of water loss)
• Curled leaves (shelter stomata from wind, slows rate of water loss)
• Waxy cuticle (waterproof & reduces rate of water evaporation)

Question 9

Ventilation- Breathing IN (Inspiration) (5)

Answer 9

1. • EIM CONTRACT,
     - diaphragm CONTRACTS> moves DOWN
2. • EIM moves ribcage UP & OUT
3. • volume of thoracic cavity INCREASES
     - Pressure DECREASES,
4. • pressure gradient created.
5. • Air flows IN lungs & DOWN p gradient, (down T & into A)

Question 10

Ventilation is controlled by: (3)

Answer 10

1. Ribcage
2. Intercostal muscles
3. Diaphragm

Question 11

Human gas exchange- Adaptations (3)

Answer 11

1) in Trachea- ridges of cartilage surround FRONT (provide protection & structure)
- None at back so oesophagus doesn’t constrict.

2) alveoli provide a large SA
3. Ribcage, IM and diaphragm control ventilation

Question 12

Ventilation- Breathing OUT (expiration)

Answer 12

1. -External IM RELAX, Internal IM CONTRACT
   
   • diaphragm RELAXES & moves UP
2. IIM moves ribcage DOWN & IN
3. -volume of thoracic cavity DECREASES, Pressure in lungs INCREASES
4. Pressure gradient established
5. -Air flows OUT of lungs, DOWN pressure gradient. (flows out A & up T)

Question 13

Alveoli- features for gas exchange (2)

Answer 13

1. Each A surrounded by network of capillaries- provides a large SA for GE
2. thin Epithelium= 1 cell thick, line A walls- (short DD (from A>C)

Question 14

Where does gas exchange in plants take place?

Answer 14

mesophyll cells