Gas exchange in Humans

Question 1

Inspiration

Answer 1

• Is an active process - requires energy
• External intercostal + diaphragm muscles contract = causes ribcage to move upwards + outwards + diaphragm flattens = increases volume of thoracic cavity - as this increases = lung pressure decreases (below atmospheric pressure) - air flows from high to low pressure so air flows down trachea into the lungs.

Question 2

Expiration

Answer 2

• Its a passive process - doesnt require energy
• External intercostal + diaphragm muscles relax + ribcage moves downwards + inwards + diaphragm becomes curved.
• volume of thoracic cavity decreases causing the air pressure to increase (above atmospheric pressure)
• air forced down the pressure gradient + out of the lungs.

Question 3

Forced Expiration

Answer 3

(e. g. blowing out a candle)
- external intercostal muscles relax + internal intercostal muscles contract (act antagonistically) - causing ribcage to be pulled down + in.

Question 4

What happens when O2 diffuses out of alveoli

Answer 4

O2 moves across the alveolar epithelium and the capillary endothelium (forms the capillary wall) + into haemoglobin in the blood.

Question 5

Dicotyledonous plants exchange gases at..

Answer 5

The surface of the mesophyll cells

Question 6

Why do plants need O2 and CO2

Answer 6

• plants need CO2 for photosynthesis, which produces O2 as a waste gas, and it needs O2 for respiration, which produces CO2 as a waste gas.

Question 7

Mesophyll cells are inside the leaf. Gases move in + out through …. in the …..

Answer 7

stomata in the epidermis

Question 8

mesophyll cells well adapted as..

Answer 8

they have a large surface area

Question 9

stomata are controlled to open or close by the …

Answer 9

guard cells

Question 10

How the guard cells open + close stomata

Answer 10

• when water enters the guard cells = makes them turgid = opens stomata
• when plant’s dehydrated = guard cells lose water become flaccid = closes pore.

Question 11

Adaptations of xerophytes (plants in warm dry environments)

Answer 11

• stomata sunken = traps moist air = reducing concentration gradient of water between leaf and air = reduces amount of water diffusing out of the leaf + evaporating.
• layers of hairs on epidermis - to trap moist air around stomata again to reduce loss of water.
• curled leaves - protects stomata from wind which would increase evaporation + diffusion + lowers exposed surface area.
• reduced number of stomata = less pores for water to escape.
• waxy waterproof cuticles on leaves/stem to reduce evaporation.