GE in plants and humans

describe and explain the process of inspiration in a mammal

Intercostal muscles contract and ribs move up and out

Diaphragm muscles contract and diaphragm flattens

Internal volume of thorax increases

Pressure in lungs/ thorax decreases

Higher/ difference in air pressure outside forces air into the lungs

Tracheoles are found on the outside of the muscle fibres suggest why the max diameter of a muscle fibre never exceeds 20 microm in diameter

Diffusion pathway would be too long, ensures a short diffusion pathway

Speed of diffusion would be too slow

To supply sufficient oxygen

9 marker 2024 a level

Describe the change in fluid level in the tracheoles during flight suggest how this change benefits gas exchange during flight

Less fluid, fluid moves into muscle fibres, fluid level decreases

More area for gas exchange and shorter diffusion pathway

Name the structure labelled A in photograph thin strands coming out of fish gills

Gill lamellae/ gill plates

Explain how inspiration is brought about

Contraction of intercostal muscles and diaphragm or Ribcage cloves up and out and diaphragm flattens/ contracts

Increased volume and decreases pressure so air moved into the lungs

Part of lung labelled

A- alveoli

B- capillary network

Blood vessels that connect C and D to the heart respectively - pulmonary artery and pulmonary vein

Important structure features of alveoli

Large SA/ highly folded

large number of capillaries

Thin alveolus walls/ one cell thick

Describe and explain how the alveoli are adaptations for efficient gas exchange

They have many alveoli which increases or provides a large SA for gas exchange, alveoli walls are thin/ one cell thick providing a short diffusion pathway/ distance for oxygen to enter the blood

Describe how blood vessels are adaptations for efficient gas exchange

many blood capillaries/ vessels are good blood supply, capillary network to maintain stepp concentration gradient

Describe and explain the process of expiration in mammals

Intercostal muscles relax allowing Ribcage to move downwards and inwards

The diaphragm muscles relaxes and becomes dome shaped

This decreases the volume of the thorax

Which increases the pressure inside the lungs

Forcing/ pushing air out of the lungs/ moving air out of the lungs down a pressure gradient

Mammals have a high oxygen demand suggest why they need a complex ventilation mechanism

Have high metabolic rates

Ventilation maintains a steep concentration gradient at the alveoli/ sufficient/ enough/ more oxygen supplied to the alveoli/ GE surface

Give two adv of humans having internal gas exchange surfaces

Minimise/ reduce heat and water loss

State one medical use of artificial surfactant and explain why it would be needed

Lowers surface tension do the fluid in the alveoli to prevent alveoli from collapsing

Premature babies/ lung transplants/ respiratory distress syndrome

Explain how the outwards movement of the Ribcage causes the changes in pleural and alveolar pressures during breathing in

Intercostal muscles contract and expand the Ribcage

Outer pleural membranes pulled out by expanding the Ribcage

Pleural pressure reduced

Inner pleural membrane pulls on lungs and expands alveoli

Alveolar pressure lowers

Air moves in when alveolar pressure is lower than atmospheric pressure and increases alveolar pressure

Plant adaptation for efficient diffusion of gases

Stomata

Large air spaces, large SA in spongy mesohpyll

Thin leaf / short diffusion distance

Moisture on cell surface

Explain how stomata are opened

K+ or malate in guard cells/ cytoplasm/ vacuole

Reduces their water potential so water enters guard cells by osmosis and trig or pressure increases/ cell becomes turgid, ends of guard cell walls are thinner central wall is thicker, ends expand which opens stomata cells are forced apart

Main RS for fish, mammal, earthworm, insect

Fish- gills / lamellae

Mammal- alveoli NOT lungs

Earthworms- skin

Insect- tracheoles NOT trachea

Explain how in a mammal the Ribcage diaphragm and pleural membranes are involved in lowering the pressure in the alveoli to below atmospheric pressure during inhalation

Ribcage moves up/ expands

Diaphragm flattens/ contracts/ moves down

Pull pleural membranes out which expands volume of the lungs and reduces pressure

Two ways an O concent gradient is maintained between alveolar air and blood

Explain why the rate of GE between the air spaces of the leaf and the leaf tissues is lower than between alveoli and blood of a mammal 1b i

Describe how the muscles of the thorax together with the pleural membranes cause the change in alveolar pressure during inspiration

External intercostal muscles contract and rib cage lifts upwards and outwards

Diaphragm muscles contract and diaphragm flattens

Outer pleural membrane pulls inner pleural membrane

Outward/ reduced pressure

% of CO2 in exhaled air is lower than in alveolar air explain why

Some CO2 remains in the trachea/ bronchi/ alveoli

Exhaled air has a slightly higher % of nitrogen than inhaled air despite the gas being inert in mammals

The proportions/ quantities of other gases have changed (so N is a different proportion of the gas mixture)

Describe a difference in appearance of the two lung samples and explain how this would decrease GE efficiency

Alveoli/ air spaces have become larger, air spaces have broken down

Reduced S.A. for gas gas exchange/ diffusion

Tissue between alveoli/ air spaces have become thickened

Increased diffusion distance for O/ CO2

Explain mechanism of stomatal opening which allows GE to take place

K+ pumped/ using AT into guard cells

Starch converted to malate ions

Lowering WP in guard cells

Water moves in by osmosis

Guard cells become turgid

Uneven beding of guard cells due to thickening of cell wall

Explain how the volume of the thorax is changed during inspiration

External intercostal muscles contract and Ribcage moves upwards and outwards

Diaphragm contracts and flattens

Role of pleural membranes

Explain change in alveolar pressure during inspiration

Pressure decreases in alveoli as thoracic volume increases

Pressure increases as air enters alveoli

During expiration there is a risk of the collapse of the alveoli due to positive pressure, suggest how alveoli are adapted to deal with this

Alveoli coated in surfactant

Reduces surface tension

A- bronchiole

B- alveolus

C- pleural membranes

Explain how a feature visible in photograph ensures the trachea can function effectively during inspiration

Ring of cartilage

Prevents trachea from collapsing due to air pressure decrease during inspiration

Explain how muscles involved in the process of inspiration bring about changes in pressure

External intercostal muscles contract and ribs move upwards and outwards

Diaphragm contracts and flattens

Role of pleural membranes

Volume do thorax increases therefore pressure decreases

Air pressure in alveoli us falls below atmospheric pressure so air rushes in