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

Explain why ventilation rate increased as temp increased and why these fish gulp air during summer

Oxygen content of water decreases as temp increases

Increased ventilation rate/ operculum open more frequently, so more/ enough oxygen could be absorbed from the water;

Gulp air when ventilation rate reaches maximum, cannot breathe any faster, cannot absorb enough oxygen from the water , air has a higher O content, can absorb oxygen from the air when oxygen content of water is low/ gulp for more oxygen

Describe the mechanism that causes stomata to open

K+ actively transported into guard cell

Starch converted to malate

Lowers the WP of the cell

Water moves into the cell by osmosis

Due to increase in water cells well up, become turgid

stomata opens as inner cell wall is thicker than the outer cell walls, walls are unevenly thickened

Advantage of plant being able to close stomata

Reduce water loss

Mean number of stomata calculated for trees alter being placed in greenhouses with different CO2 concentrations , variables that should be controlled

Temp, light intensity, humidity, frequency of watering, volume of water, soil pH

Using knowledge of the functions of stomata explain why as the CO2 concentration increases the mean number of stomata decreases/ stomatal density decreases, there are fewer stomata

Stomata open to allow CD to diffuse for PR

At higher CD concent there is an increased rate/ more CD diffusion/ uptake

Sufficient CD can be absorbed with fewer stomata, therefore less water is lost from the plant

Explain how large insects ensure an efficient supply of oxygen to their tissues

Tracheal system, tracheoles

Oxygen is delivered directly to cells/ muscles

reason why both the insect and human systems are internal

To reduce water loss

Why the nasal cavity and the series o cavity have air

To filter air/ trap solid particles

Why walls of alveoli and tracheoles are one cell thick

Short diffusion pathway

Why alveoli and tracheoles are lined with surfactant

Reduce surface tension, prevent collapse of alveoli and tracheoles during expiration , prevent alveoli/ tracheoles sticking together

During inspiration external intercostal muscles contract which causes outer pleural memerbanes to move outwards explain causes of pressure and volume changes during inspiration

Pulling on outer puleural membrane lowers pressure in pleural cavity, inner pleural membrane pulls on the lungs, which increases volume of the lungs/ alveoli/ thorax, which decreases pressure in lungs, below atmospheric pressure so air moves in

Changes to the curve during strenuous exercise

Greater/ higher pressure , faster pressure changes

Greater volume , faster changes in volume

More rapid breathing, increased breathing rate

describe and explain the common adaptions found in fish and mammals

Thin- reduce diffusion distance

Moist for gases to dissolve

Extensive blood capillary network to maiantim diffusion/ concent gradient and

The body temp of cold blooded animals varies with temp according to temp of the environment suggest why warm blooded animals which have a constant body temp such as mammals have a higher metabolic rate

Body temp not dependent on that of the environment , energy needed to generate heat to maintain body temp , provide optimum temp for enzymes, so reaction rate is higher

Explain why spiracles close

To reduce water loss

Describe the relationship between body mass and metabolic rate

The greater the mass the greater the metabolic rate

Explain the advantages of insects have a ventilation system

maintain concentration gradient so that air has high CD concent is replaced with oxygen rich air

Suggest the role of air sacs in insects tracheal systems

To provide a store of oxygen when spiracles are closed

Outline a method which the stomatal density could be determined

Cost surface do leaf with clear nail varnish , examine using a light microscope, count the number of stomata in the field of view

Plant grown in temp and light controlled conditions state other control variables

Humidity, air movement , pH of soil, water availability, concent of CD/O

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

Mammals have a ventilation system whilst plants rely on diffusion only

Higher concent gradient in mammals, lower in plants concent gradient is actively maintained in animals

Mammals have a higher rate of respiration, more active

Main tissue responsible for PT

Palisade mesophyll

Conclude whether th worst shown is from a hydrophyte or a xerophyte

hydrophyte, stomata in the upper epidermis/ surface , large air spaces in spongy mesophyll , thin cuticle on upper epidermis / surface

Explain why leaves and chloroplasts change their orientation during the day

To increase/ maximise absorption of light

So that greater S.A. of leaves face the sun

Explain why there is water loss when the stomatal diameter is 0

Water evaporates from leaf surface/ epidermis

What would happen to the rate of water loss form the plant when exposed to a high air speed

Decrease

Adv of plants closing stomata at high wind speeds

Less water loss

Suggest why increased CD concentration resulted in a reduction in stomatal density

CD is used for PT, increased CD causes increased rate of PT, higher CD concent causes faster/ more diffusion , higher concent gradient

Fewer stomata needed for the same CD intake

Give two function of stomata

Allow GE/ CD and O to enter and leave leave s

Control water loss

When guard cells are treated with cyanide the stomatal pores failed to open explain why cyanide is having this effect

Cyanide stops respiration, is a respiratory inhibitor , stops active transport of K+ ions into guard cells

Explain the distribution of the stomata

Lower surface of leaf is shaded therefore there is a higher density of stomata to reduce water loss

Use the photograph to explain why the less water vapour is lost from the stomata of one leaf then the stomata of another

Stomata are sunken, water vapours builds up in pits, reducing diffusion gradient, rate of transpiration is reduced

Other leaf has no sunken stomata, stomata are nearer to the surface

Which species are more likely to live in driest environment

Species that have the lowest stomatal density , higher % of stomata on the lower surface, lower rate of transpiration, , lower rate of water loss

Explain how investigating stomata density works

Obtain impression using clear nail varnish

Prepare a slide using impression, observe under microscope , count number of stomata in known area, repeat to obtain mean