2.2 - Adaptations for gas exchange

Question 1

What do all living organisms require to survive?

Answer 1

a source of energy

Question 2

How is energy obtained?

Answer 2

by the process of respiration

Question 3

Where does respiration occur?

Answer 3

in every cell, generating ATP using oxygen and releasing carbon dioxide as a waste product

Question 4

What is gas exchange?

Answer 4

the diffusion of these gases in opposite directions across an exchange surface

Question 5

Organisms?

Answer 5

live in different environments, some live on land whereas others live in water

Question 6

What does gas exchange involve?

Answer 6

the rapid and efficient exchange of oxygen and carbon dioxide across the respiratory surface

Question 7

What must a respiratory surface have to achieve the max rate of diffusion?

Answer 7

have a large surface area relative to the volume of the organisms to satisfy the needs of the organisms
be thin, so the length of diffusion pathway is short
be permeable - allows gases to pass through
moist - to allow a medoum in which gases dissolve before diffusion
maintain a conc gradient

Question 8

As the size of the organism is increased?

Answer 8

the surface to volume ratio decreases

Question 9

Why does this relationship have important consequences for organisms?

Answer 9

some processes such as the rate of diffusion depend on the surface are while others, such as metabolic rate depend on the volume
for example amoebe can undergo simple diffusion from its immediate environment but for larger organisms it cannot supply sufficient quantities of oxygen

Question 10

What do larger organisms have to compensate for this?

Answer 10

special respiratory exchange surfaces such as lungs, gills and tracheae

Question 11

Problems associated with gas exchange in air and water?

Answer 11

Air breathers cannot obtain the amount of oxygen they need from water
problem with breathing air =loss of water
combination of large surface area + moist membranes means that exhaled air is saturated with water vapor

Question 12

Gas exchange in single celled organisms?

Answer 12

oxygen, carbon dioxide travel the entire distance between mitochondria and the external environment by diffusion alone
as the organisms are so small, they have a very large surface area to volume ratio
their external surfaces can therefore be used to exchange gases, as the large surface area is able to supply sufficient oxygen to the small volume

Question 13

Amoeba?

Answer 13

lives in water surrouned by the materials it needs
water has a high conc of oxygen than found in organisms
water has diffuses through the plasma membrane into the cell where oxygen is at a lower conc and can reach every part of its small volume

Question 14

Gas exchange in simple multicellular animals?

Answer 14

they have modest oxygen requirements because they are slow moving and so have a very slow metabolic rate
oxygen and carbon dioxide diffuse across the skin surface and do not have any special gas exchange organs

Question 15

Flatworms?

Answer 15

are aquatic animals that have evolved a flattened shape
this considerably increase he surface area to volume ratio and ensures that no part of the body is far from the surface
( maintaining a short diffusion pathway)

Question 16

Earthworms?

Answer 16

terrestrial organism that have developed a tubular shape and are restricted to the damp environment of the soil
elongated shape provides it with a large surface area to volume ratio compared to a compact organism of the same volume
does not require a special surface for gas exchange, it does need to keep its skin moist by secreting mucus on the surface
once oxygen is inside the body, it needs to be transported somedistance to the many internal cells
earthworm has a closed circulatory system
blood also contains respiratory pigment for oxygen transport
oxygen diffuses into the blood capillaries beneath the skin surface and is carried in vessels to the cells with carbon dioxide being transported in the opposite direction
this way, blood system maintains a diffusion gradient at the respiratory surface

Question 17

Amphibians?

Answer 17

include frogs, toads and newts
frogs = typical in that they live in moist habitats as they require water for fertilisation
tadpoles also live in water and have gills
inactive adult uses moist skin as a respiratory surface and this provides sufficient oxygen for its needs
however, when active frog uses lungs as respiratory surface

Question 18

Metamorphosis?

Answer 18

transition from larva to land living adult

Question 19

Reptiles?

Answer 19

include crocodiles, lizards and snakes
far better suited to life on land than amphibians
repitles can move on all four limbs without the trunk of the body touching the ground
pairs of ribs can project from the vertebrae
ribs provide support and protection to the organs in the body cavity
ribs = also involved in the ventilation of the lungs
lung has more complex internal structure than that of amphibians with the in growth of tissues increasing the surface area for gas exchange

Question 20

Birds?

Answer 20

lungs of birds have an internal structure similar to that of mammals
however, large volumes of oxygen are needed to provide the energy for flight
( highly metabolic demanding )
ventilation of the lungs in birds = far more efficient than in other vertebrates
assisted by a system of air sacs connected to the lungs

Question 21

How do the air sacs function?

Answer 21

when a bird breathes in, any air that remains in the lungs from a previous ventilation is sucked into the sacs
lungs = filled with fresh air, avoiding the dead space that occurs in the lungs of other vertebrates such as mammals
ventilation of the lungs is brough about by the movement of the ribs
there is no diaphragm as in humans
during flight, the action of the flight muscles ventilates the lungs
gas exchange is very efficient with virtually no residual gas remaining in the lung tubes

Question 22

Insects?

Answer 22

have a segmented body with a rigid exoskeleton made of chitin
outside of the exoskeleton is covered with a layer of wax - making it impermeable to water and gases
( not suitable at all to gas exchange)

Question 23

Structure of insects breathing system?

Answer 23

tracheal system consisting of tubes leading from the outside to the inside of the body
on outside of insect’s body - small holes on each side of the segments through which gases can diffuse
holes - spiracles can open and close to control the level of ventilation

Question 24

What do the spiracles lead to?

Answer 24

system of large tubes called tracheae
each trachea has rings of chitin in its walls and it impermeable to gases
tracheae branch into smaller tubes called tracheoles
tiniest tracheoles - less than 1 nanometre in diameter and can pass between and even into the insects cell
tracheoles contain little or no chitin and are permeable to gases and therefore also to water
carbon dioxide can diffuse from the cells into the tracheoles and oxygen can diffuse from the tracheoles directly into the cells
finest tracheoles = filled with fluid because water diffuses into them from surrounding cells

Question 25

How does an insect diffuse directly between air and tissues?

Answer 25

air filled tracheal system
movement of the air in the insect tracheal system depends mainly on the diffusion of oxygen from and carbon dioxide to the outside air
in the tissues partial pressure of the oxygen is lower than that in the tracheoles so oxygen diffuses from the tracheoles into the tissue
creating a diffusion gradient between tracheoles and the air surrounding the insect
Oxygen diffuses through the spiracles and along the tracheae
since the tracheae are gas filled, diffusion is rapid
diffusion from the tracheoles to mitochondria is in fluid and therefore much slower
but diffusion pathway from tracheoles to mitochondria is very short

Question 26

Small insects?

Answer 26

total diffusion path is no more than 1 nanometre gas transport is entirely by diffusion
in larger insects, such as locusts and during periods of high activity, the tracheal system is actively ventilated by pumping movements of the abdomen
these insects compress their abdomen and squeeze air from the tracheal tubes
fresh air moves into the tubes when the body returns to its normal size

Question 27

when an insect is very active?

Answer 27

lactic acid accumulates into the cells, decreasing water potential
by osmosis, water in the tracheoles is drawn into the cells, causing more air to enter the tracheoles
means that more oxygen comes into close contact with the tissues at the time when it is required

Question 28

Some of the moisture in the tracheoles?

Answer 28

will inevitably evaporate and diffuse out through the spiracles
in hot, dry, windy conditions insects can reduce water loss through their spiracles by closing them by means of a muscular valve
hairs around the spiracles can trap moist air, also reducing water loss

Question 29

Human respiratory system?

Answer 29

most animals have evolved as land animals
their skin is adapted to conserve water and is an unsuitable surface for gas exchange
furthermore, mammals are too large to rely solely on diffusion to exchange gases
would take too long for oxygen to reach the central cells from the skin
mammals have evolved specialised internal organs, the lungs to enable them, to exchange gases without losing too much water

Question 30

Lungs consist of?

Answer 30

tubes of ever decreasing size which end in microscopic bulbous sacs called alveoli
this is where gas exchange takes place

Question 31

How does alveoli adapt for gas exchange?

Answer 31

have very thin walls
moist inner surface
huge combined surface area
rich blood supply

Question 32

Why does the lungs lie deep within the chest?

Answer 32

minimising the water loss from the alveolar surface but means the air must be constantly moved into and out of the lungs so that alveoli are in contact with a constantly changing supply of air
maintaining the diffusion gradient

Question 33

Air entering the mouth?

Answer 33

air enters the airways through the mouth or nasal cavity
air entering via the nose is filtered by hairs in the nasal passages, warmed by contact with the nasal issues and moistioned by cells of the lining mucous membranes
air entering via the mouth is not warmd or moistoned asmuch and is not filterd at all
nasal + buccal cavities lead into the pharynx
( a tube that conducts both food and air)
when food is swallowed, a flap of tissue - epiglottis closes over the opening of the trachea ( glottis)
preventing food entering the trachea
Larynx = box shaped structure just above the trachea
flow of air in and out of respiratory system makes vocal cords vibrate, producing sounds

Question 34

Air passes into trachea?

Answer 34

trachea is held open by horseshoe-shaped rings of cartilage which prevent the trachea collapsing during inspiration, when the external atmospheric pressure is higher than the pressure inside the trachea
gaps in the cartilage rings allow the trachea to be flexible so that food can pass easily down he oesophagus which runs behind trachea

Question 35

Trachea?

Answer 35

lined with mucous membrane containing ciliated epithelium
epithelial cells have microscopic hair like extensions ( cilia)
cilia beat in a wave like manner - moving mucus and any trapped dust particles and microorganisms upwards and out of hte lungs
trachwa subdivides into the left and right bronchus
bronchi = narrower than the trachea but have a similar structure
each bronchus divides repeatedly into smaller tubes called bronchioles
larger bronchioles are lined with flattened cuboidal epithelial cells
some gas exchange takes place through these
larger airways contain smooth muscle which enable them to constrict, small bronchioles can constrict completely because they lack cartilage
bronchioles terminate in numerous alveoli
where most of gas exchange takes place

Question 36

Ventilation of the lungs?

Answer 36

gases flow from a region of higher to lower pressure down a pressure gradient

Question 37

for inhalation to occur?

Answer 37

gas pressure in the alveoli must be less than that in the surrounding atmosphere

Question 38

For exhalation to occur?

Answer 38

the gas pressure in the alveoli must be greater than that of the surrounding atmosphere

Question 39

Humans inhale?

Answer 39

by enlarging the thoracic cavity, which enlarges the lungs as well
this reduces the gas pressure inside the alveoli, creating a pressure gradient which draws air into the lungs

Question 40

Expansion of thoracic cavity?

Answer 40

brought about by the combined movements of the rib cage and diaphragm

Question 41

Cage moved by?

Answer 41

2 sets of intercostal muscles between the ribs

Question 42

Inspiration process?

Answer 42

external intercostal muscles contract
ribs move up and out
diaphragm contracts + flattens
increases volume of the thorax
decreases pressure in lungs
when atmosphere is greater than thoracic pressure, air rushes into the lungs from higher to lower pressure

Question 43

What causes the lungs to expand?

Answer 43

the lungs cannot expand on their own
inner pleural membrane which covers the surface of the lungs,is closely linked to the outer pleural membrane, which lines the inside of the thorax
only a thin layer of fluid separates the 2
expansion of thorax therefore causes lungs to expand

Question 44

What does the diaphragm have to provide enough to overcome a series of resistances ?

Answer 44

the recoil of elastic tissue of the lungs and thorax
the frictional resistance of air as it passes through the hundreds of thousands of small bronchioles leading to the alveoli
the resistance created by the surface tension at the fluid-gas interfaces in the alveoli

Question 45

Exhalation process?

Answer 45

relatively pasasage process
enlargement of the thorax during inhalation, stretches hte tissues of the thorax and lungs, which recoil naturally during exhalation
The diaphragm returns to its resting position by elastic recoil
( becoming domeshaped)
this decreases the size and volume of the thoracic cavity and lungs, raising the pressure of the pressure of the gas inside the lungs
When the pressure inside the lungs exceeds the surrounding atmosphere pressure, the air moves out down its pressure gradient

Question 46

Gas exchange in plants?

Answer 46

Plants respire all the time
plant cells containing chloroplasts are also capable of photosynthesis
Both processes occur during the day
Most of carbon dioxide needed for photosynthesis diffuses into the leaf from the surrounding atmosphere
However, some carbon dioxide is provided by respiration
most of oxygen produced by the photosythesis diffuses out of the leaves, but some of it is used to fulfil the respiratory requirement
During the night, plants also respire and need a supply of oxygen from the atmosphere

Question 47

Adaptations of a leaf for gas exchange?

Answer 47

to enable gas exchange to occur efficiently?
the leaf blade ( lamina) is thin and flat has a large surface area
the spongy mesophyll allows for the circulation of gases
the plant tissues are permeated by airspaces
gases can move into and out of the lead throuh the stomatal pieces

Question 48

Adaptations of a leaf for photosynthesis?

Answer 48

In order to photosynthesise efficiently?
Leaves have a large surface area to capture as much light as possible
leaves can orientate themselves so they are held at an angle perpendicular to the sun during the day to expose the max area to the light
leaves are thin to allow light to penetrate the lower layers of cells
cuticle + epidermis are transparent to allow light to penetrate the mesophyll
Palisade cells are elongated nd densely arranged in a layer, or layers
the palisade cells are densely packed with chloroplasts and arranged with their long axis perpendicular to the surface
the chloroplasts can move within the mesophyll cells, allowing them to arrange themselves into the best positions for the efficient absorption of light
the intercellular air spaces in the spongy mesophyll allow carbon dioxide to diffuse to the cells + oxygen can diffuse away

Question 49

Stomata?

Answer 49

are small pores found on the lower epidermis of a leaf which allows the movement of gases into and out of the leaf
each stoma is surrounded by 2 guard cells which control the opening and closing of the stomatal pore
each guard cell has an unevenly thickened wall
( where the inner wall is thicker than the outer wall)

Question 49

What do guard cells do?

Answer 49

control the opening and closing of the stomata by changing the shape as a result of gaining or the losing water

Question 49

How is the loss of water prevented when the light intensity is insufficient for photosynthesis?

Answer 49

stomata are open during the day and closed during the night

Question 50

Transpiration?

Answer 50

in order for the inside of the leaf to be open to the atmosphere for gas exchange, it is inevitable that water is lost from the leaves

Question 51

Why do guard cells change shape?

Answer 51

becauseof changes in turgor
if water enters the guard cells, they become flaccid + pore closes

Question 52

What are the changes in turgidity caused by?

Answer 52

increasing the solute concenration in the guard cells

Question 53

Possible mechanism for stomatal opening?

Answer 53

K+ ions are actively transported into the guard cells from the surrounding epidermal cells
starch ( insoluble ) is converted to malate ( soluble )
water potential of the guard cells is lowered and water enters by osmosis
the guard cells become turgid + curve apart due to the uneven thickness of their walls, opening their stomatal pore

Question 54

Why do bony fish have highly efficient gas exchange?

Answer 54

gills provide a large surface area
gills = very thin
concentration gradient being maintained between the blood in the gills + the water passing over them

Question 55

Bony fish?

Answer 55

has 4 pairs of gill arches which support gill filaments on which are gill lamellae
gill lamellae provide a large surface area for gas exchange and contain blood vessels which transport respiratory gases to and from the gills
lamellae are very thin so the blood is only a very short distance from the sea water
water moves across the gill lamellae in the opposite direction to the blood flowing through them
provides a counter current exchange mechanism so water always has a higher oxygen conc than the blood it is flowing past
diffusion can therefore occur over the whole surface of the lamellae
much more efficient than parallel flow system of other fish where blood + water move in the same direction and only 50% of oxygen = absorbed

Question 56

Fish gills?

Answer 56

internal, covered by a bony flap calle the operculum
which protects the delicate gills and also provides bony fish with 2 ventilatory pumps
( an opercular suction pump and a buccal pressure pump)
which can maintain an almost continuous flow of water across the gills
the efficient gas exchange system of fish enables them to live very active lives + colonise all types of water

Question 57

Inspiration in fish?

Answer 57

Side view
buccal cavity is lowered, creating a suction in buccal cavity
operculum closed
lowers pressure
water enters from higher to lower pressure
mouth = shut
View from above
operculum flexes outwards, reducing pressure in opercular cavity
opercular valve closed
water forced through gills by opercular suction pump

Question 58

Expiration?

Answer 58

Side view

opercular valve open
mouth closed
floor of buccal cavity raised, increasing pressure in buccal cavity

View from above

muscles contract forcing operculum inwards
water forced through gills by buccal pressure pump
water ejected through the operculum