Download 2.2 Adaptations for Gas Exchange

2.2 Adaptations for Gas Exchange
Material Needs...
• What sort of things do living things need to
obtain from the environment?
• What sort of things do they need to remove
from their cells?
• Organisms are differently adapted so gas
exchange can take place whether it be in
water or on land.
• In particular oxygen is needed to convert
organic molecules into energy through the
process of respiration.
• NB: Gas exchange is the process by which
oxygen reaches cells and waste products are
removed, don’t confuse with respiration which
is energy production in cells.
• By what process does gas exchange take
place?
Diffusion and problem of size
• Diffusion occurs according to Fick’s Law:
Rate of Diffusion
Surface Area x concentration difference
distance
Think about this for a moment...
What does it mean?
An organism’s requirements may be
proportional to volume
...however diffusion is proportional to surface
area
organism
length
SA (m²)
SA/vol
(m-1)
vol (m³)
1 μm
(10-6 m)
6 x 10-12
10-18
6,000,000
amoeba
100 μm
(10-4 m)
6 x 10-8
10-12
60,000
fly
10 mm
(10-2 m)
6 x 10-4
10-6
600
dog
1m
(100 m)
6 x 100
100
6
100 m
(102 m)
6 x 104
106
0.06
bacterium
whale
• As organisms get larger their volume to
surface area increases meaning they cannot
rely on diffusion alone as the diffusion path
would be too long.
Exchange in Protozoa
• Protozoa –
single celled, hetrotroph,
which does not have a cell
wall.
E.g. paramecium, amoeba
(eukaryote)
• In small, unicellular organisms the surface
area to volume ratio is so large that diffusion
through the body surface is sufficient to supply
their needs.
• An example of this is an amoeba where the
cell membrane acts as the exchange surface, It
is thin and moist so is efficient at its job
• Multicellular organisms are an aggregation of
cells.
• Cells aggregate together to increase their size but
decreases their surface area to volume ratio
• Diffusion path increases
• Materials are needed to be exchanged between
different organs as well as the organism and the
environment.
• So diffusion is no longer a viable process of
exchange.
• Larger organisms therefore possess special
surfaces for gaseous exchange, gills for aquatic
environments, lungs for terrestrial environments.
• Gas exchange surfaces such as the gills of a fish,
the alveoli in the lungs of a mammal, the trachae
of an insect and the spongy mesophyll cells in the
leaves of a plant are effective exchange surfaces.
Exchange surfaces
• a large surface area
• a thin permeable surface
• Most are moist to allow a medium for gasses
dissolve in before diffusion
• a mechanism to maximise the diffusion
gradient by replenishing the source and/or
sink.
Systems that increase rate of Exchange
system
large surface area
small distance
high concentration gradient
human lungs
600 million alveoli with a total area of 100m²
each alveolus is only one cell thick
constant ventilation replaces the
air
Fish gills
feathery filaments with lamellae
lamellae are two cells thick
Leaves
surface area of leaves of 1 tree is 200m²,
surface area of spongy cells inside leaves
of 1 tree is 6000m².
gases diffuse straight into leaf cells
water pumped over gills in
countercurrent to blood
wind replaces air round leaves, and
photosynthesis counteracts
respiration
The large moist area for gaseous exchange is a region
of potential water loss
Worms
• Simple multicellular animals such as worms have
a low oxygen requirement
• They have an extremely low metabolic rate as
they move very slowly.
• Oxygen and carbon dioxide are able to diffuse
across the skin surface
• No specialised gas exchange surface is required
Earthworm
• Elongated shape ensures
a larger surface area to
volume ratio enabling
diffusion to take place.
• Low metabolic rate so
does not require much
oxygen.
• Mucus is secreted to keep
the skin moist
• They possess a simple circulatory system: a
closed blood system containing blood within
vessels .
• The blood contains a respiratory pigment that
transports oxygen.
• Oxygen is carried to the cells whilst carbon
dioxide is transported in the opposite direction,
thus maintaining the diffusion gradient at the
respiratory surface.
Flatworms
• Flattened shape
increases the SA: V and
ensures a short
diffusion path for
exchange.
• Lives in aquatic
environments
Fish
• Fish are more active
• In fish gaseous exchange happens at the gill.
• At the gill a specialised pumping mechanism pumps
a one way current of water over the surface.
• The density of the water keeps the gills from collapsing
in on themselves which would reduce surface area.
• Gills are made up of many folds providing a large
surface area.
• Fish can be further classified into two groups according
to the material that makes up their skeleton:
– Cartilaginous fish
– Bony Fish
Cartilaginous fish
•
•
•
•
•
Skeletons are made entirely of cartilage.
Normally live in the sea e.g. shark
Characterised by five gill clefts that open at five gill slits.
Gas exchange involves parallel flow.
Therefore blood travels through the capillaries in the same
direction as the sea water.
• This is relatively inefficient as a diffusion gradient is not
maintained.
Bony Fish
•
•
•
•
Internal skeleton made of bone
Gills are covered by the operculum
Gas exchange involves Counter current flow.
Blood in the capillaries flow in the opposite direction to
the water flowing over the gill surface.
• This is more efficient as the gradient is maintained and
exchange is able to happen over the whole gill surface
• FLASH
• Water is a dense medium with a low oxygen
content
• To increase efficiency, it needs to be forced
over the gill filaments by pressure differences
• This maintains a continuous, unidirectional
flow of water
• So how does a fish do this?
•
•
•
A lower pressure is maintained in the opercula cavity than in the bucco-pharynx.
The operculum acts as a valve
It also acts as a pump drawing water over the gill filaments.
The ventilation mechanism for forcing water over the gill is:
• mouth
• Opens
• operculum
• Closes
• Floor of buccal cavity
• lowered
• volume
• increases
• pressure
• decreases
• Water flows in
• Compared with parallel flow, counter current flow
increases efficiency because the diffusion gradient
between the adjacent flows is maintained over the
whole surface.
• Blood flows between the gill plates under pressure in
the opposite direction the blood in the capillaries.
• The blood always meets water with higher oxygen
content than itself.
• It removes 80% of the oxygen from the water.
• This high level of extraction is important as there is
25% less oxygen in water than in air.
Terrestrial Vertebrates
• What classes does this include?
• Amphibians, reptiles, birds and mammals
• Terrestrial vertebrates have adapted for exchange
with air, a less dense medium, instead of water,
so have internal lungs.
• Internal lungs minimise loss of water and heat.
Amphibians
• This was likely the first vertebrate group to
colonise the land.
• They have lungs for use on land but in water
gas exchange occurs through diffusion as they
have permeable moist skin which acts as a
respiratory surface.
• Tadpoles have gills for use in water.
• How then do frogs sit at the bottom of a pond
for hours on end?
• Can use its skin as a respiratory surface but
ONLY when it is inactive
Reptiles and Birds
• Reptiles and birds have more efficient lungs than
amphibians.
Reptiles:
• Ribs protect the inner organs and provide
ventilation to the lungs.
• Tissues in lungs provide a greater surface area.
Birds:
• Large volumes of oxygen are needed for flight.
• ventilation of the lungs are assisted by air sacs
• the action of flight muscles ventilate the
lungs.
Human Respiratory system
Ventilation
• What is ventilation?
– Ventilation is movement of air into and outside
the body
• Why do we need it?
So what is the respiratory system????
• The respiratory system includes everything we
use to breath and supply our bodies with
Oxygen is then
oxygen.
We breath air into
Our lungs
transferred into
the blood
Blood then takes the oxygen
around the body supplying
vital organs and limbs with
oxygen
Alveoli
Single layer of flattened epithelial cells
Capillaries run close by (1 cell thick)
Layer of elastic tissue holds them together
Secrete surfactant to stop alveoli collapsing
SIMPLE DIFFUSION – oxygenated air in
alveoli; deoxygenated blood in
capillaries
Gaseous exchange in the alveoli
• CO2 moves from the
blood into the
alveoli (alveolar air)
• O2 moves from
oxygen-containing
air, across to the red
blood cells (tidal
air)
Ficks Law
Rate of Diffusion
Surface Area x concentration difference
distance
How does this apply to alveoli?
Large surface area – ‘grape’ like structure of alveoli
Short diffusion distance – alveoli are 1 cell thick
Concentration gradient – continuous blood flow maintains gradient on
capillary side; air in the alveoli is constantly refreshed
Breathing…
INHALING
Diaphragm contracts and
lowers
Chest cavity volume
increases
Pressure in the lungs
decreases
Breathing…
EXHALING
Diaphragm relaxes and
moves up
Chest cavity volume
decreases
Pressure in the lungs
increases
Different types of lung capacity
• Tidal volume:
• Is the amount of air you breath in or out with each breath
• Inspiratory capacity:
• is the most air you can breath in after breathing out normally.
• Expiratory reserve volume:
• Is the most air you could force out after breathing out normally
• Vital Capacity:
• Is the most air you could possible breath in or out in one go.
• Residual Volume
• Is the amount of air left in your lungs after you’ve breathed out as much as
possible.
A SPIROMETER is used to measure these
Insects
• Insects have a relatively inefficient,
open circulatory system with no
vessels to carry oxygen to different
parts of their body.
• A centralised respiratory system, such
as lungs, would not meet the
respiratory demands of the insect's
cells.
• Insects have evolved a very simple
tracheal system that relies on a
network of small tubes that channel
O2 directly to the different parts of the
body
• The tracheal system is composed of chitin-ringed
tubes called tracheae
• these connect directly to the air through openings
in the body wall called spiracles.
• The tracheae are reinforced with rings of chitin,
the same material that makes up the exoskeleton
• Small inactive insects rely solely on diffusion
• Bigger active ones may ventilate the tracheae
Plants
Xeromorphic adaptations in flowering
plants
• Xeromorphic adaptations reduce water loss
from aerial parts
• Thicker Cuticles
Xeromorphic adaptations in flowering
plants
• Xeromorphic adaptations reduce water loss
from aerial parts
• Thicker Cuticles
• Reduction in leaf size
• Curling or rolling of leaves
Xeromorphic adaptations in flowering
plants
• Xeromorphic adaptations reduce water loss from
aerial parts
•
•
•
•
•
Thicker Cuticles
Reduction in leaf size
Curling or rolling of leaves
Number of stomata
Epidermal hairs
Hydrophytes
• Grow where water freely available:
– in, around or on ponds lakes and streams
• Some live completely submerged:
Canadian Pond weed (Elodea sp.)
Water Milfoil (Myriophyllum sp.)
No Cuticle
No Stomata
Reduced vascular / supporting tissue
Small leaves / dissected leaves
Air spaces
• Some Hydrophytes like water lilies are rooted
to bottom, leaves float on surface
• These leaves have special adaptations:
– Stomata on upper surface
– No stomata on lower surface
– Elongated lignified cells (sclerids) stop leaves
rolling up
– Thick palisade mesophyll
Stomata
•
•
•
•
•
•
•
•
Opening:
Hydrogen ions (or products) leave the
guard cells.
Potassium ions enter the guard cells.
Chloride ions subsequently enter the
guard cells.
The osmotic pressure of the cell
increases (water potential
decreases).
Water enters the guard cells.
The guard cells become turgid.
Because of the construction of the
cells, the stomata open.
• Closing:
• Potassium ions leave the guard
cells.
• Chloride ions also leave the
guard cells.
• The osmotic pressure
decreases (water potential
increases).
• Water leaves the guard cells.
• The guard cells become
flaccid.
• Because of the construction of
the cells, the stomata close.