Transcript GAS EXCHANGE SURFACES FOR BIO

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Name: CEYDA
Surname: Eren
Course: University of Bath Biology
Topic: Gas exchange
Foundation
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Submitted to the Biology Department of the
University of Bath.
RICHARD LLOPIS-GARCIA
Date: 16/03/2007
GAS EXCHANGE SURFACES
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Many organisms have developed adaptations that enable them to
exchange gases efficiently.
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Insects and plants always have to make a compromise between
the need for respiratory gases and problems with water loss.
Gas Exchange Surfaces have FOUR Major Adaptations:
1) They have large surface area to volume ratio.
2) They are thin –often they are just one layer of epithelial cells.
3) There are short diffusion pathways between the gases and
internal tissues.
4) Steep concentration gradients between the tissues where the
gases are absorbed are maintained.
Fick’s Law is used to calculate
Diffusion Rates
 The
rate at which a substance
diffuses can be worked out using
 Fick’s Law:
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Rate of diffusion = Surface area x Difference in concentration
thickness of membrane
Single celled organism
1)Protozoa --> Amoeba or Plasmodium (Malaria)
2) Algal forms --> Chorella
The body surface of a Protoctist is adapted to its
Environment
1) Protoctist are small organisms and they are very diverse organism.
2) In this group if the can not fit other group, they will be in this group.
3) They can behave like animal (protozoa) and plant (algae).
4) Protoctist have soft bodied .
5) Protoctist are unicellular organism( it means that they are single celled
organisms) .
6)Sometimes they are large enough to be seen with naked eye.
7) Sometimes they cause diseases in human such as Malaria and It’s caused
by infection with a protoctist called Plasmodium.
8) Anopheles Mosquito carries the protoctist and it is the vector.
Kingdom of Protoctista
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Cell structure : Eukaryotic, Unicellular, Colonial and Multicellular
forms.
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Cell wall: Sometimes present.
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Nutrition: Autotrophic protoctist
Heterotrophic protoctist.
Other notes: 60.000 protoctist species are aquatic (aquatic refers to
water).
Algae are immobile and they are autotrophic protoctist.
Autotrophic means that organisms are capable of synthesising energy
from inorganic material such as plant who obtain their energy from
the sun.
Protozoa are heterotrophic protoctist.
Heterotrophic means that the organisms can not synthesize their own
food. Therefore rely on other food sources found within
environment (such as Bacteria and Fungi)
Protoctist are well adapted to aquatic environments which only contain
around 1% oxygen
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1) They have all the usual features for efficient gas
exchange = a large, thin surface , and ability to
maintain high concentration gradients.
2) The short diffusion pathway in unicellular organism
means that oxygen can take part in biochemical
reactions as soon as it has diffused into the cell.
Therefore, they are small organisms.
There is no need for circulatory system.
Because Protoctist have no need of ventilation.
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The distance over which Oxygen and Carbon dioxide have
to travel in these creatures are small. So that diffusion fast
enough to meet their needs.
Fish are adapted to live in aquatic Environment
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The lungs of mammal and gills of fish both show that the basic
requirements of an efficient structure of gaseous exchange.
Both need large surface area. The gills achieved this by having
hundreds of filaments, with many branches on each filament.
Gill filaments are called lamellae.
The wall of gill lamellae are also made from very thin squamous
epithelium to minimise the diffusion distance.
A blood system carries gases between the gaseous exchange
surface and the respiring cells and the gills. There is a dense
network of capillaries which carry blood close to the surface of
the gill lamellae.
At the same time, capillaries enable rapid exchange of oxygen
and carbon dioxide between the blood and the water or air.
Capillaries are separated from the water or air by only a thin
epithelium (single layer of cells). So that the diffusion of gases is
a rapid as possible.
Location and the Structure of Fish
Gills
What is counter current system?
Although water molecule contains oxygen, this can not used by
aquatic organism.
 Oxygen comes from the atmosphere and is dissolved in the
water.
 Fish absorb dissolved Oxygen from the water by means of gills.
 Water constantly flows over the gills and the oxygen diffuses into
the blood.
 That’s because oxygen is more concentrated in the water than in
the blood inside the capillaries.
 Some of the fastest moving fish have a counter current system
where the blood and the water flow in opposite direction.
Advantage of counter current system.
 It maintains a high concentration gradient of oxygen between the
water and the blood.
 It allows 90% of the available oxygen in the water to diffuse into
the blood.
 NOTE: if blood and water flowed in the same direction, the blood
could pick up 50% of the available oxygen, and net diffusion into
the blood would stop at this concentration.
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The diagram presents a generic representation of a countercurrent exchange system, with two
parallel tubes containing fluid separated by a permeable barrier. The property to be exchanged,
whose magnitude is represented by the shading, transfers across the barrier in the direction from
greater to lesser according to the second law of thermodynamics. With the two flows moving in
opposite directions, the countercurrent exchange system maintain a constant gradient between the
two flows over their entire length. With a sufficiently long length and a sufficiently low flow rate this
can result in almost all of the property being transferred.
By contrast, in the concurrent (or co-current, parallel) exchange system the two fluid flows are in
the same direction. As the diagram shows, a concurrent exchange system has a variable gradient
over the length of the exchanger and is only capable of moving half of the property from one flow to
the other, no matter how long the exchanger is. It can't achieve more than 50%, because at that
point, equilibrium is reached, and the gradient declines to zero.
Compare the Gas Exchange System between the fish, mammal,
insects
Organism-Name of gas exchange-Is there any ventilation?-Is blood
involved?
FISH
Gills
Yes
Yes
MAMMAL
Lungs
Yes
Yes
Insects
Tracheoles
Very little
No
Insects use Trachea to Exchange Gases:
Insects are active animals and so need a lot of oxygen. The system
for gas exchange is different from that of any other group of
animals.
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Insects have a system of tubes that lead directly from the outside
atmosphere to the working tissues. The tubes called ‘tracheoles’.
Insect’s deal with gaseous exchange by having microscopic airfilled pipes called ‘trachea’. Trachea penetrates the whole of the
body from pores on the surface called spiracles.
Trachea branch off into smaller trancheoles
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Tracheoles have thin,permeable walls and go to individual
cells.
This means that gases are not transported by blood and the
oxygen diffuses directly into the respiring cells.
Trancheoles must be short. Because the diffusion need to
be slow.That’s why the insects are quite small.
NO need for circulatory system. Because insects use
rhytmic abdominal movements – to move air in and out of
spiracles.
Generally large insects can move the abdomen up and
down to pump air in and out.
Plants exchange gases at the surface of the mesophyll
cells
Plants do not have special breathing organs.
Because they do not move like animals.
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Plant leaves have large surface area to the air.
Therefore, Oxygen and carbon dioxide through
stomata into the intercellular spaces is fast enough
for respiration going in their cells by diffusion.
Most plants leaves are thin, the distances for the
diffusion are also very short.
Plants exchange gases during respiration and
photosynthesis. The main gaseous exchange is the
surface of the mesophyll cells. Mesophyll cells in the
leaves.
This is well adapted for its function: So that the plant
leaves have large surface area.
Structure of Mesophyll cells in leaves
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Upper and lower epidermis in leaves is called Mesophyll. It consists
of two zones: 1) upper palisade mesophyll
2) lower spongy mesophyll
The palisade cells are usually: Long and contain many chloroplasts.
The spongy cells are : vary in shape and fit loosely together, leaving
many spaces between them.
In daylight, some of the Oxygen produced by photosynthesis is used in
respiration and the carbon dioxide released from respiration is used
in photosynthesis.
In darkness, only respiration is going on.( Because there is no light).
So carbon dioxide released from passes out of the leaf and oxygen
diffuses in.
Chemical equation for photosynthesis:
(SUNLIGHT)
6CO2
+
UPTAKE OF CARBON DIOXE
6H20
UPTAKE OF WATER
--->
(CHLOROPHYLL)
C6H1206 +
PRODUCTION OF SUGAR
602
RELEASE OF OXYGEN
Gases pass back and forth from outside through
special minute pores and these pores are
mainly present in the lower epidermis called
stomata.
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Plants can open and close the stomata, which
helps to minimise water loss whilst allowing
photosynthesis to continue.
The stomata can open to allow exchange of
gases and close if the plant is losing too much
water.
Insects and Plants can control water loss:
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The problem with opening like stomata and spiracles are
designed to allow gases in and out is that they can lead to
water loss. Plants and insect have adapted which prevent
dehydration.
How does the insect can control water loss?
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Insects have muscles that they can use to close their
spiracles if they are losing too much water.
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They also have tiny hairs around their spiracles which
reduce evaporation.
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Insects body covered with an exoskeleton made of
chitinious cuticle.
Exoskeleton is a skeleton covering outside of body chitin is a
fairly hard waterproof covering made by the cells of
epidermis. It protects organs inside and prevents the loss of
water.
How does the plant can control water loss?
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Major environmental factors that cause the loss of water from leaves and
affect the transpiration:
4.
Humidity
Temperature
Wind
Light
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In plants, the stomata are usually kept open to allow gaseous exchange.
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During the night, Proton pumps in the guard cells pump H+ ions out of
them. This opens potassium channels, allowing K+ ions to enter to the
guard cells.
Potassium concentration in the guard cell vacuoles increase. This lower the
water potential of the cell sap and water enters the guard cell by osmosis.
This inflow of water raises the turgor pressure inside the guard cells. The cell
wall next to the stomatal pore, is thicker than elsewhere in the cell and it
is able to stretch.
Although increases turgor tends to expand the whole guard cell, the thicker wall
can not expand. This causes the guard cells to curve in such a way that the
stomatal pore between them is opened.
What is transpiration?
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1.
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4.
Process of evaporative water loss in plants is called
Transpiration.
This essentially has happened by different osmotic
pressure between the air and the leaves of plant.
If osmotic pressure of air is bigger than the osmotic
pressure within leaves.
Transpiration: %90 of water “absorbed” by roots lost
through transpiration in leaves.
Water lost by Transpiration through stomata
Transpiration rate regulated by two guard cells
surrounding each stoma.
Water needed for metabolic activity such as
photosynthesis.
If plants prevent water loss by closing guard cells then no
C02 can enter for photosynthesis.
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2) If the plants starts to get dehydrated, high light levels
and temperature cause abscisic acid to be released.
Abscisic acid is produced in most parts of the plants and
prepares the plant for dormancy ( the period when they do
not grow) by inhibiting growth.
Also plays a role in drought response.
Abscisic acid stimulates the closure of the stomata in
leaves when water is in short supply dehydration, and
inhibits germinating in seeds.
When this abscisic acid to be released, this stops the
proton pump working and no water enters the guard cell
by osmosis.
Therefore, The guard cells become flaccid, which means the
turgor pressure falls and the guard cells straighten up
and close the stomatal pores.
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THE END