1. Name: CEYDA
Surname: Eren
Course: University of Bath Biology Foundation
Topic: Gas exchange
Submitted to the Biology Department of the University of Bath.
RICHARD LLOPIS-GARCIA
Date: 16/03/2007

2. GAS EXCHANGE SURFACES
Many organisms have developed adaptations that enable them to exchange gases efficiently.
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.
They are thin –often they are just one layer of epithelial cells.
There are short diffusion pathways between the gases and internal tissues.
Steep concentration gradients between the tissues where the gases are absorbed are maintained.

3. Fick’s Law is used to calculate Diffusion Rates
The rate at which a substance diffuses can be worked out using
Fick’s Law:
Rate of diffusion = Surface area x Difference in concentration
thickness of membrane

4. 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 ) They can behave like animal (protozoa) and plant (algae) ) 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.

5. Kingdom of Protoctista
Cell structure : Eukaryotic, Unicellular, Colonial and Multicellular forms.
Cell wall: Sometimes present.
Nutrition: Autotrophic protoctist
Heterotrophic protoctist.
Other notes: 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)

6. Protoctist are well adapted to aquatic environments which only contain around 1% oxygen
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.
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.

7. Fish are adapted to live in aquatic Environment
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.

8. Location and the Structure of Fish Gills

9. 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.

10. 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.

11. 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.
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 air-filled pipes called ‘trachea’. Trachea penetrates the whole of the body from pores on the surface called spiracles.

13. Trachea branch off into smaller trancheoles
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.

14. Plants exchange gases at the surface of the mesophyll cells
Plants do not have special breathing organs.
Because they do not move like animals.
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.

15. Structure of Mesophyll cells in leaves
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)
6CO H > C6H
UPTAKE OF CARBON DIOXE UPTAKE OF WATER (CHLOROPHYLL) PRODUCTION OF SUGAR RELEASE OF OXYGEN

17. Gases pass back and forth from outside through special minute pores and these pores are mainly present in the lower epidermis called stomata.
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.

19. Insects and Plants can control water loss:
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?
Insects have muscles that they can use to close their spiracles if they are losing too much water.
They also have tiny hairs around their spiracles which reduce evaporation.
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.

20. How does the plant can control water loss?
Major environmental factors that cause the loss of water from leaves and affect the transpiration:
Humidity
Temperature
Wind
Light
In plants, the stomata are usually kept open to allow gaseous exchange.
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.

22. What is transpiration?
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.

23. 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.

26. THE END