Exchange And Transport Systems: - Exchange Of Gases In The Lungs

- Exchange Of Gases In The Lung - 

Role of the alveoli in gas exchange 

Epithelial cells // alveolus is a network of pulmonary capillaries // narrow // red blood cells are flatterned against the thin capillary walls in order to squeeze through.

Diffusion of gases between the alveoli and the blood will be very rapid.


Red blood cells slow down passing through pulmonary capillaries allowing more time for diffusion.

Distance between the alveolar air and red blood cells is reduced as red bloods are flattened against the walls of the capillaries.

Alveoli and capillaries are very thin = short diffusion pathways // made of specialised squamous cells

Exchange And Transport Systems: - Mechanisms Of Breathing.

- Mechanisms Of Breathing - 

There is two types of ventilation 

Inspiration = Active process - requires energy 

External intercostal muscle - Contracts 

Internal intercostal muscle - Relax 

Ribs - Upwards and outwards 

Thoracic cavity - Increases in volume 

Diaphragm - Contract 

Expiration = Passive process - does not require 

External intercostal muscle - Relaxes 

Internal intercostal muscle - Contracts

Ribs - Downwards and inwards 

Thoracic cavity - Decreases in volume 

Diaphragm - Relaxes 

Movement of the intercostal muscles = antagonistic - opposing. 

Exchange And Transport Systems: - Structure Of The Human Gas-Exchange System

- Structure Of The Human Gas-Exchange System - 

Mammalian lung:

Lungs are site of gas exchange in mammals 

They are in the body as the air is not dense to support and protect 

Body as whole would otherwise lose a great deal of water and dry out. 

Lungs are specialised for gas exchange:

When you breath in air this travels down the Trachea // windpipe.

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Bronchi/Bronchus is the split of the trachea at the end of the wind pipe. 

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Bronchioles is the further branching of the bronchi into smaller tubes. 

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Alveoli are at the end of the bronchioles which are 'air sacs'. 

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The rib-cage, intercostal muscles and diaphragm all work together to move air in and out. 

Exchange And Transport Systems: - Limiting Water Loss

- Limiting Water Loss - 

Limiting water loss in insects 

Insects have evolved the following adaptations:

- Small surface area to volume ratio = minimise area over which water is loss 

- Waterproofing covering = outer skeleton of chitin is covered with waterproof cuticle.

- Spiracles = opening of the tracheae at the body surface can be closed due to water loss occurs when the body is asleep. 

Limiting water loss in plants 

Terresteral plants have waterproof covering 

Some have restricted supply of water = limiting water loss through transpiration // xerophytes

Modifications of a plant is made by:

- Thick cuticles 

- Rolling up of leaves 

- Hairy leaves 

- Stomata in pits and grooves 

- Reducing surface area to volume ratio of the leaves

Exchange And Transport Systems: - Gas Exchange In Plants

- Gas Exchange in plants - 

Gas exchange is able to occur in plants due to their adaptations.

These adaptations would include - 

Thin = Short diffusion pathway// Carbon dioxide and oxygen can pass in and out of the plant cell. 

Large surface area = this would allow for an effective gas exchange because its able to occur over a larger area. 

Air spaces between the spongy mesophyll = allows a diffusion gradient to be maintained 

Guard cells = controls the amount of Carbon dioxide and oxygen diffuses in and out of the cell. 

For a most gaseous exchange to occur:
- There are many small pores // stomata // no cell is far from a stoma // short diffusion path.
- Numerous interconnecting air-spaces occur throughout the mesophyll
- Large surface area of mesophyll cells // rapid diffusion

Stomata:

Each stoma is surrounded by pair of special guard cells which open and closes the stomata pores // controls the rate of gaseous exchange // plants evolved to balance the conflict between gas exchange and controlling the water loss in the plant.

Exchange And Transport Systems: - Gas Exchange In Fish

- Gas Exchange in fish -

Fish have many different adaptation that give would give the fish large surface area for gas exchange. 

In a fish there are rows of gill filaments which are stacked like pages of a book. 

On the gill filaments there are gill lamellae which has a network of capillaries on them. This provides a larger surface area for gas exchange. 

counter-current flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

Water and blood flow over and through the lamellae in the opposite direction. // Parallel. 

When the blood first comes close to the water, water is fully saturated with oxygen and the blood has small amounts. 

This creates a steep concentration gradient // oxygen diffuses out of the water and into the blood. 

As the blood is absorbing more oxygen as it moves along the lamellae // blood reaches the end of the lamella 80% saturated with oxygen. The blood is highly saturated than it was at the beginning of the lamellae.

The concentration has continued to be maintained so it can continue to absorb oxygen from the water. 

Concurrent flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

The blood flows in same direction as the water does.

Water is slightly less saturated as it proceeds to move along the lamellae // water has still highly saturated with oxygen compared to the blood, diffusion still occurs until water and the blood have reached equal saturation. 

The steep concentration gradient continues to decrease as the diffusion of oxygen continues.

Exchange And Transport Systems: - Gas Exchange In Insects

- Gas Exchange in insects -

Insects do not have a transport system so gases would need to transported directly into the respiring tissues. 

Insects use tracheae to exchange gases 

Insects have microscopic air-filled pipes = Tracheae

The air moves into the tracheae through the pores on the surface = Spiracles 

On the insect there are spiracles which are placed along side the body // These spiracles are openings of small tubes running into the insects body. 

Oxygen moves down a concentration gradient towards the cells.

The tracheae branches off into tracheoles //
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Adaptations =
- Thin = quicker rate of diffusion
- Permeable walls = diffusion occurs down a gradient (active transport not needed to pass the molecules)
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Oxygen diffuses into the respiring cells.

Water at the end of the tracheoles allows for a concentration gradient to be maintained // the

Carbon dioxide from the respiring diffuse into the water (higher concentration of CO2 // lower concentration of 02 in the respiring cells).

Rhythmic abdominal movement = moves the air in and out of the spiracles.