Gas Exchange

The Significance of Surface Area to Volume Ratio

When a cell increases in size the diffusion pathway gets longer, as diffusion from the outer cell surface to the centre of the cell is slow. When the cell becomes very large, diffusion will not meet the cell’s needs , i.e.

to supply nutrients:

and to remove waste:

For an organism to become larger, a number of cells must come together - multicellular.

Name the organisms and state whether unicellular or multicellular

___________ ___________ ___________ ___________

Which organism has the largest surface area:volume ratio?

Surface area to volume ratio

1 2 3

4

Organism Surface Area (cm2)

Volume(cm3)

Surface Area: Volume Ratio

1

2

3

4

1. Complete the above table

2. Which size /shape represents

small mammal large mammal

amoeba earthworm

Gas Exchange - the process by which oxygen reaches cells and carbon dioxide is removed from them.

Unicellular (Single Celled ) Organisms e.g. Amoeba

Simple Multicellular Organisms e.g. Flatworm

Features of an amoeba

Features a

nd adaptations of a

flatworm

Earthworms

Larger and more advanced multicellular animals

Why do multicellular organisms require a

specialised gas exchange surface?

Specialised Gas Exchange Surfaces

Many animals and ________ have evolved specialised gas exchange surfaces so that ______________ of gases into and out of cells can take place rapidly and efficiently.

Gas exchange surfaces include :

• in fish

• in the lungs of a mammal

• of insects

In order to achieve the maximum rate of diffusion, all respiratory surfaces must be:

•

•

•

• What additional feature increases the efficiency of gas exchange in

organisms which possess a circulatory system and respiratory pigment?

•

Vertebrate group adaptations for gas exchange

The vertebrates include five classes: amphibia, reptiles, birds, fish and mammals. Life is thought to have evolved in water with animals adapting in order to colonise the land. This section looks at how terrestrial (land living) animals are adapted for gas exchange.

Amphibians The amphibians include , and .

In amphibians, the larvae (tadpoles) live in water and have __________ for gas exchange

The adult amphibians live on_______, .

Gas exchange in adults:

when inactive (at rest) -

when active (e.g. mating) -

Reptiles

These include:

Pairs of ribs project from the vertebrae (backbone)

Give 2 functions of the reptile ribs

How does the structure of reptile lungs differ from that of amphibian lungs

Birds

The lungs of birds have an internal structure similar to______________.

Why do birds need large volumes of oxygen?

Lung ventilation in birds is far more efficient than in other _____________.

Ventilation is assisted by a system of _______ sacs connected to the lungs. The air sacs function as bellows. In birds, breathing in fills the lungs with completely fresh air. The air passes through the bird’s respiratory system in one direction only, bringing the fresh air firstly into the _____________ air sacs and then into the lungs. Finally the air flows into the ____________ air sacs before it exits through the ______________.

Ventilation is brought about by the movement of the ________.

During flight the action of flight____________ ventilates the lungs.

Insects

Insects fly, which requires lots of__________ and so they need a good supply of ________ for respiration. The gas exchange system is different from other land animals, because they do not use _________ to transport gases. Air diffuses into the insect through paired holes called ___________ running along each side of the body. The spiracles lead to a system of branched chitin lined air tubes called ___________. The spiracles can open and close like valves. Why is this important?

At rest, simple diffusion of gases meets the needs of the insect.During periods of activity e.g. flight, movements of the ____________ ventilate the tracheae.

The Gas Exchange Surface of Insects

What structural feature ensures that the tracheae remain open?

Why are the gas exchange organs retained inside the body of terrestrial (land living) organisms?

The tracheae branch repeatedly until they end as very fine, thin-walled tracheoles. Oxygen diffuses directly from the end of the tracheoles into the cells, __________ __________diffuses out.

Prevents _______ loss

Prevents _______ loss

Protection - by the ________ or ___________ in insects

Fish

Cartilaginous Fish

Bony Fish

What problems are caused by living in water ?

How do fish overcome these?

Head of a bony fish with operculum pulled back to reveal gills. There are usually ___ gills on each side

Fish Anatomy

Horizontal section through the pharynx and gill region of a bony fish. Water is taken in through the mouth, passes over the gills and is expelled via the operculum. Movements of the buccal cavity floor and operculum allow a one-way current of water to flow through the gills for exchange of gases.

Ventilation mechanism in fish

Water flows in Water flows out

Mouth

Operculum

Floor of buccal cavity

Volume

Pressure

The structure of the gills of bony fish

Along each gill arch there are many thin lamellae and on these are the gill_____________. The gill lamellae therefore have a large __________ ___________ for gas exchange. Blood circulates through the gill plates - oxygen diffuses through the gill plates into the capillaries and ______________ _____________ diffuses out into the water.

Counter Current FlowWater flows between the gill plates in the _____________ direction to the blood flow.

Gas Exchange in the Gills: Counter current v. Parallel flow

Counter current flow

Parallel flow

Human Respiratory System

Inspiration Expiration

Ribs

External intercostal muscles

Diaphragm

Volume of thorax

Pressure in thorax

Outside air (atmospheric) pressure

Inspiration Expiration

Ventilation of the human lungs

Gas Exchange in Alveoli

The alveoli are suitable as a gas exchange surface because:

Surfactant

A chemical substance which covers the surface of the alveoli. Surfactant

reduces ______________ _______________ and prevents the alveoli

from sticking together and collapsing when breathing out.

Structure Function

These move the ribs to expand the thorax

Bronchi branch into these smaller tubes where some gas exchange takes place

Box shaped structure above trachea, contains vocal cords.

Main site of gas exchange, have a large surface area

Trachea splits in two of these

This prevents the alveoli from sticking together and collapsing, it also reduces surface tension

Tube held open by rings of cartilage

These bones are moved by the intercostal muscles and alter the size of the chest cavity

This dome shaped muscle relaxes and contracts altering the volume of the chest cavity

Contains pleural fluid which acts a lubricant to reduce friction during ventilation

Flap of skin that stops food entering the trachea when swallowing

Acts as a lubricant allowing friction free movement against the inner wall of the thorax

Summary of Gas Exchange

•Ventilation is the movement of a ______________ medium over the respiratory ______________ and maintains a diffusion gradient.

•Internal Transport System (blood circulation) moves gases between _________________ cells and the respiratory _____________

•Respiratory Pigment increases the ____________ carrying capacity of the blood, e.g. Haemoglobin

Organism Respiratory medium

Gas exchange surface

Ventilation Blood Circulation

RespiratoryPigment

Amoeba

Flatworm

Earthworm

Fish

Amphibian

Reptile

Bird

Insect

Mammal

Transverse section through a Leaf

One of the functions of leaves is gaseous exchange.

How are they are adapted for this function ?

•

•

•

•

Gas exchange in plants

The leaf is also adapted for photosynthesis in the following ways :-

•Large ______ _______

•Leaves can orientate themselves towards the _________

•___________ to allow _________ to penetrate lower layers

•Cuticle and epidermis are ______________

•______________ cells are elongated and densely packed together and contain many _________________

•_______________ can rotate and move within the mesophyll cells

•Intercellular air spaces allow __________ ___________ to diffuse into the cells , ________ and ______________vapour to diffuse away.

Stomata

Draw stomata in T.S. and surface view

Where in the leaf are stomata found?

What is their role?

How many guard cells surround each stoma (pore)?

What is unusual about guard cells?

they contain _________________

they have unevenly thickened cell____________.

Stomatal opening and closing

The inner cell wall is thick and the outer wall thin, so that if the guard cells become turgid the pore __________ and if the guard cells become flaccid the pore___________.

The mechanism for stomatal opening:

Why are stomata usually open during the day and closed at night?

Turgid cells Flaccid cells

Feature Day (opens) Night (closes)

Potassium pump

Carbon dioxide concentration

pH levels

Enzyme activity

Guard cells contain?

WP

Guard cells become?

Size of pore (stoma)

Mechanism of stomatal opening/closing - Summary