Mass Transport

The movement of large quantities of substances around an organism.

e.g. mammals – blood

plants – xylem, phloem

Circulatory System of a Mammal

Why do large organisms need a transport system?

Increasing size = decrease in SA:V.

Have specialised exchange systems.

Need to be linked to a transport system.

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Components of circulatory systems

Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises:

a heart

vessels through which the fluid can flow.

a fluid in which substances are transported

The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates).

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Open circulatory systems

An open circulatory system consists of a heart that pumps a fluid called haemolymph through short vessels and into a large cavity called the haemocoel.

When the heart relaxes, the haemolymph blood is sucked back in via pores called ostia.

Haemolymph moves around the haemocoel due to the movement of the organism.

heart

haemocoel

In the haemocoel, the haemolymph directly bathes organs and tissues, enabling the diffusion of substances.

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Closed circulatory systems

In a closed circulatory system, blood is fully enclosed within blood vessels at all times.

From the heart, blood is pumped through a series of progressively smaller vessels. In the smallest vessels, capillaries, substances diffuse in and out of the blood and into cells.

Blood then returns to the heart via a series of progressively larger vessels.

heart

capillaries

Features of Effective Transport Systems:

• A suitable medium in which to carry materials.

• A form of mass transport in which the transport medium is moved around in bulk over large distances.

• A closed system of tubular vessels that contains the transport medium.

Features of Effective Transport Systems:

• A mechanism for moving the transport medium within vessels.

• A mechanism to maintain the mass flow in one direction.

• A mechanism of controlling the flow of the transport medium.

Feature Solution? A suitable medium in which to

carry materials.

A closed system of tubular vessels that contains the transport

medium.

A mechanism of controlling the flow of the transport medium.

A form of mass transport in which the transport medium is moved

around in bulk over large distances.

A mechanism for moving the transport medium within vessels.

A mechanism to maintain the mass flow in one direction.

Transport System in Mammals:

• A suitable medium in which to carry materials - blood

• A form of mass transport in which the transport medium is moved around in bulk over large distances – circulatory system

• A closed system of tubular vessels that contains the transport medium – blood vessels (arteries, veins and capillaries)

Transport System in Mammals:

• A mechanism for moving the transport medium within vessels - muscular contraction of the heart

• A mechanism to maintain the mass flow in one direction – valves

• A mechanism of controlling the flow of the transport medium – heart rate, vasodilation, vasoconstriction

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Closed circulatory systems

Questions:

Name the blood vessel in each of the following descriptions:

1. Joins the right ventricle to the capillaries of the lungs pulmonary artery

2. Carries oxygenated blood away from the heart aorta

3. Carries deoxygenated blood away from the liver hepatic vein

4. The first main blood vessel that an oxygen molecule reaches after being absorbed from an alveolus pulmonary vein

5. Has the highest blood pressure aorta

Questions:

1. State two factors that make it more likely that an organism will have a circulatory pump such as the heart.

Warm blooded, large in size, fast metabolism

2. What is the main advantage of the double circulation system found in mammals?

Rapidly delivers and removes oxygen and CO2 at high pressure over longer distances