Ch15 – Animal transport + Exchange systems

Use these “I am cards” LINK ABOVE – as a revision tool. They are a nice fun way of revising. The idea is that each card has a question (2nd statement) and an answer to another question on it (first statement). You can start with any card and that will be the one you finish with. Take any card at random ask the question and find the answer from another card, then read the question on that card before finding the next. If you complete the task without all cards used, you’ve answered something wrong.

These can be used in several ways. 1. Cut them out and put them in order. or  2 Cut them out and distribute evenly between your study group.

Part 1 – Animal transport.

Special surfaces for exchange

All animals need to maintain a supply of the materials they need (for example nutrients and oxygen, and for the removal of waste products of metabolism). In single-celled organisms (unicellular) these needs can be met purely by diffusion. This is because the distances are short, mere nanometres or millimetres in length. They have a relatively large surface area in comparison with their size, so exchange can happen across their cell surface.

However, larger multicellular organisms cannot rely upon diffusion. The distances that diffusion would have to take place over (the diffusion paths) are too great and the surface area is small in comparison to larger animals’ sizes. Therefore, they need specialist exchange surfaces and a transport system to deliver materials to and from exchange surfaces and satisfy the demands created by high activity levels.

Surface-Area-to-Volume Ratio in Cubes

The size of an animal is what affects itssurface-area-to-volume ratio (SA:Vol). This is because as the size of an organism increases, its volume will increase at a much faster rate (cubic) than its surface area (squared). This means that as the size of the organism increases, the SA:Vol ratio decreases more and more.

The three cubes to the left are increasing in size from a length of 1cm, to 2cm, to 3cm. As you can see, the surface area does not increase as rapidly as volume, therefore the SA:Vol ratio quickly drops from 6 to 3 to 2, and would continue to.

The heart

You should know your heart structure from S3. You should be able to label heart diagrams and demonstrate the direction of the flow of blood.

The heart – Blood flow

You must be able to describe the path of blood as it flows through the heart.



The animation below shows how blood flows through the heart as it contracts and relaxes. Written and spoken explanations are provided with each frame.


Human Circulatory system.

You must know not only the blood flow through the hear but through the entire human circulatory system. Where does oxygenated blood go? What is it used for? Where does de-oxygenated blood come from and what is its fate?

Blood vessels.

The circulatory system has 3 main vessels, you should be able to compare the differences in the structure of these vessels. How do there structure relate to there function?

Red Blood Cells

Again you must understand the structure of a red blood cells, and how this relates to the job they do (function)

You must also understand how blood appears bright red when oxygenated and dark red when deoxygenated. In oxygen-rich environments (ie the lungs), haemoglobin combines with oxygen to form oxyhaemoglobin. In low-oxygen environments (such as body cells), oxyhaemoglobin releases the oxygen to become haemoglobin again.

This process is summarised here:

The oxygenation process


Part 2a – Organs of gaseous exchange.

The lungs (structure)


Can you label the following worksheet.

In addition where are the rings of cartilage?…. What is their function?

The lungs (Cillia and Mucus)

The lungs (Internal structure of the lung – Alveloli and capilary network)


The following website describes the structure and function of the alveoli with an animation which demonstrates the exchange of gases from lungs to blood and vice versa.

Part 2b – Food transport systems.

The Digestive system (structure)


The Digestive system (PERISTALSIS)

The end products of digestion

Part of a starch molecule is shown.  With the addition of specific enzymes the protein is broken down into separate glucose molecules.

Part of a protein molecule is shown.  With the addition of specific enzymes the protein is broken down into separate amino acids.

Fat molecules through digestion are broken down into fatty acid and glycerol molecules.

Absorption in the small intestine

Once food is broken down into small molecules they must now be absorbed and transported around the body. This is the job of the small intestine.

Again the small intestine has a very specific structure which lends itsel to being very good at its job.

Role of villi

The structure of the small intestine is specialised for rapid absorption of small soluble food molecules.

The lining of the small intestine is folded into millions of finger-like projections called villi. This provides a very large surface area, which increases the speed of absorption of small soluble food molecules.

Each villus has the following specialisations to aid absorption:

  • Its lining is only one cell thick, which increases speed of absorption.
  • Capillaries in each villus to provide a good blood supply to take up and transport glucose and amino acids.
  • A lacteal to take up and transport the products of fat digestion.
A villus in the small intestine. The lacteal, a long, relatively thin structure, is surrounded by blood capilliaries.  On one side they are oxygenated, on the other they are deoxygenated.  They are encased in a lining.


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