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Unlock This CourseEvery living thing needs to move substances around to survive. Whether it's getting oxygen to cells, removing waste products, or transporting nutrients, all organisms have ways of moving materials from one place to another. But why do some organisms need complex transport systems whilst others can manage perfectly well without them?
Key Definitions:
Tiny organisms like bacteria and amoeba don't need transport systems. They're so small that substances can easily diffuse across their cell membrane to reach every part of the cell quickly. It's like having a house so small that you can reach anything from the front door!
As organisms get bigger, they face a major challenge. Imagine trying to supply a massive shopping centre with goods through just one small door - it would be impossible! This is exactly what happens when organisms grow larger.
This is one of the most important concepts in biology. As an organism gets bigger, its volume (the space inside) increases much faster than its surface area (the outside). This creates a problem because:
High surface area to volume ratio. Lots of surface for substances to enter compared to the volume that needs supplying. Diffusion works well.
Lower surface area to volume ratio. Still manageable, but diffusion starts to become less efficient for the deepest parts.
Very low surface area to volume ratio. Diffusion alone cannot supply the inner cells quickly enough. Transport systems essential!
An elephant's heart is about the size of a small car and weighs around 25kg! This massive heart is needed because the elephant's huge body creates an enormous volume that needs oxygen and nutrients. Without a powerful circulatory system, the cells in the elephant's feet would never get enough oxygen from the lungs and the elephant would die. Compare this to a tiny shrew, whose heart beats over 1000 times per minute to supply its incredibly fast metabolism.
Diffusion is brilliant for short distances, but it becomes painfully slow over longer distances. Think of it like this: if you drop a sugar cube in a small cup of tea, it dissolves quickly. But if you drop the same sugar cube in a swimming pool, it would take forever to spread throughout the water!
In larger organisms, some cells might be centimetres or even metres away from the surface. Relying on diffusion alone would mean:
Diffusion over 1mm takes about 1 second. Over 1cm, it takes about 100 seconds. Over 10cm, it would take nearly 3 hours! No organism could survive waiting that long for oxygen.
Some organisms are like sports cars - they have high-performance engines that burn through fuel quickly. Others are more like efficient family cars. The faster an organism's metabolism, the more it needs an efficient transport system.
Animals like hummingbirds, shrews and active fish have incredibly fast metabolisms. They need:
Flying requires enormous energy. Birds have highly efficient circulatory and respiratory systems with air sacs that ensure constant oxygen flow.
Warm-blooded mammals need constant energy to maintain body temperature. Their four-chambered hearts ensure efficient oxygen transport.
Fast-swimming fish like tuna have counter-current blood flow in their gills to extract maximum oxygen from water.
Nature has evolved amazing solutions to the transport problem. Let's look at how different organisms have solved the challenge of moving substances around their bodies.
Plants might seem simple, but they have sophisticated transport networks:
Transports water and minerals from roots to leaves. Works like a one-way elevator system, always moving upwards using transpiration pull and root pressure.
Transports sugars and other organic compounds from leaves to all parts of the plant. Can move in any direction depending on where the plant needs energy.
Animals have developed even more complex systems:
A giraffe's heart must pump blood up to 2 metres to reach its brain! The blood pressure in a giraffe's legs would burst human blood vessels. Giant sequoia trees can transport water over 100 metres from their roots to their highest leaves using only the power of transpiration - no pumps needed!
Transport systems aren't just helpful - they're absolutely essential for complex life. Without them, multicellular organisms simply couldn't exist. They enable:
Understanding transport systems helps us appreciate why complex life evolved the way it did and why every multicellular organism from a daisy to a blue whale needs these amazing internal networks to survive.