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Unlock This CourseImagine dropping a drop of food colouring into a glass of water. Watch as the colour slowly spreads throughout the water without you stirring it. This is diffusion in action! Diffusion is one of the most important ways that substances move around in living things.
Every second of every day, your cells are using diffusion to get oxygen, remove waste and transport nutrients. Without diffusion, life as we know it simply wouldn't exist.
Key Definitions:
All particles are constantly moving and vibrating due to kinetic energy. When there are more particles in one area than another, more particles will randomly move from the crowded area to the less crowded area. This continues until the particles are evenly spread out - we call this equilibrium.
Think of a concentration gradient like a hill. Just as a ball naturally rolls downhill, particles naturally move from high concentration (top of the hill) to low concentration (bottom of the hill). The steeper the hill, the faster the ball rolls. The greater the concentration difference, the faster diffusion occurs.
Several factors determine how quickly diffusion happens. Understanding these helps explain why some processes in your body work faster than others.
Higher temperature means particles move faster, so diffusion speeds up. This is why perfume spreads more quickly on a hot day than a cold one.
The bigger the difference in concentration, the faster diffusion occurs. It's like having a steeper slope for particles to 'roll down'.
More surface area means more space for particles to move through. Your lungs have millions of tiny air sacs to maximise surface area for gas exchange.
If you could unfold all the tiny air sacs in your lungs, they would cover about half a tennis court! This huge surface area allows rapid diffusion of oxygen into your blood and carbon dioxide out of it.
Diffusion is everywhere in biology. From the smallest bacteria to the largest whale, all living things depend on diffusion to survive. Let's explore some key examples that show just how important this process is.
Every time you breathe, you're witnessing diffusion in action. Your lungs are perfectly designed to make gas exchange as efficient as possible.
Oxygen diffuses from the air in your lungs (high concentration) into your blood (low concentration). At the same time, carbon dioxide diffuses from your blood (high concentration) into the air in your lungs (low concentration). The thin walls of the air sacs make this process super efficient.
Plants also rely heavily on diffusion, especially for photosynthesis and respiration. Their leaves are specially adapted to make gas exchange as efficient as possible.
These are tiny pores on leaf surfaces that can open and close. They allow carbon dioxide to diffuse in for photosynthesis and oxygen to diffuse out.
Leaves are thin and have air spaces inside. This creates a large surface area and short diffusion distances for gases.
During the day, plants take in CO₂ for photosynthesis. At night, they release CO₂ from respiration, just like animals do.
Fish can't breathe air like we do, but they still need oxygen. Their gills are amazing diffusion machines! Water flows over the gills in one direction while blood flows through them in the opposite direction. This 'counter-current flow' maintains a concentration gradient along the entire length of the gill, making oxygen uptake incredibly efficient.
Every single cell in your body depends on diffusion to stay alive. Cells need to take in nutrients and oxygen while getting rid of waste products like carbon dioxide and urea.
Cell membranes are selectively permeable, meaning they let some substances through but not others. Small molecules like oxygen, carbon dioxide and water can diffuse freely through the membrane.
Small, uncharged molecules like O₂, CO₂, H₂O and alcohol can pass through cell membranes easily. Larger molecules like glucose need special transport proteins to help them across.
Diffusion isn't just something that happens in textbooks - it's all around us every day! Here are some examples you can observe yourself.
Once you understand diffusion, you'll start noticing it everywhere. These examples show how the same scientific principles work in different situations.
When someone cooks, smell molecules diffuse from the kitchen (high concentration) throughout the house (low concentration). That's why you can smell dinner from upstairs!
Tea leaves release flavour molecules that diffuse throughout the hot water. The hotter the water, the faster the diffusion and the quicker your tea brews.
Perfume molecules diffuse through the air from where you sprayed it. On a warm day, the molecules move faster and the scent spreads more quickly.
Try this at home: Fill a clear glass with cold water and another with hot water. Add a drop of food colouring to each. Watch how much faster the colour spreads in the hot water compared to the cold water. This demonstrates how temperature affects diffusion rate!
Diffusion is absolutely essential for life. Without it, cells couldn't get the materials they need or remove toxic waste products. Understanding diffusion helps us understand how living things have evolved to be so efficient at staying alive.
Evolution has produced amazing adaptations that make diffusion as efficient as possible. These adaptations follow the same basic principles we've learned about.
From the folded inner membrane of mitochondria to the villi in your small intestine, life has evolved countless ways to increase surface area and speed up diffusion. More surface area means faster transport of essential substances.
Understanding diffusion gives us insight into how life works at its most basic level. Every breath you take, every nutrient your cells absorb and every waste product your body removes depends on this fundamental process. It's a perfect example of how simple physical principles can create the complexity and beauty of life itself.