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Active transport
What is active transport?
Active transport is a way that cells move substances across their membranes. Unlike diffusion and osmosis, active transport needs
energy from respiration to work.
Active transport moves substances from areas where there are fewer of them to areas where there are more of them. This is the
opposite direction to diffusion.
Active transport lets substances move against the concentration gradient.
Note
Think of it like pushing a ball uphill - you need energy to do it! This analogy helps explain why active transport requires energy from respiration to work against the natural tendency of substances to move down concentration gradients.
How active transport works
Cell membranes contain special proteins called transport proteins. These
proteins act like tiny pumps that use energy to move substances.
Here's how it works:
Energy from respiration powers the transport protein
The protein changes shape This pushes substances from the dilute side to the concentrated side
This happens even when there are already more substances on the other side
Active transport in the gut
When you eat food, glucose enters your small intestine. Your body needs
to absorb this glucose into your blood, even when there's already lots of
glucose in your blood.
Example
Worked Example: Glucose Absorption
Sometimes there's more glucose in your blood than in your small intestine. Active transport can still move glucose from your intestine into your blood because it uses energy to work against the concentration gradient.
This process ensures your cells get the glucose they need, regardless of concentration differences.
This is really important because your cells need glucose for respiration.
The glucose goes to your mitochondria to make energy.
Active transport in roots
Plants need mineral ions like nitrate ions ( ) to grow properly and
make proteins.
The problem is that soil water contains very few mineral ions - it's a very dilute solution. But plant cells need lots of these ions.
Active transport solves this by:
Using energy to absorb mineral ions from soil water Moving ions from the dilute soil water into plant cells
NO 3 −
Active transport needs energy from respiration to work
Moves substances against the concentration gradient (from low
to high concentration)
Uses transport proteins in cell membranes that act like pumps Essential in the gut for absorbing glucose when blood glucose is
already high
Essential in plant roots for absorbing mineral ions from very
dilute soil water
Different from diffusion and osmosis because it requires energy
and can work against gradients
