Active Transport

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.8.4

Active Transport in Humans and Plants

Active transport uses energy and is in charge of moving ions and molecules across a membrane against the concentration gradient.

Carrier proteins

An important membrane adaptation for active transport is the presence of specific carrier proteins to facilitate movement.

Sugar absorption in the gut

One example of active transport is sugar absorption in the gut.
Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed into the blood from the gut, even when the sugar concentration of the blood is higher.

Mineral absorption in plants

Another example of active transport is mineral absorption in plants.
Active transport in the root hairs of plants allows plants to absorb mineral ions, which are necessary for healthy growth, even though the concentration of minerals is usually lower in the soil than in the root hair.

Rate of active transport

The main factors that affect the rate of active transport are:
The surface area of cell membranes.
The number of carrier proteins in cell membranes.

Co-Transport

Co-transport is the mechanism of transport of glucose and amino acid into the epithelial cells in the ileum. Sodium binds to co-transporter proteins to allow glucose and amino acid to be transported.

Sodium-potassium ATPase

Sodium ions are actively transported into the blood by sodium-potassium ATPase, from the inside of epithelial cells lining the ileum.
The concentration of Na⁺ is now lower inside the cell than outside.

Sodium-glucose cotransporter

Two Na⁺ ions from the lumen of the ileum bind to a transmembrane protein known as the sodium-glucose cotransporter.
At the same time, the cotransporter binds with a molecule of glucose from the ileum and moves it into the cell.
The sodium ions diffuse into the cell, moving the glucose into the cell at the same time.

Transport in Cells

The three main forms of transport in cells are:

Diffusion

Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration.
Diffusion is an example of passive transport.

Osmosis

Osmosis is a special case of diffusion where only water molecules move.
Osmosis requires a partially permeable membrane.
Osmosis is an example of passive transport.

Active transport

Active transport is the net movement of particles against a concentration gradient.
So, energy is required.

Test yourself on Active Transport

Which of the following processes does NOT happen via active transport?
Which of the following statements about cotransport are true?
Which ion binds to cotransporter proteins to transport glucose into the epithelial cells in the ileum?
Which enzyme actively transports sodium ions into the bloodstream?
Which of diffusion, osmosis and active transport are examples of passive transport?

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