Active Movement Across the Membrane
Biology: Cambridge International A Level, topic 4.2.2
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 adaption 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 (glucose) absorption in the gut.
- Active transport allows glucose molecules, which are needed for cell respiration, to be absorbed into the blood from the gut, even when the glucose 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.
Endocytosis and Exocytosis
Endocytosis and exocytosis are two other ways in which substances can be actively transported across membranes using ATP.
Endocytosis
- Endocytosis is when a cell engulfs a substance from its surroundings.
- This is achieved by the fluid cell membrane folding around the substance.
- At this point, the substance will separate from the membrane and enter into the cytoplasm in a membrane-bound vesicle.
Exocytosis
- Exocytosis is when membrane-bound vesicles fuse with plasma membranes before releasing the substances within them into their surroundings.
- Exocytosis is the process used by cells when they have produced a substance that needs to be exported (e.g. proteins) and when there are toxins that need to be removed from the cell.
Test yourself on Active Movement Across the Membrane
Which of the following processes does NOT happen via active transport?
What is the name given to the process where a cell engulfs a substance from its surroundings?
Which two processes are involved in the active transport across membranes?