Endocytosis & Exocystosis

Biology: IB Diploma Higher Level, topic 6.1.3

Endocytosis and Exocytosis

Endocytosis and exocytosis are two other ways in which substances can be actively transported across membranes using ATP.

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.

Phagocytosis (the condition of “cell eating”) is a type of endocytosis in which large particles, such as cells, are taken in by a cell.
For example, when microorganisms invade the human body, a type of white blood cell called a neutrophil will remove the invaders through this process.
In preparation for phagocytosis, a portion of the inward-facing surface of the plasma membrane becomes coated with a protein called clathrin, which stabilizes this section of the membrane.

Pinocytosis:
This is a process that takes in liquid molecules, including water, which the cell needs from the extracellular fluid.
Receptor-mediated endocytosis:
In this process the uptake of substances by the cell is targeted to a single type of substance that binds to the receptor on the external surface of the cell membrane

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.
An example of exocytosis is the secretion of neurotransmitters into the synaptic cleft by synaptic vesicles.

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?