3.5 Active Transport, Endocytosis, and Exocytosis

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3.5 Active Transport, Endocytosis, and Exocytosis
KEY CONCEPT Cells use ENERGY to transport
materials that cannot diffuse across a membrane.
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Active Transport
Active transport requires energy input from a
cell and enables a cell to move a substance
against its concentration gradient, from a region
of lower concentration to a region of higher
concentration.

• Active transport is powered by chemical energy
  (ATP).

• Active transport occurs through transport protein
  pumps.

• Cells use active transport to maintain
  homeostasis.

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Endocytosis
MAIN IDEA A cell can import and export large
materials or large amounts of material in
vesicles during the processes of endocytosis and
exocytosis. Energy is required!
Endocytosis is the process of taking material
into the cell such as liquids or fairly large
molecules by engulfing (surrounding) them in a
membrane.
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Steps of Endocytosis
During Endocytosis, the cell membrane folds
inward and fuses together. This surrounds the
substance in a pocket.
The pocket pinches off inside of the cell,
forming a vesicle.
The vesicle fuses with a lysosome or similar
vesicle. Then, enzymes break down the membrane
AND the contents inside!
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Phagocytosis

• Phagocytosis is a type of endocytosis where the
  cell membrane engulfs large particles.
• Phagocytosis actually means cell eating.
• It plays a key role in our immune systems.
• How? Some white blood cells in the human body
  are called macrophages. Their purpose is to
  help fight infection.
• They seek out foreign materials in the body,
  such as bacteria and engulf and destroy them!

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Exocytosis

• Exocytosis is the opposite of endocytosis. It is
  the release or expelling of substances out of a
  cell by the fusion of a vesicle WITH the
  membrane.

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Steps of Exocytosis
The cell forms a vesicle around material that
needs to be expelled from the cell.
The vesicle is transported to the cell membrane.
The vesicle membrane fuses with the cell membrane
and releases the contents from the cell.