• Active transport is the?movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration
  • Active transport?requires energy?in the form of?ATP?from respiration to move substances?against their?concentration gradient; hence this is an?active?process
• Active transport requires?carrier proteins
  • Each carrier protein is specific to a particular type of molecule or ion
• Energy is required to allow the carrier protein to?change shape; this transfers the molecules or ions across the cell membrane
  • The?energy required is provided by ATP?(adenosine triphosphate) produced during respiration
  • The ATP is?hydrolysed?to release energy

Active transport moves substances across a membrane from low to high concentration. Note that ATP is required for carrier proteins to change shape.

• Examples of active transport include
  • Reabsorption?of useful molecules and ions?into the blood?after filtration into the kidney tubules
  • Absorption?of some products of digestion from the digestive tract?into the blood
  • Loading sugar?from the photosynthesising cells of leaves?into the phloem?tissue for transport around the plant
  • Loading inorganic ions?from the soil?into root hair cells

Endocytosis

• Some molecules are?too large?to travel via membrane proteins, e.g.
  • Proteins
  • Lipids
  • Some carbohydrates
• In such cases a cell can?surround a substance with a section of the cell surface membrane
  • The membrane?engulfs?the substance and pinches off inside the cell?to form a?temporary vacuole?with the ingested substance contained inside
  • This is?endocytosis
    • Phagocytosis?is an example of endocytosis
• Endocytosis is an?active process?and requires a source of energy

Phagocytosis is an example of endocytosis; the cell surface membrane extends around a pathogen, engulfing it and enclosing it within a temporary vacuole inside the cell

Exocytosis

• Some substances produced by the cell need to be?secreted, such as hormones, some enzymes, and lipids
• Vesicles?containing the substance?pinch off from sacs of the Golgi apparatus
• These vesicles are moved toward the cell surface and fuse with the cell surface membrane to be released outside the cell
  • This is?exocytosis
• Exocytosis is an?active process?and requires a source of energy

The active processes of endocytosis and exocytosis

Exocytosis allows the bulk secretion of substances from cells