CELL TRANSPORT

CELL TRANSPORT

Concentration gradient

Types of cell transport

Passive transport

Active transport

Differences between passive anr active transport

CONCENTRATION GRADIENT

A concentration gradient is the movement of particles through an area with a higher number of particles to an area with a lower number of particles between two solutions. This movement is an attempt to establish equilibrium and eliminate the imbalance of solute concentrations between the two solutions.

Passive Transport

• Particles (e.g. ions or molecules) are transported along the concentration gradient.
• The particles move from areas of high concentrations to areas of low concentrations.
• The passive movement of particles, no chemical energy is spent as it takes place.

Simple Diffusion

• It´s the passage of small, hydrophobic, nonpolar molecules from a higher concentration to a lower concentration in order to pass through the membrane.
• Simple diffusion can be disrupted if the diffusion distance is increased.
• The molecule most likely to be involved in simple diffusion is water.

Facilitated Diffusion

• Is a passive transport that uses integral membrane proteins to help larger, charged, hydrophilic, and polar molecules across a concentration gradient.
• Remember that integral membrane proteins span the phospholipid bilayer, connecting the inside and the outside of the cell.

Osmosis

• In diffusion, it is about the movement of solutes. In osmosis, it is about the movement of the solvent, i.e. water molecules.
• In osmosis, the water molecules move from an area of high concentration to an area of low concentration.
• But in order to move across the cell membrane, it has to use a channel protein in the cell membrane.

The Effects of Osmosis on Cells

Example:

Hypotonic solution

Isotonic solution

Hypertonic solution

Examples:

Active Transport

• Active transport is a kind of cellular transport where substances move from an area of lower concentration to an area of higher concentration
• The energy for active transport comes from the energy-carrying molecule called ATP
• This process will require the expenditure of energy, and the assistance of membrane proteins, such as carrier proteins.

Molecular Transport

• Protein molecules act like energy requiring pumps to move molecules and ions across membrane.
• Many cells use protein pumps to move calcium, potassium and sodium ions across cell membrane.
• Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane.

Energy from ATP is used to pump small moleculesand ions across the cell membrane.

Bulk Transport

• Larger molecules, such as proteins, are too large to pass through the plasma membrane.
• These molecules cross the plasma membrane with a different sort of help, called bulk transport. Bulk transport requires energy, so it is also a form of active transport.
• There are two types of bulk transport: endocytosis and exocytosis.

Bulk Transport

1. Endocytosis

• Endocytosis is a type of vesicle transport that moves a substance into the cell.
• The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell.
• When an entire cell or other solid particle is engulfed, the process is called phagocytosis. When fluid is engulfed, the process is called pinocytosis.

(cell eating) This is the ingestion of solids from outside the cell. The plasma membrane encloses particle and buds off to form a food vacuole.

(cell drinking) This is the ingestion of fluid surrounding the cell. The plasma membrane encloses some of the fluid and pinches off to form a vesicle.

Bulk Transport

2. Exocytosis

• Exocytosis is a type of vesicle transport that moves a substance out of the cell.
• A vesicle containing the substance moves through the cytoplasm to the cell membrane. Then, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell.
• Example: The removal of water by means of a contractile vacuole.