Question

Describe the following types of transport processes in cells. simple diffusion, facilitated diffusion, active transport pinocytosis, receptor- mediated endocytosis, phagocytosis and exocytosis

Short answer

Simple diffusion is a passive transport process where small, non-polar molecules move through the cell membrane down their concentration gradient. Facilitated diffusion involves larger, charged or polar molecules moving across the cell membrane with the help of transport proteins. Active transport requires energy to move molecules against their concentration gradient using specialized transport proteins. Pinocytosis, "cell drinking," involves cells engulfing extracellular fluid containing solutes through small vesicles. Receptor-mediated endocytosis selectively transports specific molecules via ligands binding to cell-surface receptors and forming vesicles. Phagocytosis, "cell eating," involves engulfing large solid particles and forming a phagosome for enzymatic degradation. Exocytosis secretes substances like hormones, neurotransmitters, or waste products through vesicle fusion with the cell membrane, maintaining cellular homeostasis and communication.

Step-by-step solution

Simple Diffusion

Simple diffusion is a passive transport process where small, non-polar molecules like oxygen and carbon dioxide pass through the cell membrane down their concentration gradient, without the help of any transport proteins. This process does not require energy as the molecules simply move from an area of higher concentration to an area of lower concentration.

Facilitated Diffusion

Facilitated diffusion is another passive transport process where larger, charged or polar molecules like glucose or ions move across the cell membrane down their concentration gradient with the help of specific transport proteins called channels or carriers. This process also does not require energy input.

Active Transport

Active transport is an energy-consuming process that uses specialized transport proteins to move molecules or ions against their concentration gradient, from an area of low concentration to an area of high concentration. The energy required for this process typically comes from the hydrolysis of adenosine triphosphate (ATP).

Pinocytosis

Pinocytosis, also known as "cell drinking", is a type of endocytosis in which the cell takes in extracellular fluid containing dissolved solutes by engulfing it with small vesicles. This enables the cell to take in various nutrients and samples of the surrounding environment.

Receptor-Mediated Endocytosis

Receptor-mediated endocytosis is a selective transport process in which specific molecules called ligands bind to cell-surface receptors. Once the ligand binds, the cell membrane invaginates, forming a vesicle containing the ligand-receptor complex. This allows cells to internalize specific molecules from the external environment selectively efficiently.

Phagocytosis

Phagocytosis, often referred to as "cell eating", is a type of endocytosis in which a cell engulfs large solid particles such as bacteria, dead cells, or debris. The cell membrane extends around the particle and forms a vesicle called a phagosome, which then fuses with lysosomes for enzymatic degradation of the ingested material.

Exocytosis

Exocytosis is a process where cells secrete substances like hormones, neurotransmitters, or waste products via vesicle fusion with the cell membrane. The vesicle, loaded with the substance to be secreted, moves towards the cell's surface and fuses with the cell membrane, releasing its contents into the extracellular environment. This process is essential for maintaining cellular homeostasis and communication between cells.