Biology: Transport Mechanisms

Biology: Transport Mechanisms

Transport Mechanisms in Biology

• Transport mechanisms refer to the different ways substances (like water, nutrients, waste) move in and out of cells or throughout the body.
• All forms of transport mechanisms are governed by the laws of physics and chemistry.

Passive Transport

• Passive transport is a type of cell transport that does not require energy as substances move along their concentration gradient, i.e., from a region of high concentration to a region of low concentration.
• There are three main types of passive transport: diffusion, osmosis, and facilitated diffusion.

Diffusion

• Diffusion is the random movement of particles from a region of high concentration to low concentration.
• This process continues until the concentration of the substance is uniform throughout, which is called equilibrium.

Osmosis

• Osmosis is the diffusion of water across a semi-permeable membrane. Water moves from an area of low solute concentration to an area of high solute concentration.
• It is important in many biological processes such as plant cell turgor and water reabsorption in kidneys.

Facilitated Diffusion

• Facilitated diffusion involves the use of protein channels or carrier proteins in the cell membrane. It is utilised for substances that cannot easily cross the lipid bilayer like ions, large molecules, or when the concentration gradient isn’t sufficient to power diffusion.

Active Transport

• Active transport is a type of cell transport that requires energy (in the form of ATP) as substances are moved against their concentration gradient, i.e., from a region of low concentration to a region of high concentration.
• It is key for maintaining cell ions balance, such as sodium-potassium pumps in nerve cells.

Bulk Transport

• Bulk transport refers to the transport of large particles or many molecules at once by the cell membrane.
• Endocytosis is when the cell membrane engulfs the particles to bring them into the cell, forming a vesicle.
• Exocytosis occurs when a vesicle inside the cell fuses with the cell membrane to release the particles outside the cell. It is commonly seen in processes like neurotransmitter release or waste expulsion.

Transport in Plants

• In plants, water is transported from the roots to the leaves via xylem vessels, while nutrients (e.g. sugars produced in photosynthesis) are transported in the phloem.
• This movement of water and nutrients, known as translocation, is essential for the plant’s survival and growth.

Transport in Humans

• In humans, the cardiovascular system, including the heart, blood, and blood vessels, is responsible for the transport of nutrients, oxygen, hormones, and metabolic waste products.
• The cardiovascular system works in tandem with other systems, like the respiratory system for gas exchange, or the digestive system for nutrient uptake.