Transport Into and Out of Cells

Cells are surrounded by a cell membrane which controls the movement of substances into and out of the cell; it’s selectively permeable, allowing some particles through but not others.
Processes involved in the movement of substances are either passive (no energy required) or active (energy required).
Passive movements include diffusion, osmosis and facilitated diffusion.
Diffusion is the net movement of particles from an area of higher concentration to one of lower concentration. This process continues until the particles are evenly distributed.
Osmosis is a specific type of diffusion involving the movement of water molecules across a partially permeable membrane, from a region of high water concentration (dilute solution) to a region of low water concentration (concentrated solution).
Facilitated diffusion is where substances that cannot directly pass through the cell membrane are helped across by carrier proteins or protein channels.
Active transport is the process by which cells move substances from an area of lower concentration to an area of higher concentration - against the concentration gradient. Cells use energy released from respiration for this process.
Large molecules such as proteins and lipids can move into or out of cells by endocytosis or exocytosis, both active processes. In endocytosis, the cell membrane engulfs the molecule, while in exocytosis, the cell actively expels the molecules.
Both temperature and surface area to volume ratio affect the rate of transport across cell membranes. Higher temperatures make particles move more quickly, increasing the rate of diffusion. Cells with a large surface area to volume ratio can transport substances more quickly due to the greater area available for diffusion or osmosis.
It is crucial to note that any disruption to these transport processes, such as in diseases or drug action, can heavily impact cell function and thus have broader consequences on organism health.