Chapter 5 Homeostasis and Cell Transport

Passive Transport Substances crossing the cell membrane without any input of energy is known as passive transport Diffusion: simplest form of passive transport; the movement of molecules from an area of high concentration to low concentration

Diffusion Utilizes a concentration gradient Driven entirely by kinetic energy of molecules Moving from high to low concentrations Moving “down” a concentration gradient Eventually equilibrium is reached: the concentration of molecules will be the same throughout the space the molecules occupy

Passive Transport https://www.youtube.com/watch?v=1NhAALaUgzQ

Osmosis Osmosis: water molecules diffusing across a cell membrane from an area of higher concentration to lower concentration. Does not expend energy (passive transport) Net direction of osmosis depends on the concentration of solutes on the inside and outside of the cell

Osmosis https://www.youtube.com/watch?v=w3_8FSrqc-I&list=PL57nMW8-72VyRTL4Nvkac5u0TzK3r01Cf&index=5

Osmosis When the concentration of solute molecules outside of the cell is lower than the concentration in the cytosol, the solution outside is hypotonic to the cytosol

Osmosis When the concentration of solute molecules outside the cell is higher than the concentration in the cytosol, the solution outside is hypertonic to the cytosol

Osmosis When the concentrations of solutes outside and inside the cell are equal, the outside solution is said to be isotonic to the cytosol

Osmosis

Osmosis Some cells, such as the animal Paramecium, have contractile vacuoles to physically remove water from their bodies https://www.youtube.com/watch?v=9Ynm5ZOW59Q

Facilitated Diffusion Used for molecules that cannot readily pass the plasma membrane Requires no energy, relies on concentration gradient and the use of carrier proteins in the cell membrane

Diffusion through Ion Channels Ion channels transport ions across a membrane from a higher concentration to a lower concentration Ex: Na+, Cl-, K+ Ions are not soluble across the membrane, so ion channels help them Each channel usually specific to one ion Some are always open, some have “gates”

Ion Channels

Active Transport Movement of materials from a low concentration to a high concentration, or “up” their concentration gradient is known as active transport Often utilize proteins, known as “cell membrane pumps” to move substances across the membrane

Active Transport Utilizes the proteins within the membrane and energy (ATP) to move substances across the membrane against its concentration gradient Ex: Sodium-Potassium Pump

Sodium-Potassium Pump https://www.youtube.com/watch?v=P-imDC1txWw

Movement in Vesicles Endocytosis: process by which cells ingest external fluid, macromolecules, and large particles Utilizes a vesicle for transport Two main types: Pinocytosis Phagocytosis

Movement in Vesicles Pinocytosis: involves transport of solutes or fluids (cellular drinking) Phagocytosis: movement of large particles or whole cells (cellular eating)

Movement in Vesicles Exocytosis: process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface then fuses with the membrane to let the substance out of the cell