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Homeostasis and Transport Movement of cellular materials in and out of the cell.
Cell membranes help cells maintain homeostasis by controlling what substances may enter or leave cells.
Cell membranes are selectively- permeable in that they allow only certain substances to pass.
I - Passive Transport No energy input from the cell.. No ATP energy molecules used.
Simplest type of Passive Transport: (simple) Diffusion It is the (random) movement of molecules from an area of higher concentration to an area of lower concentration.
In other words… Materials move from where there’s more to where there’s less.
This difference in concentration of molecules (over a given area)is called the concentration gradient Diffusion movement occurs with, (or down) the concentration gradient.
Diffusion is driven by the kinetic energy of the molecules.
Kinetic Energy – Energy of Movement from an area of low to high concentration
Eventually the process of diffusion reaches equilibrium. At equilibrium the concentration of molecules are the same throughout the space. (The concentration gradient disappears)
Are the molecules still moving at this point (equilibrium)? Yes. Molecules of a substance are always in motion to some degree except at absolute zero. The net movement is zero.
Osmosis The process by which H 2 O molecules diffuse across a cell membrane (selectively permeable membrane) from an area of HIGH concentration to LOW concentration.
The net direction of water movement depends on the relative amount of solutes (dissolved substances) on the two sides of the cell membrane.
THE THREE BASIC TYPES OF SOLUTIONS: Hypotonic Hypertonic Isotonic
Hypotonic solute concentration outside the cell is lower than inside the cell cytosol. water diffuses into the cell
Hypertonic solute concentration outside the cell is higher than inside the cell cytosol. water diffuses out of the cell
Isotonic solute concentration outside and inside the cell are equal thus, NO net movement of water into or out of the cell
How do cells deal with osmosis? Isotonic – usually no difficulties interesting chromosome pattern makes this cell have a happy face
Hypotonic environment Unicellular freshwater organisms rid themselves of excess water by an organelle called a contractile vacuole. (Other cells cannot get rid of the water and they may burst)
What happens to an animal cell under different conditions?
What happens to a plant cell under different conditions?
Facilitated Diffusion It is a type of passive transport in which molecules pass through pores in the cell membrane. Carrier proteins help move molecules across the membrane.
II - ACTIVE TRANSPORT Cell expend energy to move materials. Active transport always needs ATP energy molecules
Active Transport is usually against the concentration gradient. Materials move from low to high concentration.
EXAMPLES OF ACTIVE TRANSPORT Cell Membrane Pumps (such as the Sodium-Potassium pump) It involves Carrier proteins Sodium-Potassium Pump is important for nerve cells.
Endocytosis - cells take in fluids, large molecules, large particles and other cells. Vesicles are formed to ingest materials.
Two major types of endocytosis: pinocytosis – movement of solutes or fluids (Cell-drinking)
phagocytosis – movement of large particles or whole cells. (cell-eating) Amoeba uses pseudopodia to engulf food.
Exocytosis (the reverse of endocytosis) Vesicles fuse with the cell membrane, releasing their contents to the outside environment.
Unicellular organisms may get rid of wastes through exocytosis.
Cells and Their Environment Chapter Passive Transport Part 1: Diffusion Remember: Living things need to maintain homeostasis (responds to external.
Homeostasis depends in part on appropriate movement of materials across the cell membrane. Homeostasis refers to the necessity of an organism to maintain.
How do cells maintain balance? Cells need to maintain a balance by controlling material that move in & out of the cell HOMEOSTASIS.
Cellular Transport. Review of Diffusion Movement of particles from an area of higher concentration to an area of lower concentration.
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