Cell Membranes Cell and organelle membranes are made
Cell Membranes Cell and organelle membranes are made of two layers - lipid bilayers.
• Cell membranes are semipermeable • It acts like a screen by letting some chemicals in & stopping others. • It is like the doors of the cell.
Passive Transport • The random movement of particles from a greater to a lesser concentration. • Uses no energy. • Three types: – Diffusion – Osmosis – Facilitated diffusion
Diffusion • The random movement of particles from a greater to a lesser concentration. . • Uses no energy. • A molecule will slide through the membrane …only if it will fit.
Simple Diffusion. • Things just naturally want to spread out. • That is what these red particle are doing. They Are DIFFUSING.
• The red particle and the blue particles are diffusing in this picture. • They have to cross a permeable membrane to do it.
Osmosis • Osmosis is the diffusion of water.
• In this case, the membrane is SEMI-permeable. • Only the small particles (the water) can get through. • When only water diffuses, it is called OSMOSIS.
Facilitated Diffusion • The molecules that are too big to get through the membrane use proteins. • Requires no energy! • There are different types of proteins: carrier and channel
A big molecule can use a CHANNEL PROTEIN to get through.
• CARRIER PROTEIN are shaped just like specific molecules. • They grab molecules, suck them in, and spit them out on the other side of the membrane. • This uses no energy. Glucose molecules
To review… Simple Diffusion, Osmosis, and Facilitated Diffusion… 1. Use no energy (Passive Transport) 2. Move particles from greater to a lesser concentration But… what if you want to concentrate a chemical on one side of a membrane?
Active Transport • A process that requires energy • Proteins move molecules across the membrane from lesser to greater concentration. • Except for the above two points, it is the same as facilitated diffusion. • 2 Types: – Molecular transport – Bulk transport • Endocytosis • Exocytosis
ACTIVE TRANSPORT! Active Transport is ACTIVE. It uses energy. Ex. Sodium Pump and minerals entering root cells
Molecular Transport: • occurs when small molecules are carried across the membranes by pumps made of proteins.
This is an example of Molecular Transport
Bulk Transport • Movement of large molecule or clumps of material by movement of the cell membrane. • Two main types: – Endocytosis – exocytisis
Endocytosis • process of taking material into the cell by infoldings or pockets of the cell membrane
A specific type of endocytosis is phagocytosis (“cell eating”) During phagocytosis, extensions of cytoplasm surround the particle and package it to a food vacuole. The cell engulfs it!
Exocytosis • Larger molecules are released by the cell in a process called exocytosis. • the membrane of the vacuole surrounding the material fuses with the cell membrane forcing out its contents.
Other terms to know about osmosis Isotonic Hypertonic Hypotonic
Isotonic: Concentration of solutes(molecules) is the same inside and out of the cell. Water moves equally in and out of cell.
Hypertonic: Solution has higher solute concentration than the cell. Water moves out of cell.
Hypotonic: Solution has lower solute concentration than the cell. Water moves into cell.
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