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Chapter 4 Cell Structure.

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Presentation on theme: "Chapter 4 Cell Structure."— Presentation transcript:

1 Chapter 4 Cell Structure

2 3A Membranes Objectives:
Describes the structure and composition of a cellular membrane Differentiate between active and passive transport Describe the processes of diffusion and osmosis

3 Membrane Structure Membrane: a thin covering that forms the outer boundary of the cell Membranes sense and respond the changes in the surrounding environment

4 Membrane Structure Composed of molecules of lipids (phospholipids and cholesterol) and proteins. The proteins perform the activities in the membrane Fluid mosaic model: the lipid molecules form a flexible two-layered film in which proteins are embedded

5 Membrane Structure Lipid Bi-layer: phospholipids organized in two layers The phospholipids are in a shape like a head and a tail Hydrophobic tails inside Hydrophilic heads outside


7 Fluidity of the Membrane
Membrane is Fluid Lipids have rapid lateral movement Fluidity depends on lipid composition

8 Fatty Acids Unsaturated Saturaded All C-C bonds are single bonds
Straight chain allows maximum interaction of fatty acid tails Make membrane less fliuid Solid at room temperature Saturaded Some C=C bond (double bonds) Bent chain keeping tails apart Make membrane more fluid Liquid at room temperature

9 Membrane Properties

10 Selective Permeability
Selective Permeability means that the plasma membrane allows some substances to cross through it while also keeping other substances out.

11 Transport of Substances Through the Cell Membrane
The cell uses two main forms of transporting substances in and out of the cell: passive transport and active transport. Passive transport requires no energy Simple diffusion Facilitated diffusion Osmosis

12 Simple Diffusion Diffusion is the passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until the concentration of substances is uniform throughout. High temperatures increase diffusion; large molecules slow diffusion

13 Facilitated Diffusion
Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Channel proteins Carrier proteins

14 Osmosis Osmosis is a special case of diffusion that involves water molecules. In osmosis water diffuses from a hypotonic (low solute concentrated) solution to a hypertonic (high solute concentrated) solution Example: paramecium

15 Active Transport Active transport is the movement of molecules across a cell membrane from an area of lower concentration to one of higher concentration Assisted by enzymes Requires energy



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