7-2 The Plasma Membrane

Mrs. Geist

Biology, Fall 2010-2011

Swansboro High School

Cell MembraneAll cells are surrounded by a thin, flexible barrier known as the cell membrane.

The cell membrane regulates what enters and leaves the cell and also provides protection and support.

Selectively permeable- allows some substances to pass and others cannot.

The lipid bilayer gives cell membranes a flexible structure.

Most cell membranes contain protein molecules embedded in the lipid bilayer.

Some of these proteins have carbohydrate molecules attached to them.

“Fluid mosaic model”

Cell Membrane

Outside of cell

Cell membrane

Inside of cell (cytoplasm)

Protein channel

Proteins

Lipid bilayer

Carbohydrate chains

The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer.

Cell Walls

Many cells also produce a strong supporting layer around the cell membrane known as a cell wall.

Provides support and protection for the cell.

Found in plants, algae, fungi, and many prokaryotes.

Most cell walls are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily.

Made up of cellulose.

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8.1 Cellular Transportpp. 195-200

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Warm-Up 09/20/2010

What is diffusion?

Describe what happens when a tea bag is placed in a cup of water.

Diffusion Through Cell Boundaries

Every living cell exists in a liquid environment.

The cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

Measuring Concentration

A solution is a mixture of two or more substances.

The substances dissolved in the solution are called solutes.

A solvent is a liquid or gas that dissolves a solute, resulting in a solution.

The concentration of a solution is the mass of solute in a given volume of solution, or mass/volume.

i.e. 12 grams of salt in 3 liters of water12 g/3 L = 4 g/L

i.e. 12 grams of salt in 6 liters of water12 g/6 L = 2g/L

Diffusion Through Cell Boundaries

Diffusion is the tendency of particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated.

When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

Equal numbers of particles move in each direction. No net change.

Diffusion does not require energy (passive).

Diffusion depends upon random particle movements.

Diffusion

Equilibrium

Higher Concentration

Lower Concentration

Particles move down the

concentration gradient

Osmosis

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Osmosis is the diffusion of water through a selectively permeable membrane.

Osmosis

Water tends to diffuse from a highly concentrated region to a less concentrated region.

If you compare two solutions, the more concentrated solution is hypertonic (“above strength”).

The more dilute solution is hypotonic (“below strength”).

When concentrations of solutions are the same on both sides of a membrane, the solutions are isotonic (“same strength”).

Equilibrium

Water out

Water in

Osmosis

Cells in large organisms are not in danger of bursting

They are bathed in fluids, such as blood, that are isotonic.

Other cells are surrounded by tough cell walls

The cell walls prevent the cells from expanding, even under tremendous osmotic pressure.

The increased osmotic pressure makes the cell extremely vulnerable to injuries to their cell walls.

Facilitated Diffusion

The movement of specific molecules across cell membranes through protein channels is known as facilitated diffusion.

Fast and specific

Passive

will only occur if there is a concentration gradient

Facilitated Diffusion

Protein channel

Glucose molecules

Molecules, such as glucose, that cannot diffuse across the cell membrane’s lipid bilayer on their own move through protein channels instead.

Active Transport

Sometimes cells move materials against a concentration gradient through a process known as active transport.

Requires energy.

Small molecules and ions are carried across membranes by proteins in the membrane.

Allows cells to concentrate substances in a particular location, even when diffusion might move them in the opposite direction.

Active Transport Molecule to be carried

Active transport of particles against a concentration gradient requires transport proteins and energy.

Protein channel

EndocytosisEndocytosis is the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane.

Form of active transport.

The pocket breaks loose from the outer portion of the cell membrane and forms a vacuole within the cytoplasm.

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Endocytosis (cont’d)

Two examples of endocytosis are:1. Phagocytosis- extensions of cytoplasm

surround a particle and package it within a food vacuole. The cell then engulfs it. o requires a considerable amount of energy.

2. Pinocytosis- tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell.

Exocytosis

Many cells also release large amounts of material from the cell, in a process called exocytosis.

During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

Form of active transport.

Endocytosis vs. Exocytosis

Endocytosis

7-2

Unlike a cell wall, a cell membraneis composed of a lipid bilayer.

provides rigid support for the surrounding cell.

allows most small molecules and ions to pass through easily.

is found only in plants, fungi, algae, and many prokaryotes.

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7-2

The concentration of a solution is defined as the

volume of solute in a given mass of solution.

mass of solute in a given volume of solution.

mass of solution in a given volume of solute.

volume of solution in a given mass of solute.

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7-2

If a substance is more highly concentrated outside the cell than inside the cell and the substance can move through the cell membrane, the substance will

move by diffusion from inside the cell to outside.

remain in high concentration outside the cell.

move by diffusion from outside to inside the cell.

cause water to enter the cell by osmosis.

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7-3

The movement of materials in a cell against a concentration difference is called

facilitated diffusion.

active transport.

osmosis.

diffusion.

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7-3

The process by which molecules diffuse across a membrane through protein channels is called

active transport.

endocytosis.

facilitated diffusion.

osmosis.

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Diversity of Cellular Life

Unicellular organisms are made up of only one cell.

Unicellular organisms dominate life on Earth.

Organisms that are made up of many cells are called multicellular.

There is a great variety among multicellular organisms.

Cells throughout an organism can develop in different ways to perform different tasks.

This process is called cell specialization.

Animal cells are specialized in many ways.

Specialized Animal Cells

Red blood cells transport oxygen.

Cells in the pancreas produce proteins.

Specialized Plant Cells

Plants exchange carbon dioxide, oxygen, water vapor, and other gases through tiny openings called stomata on the undersides of leaves.

Highly specialized cells, known as guard cells, regulate this exchange.

Stomata enclosed by guard cells.

4 Levels of Organizationindividual cells- structural and functional units of all living things.

Tissues- Similar cells are grouped into units called tissues.

A tissue is a group of similar cells that perform a particular function.

Most animals have 4 main types of tissue: (1) muscle, (2) epithelial, (3) nervous, and (4) connective

Organs- groups of tissues that work together to perform a specific function.

organ systems- a group of organs that work together to perform a specific function

Levels of Organization

Smooth muscle tissueMuscle cell Stomach Digestive system

Cell Tissue Organ Organ System

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Ch. 7

Cell specialization is characteristic ofbacteria.

all unicellular organisms.

yeasts.

multicellular organisms.

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Ch. 7

Which of the following cells is specialized for contraction?

muscle cell

red blood cell

pancreatic cell

nerve cell

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Ch. 7

The stomach is an example of a(an) tissue.

organ.

organ system.

organism.

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Ch. 7

Which of the following shows the levels of organization in an organism from the simplest to the most complex?

organ system, organ, cell, tissue

tissue, cell, organ, organ system

cell, tissue, organ, organ system

cell, organ, tissue, organ system

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Ch. 7

Which of the following would probably contain the greatest variety of specialized cells?

an organ system

a tissue

an organ

a multicellular organism