ch. 7 biology. copyright pearson prentice hall cell boundaries all cells are surrounded by a thin,...

Ch. 7

Biology

Copyright Pearson Prentice Hall

Cell Boundaries

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

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

Cell Membranes are Selectively Permeable

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


Cell Membrane The lipid bilayer gives cell membranes a

flexible structure that forms a barrier between the cell and its surroundings.


Cell Membrane The composition of

nearly all cell membranes is a double-layered sheet called a phospholipid bilayer.


http://www.bioteach.ubc.ca/Bio-industry/Inex/graphics/lipidbilayer.gif

Fluid-Mosaic Model

Membrane composed of different moleculesPhospholipidsCholesterolProteins

Phospholipid molecules form a flexible bilayerCholesterol and protein molecules are

embedded in it Carbohydrates act as cell identification tags

Molecules move laterally

Fluid Mosaic Model

Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

Selectively Permeable

Because of polar and nonpolar regions of the phospholipid bilayer, the membrane allows certain materials in and certain materials out of the cell

Permits exchange of nutrients, waste products, oxygen, and inorganic ions.

Allows some substances to cross more easily than others:

○ Hydrophobic molecules—hydrocarbons, CO2, and O2 dissolve in and cross membrane

○ Very small polar molecules, including H2O can cross easily

Cell Walls The main function of the cell wall is to provide support and

protection for the cell. Cell walls are found in plants, algae, fungi, and many prokaryotes. The cell wall lies outside the cell membrane. Most cell walls are porous enough to allow water, oxygen, carbon

dioxide, and certain other substances to pass through easily.


Diffusion Through Cell Boundaries 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.

11

Diffusion of Liquids

Passive Transport

A substance will diffuse from where it is more concentrated to where it is less concentrated

Only small, uncharged particles diffuse without assistance (H2O, CO2, and O2)

http://sussexhigh.nbed.nb.ca/swift/biology11/Cell%20Boundaries%20ONLINE.ppt#276,25,Section G

Diffusion Through Cell BoundariesDiffusion

○ Particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated.

○ This process is called diffusion. ○ When the concentration of the solute is the same throughout

a system, the system has reached equilibrium.



Diffusion Through Cell Boundaries

There is a higher concentration of solute on one side of the membrane as compared to the other side of the membrane.



Solute particles move from the side of the membrane with a higher concentration of solute to the side of the membrane with a lower concentration of solute. The solute particles will continue to diffuse across the membrane until equilibrium is reached.



When equilibrium is reached, solute particles continue to diffuse across the membrane in both directions.

Diffusion depends upon random particle movements. Therefore, substances diffuse across membranes without requiring the cell to use energy.


Osmosis Osmosis

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.

The more dilute solution is hypotonic.



Osmosis

When concentrations of solutions are the same on both sides of a membrane, the solutions are isotonic.

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What kind of solution is inside the cell?Isotonic

Outside the cell?Isotonic

Which direction will water move?In and out at the

same rate

10 % NaCl

10 % NaCl

10 % NaCl

10 % NaCl

10 % NaCl

10 % NaCl

What kind of solution is inside the cell?Hypertonic

Outside the cell?Hypotonic

Which direction will water move?Into the cell

10 % NaCl

20 % NaCl

10 % NaCl

20 % NaCl

10 % NaCl

20 % NaCl

What kind of solution is inside the cell?Hypotonic

Outside the cell?Hypertonic

Which direction will water move?Out of the cell

30 % NaCl

10 % NaCl

30 % NaCl

10 % NaCl

30 % NaCl

10 % NaCl


Osmosis

Osmotic Pressure Osmosis exerts a pressure known as osmotic

pressure on the hypertonic side of a selectively permeable membrane.

Because the cell is filled with salts, sugars, proteins, and other molecules, it will almost always be hypertonic to fresh water.

If so, the osmotic pressure should produce a net movement of water into the cell. As a result, the volume of the cell will increase until the cell becomes swollen or bursts.


Osmoregulation Water balance between cells and their

surroundings is crucial to organisms The control of water balance is

osmoregulation Cells in large organisms are not in danger

of bursting because they are bathed in fluids, such as blood, that are isotonic.

Other cells are surrounded by tough cell walls that prevent the cells from expanding even under tremendous osmotic pressure.

Osmosis

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http://kvhs.nbed.nb.ca/gallant/biology/water_balance.jpg

Animal cell

Plantcell

FlaccidPlasmolysis Turgid

Facilitated Diffusion The movement of specific molecules across cell

membranes through protein channels is known as facilitated diffusion.

Hundreds of different protein channels have been found that allow particular substances to cross different membranes.

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Facilitated Diffusion Although facilitated diffusion is fast and specific, it

is still diffusion. Therefore, facilitated diffusion will only occur if

there is a higher concentration of the particular molecules on one side of a cell membrane as compared to the other side.

No energy is used.

Solutemolecule

Transportprotein

http://sussexhigh.nbed.nb.ca/swift/biology11/Cell%20Boundaries%20ONLINE.ppt#276,25,Section G

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Facilitated Diffusion

Molecules will randomly move through the pores in Channel Proteins.

https://mattwells.wikispaces.com/file/view/PLASMA~1.PPT

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Facilitated Diffusion Some carrier

proteins do not extend through the membrane.

They bond and drag molecules through the lipid bilayer and release them on the opposite side.



Active Transport

Substances are transported across a membrane, against the concentration gradient

Use carrier proteins embedded in the membrane

Use energy (ATP)

http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/images/sppump.gif

Active transport in two solutes across a membrane

Figure 5.18

Transportprotein

1

FLUIDOUTSIDECELL

Firstsolute

First solute, inside cell, binds to protein

Phosphorylated transport protein

2 ATP transfers phosphate to protein

3 Protein releases solute outside cell

4 Second solute binds to protein

Second solute

5 Phosphate detaches from protein

6 Protein releases second solute into cell

Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

Active Transport:Sodium Potassium Pump

Sodium-Potassium Pump

1. 3 Na+ ions inside the cell bind to the pump. ATP donates a phosphate to the pump

2. The pump changes shape, transporting 3 Na+ across the membrane, and are released outside of the cell

3. 2 K+ ions outside the cell bind to the pump

4. The phosphate group is released and

5. 2 K+ ions are transported across the membrane

6. 2 K+ are released inside the cell

http://gotoknow.org/file/somluckv/Cell_membrane06.jpg


Active TransportEndocytosis and Exocytosis

○ Large molecules and even solid clumps of material may undergo active transport by means of the cell membrane.

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

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

Endocytosis Phagocytosis —

endocytosis of solid particles Forms food vacuoles that

fuse with lysosome to be digested

Pinocytosis —endocytosis of fluid droplets Takes in solutes

dissolved in the droplet

http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/images/phagocyt.gif

http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/images/pinocyt.gif

Active TransportExocytosis

○ 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.

http://www.stanford.edu/group/Urchin/GIFS/exocyt.gif

Three kinds of endocytosis

Figure 5.19C

Pseudopod of amoeba

Food being ingested

Plasma membrane

Material bound to receptor proteins

PIT

Cytoplasm

Vesicle forms from a localized region of cell membrane that sinks inward; pinches off into cytoplasm

Vesicle usually budded from the ER or Golgi and migrates to cell membrane

Used by cells to incorporate extracellular substances

Used by secretory cells to export products (insulin in pancreas; neurotransmitter from neuron)

Process of importing macromolecules into a cell by forming vesicles derived from the cell membrane

Process of exporting macromolecules from a cell by fusion of vesicles with the cell membrane

EndocytosisExocytosis

Figure 5.19A Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

Figure 5.19B

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html

Receptor-mediated Endocytosis

Imports specific macromolecules into the cell by inward budding of vesicles formed from coated pits Occurs in response to binding specific ligands to receptors

on cell’s surface Harmful levels of cholesterol can accumulate in the

blood if membranes lack cholesterol receptors

Figure 5.19

Cell Boundaries and Transport


Unlike a cell wall, a cell membranea) is composed of a lipid bilayer.

b) provides rigid support for the surrounding cell.

c) allows most small molecules and ions to pass through easily.

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


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

a) move by diffusion from inside the cell to outside.

b) remain in high concentration outside the cell.

c) move by diffusion from outside to inside the cell.

d) cause water to enter the cell by osmosis.


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

a) facilitated diffusion.

b) active transport.

c) osmosis.

d) diffusion.


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

a) active transport.

b) endocytosis.

c) facilitated diffusion.

d) osmosis.


The Diversity of Cellular Life The differences among living things

arise from the ways in which cells are specialized to perform certain tasks and the ways in which cells associate with one another to form multicellular organisms.

Unicellular Organisms

Unicellular Organisms○ Unicellular organisms are made up of only

one cell.○ Unicellular organisms dominate life on Earth.

Parameciumhttp://www1.broward.edu/~ssimpson/imgev5.jpg

Euglenahttp://media-2.web.britannica.com/eb-media/15/12015-004-F85E856C.jpg

Lactobacillus acidophilishttp://bioinfo.bact.wisc.edu/themicrobialworld/Lactobacillus.jpg

Multicellular Organisms Organisms that are

made up of many cells are called multicellular.

There is a great variety among multicellular organisms.

http://api.ning.com/files/ORxcmZcFiP6I7PYb0qOoWVxTv5ycZwBGGYXUO8Q5Vt4Jt2C1cvgUvrvIFwf4erW0i31kd7vYS-0skTwphV6eIL6-9sBS254X/Animal_diversity_October_2007.jpg

Multicellular Organisms Cells throughout an

organism can develop in different ways to perform different tasks.

This process is called cell specialization.


http://219.221.200.61/ywwy/zbsw(E)/pic/ech12-2.jpg

Animal cells are specialized in many ways.

Red blood cells transport oxygen. Cells in the pancreas

produce proteins.

Animal cells are specialized in many ways.

Muscle cells allow movement.

Nerve cells coordinate functions throughout the body.


Multicellular OrganismsSpecialized 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.


Levels of Organization Levels of Organization

The levels of organization in a multicellular organism are:○ individual cells○ tissues○ organs○ organ systems

http://www.learner.org/courses/essential/life/images/show1.levels.jpg


Levels of OrganizationIn multicellular organisms, cells are the first level of organization.


Levels of OrganizationTissues

○ Similar cells are grouped into units called tissues.

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


Levels of Organization

Most animals have four main types of tissue:

○ muscle○ epithelial○ nervous○ connective


Levels of OrganizationOrgans

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

Levels of Organization Organ Systems

In most cases, an organ completes a series of specialized tasks.

A group of organs that work together to perform a specific function is called an organ system.


Cell Diversity


Cell specialization is characteristic ofa) bacteria.

b) all unicellular organisms.

c) yeasts.

d) multicellular organisms.


Which of the following cells is specialized for contraction?

a) muscle cell

b) red blood cell

c) pancreatic cell

d) nerve cell


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

b) organ.

c) organ system.

d) organism.


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

a) organ system, organ, cell, tissue

b) tissue, cell, organ, organ system

c) cell, tissue, organ, organ system

d) cell, organ, tissue, organ system


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

a) an organ system

b) a tissue

c) an organ

d) a multicellular organism

Acknowledgements Biology, by Miller and Levine. These images have been

produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without

Essential Biology with Physiology, 2nd ed., by Campbell, Reece, and Simon, ©2007. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2001. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

ch. 7 biology. copyright pearson prentice hall cell boundaries all cells are surrounded by a thin,...

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