1. Cell Boundaries and transport
Ch. 7
Biology
Cell Boundaries and transport

2. 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.
Copyright Pearson Prentice Hall

3. Cell Membranes are Selectively Permeable
The cell membrane regulates what enters and leaves the cell and also provides protection and support.
Copyright Pearson Prentice Hall

4. Copyright Pearson Prentice Hall
Cell Membrane
The lipid bilayer gives cell membranes a flexible structure that forms a barrier between the cell and its surroundings.
Copyright Pearson Prentice Hall

5. Copyright Pearson Prentice Hall
Cell Membrane
The composition of nearly all cell membranes is a double-layered sheet called a phospholipid bilayer.
The cell membrane regulates what enters and leaves the cell.
Copyright Pearson Prentice Hall

6. Fluid-Mosaic Model Membrane composed of different molecules
Phospholipids
Cholesterol
Proteins
Phospholipid molecules form a flexible bilayer
Cholesterol and protein molecules are embedded in it
Carbohydrates act as cell identification tags
Molecules move laterally

7. Fluid Mosaic Model
Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

8. 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

9. 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.

10. 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.
Copyright Pearson Prentice Hall

11. Diffusion of Liquids The Plasma Membrane 4/23/2017
G. Podgorski, Biol. 1010

12. 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) G

13. Diffusion Through Cell Boundaries
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.
Copyright Pearson Prentice Hall

14. 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.
Diffusion is the process by which molecules of a substance move from areas of higher concentration to areas of lower concentration. Diffusion does not require the cell to use energy.
Copyright Pearson Prentice Hall

15. Diffusion Through Cell Boundaries
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.
Diffusion is the process by which molecules of a substance move from areas of higher concentration to areas of lower concentration. Diffusion does not require the cell to use energy.
Copyright Pearson Prentice Hall

16. Diffusion Through Cell Boundaries
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.
Diffusion is the process by which molecules of a substance move from areas of higher concentration to areas of lower concentration. Diffusion does not require the cell to use energy.
Copyright Pearson Prentice Hall

17. Copyright Pearson Prentice Hall
Osmosis
Osmosis
Osmosis is the diffusion of water through a selectively permeable membrane.
Copyright Pearson Prentice Hall

18. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

19. Copyright Pearson Prentice Hall
Osmosis
When concentrations of solutions are the same on both sides of a membrane, the solutions are isotonic.
Copyright Pearson Prentice Hall

20. What kind of solution is inside the cell?
Isotonic
Outside the cell?
Which direction will water move?
In and out at the same rate

21. What kind of solution is inside the cell?
Hypertonic
Outside the cell?
Hypotonic
Which direction will water move?
Into the cell

22. What kind of solution is inside the cell?
Hypotonic
Outside the cell?
Hypertonic
Which direction will water move?
Out of the cell

23. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

24. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

25. Osmosis Animal cell Plant cell Plasmolysis Flaccid Turgid
Animal cell
Plant
cell
Plasmolysis
Flaccid
Turgid

26. 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.
Copyright Pearson Prentice Hall

27. 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.
Solute molecule
Transport protein G
Copyright Pearson Prentice Hall

28. Facilitated Diffusion
The Plasma Membrane
4/23/2017
Facilitated Diffusion
Molecules will randomly move through the pores in Channel Proteins.
G. Podgorski, Biol. 1010

29. Facilitated Diffusion
The Plasma Membrane
4/23/2017
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.
G. Podgorski, Biol. 1010

30. Active Transport
Substances are transported across a membrane, against the concentration gradient
Use carrier proteins embedded in the membrane
Use energy (ATP)

31. Active transport in two solutes across a membrane
FLUID OUTSIDE CELL
Phosphorylated transport protein
Active transport in two solutes across a membrane
Transport protein
First solute 1
First solute, inside cell, binds to protein 2
ATP transfers phosphate to protein 3
Protein releases solute outside cell
Second solute 4
Second solute binds to protein 5
Phosphate detaches from protein 6
Protein releases second solute into cell
Figure 5.18
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

32. Active Transport: Sodium Potassium Pump

33. Sodium-Potassium Pump
3 Na+ ions inside the cell bind to the pump. ATP donates a phosphate to the pump
The pump changes shape, transporting 3 Na+ across the membrane, and are released outside of the cell
2 K+ ions outside the cell bind to the pump
The phosphate group is released and
2 K+ ions are transported across the membrane
2 K+ are released inside the cell

34. Copyright Pearson Prentice Hall
Active Transport
Endocytosis 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.
Copyright Pearson Prentice Hall

35. 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

36. Active Transport 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.

37. Material bound to receptor proteins
Three kinds of endocytosis
Pseudopod of amoeba
Food being ingested
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Figure 5.19C

38. Used by cells to incorporate extracellular substances
Exocytosis
Endocytosis
Process of exporting macromolecules from a cell by fusion of vesicles with the cell membrane
Process of importing macromolecules into a cell by forming vesicles derived from the cell membrane
Vesicle usually budded from the ER or Golgi and migrates to cell membrane
Vesicle forms from a localized region of cell membrane that sinks inward; pinches off into cytoplasm
Used by secretory cells to export products (insulin in pancreas; neurotransmitter from neuron)
Used by cells to incorporate extracellular substances
Figure 5.19B
Figure 5.19A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

39. 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

40. Cell Boundaries and Transport
Quiz
Wiz

41. Copyright Pearson Prentice Hall
Unlike a cell wall, a cell membrane
is 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.
Copyright Pearson Prentice Hall

42. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

43. Copyright Pearson Prentice Hall
The movement of materials in a cell against a concentration difference is called
facilitated diffusion.
active transport.
osmosis.
diffusion.
Copyright Pearson Prentice Hall

44. Copyright Pearson Prentice Hall
The process by which molecules diffuse across a membrane through protein channels is called
active transport.
endocytosis.
facilitated diffusion.
osmosis.
Copyright Pearson Prentice Hall

45. 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.
Copyright Pearson Prentice Hall

46. Unicellular Organisms
Unicellular organisms are made up of only one cell.
Unicellular organisms dominate life on Earth.
Paramecium
Euglena
Lactobacillus acidophilis

47. Multicellular Organisms
Organisms that are made up of many cells are called multicellular.
There is a great variety among multicellular organisms.

48. Multicellular Organisms
Cells throughout an organism can develop in different ways to perform different tasks.
This process is called cell specialization.
Copyright Pearson Prentice Hall

49. Animal cells are specialized in many ways.
Red blood cells transport oxygen.
Cells in the pancreas produce proteins.

50. Animal cells are specialized in many ways.
Muscle cells allow movement.
Nerve cells coordinate functions throughout the body.

51. Multicellular Organisms
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.
Copyright Pearson Prentice Hall

52. Levels of Organization
The levels of organization in a multicellular organism are:
individual cells
tissues
organs
organ systems
Copyright Pearson Prentice Hall

53. Levels of Organization
In multicellular organisms, cells are the first level of organization.
Copyright Pearson Prentice Hall

54. Levels of Organization
Tissues
Similar cells are grouped into units called tissues.
A tissue is a group of similar cells that perform a particular function.
Copyright Pearson Prentice Hall

55. Levels of Organization
Most animals have four main types of tissue:
muscle
epithelial
nervous
connective
Copyright Pearson Prentice Hall

56. Levels of Organization
Organs 
Organs are groups of tissues that work together to perform a specific function.
Copyright Pearson Prentice Hall

57. 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.
Copyright Pearson Prentice Hall

58. Cell Diversity
Quiz
Wiz

59. Copyright Pearson Prentice Hall
Cell specialization is characteristic of
bacteria.
all unicellular organisms.
yeasts.
multicellular organisms.
Copyright Pearson Prentice Hall

60. Copyright Pearson Prentice Hall
Which of the following cells is specialized for contraction?
muscle cell
red blood cell
pancreatic cell
nerve cell
Copyright Pearson Prentice Hall

61. Copyright Pearson Prentice Hall
The stomach is an example of a(an)
tissue.
organ.
organ system.
organism.
Copyright Pearson Prentice Hall

62. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

63. Copyright Pearson Prentice Hall
Which of the following would probably contain the greatest variety of specialized cells?
an organ system
a tissue
an organ
a multicellular organism
Copyright Pearson Prentice Hall

64. 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.