1. Chapter 3: Cell Structure and Function
UNIT A
Chapter 3: Cell Structure and Function
Chapter 3: Cell Structure and Function
In this chapter, you will learn about how cell structures have critical roles to play in the health of an organism.
What other cellular organelles have a similar function to the lysosome?
Why doesn’t the cell “clean up” the faulty lysosomes?
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2. 3.5 The Permeability of the Plasma Membrane
UNIT A
Chapter 3: Cell Structure and Function
Section 3.5
3.5 The Permeability of the Plasma Membrane
The plasma membrane is selectively permeable, allowing passage of only certain molecules.
Figure 3.17 How molecules cross the plasma membrane. Molecules that can diffuse across the plasma membrane are shown with long back-and-forth arrows. Substances that cannot diffuse across the membrane are indicated by the curved arrows.
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4. UNIT A Chapter 3: Cell Structure and Function Section 3.5
Some substances freely cross the membrane. They move “down” their concentration gradient (from high concentration to low concentration).
Some substances are unable to freely cross and are transported by proteins or vesicles. They may go “up,” or against, their concentration gradient.
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5. UNIT A Chapter 3: Cell Structure and Function Section 3.5
Diffusion is the movement of molecules down their concentration gradient. It does not require energy. The rate of diffusion is affected by factors such as temperature, pressure, and molecule size.
A solution contains a solute in a solvent. Diffusion occurs until there is an equal distribution of solute and solvent.
Figure 3.18 Process of Diffusion.
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10. Diffusion of Oxygen UNIT A Chapter 3: Cell Structure and Function
Section 3.5
Diffusion of Oxygen
Only a few types of molecules can diffuse across the plasma membrane.
Gases can diffuse across the bilayer
Oxygen enters cells and carbon dioxide leaves
In lungs, oxygen moves from the alveoli to blood in the capillaries
Figure 3.19 Gas exchange in lungs. Oxygen (O2) diffuses into the capillaries of the lungs because there is a higher concentration of oxygen in the alveoli (air sacs) than in the capillaries.
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11. Osmosis UNIT A Chapter 3: Cell Structure and Function Section 3.5
Osmosis is the diffusion of water molecules across a selectively permeable membrane due to a difference in concentration.
There is a net movement of water and changes in solute concentration on both sides of the membrane
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Figure 3.20 Osmosis demonstration.

16. Isotonic, Hypotonic, and Hypertonic Solutions
UNIT A
Chapter 3: Cell Structure and Function
Section 3.5
Isotonic, Hypotonic, and Hypertonic Solutions
Isotonic solutions have the same concentration of solute and solvent as the solution inside the cell, and water will not enter or leave the cell.
Hypotonic solutions have a lower concentration of solute than solution inside the cell, and water will enter the cell.
Hypertonic solutions have a higher concentration of solute than solution inside the cell, and water will leave the cell.
Prefixes:
iso: the same as
hypo: less than
hyper: more than
_____________
tonicity: refers to osmotic pressure
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21. UNIT A Chapter 3: Cell Structure and Function Section 3.5
Figure 3.21 Osmosis in animal and plant cells.
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22. Transport by Carrier Proteins
UNIT A
Chapter 3: Cell Structure and Function
Section 3.5
Transport by Carrier Proteins
The plasma membrane stops the passage of most molecules into and out of the cell. However, biologically important molecules do pass. They do so because of carrier proteins that exist in the plasma membrane.
Carrier proteins are specific and each binds to specific molecules
Carrier proteins are required for both facilitated transport and active transport of substances across the plasma membrane
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23. Facilitated Transport
UNIT A
Chapter 3: Cell Structure and Function
Section 3.5
Facilitated Transport
Assists in transport of molecules across the membrane by binding to those molecules
Occurs down a concentration gradient and does not require ATP
Figure 3.22 Facilitated transport.
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25. Active Transport UNIT A Chapter 3: Cell Structure and Function
Section 3.5
Active Transport
Assists transport of substances across the membrane by binding to them
Occurs against a concentration gradient and requires energy, usually in the form of ATP
Proteins involved in active transport are often called pumps because they use energy to pump substances against their concentration gradient.
One important carrier protein pump is the sodium-potassium pump. It moves sodium ions to the outside of the cell and potassium ions to the inside of the cell.
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26. UNIT A Chapter 3: Cell Structure and Function Section 3.5
Figure 3.23 The sodium-potassium pump. The same carrier protein transports sodium ions (Na+) to the outside of the cell and potassium ions (K+) to the inside of the cell because it undergoes an ATP-dependent change in shape. Three sodium ions are carried outward for every two potassium ions carried inward. Therefore, the inside of the cell is negatively charged compared to the outside.
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27. Bulk Transport UNIT A Chapter 3: Cell Structure and Function
Section 3.5
Bulk Transport
Macromolecules are transported into and out of the cell by vesicle formation, called membrane-assisted transport in energy-dependent processes.
Exocytosis is a way substances can exit a cell
Endocytosis is way substances can enter a cell
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28. Exocytosis UNIT A Chapter 3: Cell Structure and Function Section 3.5
During exocytosis, a vesicle fuses with the membrane and the substance it is carrying is secreted outside of the cell.
Neurotransmitters, hormones, and digestive enzymes are examples of substances secreted in this way
Figure 3.24 Exocytosis. Exocytosis
deposits substances on the outside of the cell and allows secretion to occur.
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29. Endocytosis UNIT A Chapter 3: Cell Structure and Function Section 3.5
During endocytosis, cells take in substances by vesicle formation.
The plasma membrane folds in on itself and then pinches off to form an intracellular vesicle
Endocytosis occurs in one of three ways.
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
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31. Phagocytosis UNIT A Chapter 3: Cell Structure and Function Section 3.5
During phagocytosis, the material being taken into the cell is large, such as a food particle or another cell.
Common in unicellular organisms and occurs in certain types of human white blood cells
From Figure 3.25 Three methods of endocytosis. a. Phagocytosis occurs when the substance to be transported into the cell is large. Amoebas ingest by phagocytosis. Digestion occurs when the resulting vacuole fuses with a lysosome.
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32. Pinocytosis UNIT A Chapter 3: Cell Structure and Function Section 3.5
During pinocytosis, vesicles form around liquid or very small particles.
Common in blood cells, intestinal cells, and plant root cells
From Figure 3.25 Three methods of endocytosis. b. Pinocytosis occurs when a macromolecule such as a polypeptide is transported into the cell. The result is a vesicle (small vacuole).
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33. UNIT A Chapter 3: Cell Structure and Function Section 3.5
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34. UNIT A Chapter 3: Cell Structure and Function Section 3.5
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35. UNIT A Chapter 3: Cell Structure and Function Section 3.5
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