1. Review
ATP is the most important form of energy used by cells (“universal energy currency”)
A solute is the material that is dissolved in a solution
A solvent is the liquid in the solution that dissolves the solute

2. Cell Doctrine All living things are composed of cells
A single cell is the smallest unit that exhibits all of the characteristics of life
All cells come only from preexisting cells

3. Two Basic Cell Types Classified by Internal Organization
Prokaryotic Cells
Eukaryotic Cells
Plasma membrane
No nucleus
Cytoplasm: fluid within membrane
No true organelles
(except for ribosomes,
cilia, & flagella)
Plasma membrane
Nucleus: information center
Cytoplasm: fluid within membrane
Organelles: structures with specialized functions
All human cells are eukaryotic

4. a) A eukaryotic animal cell has a large
Plasma
membrane
Cytoplasm
Organelles
Nucleus
a) A eukaryotic animal cell has a large
nucleus and numerous small organelles.
The cytoplasm is enclosed by a flexible
plasma membrane.
Figure 3.1a

5. b) Prokaryotic cells such as this bacterium have a
Plasma
membrane
Cell wall
b) Prokaryotic cells such as this bacterium have a
rigid cell wall surrounding the plasma membrane.
The genetic material is not surrounded by a
membrane, and there are no organelles in the cell.
The elongated bacterium in the center of the photo
is about to divide in two, as its genetic material is
concentrated at both ends of the cell.
Figure 3.1b

6. Cell Structure Reflects Cell Function
Though eukaryotic cells are remarkably similar, there are structural differences
Examples:
Muscle cells
Contain numerous organelles providing energy needed for muscle contraction
Nerve cells
Long and thin to carry impulses over distance
Small size is efficient

7. A portion of several muscle cells of the heart (X1,500).
Figure 3.2a

8. b) Nerve cells of the central nervous system (X 830).
Figure 3.2b

9. c) Cells lining a tubule of a kidney (X 250).
Figure 3.2c

10. Cells Remain Small to Stay Efficient
Small cells have a higher surface:volume ratio
High surface:volume ratio promotes efficiency in
Acquisition of nutrients
Disposal of wastes

11. One large
cell.
Figure 3.4a

12. b) Eight small
cells.
Figure 3.4b

13. Cell with
microvilli
on one surface.
Figure 3.4c

14. Plasma Membrane Surrounds the Cell
Separates a cell from its environment
Selectively permeable
Permits movement of some substances into and out of the cell, but blocks others
Enables communication between environment and cell (an example is insulin, from the pancreas, binding to a part of a liver cell membrane, “telling” it to take up more glucose)

15. A Plasma Membrane Surrounds the Cell
Plasma membrane is a phospholipid bilayer
Phospholipids: polar head and nonpolar tail
Cholesterol: makes membrane a bit more rigid
Proteins: provide means of transport through membrane & some are receptor proteins
Carbohydrates: recognition patterns for cells and organisms
Nonrigid
Fluid mosaic

16. Extracellular environment
Receptor
protein
Channel
protein
(always open)
Gated
channel
protein
(closed
position)
Carbohydrate
groups
Cytoskeleton
filaments
Phospholipid
Lipid
bilayer
Transport
protein
Glycoprotein
Cytoplasm
Cholesterol
Figure 3.5

17. Membrane Structure

18. Non-polar, small molecules (O2, CO2), & water can pass through the membrane without having to use special channels
Polar molecules, larger molecules, & ions require specific channels to pass through the membrane

19. Molecules Cross the Plasma Membrane in Several Ways
Passive transport
Cell does not need to expend energy for this
Diffusion
Osmosis
Active transport – cell must expend energy
Bulk transport
Involves membranous vesicles to move larger substances
Endocytosis
Exocytosis

20. Passive Transport Moves with the Concentration Gradient
Passive transport is powered by the concentration gradient. In the cell it occurs as
Diffusion through lipid layer
Diffusion through protein channels
Facilitated transport
Transport or carrier proteins in the membrane assist in moving molecules across the membrane, down the concentration gradient, without expending energy

21. Higher
concentration
Lower
concentration
Diffusion through the lipid
layer. Lipid-soluble molecules
such as O2 and CO2 diffuse
freely through the plasma
membrane.
Diffusion through channels.
Some polar and charged
molecules diffuse through
protein channels that span
the membrane. Water
is a typical example.
Facilitated transport. Certain
molecules bind to a protein,
triggering a change in protein
shape that transports the
molecule across the membrane.
Glucose typically enters cells by
this method.
Figure 3.8

22. Active Transport
Active transport moves substances from an area of lower concentration to an area of higher concentration
Requires a membrane protein (transporter)
Requires ATP or other energy source

23. a) In active transport using ATP, energy
derived from the breakdown of ATP
is used to change the shape of the
carrier protein.
Figure 3.9a 23

24. b) Some carrier proteins use energy
derived from the downhill transport of
one molecule to transport another
molecule uphill. In this example, the
energy to transport the square molecules
comes from the facilitated transport of the
spearhead molecules.
Figure 3.9b 24

25. Passive and Active Transport

26. Endocytosis and Exocytosis Move Materials in Bulk
Used to move larger molecules
Endocytosis: brings substances into the cell
Exocytosis: expels substances from the cell

27. Extracellular environment
Plasma membrane
Cytoplasm
Vesicle
a) Endocytosis. In endocytosis, material is surrounded by
the cell membrane and brought into the cell.
Figure 3.10a

28. b) Exocytosis. In exocytosis, a membranous vesicle fuses
with the plasma membrane, expelling its contents outside
the cell.
Figure 3.10b

29. Endocytosis and Exocytosis

30. Information Transfer Across the Plasma Membrane
Receptor proteins span membrane – required for transmission of information to and from cell
Receptor sites (on receptor proteins) – interact specifically with signal molecules
A change is triggered within the cell as a result of binding of signal molecule to receptor site
Different cell types have different receptor proteins

31. Extracellular environment
Receptor site
Substrate
Product
Cytoplasm
Figure 3.11

32. The Sodium–Potassium Pump: Helps Maintains Cell Volume
Sodium–potassium pump expels unwanted ions, keeps needed ones, and maintains cell volume
ATP is used to expel 3 sodium ions for every 2 potassium ions brought into the cell
Increase in cell volume = increase in water in cytoplasm by decreasing pumping and allowing more sodium inside cell
Decrease in cell volume = less water in cytoplasm by increasing pumping and expelling more sodium ions

33. Figure 3.12a 1 2 7 3 6 4 5 Extracelluar fluid Sodium ions bind to
binding sites accessible
only from the cytoplasm. 2
Binding of three cytoplasmic Na+ to the sodium-potassium pump stimulates the breakdown of ATP. 7
Most of the potassium
diffuses out of the cell, but sodium diffuses in only
very slowly 3
Energy released by ATP
causes the protein to
change its shape,
expelling the sodium ions.
Cytoplasm 6
Potassium is transported
into the cell, and the sodium
binding sites become
exposed again. 4
The loss of sodium exposes two binding sites for potassium. 5
Potassium binding triggers
another change of shape.
a) The cell membrane contains Na+ - K+ pumps, and also channels that permit the rapid outward diffusion of K+
but only a slow inward diffusion of Na+.
Figure 3.12a

34. Key:
Active transport of Na+
Sodium-potassium pump
Diffusion of K+
Diffusion of Na+
Diffusion of H2O
In the steady-state, the rate of outward sodium transport equals the rate of inward diffusion.
When the rate of outward sodium transport exceeds inward diffusion, water diffuses out and the cell shrinks.
When the rate of outward sodium transport is less than the rate of inward diffusion, water diffuses in and the cell swells
b) The rate of transport by the Na+ - K+ pumps determines cell volume.
Figure 3.12b

35. Isotonic Extracellular Fluid Maintains Cell Volume
Tonicity: relative concentration of solutes in two fluids
Isotonic
Extracellular and intracellular ionic concentrations are equal
Cells maintain a normal volume in isotonic extracellular fluids
Regulatory mechanisms maintain extracellular fluid that is isotonic with intracellular fluid

36. Isotonic Extracellular Fluid Maintains Cell Volume
Variations in tonicity
Hypertonic
Extracellular ionic concentration higher than intracellular
Water will diffuse out of cell
Cell will shrink and die
Hypotonic
Extracellular ionic concentration lower than intracellular
Water will diffuse into cell
Cell may swell and burst

37. a) Water movement into and out of human red blood
Isotonic
Hypertonic
Hypotonic
9 grams of
salt in 1 liter
of solution
18 grams of
salt in 1 liter
of solution
Pure water
a) Water movement into and out of human red blood
cells placed in isotonic, hypertonic, and hypotonic
solutions. The amount of water movement is indicated
by the sizes of the arrows.
Figure 3.13a

38. b) Scanning of electron micrographs of red blood cells
placed in similar solutions.
Figure 3.13b