1. Biology 101 Medgar Evers College Fall 2017
Movement across the cell membrane, Photosynthesis, and Cell Division
Biology 101 Medgar Evers College Fall 2017

2. Overview: Life at the Edge
The plasma membrane is the boundary that separates the living cell from its surroundings.
The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. The Fluid Mosaic Model Singer and Nicholson: Phospholipid bilayer
Figure 7.3 The fluid mosaic model for membranes
Hydrophobic regions
of protein
Hydrophilic
regions of protein

4. Passive Transport
The movement of material from high concentration to low concentration
Osmosis is the diffusion of water across a selectively permeable membrane.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. Water Balance of Cells
Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane.
Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water. Cell shrinks.
Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. Osmosis: Three Types of Solutions
Hypotonic solution
Isotonic solution
Hypertonic solution
H2O
H2O
H2O
H2O
(a) Animal
cell
Normal
Shriveled
Lysed
H2O
H2O
H2O
H2O
Figure 7.13 The water balance of living cells
(b) Plant
cell
Turgid (normal)
Flaccid
Plasmolyzed

7. Facilitated Diffusion: Passive Transport Aided by Proteins
In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane.
Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane.
Channel proteins include
Aquaporins, for facilitated diffusion of water
Ion channels that open or close in response to a stimulus (gated channels).
For the Cell Biology Video Water Movement through an Aquaporin, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. Solute Channel protein Carrier protein
Carrier proteins undergo a subtle change in shape
that translocates the solute-binding site across the membrane
EXTRACELLULAR FLUID
Solute
Channel protein
CYTOPLASM
A channel protein
Figure 7.15 Two types of transport proteins that carry out facilitated diffusion
Solute
Carrier protein
A carrier protein: shape change

9. Active transport uses cell energy to move solutes against their gradients
The movement of material from low concentration to high concentration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10. The Need for Energy in Active Transport
Active transport moves substances against their concentration gradient / uphill.
Active transport requires energy, usually in the form of ATP
Active transport is performed by specific membrane carrier proteins that use ATP energy to change shape, thereby pumping the solute across the membrane.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. Review: Passive transport Active transport Diffusion
ATP
Diffusion
Facilitated diffusion
Figure 7.17 Review: passive and active transport

12. Photosynthesis Organisms like plants and algae are known as producers!
They undergo photosynthesis to make sugars, release oxygen and water!
Photosynthesis occurs in specialized organelles called chloroplast.
Two reactions; light reaction and dark reaction

14. Chloroplast

15. Reactions of photosynthesis
Light reaction occurs in the grana
Dark reaction occurs in the stroma
In the light reaction, water is split into oxygen, and hydrogens, and some ATP is made.
In the dark reaction, the hydrogens are combined with carbon dioxide to form sugars such as glucose.
Plants store excess sugars in the form of starch

16. Mitosis
Cell division in plant and animal cells that results in two new cells.
Organisms must undergo cell division in order to grow, regenerate damage cells and replicate.
Mitosis results in two genetically identical cells!
Mitosis produces cells with the full set of chromosomes known as diploid cells.
Mitosis takes place all over the body.

17. Cell cycle

18. Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase

19. Meiosis
A special form of cell division that takes place in the gonads resulting in cells that have half the number of chromosomes. These are haploid cells.

21. Differences between Meiosis and Mitosis

22. Differences between mitosis and meiosis
# of divisions
# of daughter cells
Types of cells produced
Location where it occurs
Genetic variation
Y/N