1. 7-4
Cellular Transport

2. Chapter 7
Section 1 Passive Transport
Cell Size
Surface area-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate wastes
As cells increase in volume, the relative surface area decrease and demand for material resources increases
More cellular structures are necessary to adequately exchange materials and energy with the environment

3. Chapter 7
Section 1 Passive Transport
Cell Size

4. Chapter 7
Section 1 Passive Transport
Cell Size
The surface area of the plasma membrane must be large enough to adequately exchange materials
In other words, smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

5. Chapter 7
Section 1 Passive Transport
Cell Size
Examples of how increasing surface area increases the function of the cell include
Root hairs - increases water absorption in roots of plants
Cells of the alveoli - increase gas exchange in the lungs
Cells of the villi or microvilli - increases absorption of food in the intestinal lining

6. Root Hairs

7. Alveoli

8. Chapter 7 Diffusion Section 1 Passive Transport
Recall that when organisms adjust internally to changing external conditions they are maintaining homeostasis
One way cells maintain homeostasis is by controlling the movement of substances across their cell membrane.
Cells must use energy to transport some substances across the cell membrane by active transport
Other substances move across the cell membrane without any use of energy by the cell by passive transport.

10. Chapter 7 Diffusion, continued Random Motion and Concentration
Section 1 Passive Transport
Diffusion, continued
Random Motion and Concentration
Movement across the cell membrane that does not require energy from the cell is called passive transport.
A difference in the concentration of a substance across a space is called a concentration gradient.
Equilibrium is a condition in which the concentration of a substance is equal throughout a space.

11. Chapter 7
Section 1 Passive Transport
Equilibrium

12. Chapter 7 Diffusion, continued Movement of Substances
Section 1 Passive Transport
Diffusion, continued
Movement of Substances
The movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance is called diffusion.
Many substances, such as molecules and ions dissolved in the cytoplasm and in the fluid outside cells, enter or leave cells by diffusing across the cell membrane.

13. Chapter 7
Section 1 Passive Transport
Diffusion

14. Chapter 7 Diffusion, continued Section 1 Passive Transport
Because of diffusion, food coloring (blue) will gradually move through uncolored gelatin (yellow), as shown in the beakers below.

15. https://www. youtube. com/watch

16. Chapter 7
Section 1 Passive Transport
Osmosis
The diffusion of water through a selectively permeable membrane is called osmosis.
Like other forms of diffusion, osmosis involves the movement of a substance—water—down its concentration gradient.
Osmosis is a type of passive transport.

17. Chapter 7
Section 1 Passive Transport
Osmosis

18. Chapter 7
Section 1 Passive Transport
Osmosis

19. Chapter 7 Osmosis, continued Section 1 Passive Transport
There are three possibilities for the direction of water movement:
Water moves out. When water diffuses out of the cell, the cell shrinks. A solution that causes a cell to shrink due to osmosis is a hypertonic solution.
Water moves in. When water diffuses into the cell, the cell swells. This is a hypotonic solution.
If too much water enters the cell it will rupture.
No net water movement. A solution that produces no change in cell volume because of osmosis is called an isotonic solution.

21. Chapter 7 Osmosis, continued Section 1 Passive Transport
In a hypertonic solution a plant cell will lose water, mainly from the central vacuole. The membrane shrinks away from the cell wall. This causes wilting. [plasmolysis]
In a hypotonic solution the central vacuole fills with water, pushing the membrane against the cell wall. The cell becomes firmer because turgor pressure has increased.

22. Hypertonic, Hypotonic, and Isotonic Solutions
Chapter 7
Section 1 Passive Transport
Hypertonic, Hypotonic, and Isotonic Solutions

24. Crossing the Cell Membrane
Chapter 7
Section 1 Passive Transport
Crossing the Cell Membrane
Diffusion Through Ion Channels
An ion channel is a transport protein with a polar pore through which ions can pass.
The pore of an ion channel spans the thickness of the cell membrane.
An ion that enters the pore can cross the cell membrane without contacting the nonpolar interior of the lipid bilayer.

25. Chapter 7
Section 1 Passive Transport
Ion Channels

26. Diffusion Through Ion Channels
Chapter 7
Section 1 Passive Transport
Diffusion Through Ion Channels

27. Crossing the Cell Membrane
Chapter 7
Section 1 Passive Transport
Crossing the Cell Membrane
Facilitated Diffusion
Most cells also have a different kind of transport protein, called carrier proteins, that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side.
When carrier proteins are used to transport specific substances—such as amino acids and sugars—down their concentration gradient, that transport is called facilitated diffusion.

28. Facilitated Diffusion
Chapter 7
Section 1 Passive Transport
Facilitated Diffusion

29. https://www. youtube. com/watch

30. Passive Transport: Facilitated Diffusion
Chapter 7
Section 1 Passive Transport
Passive Transport: Facilitated Diffusion

31. Active vs. Passive
Passive Transport = High Concentration  Low Concentration
No energy expenditure from the cell.
Active Transport = Low Concentration  high Concentration
Energy need; ATP

32. Comparing Active and Passive Transport
Chapter 7
Section 2 Active Transport
Comparing Active and Passive Transport

33. Movement Against a Concentration Gradient
Chapter 7
Section 2 Active Transport
Movement Against a Concentration Gradient
The transport of a substance across the cell membrane against its concentration gradient is called active transport. (Requires Energy)
Most often, the energy needed for active transport is supplied directly or indirectly by ATP.

34. Chapter 7
Section 2 Active Transport
Active Transport

35. Movement Against a Concentration Gradient, continued
Chapter 4
Section 2 Active Transport
Movement Against a Concentration Gradient, continued
Sodium-Potassium Pump
One of the most important membrane pumps in animal cells is a carrier protein called the sodium-potassium pump.
In a complete cycle, the sodium-potassium pump transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell.
Without the pump, the sodium ions in the cell would cause water to diffuse into the cell in turn causing it to burst.

36. Sodium-Potassium Pump
Chapter 7
Section 2 Active Transport
Sodium-Potassium Pump

37. Sodium-Potassium Pump
Chapter 7
Section 2 Active Transport
Sodium-Potassium Pump

39. Chapter 7 Movement in Vesicles
Section 2 Active Transport
Movement in Vesicles
Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. These substances are moved across the cell membrane by vesicles.
The movement of a substance into a cell by a vesicle is called endocytosis.
The movement of a substance by a vesicle to the outside of a cell is called exocytosis.

40. https://www. youtube. com/watch

41. Endocytosis and Exocytosis
Chapter 7
Section 2 Active Transport
Endocytosis and Exocytosis

42. Endocytosis and Exocytosis
Chapter 7
Section 2 Active Transport
Endocytosis and Exocytosis