Transportation and the Cell

1. Transportation and the Cell

2. Transportation is the movement of materials in and out of the cell by way of the cell membrane, or around the cell by way of the endoplasmic reticulum. Most substances are transported in liquid form therefore the ability of a substance to dissolve in water is important. This ability is called solubility. The two major forms of transport are passive and active transport.

3. Passive Transport • Definition: movement of molecules across cell membranes without the expenditureofcellular energy. It is called a downhill process. Direction of movement is determined by the concentration gradient (difference between a region of high concentration and a region of lower concentration)and the kinetic energy of the molecules themselves • There are 3 major forms of passive transport.

4. 1. Diffusion • Definition: occurs only if there is a concentration gradient. The movement of molecules from an area of greater concentration to an area of lower concentration. It is the most common type of transportation in the cell. • It resuslts in equal distribution of molecules on the inside and outside of cell. • It occurs because the molecules are in constant motion.

5. Diffusion cont`d • Factors: There are various factors that influence diffusion through the cell membrane. Types of factors: • A. Permeability • B. Concentartion • C. temperature • D.Pressure

6. (A) Permeability of the Membrane This is the ability to allow molecules to flow through an object. There are 3 possibilities: (i). Permeable - all materials pass through (ii). Impermeable - no materials pass through (iii). Semipermeable - some materials pass through, while others do not

7. (B) Concentration of Materials: a concentration gradient is required.The greater the difference between area of high and low concentration gradient the faster diffusion occurs (C) Temperature: higher temperature increases the rate of diffusion (D) Pressure: as osmotic pressure increases diffusion will slow so the cell is less likely to rupture

8. Examples of Diffusion • Digestion - movement of nutrients from the blood stream into the body cells. • Breathing - the movement of oxygen into the blood stream and carbon dioxide out of the blood and into the lungs.

9. 2. Facilitated Diffusion • Definition: movement of materials from an area of high concentration to one of lower concentration by a protein carrier present in the cell membrane because molecules are too big to cross themselves. This form of diffusion is more rapid than normal diffusion. • Example of facilitated diffusion: Transport of glucose from your blood into the cells of your body.

10. 3. Osmosis • Definition: a special type of diffusion. It is a movement of water molecules from an area of greater concentration to an area of lesser concentration through a semipermeable membrane. • Osmosis will continue until the rate of water diffusion across the cell membrane in both directions is equal. This is called osmotic balance. • The pressure generated from this movement of water is called osmotic pressure. • Concentration and pressure work together to mainatin this balance.

11. Effects of Osmosis • The effects of osmosis can be seen by placing animal cells into solutions containing different concentrations of water. (page 55; figure 2.26) • A. Isotonic Solution • B. Hypotonic Solution • C. Hypertonic Solution

12. (A) Isotonic Solution • Has the same concentration of dissolved substances as the cell placed in it. • The concentration of water molecules in the cell and in an isotonic solution is the same. • Since the concentration gradient is zero, there is no net gain or loss of water in the cell.

13. (B) Hypotonic Solution • Contains a lower concentration of dissolved substances than the cell put in it. (i.e. the solution is mostly H2O) • The concentration of water molecules is higher in the hypotonic solution than it is in the cell. • Since the concentration of water molecules is higher outside the cell than inside, there is a net movement of water into the cell. • Osmotic pressure produced by water entering the cell causes it to swell and burst. (e.g. blood cell in water will burst) • In plant cells the central vacuole swells and pushes the contents against the cell wall. This is called turgor pressure.

14. A cell in hypotonic solution 98% H2O 2% salt - through osmosis, water will diffuse into the cell causing the cell to swell and burst 100% H2O

15. (C) Hypertonic Solution • Contains a higher concentration of dissolved substances than the cell placed in it. • The concentration of water molecules is lower in the hypertonic solution than it is in the cell. • Since the concentration of water molecules is higher inside the cell than outside, there is a net movement of water out of the cell. • Water leaving the cell causes it to shrink. • The animal cell will shrink and the vacuole of the plant cell will collapse. The shrinking of the cytoplasm is called plasmolysis.

16. A cell in hypertonic solution 98% H2O 2% salt - through osmosis, water will diffuse out of the cell causing the cell to shrink 90% H2O 10% salt

17. Active Transport • Definition: movement of molecules across a cell membrane requiring the expenditure ofcellular energy. It is called an uphill process. Movement is from an area of low concentration to an area of high concentration. • There are 2 mechanisms of active transport:

18. 1. Carrier Proteins • Carrier proteins located in the cell membrane receive an energy boost. The energized proteins capture specific solute molecules and move them either into or out of the cell against the concentration gradient. • It requires energy in the form of ATP to move the molecules against the concentration gradient.

19. 2. Vesicles(Bulk Transport) • Energy is used to bring about a folding of the cell membrane to form pockets. • 2 forms of this movement: (A) Exocytosis - movement of materials out of the cell . A vacuole or vesicle containing materials within the cell fuses to the inside surface of the cell membrane. Its contents are then released outside the cell. (B) Endocytosis - movement of materials into the cell. Materials become impocketed in the cell membrane.. The membrane closes and pinches of to become a sac or vesicle and the materials are released to the outside.

20. Two Forms of Endocytosis: • (i) Pinocytosis - liquid droplets are taken into the cell. Contents of the vesicle are released directly into cell. (Cell drinking) • (ii) Phagocytosis - solid particles are taken into the cell.This requires a large impocketing. Food vacuoles instead of vesicles can be formed so that digestive enzymes can be used to break down food. Ex. Macrophages( cell eating) • www.maximum.com/physiology/Endocytosis%20and%20Exotyosis/ee4.swf