Lab Textbook Chapter 5- The Cell: Transport Mechanisms and Cell Permeability

Question 1

Passive Processes: Diffusion

Answer 1

• The driving force for diffusion is kinetic energy of the molecules themselves, and the speed of diffusion depends on molecular size and temp.
• concentration gradient (difference in concentration)- the molecules eventually become evenly distributed throughout the environment
• diffusion is the movement of molecules from a region of their higher concentration to a region of their lower concentration
• Is is the unassisted diffusion of solutes (dissolved substances) through a selectively permeable membrane (simple diffusion)

Question 2

Passive Processes- Facilitated Diffusion

Answer 2

• As with simple diffusion, the substances move from an area of higher concentration to one of lower concentration (down their concentration gradients)
• Certain molecules, for ex. glucose, are transported across the plasma membrane with the assistance of a protein carrier molecule
• Small ions cross the membrane by moving through water filled protein channels

Question 3

Passive Processes: Osmosis

Answer 3

• The flow of water across a selectively permeable membrane is called osmosis
• During osmosis, water moves down its concentration gradient
• The concentration of water is inversely related to the concentration of solutes

Question 4

Isotonic Solutions

Answer 4

• Cells retain their normal size and shape because there is equal concentration of solute/water in either side of the cell
• no net osmosis

Question 5

Hypotonic Solutions

Answer 5

• A solution surrounding a cell is hypotonic if it contains fewer nonpenetrating solute particles than the interior of the cell (higher concentration of solutes inside the cell)
• Cells take on water by osmosis until they become bloated and burst (lyse)

Question 6

Hypertonic Solution

Answer 6

• Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of solutes outside the cell)
• Water moves from interior of the cell into surrounding solution

Question 7

Passive Processes: Filtration

Answer 7

• Filtration is a passive process in which water and solutes are forced through a membrane by hydrostatic (fluid) pressure
• Filtration is not selective
• The amount of filtrate (fluids and solutes) formed depends almost entirely on the pressure gradient (difference in pressure on the two sides of the membrane) and on the size of the membrane pores
• i.e. Fluids and solutes filter out of the capillaries in the kidney and into kidney tubules because the blood pressure in the capillaries is greater than the fluid pressure in the tubules

Question 8

Active Processes: Active Transport

Answer 8

• Active transport is whenver a cell uses the bond energy of ATP to move substances across its boundaries
• Substances moved by active means are generally unable to pass by diffusion
• They may not be lipid soluble; too large; to have to move against rather than with a concentration gradient
• Active transport requires carrier proteins that combine specifically with the transported substance
  
  • i.e. substances like amino acids and sugars

Question 9

Active Processes: Vesicular Transport

Answer 9

• In vesicular transport, fluids containing large particles and macromolecules are transported across cellular membranes inside membranous sacs called vesicles
• Moves substances into the cell (endocytosis) and out of the cell (exocytosis)
• Exocytosis is a vesicular transport process that ejects substances from the cell into the extracellular fluid
• Requires energy usually in the form of ATP, and all forms of vesicular transport involve protein-coated vesicles to some extent
• 3 types of endocytosis
• Phagocytosis - “cell eating”; the cell engulfs some relatively large or solid material (i.e. bacteria, cell debris. or inanimate particles)
  
  • when a particle binds to the receptors on the cell’s surface, cytoplasmic extensions caled pseudopods form and flow around the particle (becomes a phagosome)
• Pinocytosis- “cell drinking”, also called fluid phase endocytosis, the cell “gulps” a drop of extracellular fluid containing dissolved molecules
  
  • since no receptors are involved the process is nonspecific
  • Unlike phagocytosis, pinocytosis is a routine activity of most cells, affording them a way of sampling the extracelluar fluid
  • esp. important in cells that absorb nutrients (i.e. intestine cells)
• Receptor-mediated endocytosis
  
  • the receptors for this process are plasma membrane proteins that bind only to certain substances
  • this selective mechanism allows cells to concentrate material that is present only in small amounts in the extracellular fluid
  • The ingested vesicle may fuse with a lysosome that either digests or releases its contents by exocytosis
  • substances taken up include enzymes, insulin, and other hormones, cholesterol and iron