Chapter 3: Cell Processes and Applications (Transport Across Cell Membrane)

Question 1

explain the structure and function of the fluid mosaic membrane model using the following key words/ phrases: main function, fluid, mosaic, phospholipid bilayer, proteins, phospholipids, glycoprotein, cholesterol, and peripheral protein

Answer 1

The main function of the cell membrane is to define the cell boundary and regulate molecule passage into and out of the cell. The fluid part of the model represents the lipid bilayer and the mosaic part represents the proteins. The mosaic pattern of the cell membrane is composed of a phospholipid bilayer that has a fluid consistency. Proteins are embedded (integral proteins) into the bilayer or associate with the cytoplasmic (peripheral proteins). Phospholipids create a barrier against certain substances and provides fluidity. Glycoprotein assist in identification of cells and cholesterol regulates membrane fluidity while stiffening and strengthening the membrane. The peripheral protein provides a structural role which stabilizes and shapes the plasma membrane.

Question 2

explain why the cell membrane is described as “selectively permeable”

Answer 2

The cell membrane is selectively permeable because because certain substances can move across the membrane while others cannot.

Question 3

osmosis

Answer 3

diffusion of water across a selectively permeable membrane due to concentration differences

Question 4

diffusion

Answer 4

movement of molecules from higher to lower concentration (down the concentration gradient) until equilibrium is achieved and distribution is equal

Question 5

facilitated transport

Answer 5

act of a carrier assisting passage of a molecule across the plasma membrane with no expenditure of energy

Question 6

active transport

Answer 6

movement of molecules or ions through the plasma membrane against the concentration gradient

Question 7

compare osmosis and diffusion

Answer 7

both osmosis and diffusion work to achieve equilibrium and the movement of molecules balance concentration and move down the concentration gradient

Question 8

compare osmosis, diffusion, and facilitated transport

Answer 8

osmosis, diffusion, and facilitated transport have molecules move down the concentration gradient meaning they require no energy

Question 9

contrast active transport from osmosis, diffusion, and facilitated transport

Answer 9

active transport moves against the concentration gradient and requires energy

Question 10

contrast osmosis from diffusion, facilitated transport, and active transport

Answer 10

osmosis specifically deals with water and is a TYPE of diffusion

Question 11

explain the factors (4) that affect the rate of diffusion across a cell membrane

Answer 11

• As temperature increases, the rate of diffusion increases: rate of diffusion is higher at 20°C than 10°C.
• As molecule size decreases, the rate of diffusion increases: a starch polysaccharide chain will have more difficulty passing through a cell membrane than a water molecule will.
• Non-charged molecules pass through the cell membrane much more easily than charged molecules: a charged molecule will require energy and carrier proteins to pass through the membrane whereas a non-charged molecule can freely move across the membrane because of diffusion
• The greater the concentration gradient, the greater the rate of diffusion: 100 molecules on 1 side and 10 on the other would make a much larger concentration gradient than 20 molecules on 1 side and 10 on the other.

Question 12

describe endocytosis, including phagocytosis and pinocytosis, and contrast it with exocytosis

Answer 12

endocytosis - a way substances can ENTER a cell; cells take in substances by vesicle formation
phagocytosis - a way to transport large substances into cells (like viruses)
pinocytosis - a way to transport small substances into cells (macromolecules)
exocytosis - a way substances can EXIT a cell; a vesicle will fuse with the plasma membrane as secretion occurs

Question 13

predict the effects of hypertonic, isotonic, and hypotonic environment on animal cells

Answer 13

isotonic solution - there is no net movement of water, animal cell remains the same
hypotonic solution - water enters the animal cell, which may burst (lysis)
hypertonic solution - water leaves the animal cell, which shrivels (crenation)

Question 14

state the relationship and significance of surface area to volume with reference to cell size

Answer 14

when cell size increases, it’s volume increases faster: if a cell doubles in size, its volume increases by eight-fold while its surface area only increases by four-fold. A greater surface area to volume ratio is important and preferred. This is why cells tend to be small and not large. This preferred ratio will require less nutrients, produce less waste, and have more adequate surface area for exchanging nutrients and waste.