Lab 6: Membrane Permeability

Question 1

Lipid membranes are made up of _____

Answer 1

phospholipids

Question 2

“Mosaic” part of the fluid mosaic model

Answer 2

due to proteins, cholesterol and other molecules that are a part of the membrane surface

Question 3

“Fluid” part of the fluid mosaic model

Answer 3

phospholipids can diffuse rapidly through the membrane. proteins can also diffuse, but are slower due to larger sizes.

Question 4

A protein that spans the entire membrane and often as a hydrophobic core but hydrophillic end is aka ______

Answer 4

integral protein

Question 5

a loosely attached protein on one face of the membrane is known as a ____

Answer 5

peripheral protein

Question 6

how is a peripheral protein anchored onto the lipid membrane face?

Answer 6

by non-covalent forces, can be easily stripped with detergent.

Question 7

Oligosaccharide

Answer 7

chain of 3-7 sugars. Often used for cell recognition and communication

Question 8

Glycoprotein

Answer 8

protein with an oligosaccharide linkage

Question 9

glycolipid

Answer 9

lipid with oligosaccharide linked to phosphate head.

Question 10

Membranes are semi permeable. What does this mean?

Answer 10

they are permeable to lipid soluble, uncharged, and small molecules, but are impermeable to larger molecules.

Question 11

2 properties about a molecule that dictates how it can pass through a membrane

Answer 11

1) the size of the molecule

2) the ability to enter the hydrophobic interior of the membrane

Question 12

osmosis

Answer 12

the movement of water across a SEMIPERMEABLE membrane down it’s concentration gradient

Question 13

three ways solutes can be moved

Answer 13

1) diffusion
2) facilitated diffusion
3) active transport

Question 14

how is water moved across a membrane

Answer 14

osmosis

Question 15

3 cellular functions that rely on membrane transport

Answer 15

1) acquiring nutrients
2) disposing of waste
3) maintaining cell volume

Question 16

Why are red onions good specimans to analyze H2O movement?

Answer 16

• has large and translucent cells, easily defined cell wall

- cell is mostly comprised of the central vacuole, which can be easily seen due to red and purple pigment

Question 17

central vacuole membrane of a plant cell is also known as a

Answer 17

tonoplast

Question 18

vacuoles in onion cells contain _____ that accounts for the red and purple pigments

Answer 18

anthocyanins

Question 19

Effects of a hypotonic solution on a cell

Answer 19

cell is more salty than the hypotonic solution. Water will enter the cell via osmosis. If cell has a cell wall, the wall will provide support for the water pressure and the cell will become turgid. if there is no cell wall, the cell may burst if water rushes into it too fast.

Question 20

How does a cell become turgid?

Answer 20

when water enters the central vacuole of the cell, and the tonoplast (membrane surrounding the vacuole) presses up against the cell wall.

Question 21

Effects of a hypertonic solution on a cell?

Answer 21

the cell is in a salty solution. Water will LEAVE the cell via osmosis and the central vacuole will shrink away from the cell wall, resulting in PLASMOLYSIS

Question 22

what is deplasmolysis

Answer 22

when a plasmolyzed cell is returned back to a hypotonic solution (or isotonic) and the vacuoles swell up again to full turgidity.

Question 23

How can you trigger deplasmolysis?

Answer 23

place the cells in a HYPERTONIC solution with DIFFUSABLE SOLUTES.

• first, water will rush out of vacuole into the hypertonic solution and the cell will plasmolyze
• solutes will begin to slowly diffuse across the membrane into the cell, making the cell more “salty”
• when solutes enter the cells,water will follow, resulting in more water in the cell, allowing it to regain its turgidity.

Question 24

what is the iso-osmotic threshold

Answer 24

the concentration of solute in solution required for the cell to remain in a normal turgid or isotonic state

Question 25

how would you find a more specific isoosmotic threshold?

Answer 25

use smaller increments of solute

Question 26

Why is the NaCl isoosmotic threshold lower than the sucrose threshold?

Answer 26

NaCl will dissociate into 2 ions (Na+, Cl-), contributing to 2x the amount of solute particles present in the water than that of a sucrose solution, which does not dissociate.
- ideally, the NCl solution would have an isoosmotic threshold thats 1/2 that of sucrose.

Question 27

would sucrose or NaCl solution create a faster rate of deplasmolysis? Why?

Answer 27

Nacl.

Recall: deplasmolysis occurs when diffusable solutes move into the cell and then water follows. The rate of deplasmolysis is reliant on the ability for the solute to first enter the cell:

• both Nacl and sucrose are polar. therefor, the polarity will cause both of them to move slow
• Nacl dissociates into two ions,there for there is 2x the solute concentration and a steeper concentration gradient, NaCl is more likely to enter the cell at a faster rate because of the steeper gradient.
• molecular size will play a role on the rate of deplasmolysis
• NaCl is smaller than sucrose and could diffuse into the membrane faster

Question 28

How is the rate of de-plasmolysis affected by biological mechanisms

Answer 28

affected by osmoregulation

Question 29

specific example of how osmoregulation regulates the rate of de-plasmolysis

Answer 29

how the stomata of plants can open and close in order to prevent water loss. the stomata is reliant on the Absicsic Acid hormone, causing stomata closing and stimulates root growth so that water can be absorbed, aiding in WATER CONSERVATION. surplus of water would allow water to flow back into the cells, deplasmolyzing them and preventing wilting.