chapter 3 - the plasma membrane

Question 1

the function of the plasma membrane

Answer 1

is selectively permeable, which means that only particular molecules can enter and exit the cell.

Question 2

the structure of the plasma membrane

Answer 2

is a phospholipid bilayer (arranged in two layers) embedded with proteins, carbohydrates, and cholesterol.

Question 3

structure of phospholipid

Answer 3

phosphate head
made up of glycerol and a phosphate group.
negatively charged, making it hydrophilic and polar (eg water).

2 fatty acid chains
made up of long chains of carbon and hydrogen.
uncharged, making it hydrophobic and non-polar.

amphipathic molecule
makes plasma membrane stable.

Question 4

types of protein

Answer 4

integral: permanent part of the membrane
transmembrane: integral proteins that span the entire bilayer
peripheral: temporarily attached to the plasma membrane

Question 5

function of protein

Answer 5

transport
communication
catalysis
adhesion

Question 6

structure of carbohydrates

Answer 6

usually in chains that extend outside the cell, rooted in the membrane to lipids (glycolipids) or proteins (glycoproteins).

Question 7

function of carbohydrates

Answer 7

aids with:
cell-cell communication
signalling
adhesion
recognition of molecules

Question 8

structure of cholesterol

Answer 8

lipid steroid that embeds itself between the fatty acid tails of the phospholipid bilayer in animal cells.
is replaced with similar molecules in other kingdoms, but are all functionally similar.

Question 9

function of cholesterol

Answer 9

regulates fluidity of membrane
at higher temperatures, it keeps phospholipids bound together.
at lower temperatures, it stops phospholipids from becoming solid.

Question 10

the fluid mosaic model

Answer 10

the plasma membrane is fluid because phospholipids continually move laterally (side to side) in the membrane.
the mosaic component of the model comes from the proteins and carbohydrates embedded in the model.

explains:
molecules that make up the membrane are not held static in one place.
many different types of molecules are embedded in the plasma membrane.

Question 11

diffusion

Answer 11

the movement of particles down the concentration gradient

Question 12

passive transport

Answer 12

process that doesn’t require energy to move things across the plasma membrane.

Question 13

simple diffusion

Answer 13

when molecules move from an area of high concentration to an area on low concentration (down concentration gradient)

happens due to kinetic energy stored inside each molecule which causes them to move around and bounce off each other.

leads to even dispersion of the molecules in an area

Question 14

which molecules can freely diffuse across the plasma membrane?

Answer 14

non-polar and small (like water) molecules

Question 15

facilitated diffusion

Answer 15

passive movement of molecules down the concentration gradient through membrane bound proteins (proteins channels).

allows large molecules to move between the intra and extracellular environments.

protein channels and carrier proteins both are specific to the molecules they transport and the selective permeability of the plasma membrane.

Question 16

protein channels

Answer 16

pores or holes in the membrane that let specific substances in

Question 17

carrier proteins

Answer 17

binds to the surface that is being transported and undergoes a conformational change to push the substance down the concentration gradient.

Question 18

osmosis

Answer 18

the diffusion of water across a selectively permeable membrane from low solute concentration areas to high solute concentration areas.
water can move through the membrane as it is so small even though it is hydrophilic.

Question 19

tonicity

Answer 19

differences in solute concentrations between compartments

Question 20

hypertonic

Answer 20

solutions have comparatively high solute concentrations, so water moves into the hypertonic solution from adjacent areas with lower solute concentrations.

Question 21

isotonic

Answer 21

solutions have equal solute concentrations, so there is no net movement of water.

Question 22

hypotonic

Answer 22

solutions have comparatively lower solute concentrations, so water moves from a hypotonic solution into adjacent areas with a higher solute concentration.

Question 23

what happens to cells in a hypotonic solution?

Answer 23

animal: lysed (filled with h2o and can burst)
plant: turgid (normal state, swollen with h2o, can occur due to cell wall)

Question 24

what happens to cells in an isotonic solution?

Answer 24

animal: normal (h2o flowing in and out)
plant: flaccid (h2o flowing in and out)
no net movement

Question 25

what happens to cells in a hypertonic solution?

Answer 25

animal: shrivelled (crenate, water flowing out)
plant: plasmolysed (water flowing out)

Question 26

how does tonicity affect cells?
biological importance?

Answer 26

it affects the cell size

high turgor (normal) pressure keeps plants from wilting

saline solution is isotonic to our cells, ensuring they don’t shrivel (hyper) or lyse (hypo)

Question 27

active transport

Answer 27

uses protein pumps to move molecules against the concentration gradient
uses energy (ATP)
2 types (protein mediated and bulk)

Question 28

protein mediated transport

Answer 28

cells must use energy and protein pumps to move the ions against the concentration and into the cytoplasm.
requires energy (ATP) and membrane proteins.

Question 29

process of active transport

Answer 29

binding: target molecules binds to the specific protein pump
conformational change: one P from ATP causes a conformational change in the protein pump
release: target molecule is pushed through the protein and released to the other side of the membrane.

Question 30

bulk transport

Answer 30

type of active transport that moves large molecules or groups of molecules (amino acids, proteins, signalling molecules or pathogens) into or out of a cell using vesicles.
two types (endocytosis and exocytosis)

Question 31

exocytosis

Answer 31

process that releases contents from a cell
proteins are made by ribosomes located on the surface of the ER, are sorted, packaged, and modified at the end of the Golgi apparatus and then transported in vesicles.
when a vesicle fuses with the plasma membrane, it adds phospholipids to the membrane making the cell slightly bigger.

Question 32

steps of exocytosis

Answer 32

vesicular transport: a vesicle containing secretory produce is transported to the membrane.
fusion: membranes of the vesicle and cell fuse.
release: secretory products are released from the vesicle and out of the cell.

Question 33

endocytosis

Answer 33

involves transporting molecules or groups of molecules into the cell.
many molecules that the cell requires to survive are too big to enter via protein channels.
takes phospholipids from the plasma membrane, so if large amounts of endocytosis occur the cell can shrink.

Question 34

steps of endocytosis

Answer 34

fold: plasma membrane folds inwards to form a cavity that fills with extracellular fluid and the target molecule.

trap: plasma membrane continues to fold back on itself until the two ends of the plasma membrane meet and fuse together.

bud: vesicle (endosome) pinches off the membrane. It can then be transported to the appropriate cellular location.

Question 35

types of endocytosis

Answer 35

phagocytosis (cell eating)
-endocytosis of solid materials or food particles

pinocytosis (cell drinking)
-process of engulfing molecules dissolved in extracellular fluid.

Question 36

the concentration of potassium ions, K+, in human blood plasma is approximately 4 mM. in the cytoplasm of red blood cells the concentration of these ions is around 100 mM. explain how this difference in concentration is maintained.

Answer 36

this difference in concentration is maintained using active transport.
in active transport, ATP is used by specific protein pumps to transport K+ against its concentration gradient into the red blood cells, increasing the concentration of K+ in the cell. K+ is charged so cannot easily diffuse across the plasma membrane, meaning the cytoplasm remains hypertonic to the blood plasma in terms of K+.

Question 37

example of simple diffusion

Answer 37

oxygen/carbon dioxide
uses phospholipids
down concentration gradient

Question 38

example of osmosis

Answer 38

water
uses phospholipids
down concentration gradient

Question 39

example of facilitated diffusion

Answer 39

glucose
uses protein channels
down concentration gradient

Question 40

example of active transport

Answer 40

amino acids
uses protein pumps
up concentration gradient