Membrane Structure and
Function
Model 1 – Simple Diffusion
1) Two types of molecules
2) Triangles – 14 on left
Cirlces – 12 on left, 13 on right
3) Triangle is larger
4) The molecules will move in all
directions (that’s diffusion)
5) The dots can fit through the gaps
because they are small and they
are equally distributed on both
sides
6) No change from this point since
the triangles are too big to fit
through the membrane and the
dots are already spread out
evenly
Model 2 – The Selectively
Permeable Cell Membrane
7) Phospholipids and Proteins
8) Four - 2 types of surface proteins and
2 membrane-spanning proteins
9) Surface protein is either on the inside or
outside whereas the membrane-spanning
proteins reach across the whole membrane
10) Glycoprotein
11) Glycolipid
12) Small polar and nonpolar molecules
13) Between phospholipids
14) More small molecules are outside
compared to the inside so we say … the
concentration is higher outside
15) No, molecules are moving in as shown by
the arrows because it started with more
outside.
Concentration Gradients (high to low = downhill)
1) Dots in Model 1, small molecules in Model 2
2) A) Diffusion is the net movement of molecules from an area of HIGH
to LOW concentration.
B) The molecules continue to move along the concentration gradient
until reaching equilibrium.
C) Molecules continue to move randomly.
Model 3 – Facilitated Diffusion
18) Membrane spanning
protein
19) Gated channel
20) Hormones
21) Hormone attaches and
works like a “key” to
open the gate.
22) The protein channel acts like a gate with the hormone as the key
23) Facilitated means the molecules get “help” to move across the
membrane, but they still move from high to low concentration
24) The nonpolar phospholipid tails provide a barrier that prevents the
Na+ and K+ from crossing the membrane unless through a channel.
Model 4 – Active Transport
25) Membrane spanning proteins
26) Diamond
27) ATP and ion binding sites
28) Low to High concentration
29) No, the substance is being moved
up a concentration gradient
30) Energy (ATP) is used to change the
shape of the protein channel
31) ATP changes to ADP
32) Active transport moves molecules
up concentration gradients whereas
passive transport moves molecules
down concentration gradients
Complete the Summary Chart - #33
Active Transport Definition - #34
• Movement of a substance up it’s concentration gradient,
using energy input (ATP) from the cell and requiring
membrane protein channels.
Extension Questions
35) Active Transport
36) Diffusion
37) Facilitated diffusion
relies on proteins … the #
of protein channels will
set a limit as to how fast
diffusion can happen
38) Active transport does not
rely on concentration
gradient. It relies on a
supply of energy.