The structure of the plasma membrane and membrane transport mechanisms

1. The Cell Membrane

6. objectives
• Be able to:
1. Describe and draw a model of the structure of the cell
membrane
2. Explain how different substances move across the
membrane
NGSS HS-LS1.A Systems of specialized cells within organisms help them
perform the essential functions of life

7. As always…
• Write down content that is underlined
• Vocab terms are in green

8. Membrane Structure
• Made of lipids with 2
parts to them:
1. Phosphate “heads”
1. These “love” water -
they are hydrophilic
2. Fatty acid “tails”
1. These “hate” water -
they are hydrophobic

9. Label hydrophobic and hydrophilic on your
picture
Hydrophilic
“heads”
Hydrophobic “tails”

10. Whiteboards
What does hydrophobic mean?

11. Phobias
• Beards.....................pogonophobia
• Being stared at........opthalmophobia
• Tickling with feathers...pternonphobia
• Opening one’s eyes....optophobia
• Clowns........................coulrophobia
• Foreign languages......xenoglossophobia
• Going to school...........didaskaleinophobia
• Gravity.........................barophobia
• Hair..............................trichopathophobia
• Kissing.........................philematophobia
• Snow............................chionophobia

12. • Since phospholipids
have 2 sides, they
can block out
certain molecules
–This makes the
membrane
semipermeable

13. What else might be semipermeable?
• Rank these items - from MOST
permeable to LEAST permeable
Name at least one other thing that isName at least one other thing that is
semipermeablesemipermeable

14. What can get through?
• Very small things like:
– Oxygen (O2)
– Carbon dioxide(CO2)
– Water
• Hydrophobic things like
– Fats and oils (lipids)
• They move from high concentration to low
concentration

15. Draw some oxygen molecules moving
through the membrane

16. Large and hydrophilic molecules
– Proteins
– Sugars
– Wastes
– Salts
• Pass through protein
channels in the cell
membrane
• Proteins are specialized
for one type of substance

17. Add some glucose molecules moving
through a protein doorway

18. Quick check
1. Whiteboards: What are the 2 main macromolecules
that make up the cell membrane?

19. Whiteboards
• What kinds of things can slip right through the
phospholipid bilayer?
• What kinds of things must go through the
protein channels?

20. Discussion
Elbow partner discussion:
The membrane is selectively permeable
•Partner A: What is it about the phospholipids
that allows the membrane to be selectively
permeable?
•Partner B: What is it about the proteins that
allows the membrane to be selectively
permeable?

21. So…
• The cell membrane
– Has 2 main components:
• PhospholipidsPhospholipids that have a
hydrophilic side and a
hydrophobic side
– Only small things or lipids can get
through it
• Proteins
– Work like doorways to move big
things or hydrophilic things across
the membrane

22. Passive Transport
• Passive transport = no
energy
• Molecules move down their
concentration gradient
• From high to low
concentration
• Label diffusion on your
diagram

23. Osmosis
• A type of passive transport
• Movement of water across a membrane
• From more water to less water

24. Glue your diagram into your
notebook

25. • When cells are surrounded by many solutes – water
rushes out of them
• The solution is hypertonic compared to the cell

26. • When cells are surrounded by few solutes –
water rushes into them
• The solution is hypotonic compared to the cell

27. • When cells are in an environment with equal solutes
– water moves in and out equally
• The solution is isotonic compared to the cell

28. Discussion
• A person has been in a terrible car accident
and needs to be given an IV with medicine.
What kind of solution should the doctor
prescribe? Why?
Person B: The doctor
should use a ______
solution in the IV
because ________
Partner A: I
agree/disagree
because
________________

29. Discussion - “yes, and”
• All living things are made of cells.
• All living things respond to their environment.
• All living things maintain homeostasis.
Why is it important that the cell membrane is
selectively permeable?
• First, jot down as many ideas as you can on this topic
• Next, have a discussion with your partner (Partner A first.)
• When you respond, start with “yes, and…” and then add to
their response
• Go back and forth at least 2 times

30. Active Transport
• Sometimes cells need to “push” molecules
against their concentration gradient
• They use protein channels to do this
• It takes energy (ATP) to do this

31. Transport by vesicles
• Cells can use vesicles to send large amounts
out of or into the cell
• Endocytosis – vesicles bring material into cell
• Exocytosis – vesicle sends materials out of cell

32. What is this diagram showing?

33. Closure
Make a diagram of the cell membrane.
1.Draw Carbon Dioxide (CO2 ) molecules moving
by diffusion across the membrane
2.Draw potassium (K+) atoms moving by
diffusion through a protein
3.Draw sodium (Na+) atoms moving by active
transport
4.Explain in writing how the cell transports bulk
materials like proteins out of the cell

34. So can you do these things?
• On the back of your quick check paper:
1. Draw the structure of the cell membrane
1. Label the :
1. hydrophilic heads
2. hydrophobic tails
3. protein doorways
2. Draw in some carbon dioxide molecules ( )and draw them
crossing the cell membrane.
1. Use an arrow to show the direction the CO2 molecules move
3. Draw in some salt ( )molecules and draw them crossing the
membrane through a protein doorway.
1. Use an arrow to show the direction the salt molecules move
4. Describe what it means to be semipermeable