Cell Membrane and Transport of the cells.pdf

Cambridge Biology A/AS Level : Transport Across the Cell

1. Cell Membrane and
Transport of the cells

2. Chapter Outline
•Components and structure
•Passive transport
•Active transport
•Bulk transport

3. Cell Membrane
•The cell membrane, also called the plasma membrane, is found in all
cells and separates the interior of the cell from the outside
environment.
•The cell membrane regulates the transport of materialsentering and
exiting the cell.

4. Structure of membrane cells

5. What’s it made up of?
•The cell membrane is primarily
made up of three things:
1. Phospholipids
2. Cholesterol
3. Proteins

6. Phospholipid
•The cell membrane consists of a phospholipid bilayerthat is semipermeable
•A phospholipid is an amphipathicmolecule, meaning it has both a hydrophilic
(“water-loving”)region and a hydrophobic (“water-fearing”) region
•The phosphate heads in each layer face the aqueous or watery environmenton
either side, and the tails hide away from the water between the layers of heads,
because they are hydrophobic.
Phosphate
Lipids

7. Fluid mossaic model
•We call the cell membrane fluid is because these pieces in our cell
membrane can actually move around, adjust to environmental
conditions
Fluid viscous
Lateral movement
Place exchange

8. Cholesterol
•Cholesterol is a type of steroid (lipids) which is helpful in regulating
molecules entering and exiting the cell.
•The cholesterol molecules are randomly distributed across the
phospholipid bilayer, helping the bilayer stay fluid in different
environmental conditions
•The interaction of the phospholipid tails with the cholesterol
molecules helps to stabilise cells At low and high temperatures

10. Proteins
•The cell is made up of two different types, or “classes”, of proteins.
A. Integral proteins/ intrinsic proteins
-Integral protein are nestled into the phospholipid bilayer and stick
out on either end.
-Integral proteins are helpful for transporting larger molecules, like
glucose, across the cell membrane
B. peripheral proteins
-protein, which don’t extend across themembrane.
-They can be attached to the ends of integral proteins, or not, and
help transport or communication of the cell.

12. Other parts of cell membrane
•Carbohydrates are the other component of plasma membranes. They
are always found on the exterior surface of cells and are bound either
to proteins (forming glycoproteins)or to lipids (forming glycolipids)
•Some glycoproteins serve as identification tags that are specifically
recognized by membrane proteins of other cells

14. Transport across cell
membrane

15. Movement of substances into and out of cells
•Phospholipid bilayer (cell membrane) around cells makes a very
effective barrier
•However, some exchange between the cell and its environment is
essential
•There are three basic mechanisms transports of the cell : passive
transport, active transport and bulk transport

16. Passive transport
•The movement of materials across the cell membrane withoutusing
energy
•Caused by concentration gradient (A region of space over which the
concentration of a substance changes)
•Works in both directions(when a substance enters or leaves the cell)
•Three types of passive transport:
•Diffusion
•Facilitated diffusion
•Osmosis

18. Difussion

19. Difussion
•The process by which substance move or spread from an area of high
concentrationto an area of low concentration, until the concentration
becomes equal throughout a space.
Substance movement

20. •Some examples of diffusion that occurs in our daily life.
A. Dipping the tea bags in hot water will diffuse the tea in
hot water
B. Opening the Soda/Cold Drinks bottle and the CO2 diffuses in
the air.
C. dropping dye into the water
D. Breathing (gas exchange on alveolus)

21. Facilitated diffusion
•Large polar molecules, such as glucose and amino acids, cannot diffuse
through the phospholipid bilayer. Nor can ions such as sodium (Na+) or
chloride (Cl-).
•These can only cross the membrane with the help of certain protein
molecules.
•There are two types of protein involved, namely channel proteinsand
carrier proteins

23. Osmosis

24. Osmosis
•Osmosis is the net movement of water moleculesfrom a region of
higher water potential to a region of lower water potential, through a
partially permeable membrane.
•In the explanations that follow, remember
that:
•In a sugar solution, for example, the solute is sugarand the solvent is
water.

25. Hypotonic Vs Hypertonic Solution
•A hypotonic solution isa solution that has a lower solute concentration
compared to another (solvent) solution.
(Solvent > Solute)
•A hypertonic solution is a solution that has higher solute concentration
compared to another (solvent) solution.
(Solvent < Solute)
Hypertonic
Hypotonic

26. Osmosis on Plant and Animal Cells

27. Active Transport

28. •Active transport is type of transport that requires an input of energy
(ATP)
•During active transport, substances move against the concentration
gradient, from an area of low concentrationto an area of high
concentration
•The energy is used to transferring the molecules or ions across the
membrane in the process
•An example of a carrier protein used for active transport is the
sodium–potassium (Na+ –K+) pump

30. Bulk Transport

31. Bulk transport
•Large molecules such as proteins or polysaccharides, parts of
cells or even whole cellsmay be transported across the membrane.
•Mechanisms also exist for the bulk transportof large quantities of
materials into cells (endocytosis)or out of cells (exocytosis).
•This requires energy, so it is a form of active transport.

32. Endocytosis
•Endocytosis(endo= internal,cytosis= transport mechanism) is a
general term for the various types of active transportthat move
particles into a cell by enclosingthem in a vesiclemade out of
plasma membrane.
•Endocytosis can be further subdivided into the following categories:
phagocytosis, pinocytosis.

33. Phagocytosis
•Phagocytosis or ‘cell eating’ –
this is the bulk uptake of solid
material.
Pinocytosis
•Pinocytosis or ‘cell drinking’ –
this is the bulk uptake of liquid.

34. Exocytosis
•Exocytosis is the bulk movement of liquids or solids out of a cell, by
the fusion of vesicles containing the substance with the cell surface
membrane; exocytosis is an active process requiring ATP