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HydrophilicheadHydrophobictail
WATER
WATER
Chapter 3: Movement of Substances Across The Plasma Membrane
1. The movement of substances in and out of cells occurs across plasma membrane.2. The Plasma Membrane: is a semi-permeable lipid bilayer found in all cells that
controls water and certain substances in and out of the cell.3. Function of the Plasma Membrane:
-Protects the cell.-Separates the intracellular components from the extracellular
environment.-Controls what enters and exits the cell
4. Necessities for the Movement of Substances across the Plasma Membrane:
-To transport nutrients into the cell.-For gases exchange.-To excrete metabolic waste.-To maintain the pH value and ionic concentration of the cell.
3.1 The Movements of Substances Across The Plasma Membrane
The Structure of Plasma Membrane and Its Components
Glycoprotein
Carbohydrate
Microfilamentsof cytoskeleton Cholesterol Peripheral
Protein (hanya sebahagian drpd. badan protein yg terbenam dlm. Phospholipid bilayer)
IntegralProtein(seluruh badan protein terbenam dlm. Phospholipid bilayer)
CYTOPLASMIC SIDE
OF MEMBRANE
EXTRACELLULARSIDE OF
MEMBRANE
Glycolipid
Glycoprotein = Carbohydrate+ProteinGlycolipid = Carbohydrate+Lipid
Lateral movement(~107 times per second)
Flip-flop(~ once per month)
(a) Movement of phospholipids
Hydrophilic head Hydrophobic tail
Phospholipid bilayer
The Structure of Plasma Membrane
5. The plasma membrane consists mainly of phospholipids and proteins.6. Each phospholipid molecules consist of 2 parts:
-a polar hydrophilic head (hydro=water, philic=love)-a non-polar hyrophobic tail (hydro=water, phobic=hate)
7. In plasma membrane, phospholipids are arranged in 2 layers called phospholipid bilayer.
8. The plasma membrane display the fluid mosaic model (FMM).9. FMM:
- phospholipids, proteins and other components of membrane are not rigid or static.- the protein molecules float freely in phospholipid bilayer.-the proteins and phospholipids can move side-by-side within membrane. It shows fluid characteristic.
10. Contains cholesterol stabilize and strengthen plasma membrane11. Pore/channel protein forms channel/pore12. Carrier protein acts as carrier13. Glycoprotein protein with carbohydrate attached14. Glycolipid lipid with carbohydrate attached
Act as cell-cell recognition
14. The plasma membrane = semi-permeable/partially permeable = certain substances can move in/out of the cell.
15. Membranes that envelope nucleus, mitochondria and chloroplast are semi-permeable.16. Other example of semi-permeable membrane: Visking tube, cellophane tape, egg
membranes.15. The permeability of the phospholipids bilayer is determined by:
- the size- the charge and- the polarity
of the substances pass through it.
Two ways of the Movement of Substances Across The Plasma Membrane
Movement of Substances Across The Plasma Membrane
Passive Transport ActiveTransport
Molecules transported down the concentration gradient
Molecules transported against (berlawanan)
the concentration gradient
Simple Diffusion Facilitated DiffusionOsmosis
16. What is passive transport?
- Passive transport is the movement of substances across the cell membrane without the use of energy by the cell.
- During passive transport, substances move down their concentration gradient, hence no energy is required.
- Passive transports can happen through three different channels, namelya) lipid bilayerb) pore/channel proteinc) carrier protein
17. What is diffusion?
- Diffusion is the movement of molecules/ions from a high concentration region to a low concentration region.
- No energy is needed and no membrane involves in diffusion.
18. What is “down the concentration gradient”?- is the difference in the concentration of a substances between 2 regions.
19. Particles that Move Through the Plasma Membrane Through Diffusion- Substances soluble in fat: fatty acid, glycerol, some vitamins (A,D,E,K)- Neutral particles: water, oxygen, carbon dioxide,
20. Examples of Simple Diffusion: - gaseous exchange in alveolus and blood capillary- gaseous exchange through stomata of leaves during photosynthesis- gaseous exchange in unicellular organism such as Amoeba sp.
21. The Dynamic Equilibrium- Diffusion will continue until the concentration in all region is the same. - When this happen, we say it has reached the dynamic equilibrium.
22. Factors Affecting the Rate of Diffusion (How fast diffusion happens)
Water Molecules=Solvent (Pelarut)
=Solutes (Benda yg dilarutkan)
(a)(b)
(c)(d)(a) 1st, the sugar is concentrated in 1 area.
(b) The sugar and water molecules move randomly in all direction.(c) The random movements results in net movements of both molecules;
from region of high concentration to region of low concentration, down the concentration gradient.
(d) The sugar molecule finally evenly dispersed (tersebar rata). This stage is called a dynamic equilibrium.
23. What is Osmosis?- Osmosis is the diffusion of a water through a semi-permeable membrane, from a region of
low solute concentration to a region with high solute concentration ( or high [water] to low [water] )
Important Points:• It is the diffusion of water (normally) through a semi-permeable membrane.• It is from a dilute solution to a more concentrated solution.• NO ENERGY REQUIRED (TAK PERLU TENAGA).• Water molecules move through phospholipid bilayer and pore protein.
DILUTE SOLUTION = HIGH CONCENTRATION OF WATER = LOW CONCENTRATION OF SOLUTES (bhn. yg. dilarutkan)
CONCENTRATED SOLUTION = LOW CONCENTRATION OF WATER = HIGH CONCENTRATION OF SOLUTES (bhn. yg. dilarutkan)
24. Examples of Osmosis:
- Absorption of water from soil solution by plant root hairs.- Reabsorption of water by kidney tubules.- Osmoregulation in aquatic organisms.
Watermolecule
Selectivelypermeablemembrane
Solutemolecule
H2O
Lowerconcentration
of solute
Higherconcentration
of solute
Equalconcentration
of solute
Solute molecule withcluster of water molecules
Net flow of water
(a) - the left side of u-tube contains high [water], low [solutes].- the right side of u-tube contains low [water], high [solutes].- between left and right side of u-tube is semi permeable
membrane.- water molecules move in both directions. Water molecules move from a
region of high [water] at the left side to a region of low [water] at the right side.
- as water flows from left to right, the osmotic pressure is created within right side of u-tube.- since water molecules can pass through semi permeable membrane but not sugar molecules, the level of the solution at the right side of u-tube rises.
(b) A dynamic equilibrium is reached.
The Mechanism of Osmosis:
25. What is Facilitated Diffusion?- Facilitated diffusion is the movement of hydrophilic molecules or ions across the plasma
membrane with the help of transport proteins.- It moves down the concentration gradient.
26. What Substances Can Pass through the Plasma Membrane through Facilitated Diffusion?Particles undergo facilitated diffusion are the particles that cannot diffuse through the phospholipid bilayer such as:
• Large particles such as glucose, amino acids, proteins and nucleic acids• Some ions such as the sodium ions and chloride ions
27. Facilitated diffusion occurs through 2 types of transport protein, namely: • Channel/Pore Protein• Carrier Protein
28. Examples of Facilitated Diffusion:- Movement of small molecules such as glucose and amino acids into the blood capillaries of the villi.
Channel/Pore Proteins: -Provide corridors (lorong/laluan) that allow a specific molecule or ion to cross the membrane.
EXTRACELLULARFLUID
Channel proteinSolute
CYTOPLASM
A channel protein (purple) has a channel through which water molecules or a specific solute can pass.
(a)
(Outside the cell)
(Inside the cell)
Carrier Proteins:- Undergo a subtle change in shape that translocates the solute-binding site across the membrane.
Carrier proteinSolute
A carrier protein alternates between two conformations, moving a solute across the membrane as the shape of the protein changes. The protein can transport the solute in either direction, with the net movement being down the concentration gradient of the solute.
(b)
THE MECHANISM of CARIER PROTEINS IN FACILITATED DIFFUSION
1. The solute moves to the binding site of the specific carrier protein.
2. The solute binds to the carrier protein at the binding site & triggers (mendorong) the carrier protein to change its shape.
3. The carrier protein changes its shape & moves the solute across the membrane.
4. The carrier protein returns back to its original shape.
29. What is Active Transport?- Active transport is the movement of molecules/ions across the plasma membrane of cells
against (berlawanan) the concentration gradient (From lower concentration to higher concentration).
- Since it is against the concentration gradient, energy is needed in the process.
30. Basic Requirements (keperluan) in Active Transport:• Presence of the carrier protein (carrier proteins in active transport often called as PUMPS)• Presence of ATP (Adenosine Triphosphate)
31. Function of the ATP:- ATP is the source of energy in active transport. It supplies energy to the carrier protein to carry
out the process. It is converted into ADP (Adenosine Diphosphate) after the reaction.
32. Active transport results in the accumulation and elimination of molecules/ions from the cell.
33. Examples of Active Transport- Intake of mineral salts and ions by the root hairs of a plant.- The movement of sodium ions into the cells lining the kidney tubules.- The accumulation (pengumpulan) of iodine in the cells of the thyroid gland.
Mechanism of Active TransportThe diagram below is one type of active transport system which shows how sodium ions and potassium ions are transported through the plasma membrane by a carrier protein.
2. Na+ ions binding stimulates (mendorong) Splitting (memisah) ATP to ADP + P to RELEASE ENERGY.
2
1. Cytoplasmic Na+ ions binds to the sodium-potassium pump.
•The shape of sodium-potassium pump allows it to take up 3 sodium ions at a time.
6. K+ ions is released and Na+
sites are receptive again; the cycle repeats.
3. The one phosphate group attach to the carrier protein. Energy from the ATP, changes the shape of carrier protein, and expelling (mengeluarkan) Na+ ions to the outside.
4. Extracellular K+ ions binds to the Carrier protein and stimulates the release of the Phosphate group.
5. Loss of the phosphaterestores (mengembalikan) the protein’s original shape.
Na+
CYTOPLASM
[Na+] low[K+] high
Na+
Na+
Na+
Na+
Na+
PATP
Na+
Na+
Na+
P
ADP
K+
K+
K+
K+K+
K+
[Na+] high[K+] low
PP
Review: Passive and active transport compared
Passive transport. Substances diffuse spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. The rate of diffusion can be greatly increased by transport proteins in the membrane.
Active transport. Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP.
Diffusion. Hydrophobicmolecules and (at a slow rate) very small uncharged polar molecules can diffuse through the lipid bilayer.
Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins,either channel or carrier proteins.
ATP
Characteristics Passive Transport Active Transport
Types of transport Simple Diffusion Facilitated Diffusion Osmosis Active Transport
Ways of transport Transport of substances across the plasma membrane.Need concentration gradient (or difference in the concentration of substances) between
extracellular cell and intracellular cell.
Concentration gradient
Follow concentration gradient Against concentration gradient
Cellular energy; ATP Cellular energy; ATP IS NOT REQUIRED Cellular energy; ATP IS REQUIRED
Outcome of the process
Until an equilibrium is reached Depends on the cells requirement (no need
to reach an equilibrium)
Occurs in Non-living & living organisms Living organisms only
Molecules which can pass through
Lipid- soluble molecules (vitamins A,D,E,K, fatty acids, glycerols), small molecules (H2O), dissolved gases (O2, CO2).
Large molecules (glucose, amino acids), specific ions.
Water only Specific ions usually sodium ions (Na+) and potassium ions (K+)
1. What is Hypotonic Solution?Hypotonic solution is the solution with a lower solute concentration. (Hypo=less).
2. Water Concentration and Solute Concentration of a Cell in a Hypotonic Solution:
Water concentration: Water concentration inside the cell is lower than outside the cell.Solute Concentration: Solute concentration inside the cell is higher than outside the cell.
3. What is Isotonic Solution?In isotonic solutions, both solutions have equal concentration of solutes. (iso=same).
4. Water Concentration and Solute Concentration of a Cell in a Isotonic SolutionWater concentration and solute concentration are equal in both solutions.
5. What is Hypertonic Solution?Hypotonic solution is the solution with a higher solute concentration. (Hyper=more).
6. Water Concentration and Solute Concentration of a Cell in a Hypertonic SolutionWater concentration: Water concentration inside the cell is higher than outside the cell.Solute Concentration: Solute concentration inside the cell is lower than outside the cell.
3.2 The Movements of Substances Across The Plasma Membrane in Everyday Life
7. The movement of water across plasma membrane is determine by the concentration of the substances in the interstitial fluid which bathes (membasahi) cells.
8. Since living cells need to be in the stable internal environment, the interstitial fluid of animal cells is usually isotonic to the cytoplasmic fluid within the cells.
A portion of internal environment
Cells
Interstitial fluid
Cytoplasmic fluid
WHY MUST BE ISOTONIC?To ensure the shape of the cell remains same and prevent the cells from shrinking (mengecut) or swelling (mengembung).
Animal & plant cells in Isotonic solutions
9. If an animal cell such as red blood cell (RBC) is placed into an isotonic solution, amount of water molecules is transported into the red blood cells by osmosis is equal to the amount of water molecules transported out from the cell (as shown in the diagram beside).
10. Therefore the amount of water in the cell remain unchanged (no net movement of water across plasma membrane).
11. The red blood cells maintain their shape.
12. When a plant cell is placed in an isotonic solution, solute concentration in the external solution is equal to the solute concentration in the cell sap.
13. Therefore the rate of diffusion of water into the cell is equal to the rate of diffusion of water out from the cell.
14. As a result, the shape of the cell remain unchanged.
Animal & plant cells in Hypotonic solutions
15. If an animal cell such as red blood cell is placed into a hypotonic solution, water molecules is transported into the red blood cells by osmosis(as shown in the diagram beside).
16. The red blood cells will inflate (mengembung) and finally burst (pecah) because the thin membrane cannot withstand the high pressure inside the cell (tidak mampu menahan tekanan yg. tinggi di dalam sel).
17. The red blood cells are said to undergo haemolysis.
18. When a plant cell is placed in a hypotonic solution, water molecules is transported into the cell by osmosis.
19. The water is then stored in vacuole causing it to expand (mengembang) and exerts (mengenakan) pressure on the cell wall. This pressure is called turgor pressure.
20. The turgor pressure caused the plant cell to become firm or turgid.
21. The rigid cell wall prevents cell from bursting.22. Turgidity of a plant cells is also responsible for
causing the GUARD CELLS in leaves to swell so that stomata can remain open for photosynthesis.
Animal & plant cells in Hypertonic solutions
23. If an animal cell such as red blood cell is placed into a hypertonic solution, water molecules is transported out from the red blood cells by osmosis (as shown in the diagram beside).
24. The red blood cells will shrink or crenate (mengecut) because of the lost of water from the cell and probably die.
25. The red blood cells are said to undergo crenation.
26. When a plant cell is placed in a hypertonic solution, water molecules is transported out from the cell by osmosis.
27. The vacuole and cytoplasm are then shrink due to lost of water.
28. The plasma membrane is pulled away from the cell wall.
29. The cell wall maintain its shape.30. The process is called plasmolysed.31. If a plasmolysed plant cell is immersed
back (direndam semula) in a hypotonic solution, the cell become turgid again. This condition is called deplasmolysed.
The Effects and Applications of Osmosis in Daily Life
32. Wilting (Layu) in plants:- Wilting occurs in plants when too much fertilizers like potassium nitrate is given. - The fertilisers + Soil = dissolves in the soil water. - Then turn soil water into hypertonic to the cell sap of the plant root. - As a result, water diffuses from the cell sap into the soil by osmosis and the cell is
plasmolysed. - Water shortage (kekurangan) in soil also causes the plant to wilt.- When soil dries out = the soil become more concentrated or hypertonic.- Makes the water diffuse out from plant cell into the soil = the plant cell loss water to soil.
33. Food Preservation (Pengawet):- Foods such as mushrooms, fruits and fish can be preserved using natural preservatives (salt and sugar). - The preservatives makes the surroundings more hypertonic to the food and causes water to leave through osmosis. - The food becomes dehydrated (the food become very-very dry). - Microbes lose water to the surrounding. Without water, bacteria and fungus cannot
survive and dies.
34. The proper functioning of plasma membrane is important to:
- Controls/regulates what goes in and out of the cell as the plasma membrane acts as selective permeable or ‘gatekeeper’ (pengawal pintu).
- Maintain a suitable pH and ionic concentration inside the cell for enzymatic activities.
- Obtain certain food supplies for energy and raw materials.- Remove waste products and toxic substances out of the cell.
35. To maintain proper functioning of a plasma membrane and the whole cells, it is important to:
- Apply balanced diet (makan pelbagai jenis kelas makanan macam karbohydrat, proteins, lipids, serat, vitamins)
- Drink sufficient water (minum air secukupnya) everyday to prevent our body cells from dehydrated.
3.3 Appreciating The Movements of Substances Across The Plasma Membrane
