Plasma Membrane

1. Each phospholipid consist of two parts: (a) Hydrophilic head-attracted to water (b) Hydrophobic tail-repeled by water

2. Cholesterol in the phospholipid bilayer makes the bilayer stronger, more flexible and less permeable to water-soluble substances such as ions.3. Fluid Mosaic Model: (a) not rigid or static but form a dynamic and fluid structure. (b) protein molecules float about freely in phospholipid bilayer (c) free to move sideways thus they have fluid characteristics (d) form a mosaic pattern

Simple diffusion-the net movement of molecules or ions from a region of high concentration to a region of lower concentration.(down the concentration gradient)(a) lipid-soluble molecules such as vitamins A,D,E,K.(b) small molecules such as water(c) Dissolved gas such as oxygen and carbon dioxide

Osmosis-diffusion of water molecules across a semi-permeable membrane.-net movement of water molecules from a region of low solute concentration to a region of high solute concentration through a semi-permeable membrane.- Characteristics:does not require energy :move across the phospholipid bilayer and pore protein

Permeability of phospholipid bilayer

Permeable-non-polar molecules(lipid soluble)-small molecule-uncharged molecules

Not permeable-charged ions-polar molecules(lipid insoluble)

Similarities and differences between simple diffusion and osmosisSimilarities

-does not require energy-move down the concentration gradient-molecules move from regions of higher concentration to a region of lower concentration until a state of dynamic equilibrium is reached.

DifferencesSimple diffusion Osmosis

Involves the movement of any molecules

Involves only the movement of water molecules

Does not require a semi-permeable membrane.

Occurs through a semi-permeable membrane

Facilitated diffusion-the movement of hydrophilic molecules or ions across the plasma membrane with the help of transport molecules.-Characteristics : does not require energy : move down the concentration gradient : two types of transport protein-carrier protein/pore protein

The mechanism of facilitated diffusion through carrier protein1. Molecules such as glucose, small proteins and amino acids move towards the binding sites of the specific carrier proteins.2. The molecule binds to a specific site of the carrier protein.3. The carrier protein changes its shape to transport the molecule across the

plasma membrane.4. The carrier protein assumes its original shape and is free to assist the passage of other similar molecules into the cell.

Active Transport-the movement of molecules or ions from a region of lower concentration to a region of higher concentration across the plasma membrane.-Characteristics : (a) requires energy -cellular energy in the form of adenosine triphosphate (ATP)

1. The concentration of sodium ions is higher on the outside of the cell.2. The sodium ions approach the carrier protein. The carrier protein has a site for the sodium ions and another site to bind the ATP molecule.3. The carrier protein changes its shape to allow it to take up three sodium at a time.4. The carrier protein binds the sodium ions. The ATP molecule is split into

adenosine diphosphate(ADP) and phosphate(P). The splitting of ATP releases energy to the carrier protein. Energy from the ATP changes the shape of the carrier protein.

5. Sodium ions are released outside the cell.

Differences between passive transport and active transport

Passive Transport Active transportMovement of substances follows the concentration gradient

Substances move against the concentration gradient

Cellular energy is required Cellular energy(ATP) is requiredProcess continues until a dynamic equilibrium is reached.

Results in the accumulation of or elimination of substances from the cell.

Not influenced by inhibitors Inhibited by inhibitors such as cyanide

The effects of hypotonic, hypertonic and isotonic solutions on animal and plant cell(a) Hypertonic solution-higher solute concentration(b) Hypotonic solution-lower solute concentration(c) Isotonic solution-concentration of solutes are equal

1. Isotonic solution (a)water diffuses into and out the cell at equal rates (b)no net movement of water across the plasma membrane

2. Hypotonic solution

-When red blood cells are immersed in a hypotonic solution, water diffuses into the cells by osmosis.-The cell starts to swell and eventually burst.-The plasma membrane of red blood cell is too thin to withstand the osmotic pressure developed.-This condition is known as haemolysis.

-When plant cells are immersed in a hypotonic solution, water diffuses into the large central vacuole by osmosis.-The large central vacuole swells up and press outwards against the plasma membrane.-The plant does not burst because its rigid cell wall is strong enough to resist the increasing pressure. Turgor pressure is created.-Turgidity of plant cells is responsible for causing guard cells to swell so that

the stomata remain open for photosynthesis.

3. Hypertonic Solution

-When red blood cells are immersed in a hypertonic solution, water diffuses out of the cell by osmosis.-The cell loses water and the plasma membrane crinkles up.-This condition is known as crenation.

-When plant cells are immersed in a hypertonic solution, water diffuses out of the cell by osmosis.-This phenomenon is called plasmolysis.-The plant cell becomes flaccid and less turgid.-The cell wall does not shrink because it is strong and rigid.-A plasmolysed plant cell can become turgid again by immersing the cell in a hypotonic solution like pure water. Water moves into the cell by osmosis and the cell becomes turgid again.-The plant cell have undergone deplasmolysis.

The effects of isotonic, hypotonic and hypertonic solutions on the stems of non-woody plantsSolution Distilled water

(hypotonic solution)17% sucrose solution(isotonic solution)

30% sucrose solution(hypertonic solution)

Shape

Appearance -Longer, thicker , turgid and firm-Curves outwards with epidermal layer inside

-Remains unchanged

-Shorter, thinner and softer-Curves inwards with epidermal layer outside

Discussion -Water enters the cell by osmosis through the cut surface causes the cells to swell-Epidermis is protected by a layer of cuticle which is waterproof so it is not affected by osmosis

-Water enters and leaves the cells at the same rate

-Water leaves the cell by osmosis through the cut surface causing the cells become flaccid