Cell bound by membrane: Fluid-Mosaic Model --> Phospholipid bilayer --> separates the cytoplasm & extracellular fluid --> the phosholipid = polar (slight charge within normal covalent bond) phosphate group (head) + non-polar (neutral) fatty acids group (tail)

Head: water-soluble (since water molecule is polar) --> hydrophilic: water loving

Tail: water-insoluble --> hydrophobic: water hating

Fluid-Mosaic Model: membrane can move laterally like a fluid --> restrained by cholestral --> protein moelcules also binds like a mosaic

Molecules attached to the cell membrane surface:

Carbohydrates: signature moelcules --> enables antibodies to recognise foreign moelcules

Glycoprotein: attached proteins

Glycolipid: attached lipids

Cellular homeostasis: the maintenance of a relatively constant environment within a cell --> through movement of moelcules across cellular membrane

Selective permeability:

allows: water, CO2, glucose, oxygen

prevents: hemoglobin (protein), starch

Pollen grains in water: 1st person to discover movement of molecules in water --> in 1827, observed using microscopes --> Brownian motion: random motion & collision of molecules

Diffusion: movement of particles from region of higher concentration to region of lower concentration

Concentration gradient: difference in concentration between regions

Dynamic equilibrium: particles move & collide, but the concentration remains constant

Mechanism to move molecules through the membrane:

1) Diffusion: molecule movement due to concentration gradient

2) Osmosis: diffusion of water moelcules across a selectively permeable membrane --> osmotic pressure: an increase in pressure due to osmosis --> movement of water molecules --> solution surrounding cell affects the solution inside cell

Isotonic solution: solution in which the concentration of dissolved substances is equal to that of another solution (e.g. cytoplasm)

Hypotonic solution: solution in which the concentration of dissolved substances is less than that of another solution (e.g. hemoglobin takes in water, swells, if much, bursts)

In plants, this gives rise to turgor pressure: water pressure within plant cell that gives plants shape & support

Hypertonic solution: solution in which the concentration of dissolved substances is greater than that of another solution (e.g. water exits the cell, causing cell to shrink) --> reduced turgor pressure --> plasmolysis: shrinking of cytoplasm by osmosis

3) Passive transport: moving particles by diffusion, concentration gradient only without energy applied

4) Facilitated transport: through transport proteins to allow larger molecules to move across membrane --> one type of transport proteins bind to one type of moelcule to exit on the other side of the mebrane --> e.g. glucose is transported in this way to our cells

5) Active transport: from low concentration to high concentration --> 2 processes:

5a) Facilitated diffusion --> energy expended --> using ATP --> ADP --> e.g. nerve cell conducts impulses through facilitated diffusion using transport proteins

5b) Endocytosis: mechanism by which cell surrounds & takes in a substance from the environment --> to form some vesicles (food vascuoles) --> digested by enzymes within each vascuole

Receptor-mediated endocytosis: mechanism by which large molecules are taken into a cell in vesicles formed from coated pits in the plasma membrane --> coated with Clathrin --> Clathrin-coated vesicle

5c) Exocytosis: mechanism by which cell releases waste materials to the extracellular fluids

Passive transport:

Diffusion

Osmosis

Facilitated transport

Active transport: uses energy ATP with vascular proteins

Endocytosis

Exocytosis