f4 chapter 3 notes

8/7/2019 F4 Chapter 3 notes

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Chapter 3

1. Uniqueness of PlasmaMembrane (also known as cell membrane):

y it is a semi-permeable cell membrane

y it allows water and certain substances to move in and out of the cell.

2. Importance ofPlasma Membrane:

y - cells obtain nutrients and gases

y cells excrete metabolic wastes

y cells can maintain pH for enzyme activity

y cells can maintain ionic concentration of the cells for enzyme activity

y control the types and the amount of substances

y allow useful substance (hormones/enzymes) to secrete from cells

y protect cells

y a boundary between the inside and outside of cell.

3. Structure of the basic unit of plasma membrane

y Phospholipid molecule:Head hydrophilic: a polar phosphate molecule (philic~loves water / attracted to water)Tail hydrophobic: two non-polar fatty acids (phobic~hates water / repelled to water)

y Formation:Hydrophilic heads pointing outwardsHydrophobic tails pointing inwards(Bilayer phospolipid)

Fluid Mosaic Model (Protein embedded in the bilayer)

Carrier protein

y carrier for some molecules (glucose, amino acids, proteins and nucleic acids)

y controls the movement of ions and particles (Na+, Ca

2+and K

+)

y Glycoprotein

Glycolipid

y combination of lipids and polysaccharides

4. Permeability

Permeable (allow to pass through)

y small non-polar molecules (vitamins A, D, E, K, fatty acids, glycerol and steroids)

Impermeable (not allow to pass through but with help of carrier protein and cellular energy, it is allow to pass

through)

y large polar molecules (glucose, amino acids, mucleic acids and polysaccharides)

y charged ions (H+, Na+, K+, Cl- and Ca2+)

Substances that are allowed to move in the cell:

y CO2

y O2

y excess H2O


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y waste: nitrogenous

Substances that are allowed to move out of the cell:

y CO2

y O2

y amino acids

y ionic saltsy glucose

Materials must be able to move through the plasma membrane in order for the cell cytoplasma to interact with theexternal environment. Therefore, the movement of soluble substances can occur in several mechanisms:

y A. Process of Passive Transport

y B. Process of Active Transport

A. Passive Transport

i) Simple Diffusion

y not selective: lipid-soluble molecules, gases and water.y not control by cell.

y movement of the molecules from a region of higher concentration to a region of lower concentration.

y Factors affecting the rate of diffusion are temperature, size of molecules/ions, diffusion gradient, surfacearea and diffusion medium.

y example: diffusion of oxygen and carbon dioxide at the alveolus.

ii) Osmosis:

y only water molecules.

y not control by cell.

y movement of water from a region of higher concentration to one of lower concentrationand often occursacross a semipermeable membrane.

y strong sucrose solution = less water molecule = low water potential.

y weak sucrose solution = more water molecule = high water potential.

y example: absorption of water by root hairs.

iii) Facilitated Diffusion:

y very specific: glucose, nucleic aicds, amino acids, protein and mineral ions.

y control by cell.

y transport of molecules (only certain molecules) across the outer membrane of living cell by a processof carrier protein (hydrophilic group) / channel protein (Ions: Na

+, Ca

2+, K

+) within the cell membrane.

y normally take place from a region with higher concentration of molecules to a region of lowerconcentration.

y example: absorption of digested food in the villus.

B. Process of Active Transport

y very specific: minerals ions and amino acids.

y control by cell.

y This process needs carrier proteins and energy (due to against concentration gradient) from a region oflower concentration to a region of higher concentration).

y Cell must expend energy that derived from ATP (adenosine triphosphate)y example: human nerve cells (sodium ions are constantly transport out of the cell) / ions intake by root

hairs of a plant.


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f4 chapter 3 notes

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