Chapter 3 - Cells

Cytology - the study of cells

Cells vary greatly in SIZE and STRUCTURE
Cells have two main parts - NUCLEUS & CYTOPLASM,

Enclosed in a CELL MEMBRANE (also called PLASMA MEMBRANE), which is extremely thin, often has folds and pouches, and allows certain substances to pass through it.

Selectively Permeable = controls what enters and leaves the cell, it allows some things to pass but not others, this is the MAIN FUNCTION of the cell membrane

CYTOPLASM - the area between the plasma membrane and nucleus. Where most metabolic reactions/activities take place. Filled with a clear fluid called CYTOSOL. Contains many structures called ORGANELLES


1. ENDOPLASMIC RETICULUM (E.R.) - complex system or network of interconnected membranes, canals, or channels. Connected to cell membrane, nuclear membrane, and organelles

A. Rough ER - where ribosomes are located. Ribosomes manufacture (synthesize) proteins
B. Smooth ER - no ribosomes, where lipid synthesis takes place

smooth er

2. GOLGI APPARATUS (BODIES) - series of flattened, membranous sacs near the nucleus
Function = "Refining", "Packaging", Delivery of proteins

golgi body

3. MITOCHONDRIA (-ion = sing.) - Usually numerous, double layer membrane - inner layer folded to form CRISTAE.
Function = where chemical energy (food substances) is transformed into a useable form - molecules of ATP (adenosine triphosphate) that are like "packets" of energy. The process of releasing/transforming the energy from food involves OXYGEN and is called CELLULAR RESPIRATION


4. LYSOSOMES - quite variable in size and shape. Contain powerful digesting enzymes - breakdown and destroy foreign particles, microorganisms, damaged or worn out cells and cell parts

5. CENTROSOME (central body) - Usually near the G.A. and nucleus. Composed of 2 "cylinders" called CENTRIOLES (each composed of numerous microtubules), which always lie perpendicular to each other. Active involved in cell reproduction - SPINDLE forms from the centrioles

6. VESICLES - tiny sacs in which substances are transported

7. MICROFILAMENTS & MICROTUBULES - threadlike structures
MICROFILAMENTS - involved in cellular movement, as in muscle cells
MICROTUBULES - larger than filaments, maintain shape ("skeleton" of the cell)



The NUCLEUS - directs the activities of a cell. Contains GENETIC materials. Surrounded by a selectively permeable membrane called the NUCLEAR MEMBRANE or ENVELOPE. Filled with fluid called NUCLEOPLASM

1. NUCLEOLUS - small, dense structures within nucleus, made of proteins and RNA. No membrane
FUNCTION = produces ribosomes

2. CHROMATIN - loosely coiled "fibers" in nucleoplasm. Forms CHROMOSOMES during cell reproduction. Composed mainly of DNA (deoxyribonucleic acid) and PROTEIN. Contains coded information that directs protein synthesis in the cell (summary page 56)


Movement of Substances Through the Cell Membrane

DIFFUSION - molecules move spontaneously (no cellular energy used) from an area of higher concentration to an area of lower concentration

FACILITATED DIFFUSION - molecules diffuse through a membrane by means of a carrier molecule transports (requires no energy = PASSIVE TRANSPORT)

OSMOSIS - the diffusion of water through a selectively permeable membrane. OSMOTIC PRESSURE = pressure to stop osmosis


Solute = Substance dissolved
Solvent = Substance in which a solute is dissolved (usually water)
Hypertonic Solution = conc. of solute particles is greater outside the cell
Hypotonic Solution = conc. of solute particles is lower outside the cell
Isotonic Solution = conc of solute particles is the same inside and outside the cell

FILTRATION - molecules are forced through a membrane by hydrostatic pressure

ACTIVE TRANSPORT - molecules are moved against the concentration gradient. This requires the use of cellular energy, also usually involves a carrier molecule.

Exocytosis = transport of particles out of the cell
Endocytosis = transport of particles into th cell
Pinocytosis - liquids taken in, cell engulfs a droplet of water
Phagocytosis -solids taken in. a vesicle forms.


The Life Cycle of a Cell

A. Mitosis (nuclear division)
B. Cytoplasmic Division (cytokinesis)
C. Interphase (growth)
D. Differentiation - cells become specialized, developing characteristics in structure and function







INTERPHASE - growth of cell occurs, chromosomes are duplicated and other structures and organelles are produced

DIFFERENTIATION - occurs as cells multiply and organism develops and grows