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Cells
Chapter 3
Humans have about
75-100 trillion cells
They vary in shape and
size
Shape & size--closely
related to function
2 Major Parts
1) Nucleus
Inner most part
The control center
Surrounded by a thin
double layered
membrane
(nuclear envelope)
2) Cytoplasm
Fluid that surrounds
the nucleus
Encircled by the cell
membrane
(AKA: plasma membrane)
-Cytoplasm is
responsible for
metabolism
-Appears to be clear
liquid with tiny specks
-Where all cell
activities occur
Within the cytoplasm
are parts called
Organelles
They conduct special
metabolic functions for
all cells
Cell Membrane
(Plasma Membrane)
Very thin—only visible
with electron
microscope
Is flexible and elastic
Keeps the cell intact
Is selectively
permeable; controls
what enters and leaves
the cell
Composed of lipids and
proteins
Is a bi-layer of
phospholipid
molecules
Organelles:
Endoplasmic Reticulum
(ER)—very complex
Functions as tubular
communication
system…
and it transfers
molecules from one
part of the cell to the
other
Helps produce
ribosomes
Rough ER
Contains ribosomes
Ribosomes
Structure: particles
composed of proteins
and RNA molecules
Function: They
synthesize proteins
Golgi Apparatus
Structure: group of
flattened membrane
sacs
Function: packages
protein molecules for
transportation and
secretion
Mitochondria
Structure: fluid filled
sacs, which vary in
shape and size
Function: release
energy from food
molecules & transform
energy into usable
forms
Lysosomes
Structure:
membranous sacs
Function: digests worn
cellular parts or foreign
objects that enters cell
Centrosome
Structure: nonmembranous
structure, composed of
2 rod-like centrioles
Function: helps
distribute
chromosomes to new
cells during cell
reproduction
Vesicles
Structure: membrane sacs
Function: contain
various substances
that enter & exit the
cell
Cilia & Flagella
Structure: motile
projections attached
beneath the cell
membrane
Function: propels fluid
over cellular surfaces
and enable movement
Flagella=sperm
Cilia=epithelial cell
Microfilaments &
Microtubules
Structure: thin rods
and tubes
Function: provide
support to the
cytoplasm and help
substances and
organelles into the
cytoplasm
Movement Through
Cell Membrane
*Passive mechanisms
require NO energy
Chart 3.2 page 61
1. Diffusion
A process by which
molecules or ions
become scattered or
spread spontaneously
from region where
they are in higher…
concentration toward
region where they are
in lower concentration
It is by diffusion that
oxygen and carbon
dioxide molecules are
exchange between air and
blood in the lungs, and
between the blood and
the cells of various tissues
When molecules have
been equally
distributed, a state of
Equilibrium results
Facilitated Diffusion
Occurs in most cells
It is when a glucose
molecule combines
with a protein carrier…
there, the glucose and
the carrier form a
compound; they then
can diffuse through the
other side of the lipid
bi-layer
Once inside, the
glucose is released and
the carrier returns to
the outside
Insulin
A special hormone that
promotes facilitated
diffusion of glucose
through certain cells
Osmosis
Special case of
diffusion
(diffusion of water)
Occurs when water
molecules diffuse from a
region of higher
concentration to a region
of lower concentration,
through a selectively
permeable membrane
Osmotic Pressure
The amount of
pressure needed to
stop osmosis
3 Types of Osmosis
1) Hypertonic Solution
Greater concentration
of solute outside the
cell than inside
(more water leaving
than entering)
*Cell shrinks
2) Hypotonic Solution
Greater concentration
of solute inside the cell
than outside
(more water is
entering than leaving)
*Cell swells
3) Isotonic Solution
Same concentration
inside and outside the
cell
*Cell stays the same
Active Transport (p 61)
Molecules are carried
through the cell
membranes by other
molecules from a lower
concentration to a
higher concentration…
through the use of
special carrier
molecules
*Endocytosis
Particles are too large
to enter the cell by
diffusion or active
transport
A vesicle is made
*Pinocytosis
(cell drinking)
Cells bring in droplets
of liquid from its
surroundings. The cell
becomes indented by
the liquid
The cell forms a seal
around the droplet.
The liquid particle
becomes part of the
cytoplasm
*Phagocytosis
Exact same process as
pinocytosis, except it
brings is solids
*Exocytosis
(cell puking)
“Junk” is spit out of
cell
Life of a Cell
Life cycle of a nonreproductive cell…
The series of changes
that a cell undergoes
from the time it is
formed until it
reproduces is called its
Life Cycle (cell cycle)
Cell cycle is made up of
Interphase (G1 phase,
G2 phase, S phase)
and mitosis
Interphase
Cell grows and
prepares for mitosis
Gap 2 (G2)
Mitosis
S Phase
(DNA synthesis)
Gap 1 (G1)
Cells that cease
division
Mitosis
Division of nuclear
parts and also
cytoplasm
Contains information
on DNA formation
Mitosis is continual
(20 hours)
Stages:
(PMAT)
Prophase
First indication of
something taking place
Chromosomes become
scattered throughout
the nucleus (appear)
Metaphase
Spindle fibers attach to
centromere
Chromosomes line up
on the equator of the
cell
Anaphase
Centromeres split
Chromatids move to
opposite poles
(to ends of cell)
Telophase
Cell membrane starts
to divide cytoplasm