Download Cell Theory

Cell Structure & Function
History:
1665 - Robert Hooke
viewed thin slices of cork and
called the hollow boxes cells
1674 - Anton van Leeuwenhoek
observed living cells in water
1838 - Matthias Schleiden
concludes that all plants are
made up of cells
1839 - Theodor Schwann
concludes that all animals are
made up of cells
1855 - Rudolph Virchow
concludes that all cells reproduce
1970 - Lynn Margulis
proposes endosymbiont hypothesis
that some cell parts may have
once been cells themselves
Cell Theory
1. all living things are
made of cells
2. cells are the basic unit
of structure and
function in living things
3. new cells come from
pre-existing cells
There are 2 types of cells
Prokaryotic
Eukaryotic
Characteristics of prokaryotes:
All are bacteria
No organized nucleus
No organelles
Small ribosomes
Characteristics of eukaryotes:
Typical cells of:
plants
animals
fungus
protists
Have an organized nucleus and many
small organelles
Cell parts:
Cell (plasma) membrane
controls what goes in or out
Cell wall
provides support
Cytoplasm (cytosol)
liquid containing cell parts
Nucleus
control center containing
Chromosomes
genetic material
Nucleolus
makes ribosomes
Cilia
short fibers for movement
Flagella
long strands for movement
Cell organelles:
Ribosomes
site of protein synthesis
Mitochondria
produce energy
Golgi apparatus
modify and package proteins
Lysosomes
contain digestive enzymes
Peroxisomes
contain special enzymes
Endoplasmic reticulum (ER)
membrane transport system
site of product synthesis
Vacuoles
storage units
Centrioles
help in cell reproduction
Plastids
specialized storage units
amyloplasts
store starch
chloroplasts
store chlorophyll
chromoplasts
store pigments
Cytoskeleton
fibers for support
microtubules
microfilaments
Levels of organization:
unicellular
multicellular
tissue - organ
organ system – organism
CELL MEMBRANES
Cell membranes help maintain
Homeostasis.
Some substances cross the membrane
with no energy required by the cell.
This is called passive transport.
Small molecules like O2, H2O, CO2
can move in and out freely,
Large molecules like proteins and
carbohydrates cannot.
The cell membrane is semi-permeable
or selectively permeable .
Diffusion across a membrane is
passive transport.
Diffusion is movement from high
to low concentration.
The difference in concentration
across a membrane is called a
concentration gradient.
Diffusion is driven by kinetic energy.
Kinetic energy keeps molecules in
constant motion.
The rate of diffusion depends on:
Temperature
Molecular size
Type of molecule
Molecules diffuse faster at higher
temperatures.
Small molecules diffuse faster than
large molecules.
Diffusion always occurs down a
concentration gradient.
Diffusion occurs until there is
equal concentration.
When there is no concentration
gradient, there is equilibrium,
but molecules continue to move.
Diffusion of water across a
membrane is called osmosis.
Diffusion of water down a gradient
does not require energy.
Cytoplasm is mostly water that
contains dissolved solutes.
Concentrated solutions have many
solute particles and less water.
Water moves from areas of low
solute concentration to areas of
high solute concentration.
There are three types of solution
based on concentration :
Hypertonic
Isotonic
Hypotonic
Hypertonic
Solute concentration outside
the cell is high (like salt water).
Water diffuses out of the cell
and the cell contents shrink.
Called plasmolysis in animal cells
In plant cells it results in wilting
Isotonic
Solute concentration is the same
inside and outside the cell and
water moves in and out of the
cell at the same rate.
The cell remains normal.
Animal cells do best here.
Plant cells remain normal.
Hypotonic
Solute concentration is greater
inside the cell.
Water diffuses into the cell.
The cell contents swell and the
cell may rupture.
In animal cells it is called lysis.
In plant cells, the result is turgidity.
Plants do best here.
Most animal cells exist in isotonic
environments.
Cells in fresh water are in
hypotonic solution.
They must pump water out using
contractile vacuoles.
Plant cells have a cell wall that
prevents them from bursting.
Facilitated diffusion
Faster than simple diffusion, it
is considered passive transport.
It uses carrier proteins that
can change shape.
It helps move certain solutes
like glucose across the membrane.
Facilitated diffusion may also use
channel proteins that can form open
paths through the membrane or have
gated channels that open and close
in response to concentration.
Osmosis occurs through aquaporins
Active transport
Requires energy from ATP.
Moves substances against or up
A concentration gradient.
It may involve membrane proteins.
It is used to move ions like Na+,
Ca++, or K+ across the membrane.
Bulk transport
Moves large complex molecules
across the cell membrane
Endocytosis moves large quantities
of substances into the cell.
phagocytosis moves solid
particles into the cell,
pinocytosis moves fluid drops
into the cell.
Exocytosis
Used to remove large particles
from the cell such as waste,
mucus, and cell products like
insulin