Cell Structure and Function
Chapter 3
I.
Cell Theory
A. Discovery of Cells
1. Robert Hooke (1665)
a. first to identify cells by looking at slices of cork
under a microscope
b. Hooke named cells, he thought they looked like the
rooms (cells) monks lived in
2. Anton van Leeuwenhoek (1674) - made a better
microscope, one of the first to describe living cells he
observed swimming in a drop of pond water
B. Development of the Cell Theory
1. Matthias Schleiden (1838) – first to note that plants
are made of cells
2. Theodor Schwann (1839) – first to note that animals
are made of cells, concluded that all living things are
made of cells
3. Rudolf Virchow (1855) – reported all cells come from
preexisting cells
4. Cell Theory (three parts)
a. all organisms are made of cells
b. all existing cells are produced by other living cells
c. the cell is the most basic unit of life
C. Prokaryotic cells and eukaryotic cells
1. Prokaryotic cells do not have a nucleus or other
membrane bound organelles
Examples - bacteria
2. Eukaryotic cells have a nucleus and other membranebound organelles
Examples: Animals, plants, fungus, protist
II. Cell Organelles – structures specialized to perform distinct
processes within a cell
A. Cells have an internal structure
1. Cytoskeleton – network of proteins, such as
microtubules and microfilaments inside a eukaryotic
cell
a. Microtubules – long hollow tubes, give cell shape
and act as tracks for the movement of organelles
b. Microfilaments – tiny threads that enable cells to
move and divide
2. Cytoplasm – jellylike substance inside cells that
contains molecules, helps cells maintain shape
B. Organelles involved in making and processing proteins
1. Nucleus – storehouse for genetic information (DNA)
2. Nuclear Envelope – double membrane that encloses
the nucleus
3. Endoplasmic reticulum (ER) – interconnected network
of thin folded membranes that produce, process and
distribute proteins
a. smooth ER – lacks ribosomes
b. rough ER – studded with ribosomes
4. Ribosomes – tiny organelles that link amino acids
together to form proteins (site of protein synthesis)
5. Golgi Apparatus – closely layered stacks of
membrane-enclosed spaces that process, sort,
packages, and deliver proteins
6. Vesicles – small organelle that contains and transports
materials within the cytoplasm
C. Other Organelles
1. Mitochondria – Supply energy to the cell, bean shaped
and have two membranes, inner membrane has many
folds that increases surface area
2. Vacuole – fluid-filled sack used for storage of materials
needed by the cell
a. animal cells usually have many small vacuoles
b. plant cells have a single, large vacuole
3. lysosomes – membrane-bound organelle that contains
enzymes, defends cell from invading bacteria and
viruses, they also break down damaged or worn-out
cell parts
4. centrosome – small region of cytoplasm that produces
microtubules
5. centriole – small cylinder-shaped organelle in animal
cells
D. Plant cells have cell walls and chloroplast
1. Cell walls - rigid layer that surrounds the cell
membrane, gives protection, support, and shape to the
cell, found in plants, algae, fungi, and most bacteria,
the cell wall is made primarily of cellulose
2. Chloroplasts – organelle that carries out
photosynthesis
III. Cell Membrane
A. Cell Membranes are composed of two phospholipids layers
1. Cell membrane (Plasma membrane)
a. forms a boundary between a cell and the outside
environment
b. controls the passage of material into and out of a
cell
2. Phospholipid molecules make up the cell membrane
a. Three parts to each phospholipids
1) a charged phosphate head
2) a glycerol
3) two fatty acid chains
b. the phosphate head and the glycerol form a polar
head (hydrophilic)
c. the fatty acids form the nonpolar tails
(hydrophobic)
3. Cholesterol molecules strengthen the cell membrane
4. proteins extend through the phospholipids layers and
help materials across the membrane
B. Fluid Mosaic Model – describes the arrangement of
molecules that make up the membrane
(see page 82)
C. Selective permeability (semipermiable) – allows some, but
not all, materials to cross
D. Chemical signals are transmitted across the cell membrane
1. receptor – a protein that detects a signal molecule and
performs an action in response
2. intracellular receptor – within the cell
3. Membrane Receptor – located within the cell
membrane
IV. Diffusion and Osmosis
A. Passive Transport – movement of molecules across a cell
membrane without energy input from the cell
1. Diffusion – movement of molecules from a region of
higher concentration to a region of lower
concentration
a. Concentration gradient – difference in the
concentration of a substance from one location to
another
b. Molecules diffuse down their concentration
gradient (from high to low concentration)
c. Example – oxygen easily diffuses into a cell without
the cell expending energy
2. Osmosis – the movement of water molecules across a
semipermeable membrane from an area of high
concentration to an area of low concentration
a. Isotonic solution (iso = same) – a solution has the
same concentration of dissolved particles as the cell
b. Hypertonic solution (hyper = higher) – a solution
has a higher concentration of dissolved particles
than a cell
c. Hypotonic solution (hypo = lower) a solution has a
lower concentration of dissolved particles than a
cell
3. Facilitated diffusion – the diffusion of molecules across
a membrane through transport proteins (passive
transport)
V.
Active Transport – movement of molecules across a membrane
from an area of low concentration to an area of high
concentration, requires an input of energy
A. Proteins can transport materials against the concentration
gradient
B. Active transport with vesicles
1. Endocytosis – uptake of liquids or large molecules into
a cell by inward folding of the cell membrane
2. Phagocytosis - uptake of a solid particle into a cell by
engulfing the particle
3. Exocytosis – release of substances out of a cell by the
fusion of a vesicle with the membrane
4. Process when a cell engulfs a liquid (cell drinking)