Biology Chapter 7.2-7.3 Notes-Cells
Voc. Words: Plasma membrane, Selective permeable, permeable, impermeable, phospholipids, fluid
mosaic model, cholesterol, transport proteins, cellulose, chromatin, translated RNA, Nucleolus,
Ribosomes, nuclear envelope, nuclear pores, vesicles, thylakoid membranes, grana, stroma, plastids,
microtubules, microfilaments, centrioles, cilia, and flagella
Section 7.2 -The Plasma Membrane
Plasma membrane-Function is to be a flexible boundary between the cell and its environment
 Cells need nutrients such as glucose, amino acids, and lipids
 This structure allows the proper balance of all things needed into the cells
 Selective permeable-the plasma membrane allows certain molecules in and
keeps others out
o Permeable-material can easily flow through
o Impermeable-material can not easily flow through
Structure of the Plasma Membrane
a. Remember that lipids are large molecules that are composed of glycerol and three fatty
acids. If a phosphate group releases a fatty acid, a phospholipid is formed.
o Phospholipid molecule (see page 177) has a Polar head (includes phosphate
group) and Nonpolar tails (two fatty acids)
b. The Plasma Membrane is composed of a Phospholipid bilayer (two layers of
phospholipids)
o Water is a key component to living organisms, both inside and outside of the cell
o The polar phosphate group allows the cell membrane to interact with the watery
environment since water is also polar.
o The two layers act as a barrier creating a water soluble layer at the outer
surfaces and a water-insoluble layer in the middle
 Water soluble molecules will not move easily through the membrane
because the insoluble layer is blocking it
c. The Plasma membrane is called the fluid mosaic model because the phospholipids
move within the membrane as water molecules move with the ocean currents
d. Cholesterol is also found in the Plasma membrane and its function is to stabilize the
phospholipids by preventing the fatty acid tails from sticking together
e. Transport proteins are used to move needed substances or waste material through the
plasma membrane
o Proteins are found within the lipid membrane
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o Transport proteins are needed to help form the selectively permeable
o membrane that regulates which molecules enter and which exit the cell
Section 7.3- Eukaryotic Cell Structures
Two types of eukaryotic cells: Plant and Animal
Structures of cells
a. Cell wall-fairly rigid structure found outside the plasma membrane
 Provides added support and protection to the cell
 Composed of a carbohydrate called cellulose-tough mesh of fibers (very porous
and allows molecules in the cell)
 Found in plant cells and prokaryotic cells
b. Nucleus-contains the directions to make proteins (True nucleus only in eukaryotic cells)
 Chromatin are strands of genetic material that are found in the nucleus and
contains the master set of directions to make proteins-only found in eukaryotic
cells

When a cell divides, the chromatin condenses to form
chromosomes
 Nucleolus are found in the nucleus and make the ribosomes
 Ribosomes are the sites where the cell produces proteins according to the DNA

Unlike other organelles ribosomes are not bound by a membrane

Some are free in the cytoplasm while others attach to the
Endoplasmic reticulum

Ribosomes and translated RNA must leave the nucleus and enter
the cytoplasm to produce proteins
 Translated RNA are the blueprints containing DNA
c. Cytoplasm is the clear, gelatinous fluid inside a cell
 The ribosomes and translated RNA reach the cytoplasm through the nuclear
envelope-a structure that separates the nucleus from the cytoplasm (double
membrane composed of two layers of phospholipid bilayers containing small
nuclear pores for substances to pass through)
 Cytoplasm suspends the cell’s organelles
d. Endoplasmic reticulum (ER)(Only found in eukaryotic cells) is the site where cellular
chemical reactions occur
 Arranged on a series of folded membranes in cytoplasm-like an accordion
 ER with ribosomes attached are called rough endoplasmic reticulum
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
e.
f.
g.
h.
i.
Where protein synthesis occurs
 Each type of protein made has a specific job
 ER without ribosomes are called smooth endoplasmic reticulum
 Free ribosomes make proteins specialized to perform tasks within the cytoplasm
 After proteins are made, they are transferred to the Golgi apparatus
Golgi apparatus (Only found in eukaryotic cells) is a flattened stack of tubular
membranes that modify the proteins
 Sorts proteins into packages and packs them into membrane-bound structures
called vesicles that send the proteins packages to the proper destinations (like
the post office sorts the mail)
Vacuoles (Only found in eukaryotic cells) are membrane bound compartments that
temporary store materials.
 Some store food, while others store waste, enzymes, and other materials
Lysosomes (Only found in some eukaryotic cells) are organelles that contain digestive
enzymes
 They digest excess and worn organelles, food particles, and engulf viruses or
bacteria
 The membrane surrounding a lysosome prevents the digestive enzymes inside
from digesting the cell
 Lysosomes can fuse to vacuoles and allow the enzymes to go into the vacuole
and eat the contents
Chloroplast (found in green plant cells and some protists) are like the nucleus, has a
double membrane
 The inner membrane system is called thylakoid membranes

Function is to catch the energy from the sun

Arranged in stacks of membranous sacs called grana, which
resemble stacks of coins

The fluid that surrounds the stacks of grana are stroma
 The chloroplast belongs to a group of plant organelles called plastids which are
used for storage

Plastids are named according to its color
 Chloroplast with green pigment is called chlorophyll
 Chlorophyll traps the light energy and gives leaves and stems
their green color
Mitochondria-(Only found in eukaryotic cells) power house membrane-bound organelle
found in all eukaryotic cells.
 Sugar molecule bonds are broken down here providing energy to the cells
 Has an outer membrane and a highly folded inner membrane
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 Energy-storing molecules are formed in the inner folds
 Mitochondria vary in number depending on the organism
j. Cytoskeleton (Only found in eukaryotic cells) forms the framework of the cell (like the
skeleton inside us)
 A network of tiny rods and filaments

Microtubules-thin cylinder rods made of proteins

Microfilaments-are smaller, solid protein filaments

They work together to give the cell its shape
k. Centrioles-organelles found in the cells of animals and most protists
 They occur in pairs and are made up of microtubules-play a role in cell division
l. Cilia and flagella-Found on some cell surfaces are used for locomotion
 Cilia are numerous short hair-like projections
 Flagella are longer projections that have a whip-like motion (one or two usually)

Allows locomotion of unicellular organisms
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