The student will investigate and understand relationships between cell structure and function. Key
a) characteristics of prokaryotic and eukaryotic cells;
The essential difference between prokaryotic and eukaryotic cells is that prokaryotes lack a nuclear
membrane and differentiated cellular organelles. DNA is a circular strand and is located in the cytoplasm.
A prokaryote is surrounded by a cellular membrane and may have a cell wall. Like a eukaryotic cell, it
contains ribosomes, the site of protein manufacture. Reproduction is through binary fission, a form of
cloning in which DNA is copied and divided between two identical daughter cells.
Eukaryotic cells have a well defined nucleus in which DNA is organized into chromosomes. In the
nucleus are found one or more nucleoli, the site of ribosome manufacture. The nuclear envelope is a
double phospholipid bilayer with nuclear pores which allow information molecules to pass from the nucleus
to the cytoplasm and vice versa. Within the cytoplasm, there is a series of membrane bound organelles
which are derived from the outer layer of the nuclear envelope: rough and smooth endoplasmic reticula; the
Golgi apparatus (aka body); and various vacuoles which have different functions and may bud off and
merge with the cell membrane, and are the source of the cell membrane. When this merger occurs, the
inner side of the vacuole membrane becomes the outer side of the cell membrane. Ribosomes are found
attached to the rough endoplasmic reticulum where they manufacture proteins for export from the cell.
They are also found free in the cytoplasm where they manufacture enzymes and other proteins for use in
the cell. All eukaryotic cells contain mitochondria. Mitochondria have their own circular strand of DNA and
divide independently of the cell; mitochondria are the site of the Krebs Cycle of cellular respiration. Plant
cells and photosynthetic protista contain chlorplasts that also have their own circular strand of DNA.
Eukaryotic cells may or may not have a cell wall or central vacuole. Eukaryotic cells reproduce by mitosis
in which identical daughters are produced. There are specialized organelles (centrioles & asters) which aid
in this process. In multicellular organisms, specialized reproductive cells produce gametes (sperm & eggs)
through meiosis. This form of cell division involves a halving of the DNA (called a reduction division).
Gametes unite in sexual reproduction and thus achieve the full complement of DNA in the developing
Please view the power point on Cells and Cell Organelles
b) exploring the diversity and variation of eukaryotes
Depending on the kingdom, eukaryotes may contain different organelles. For example, fungi are
heterotrophs (obtain energy by consuming other organisms) and so have no chloroplasts. They do have a
cell wall. Plants are photosynthetic and so contain chloroplasts and also have a cell wall. They are
autotrophs that produce their own food. In animals, there are neither chloroplasts, nor is there a cell wall.
In multicellular organisms, eukaryotic cells may contain an abundance of one particular kind of
organelle, depending on their function in that particular tissue. For example, muscle cells contain an
abundance of mitochondria as their need for energy is large. These cells never divide, so they would lack
the paraphernalia of cell division. Liver cells contain large amounts of the smooth endoplasmic reticulum.
If a person is a drug addict or a heavy drinker, smooth endoplasmic reticulum with dominate the cells as it
functions in detoxification.
c) similarities between a single cell and a whole organism;
A single cell must have a means of obtaining the materials needed for metabolism (gases,
nutrients, ions, food) as well as eliminate waste products. It achieves this through endocytosis and
exocytosis as well as active and passive transport across the cell membrane. It must be able to keep out
toxic materials or have means to detoxify them, a function achieved by being surrounded by a semi-
permeable membrane. It must have a means of growth and reproduction (mitosis & binary fission), and in
some instances locomotion (cilia & flagella). A single cell must be able to move materials around in the cell
to places where they are needed, just as a multicellular organism must move materials around. A cell may
need a means of support. Both of these can be achieved through the action of cytoskeletons and in some
instances cell walls. All of these functions are achieved in multicellular organisms through specialized
tissues organized into organs and organ systems.
Because single cells must carry out all of these functions, they are necessarily limited in size. A
smaller size means that there is more surface area per unit volume than in larger cells. Thus a small cell
size allows functions that must occur across the membrane to occur more efficiently.
d) and, the cell membrane model (diffusion, osmosis, and active transport).
Since the cell membrane is the primary barrier between life functions and the external environment
its characteristics are extremely important. Cell membranes consist of a phospholipid bilayer. A
phospholipid is a phosphate head that is hydrophyllic ( water loving, polar &/or charged) with lipid tails (two
chains) that are hydrophobic (water fearing, non polar). There are two layers so that the phosphate heads
are in contact with the external and internal fluids of the cell and they lipids extend inward and form a
hydrophobic core to the membrane. Imbedded in this bilayer are various enzymes and proteins which
serve as sensors, receivers of signals, and pathways for ions and larger particles across the membrane.
These and other attached carbohydrates and steroids keep the membrane fluid and dynamic, hence it is
called the fluid mosaic model of a cell membrane or a plasma membrane.
If someone in a corner of a large room sprays perfume into the air, people on the other side of the
room will soon detect the scent of that perfume. Molecules, through random motion, will diffuse from an
area of high concentration to an area of low concentration. This is referred to a movement down a
concentration gradient and it cannot be prevented. Cell membranes are semi-permeable. Only very small
molecules such as water can diffuse into the cell, so cells often maintain a concentration gradient between
their internal fluids and the environment, especially with regard to large molecules or highly charged ions
which cannot pass through the hydrophobic lipid core of the membrane. However, proteins in the
membrane can provide polar channels through which polar or charged ions can move across the
membrane. This is called facilitated diffusion.
Osmosis is the diffusion of water which will occur across a cell membrane from a region of a dilute
solution (high water concentration) to a more concentrated solution (low water concentration). If the
external solution is hypotonic to the interior, water will diffuse into the cell and the cell will swell. The cell
wall in plant cells prevents too much swelling to the point of lysis and excess water will fill the central
vacuole. This will happen if potato cores are placed in distilled water over night. If the external fluids are
hypertonic to the interior, the cell will shrink and water flows out of the cell. This will happen if potato cores
are placed in salt water over night. Looking at living Elodea cells under a light microscope while flooding
the slide with salt water will result in the cell membrane pulling away from the cell wall, crowding all the
chloroplasts together. The proper cell structure can be restored by replacing the salt water with distilled
water! Isotonic solutions have the same water concentration inside as well as outside, so there is no net
change in the cell.
Sometimes it is necessary to move substances into or out of a cell against their concentration
gradient. This requires the expenditure of energy in the form of ATP and is called active transport. During
active transport, enzymes imbedded in the cell membrane function as carriers of the substance in question,
but will not release the substance unless a molecule of ATP is provided. The most important active
transport system is the sodium – potassium pump. Sodium concentrations are higher outside the cell and
potassium ion concentrations are higher inside the cell. The pump transports three sodium ions out of the
cell and two potassium ions inside the cell as one ATP molecule is broken releasing a phosphate and an
ADP molecule. This is one of the reasons that it is critically important to maintain the proper ratio of sodium
to potassium in our diet.
Please view the power point on cell organelles, especially the membrane portion
This website has an animation of the sodium-potassium pump with very annoying sound effects.
This is in the form of an animation of the sodium potassium pump with narration.
This is a summary of osmosis.
good simple diagrams of hyper, hypo & isotonic solutions
This website has an animation with narration of osmosis.
After reviewing material in your textbook, go to the file labeled BIO.4 Review Response and open it in
Word. Type your answers below each question and make them a distinctive readable color or font. E-mail
this file as an attachment