Download Reading Cellular Boundaries Name Period All cells contain cell

Reading Cellular Boundaries
Name
Period
All cells contain cell membranes, which almost always are made up of a double-layered sheet called a lipid bilayer.
Read below to determine the structure and function of the cell membrane and details about transport of molecules
through the membrane. Directions Read through the following- highlight the main topic of each paragraph. Next
underline the supporting facts of the main topic. Circle examples of the supporting facts. Provide a title of each sections.
For example-The structure of the cell membrane. Once the first reading is complete go back and provide questions and
examples along the left side. Include vocabulary you don’t understand. Place a + by the ideas you understand and – by
the ideas you don’t understand. 10 Points
Title of this Section:
The layered structure of cell
membrane reflects the chemical properties of the lipids that make them up. Lipids have a hydrophobic (waterhating) portion attached to two hydrophilic (water-loving) chemical group. When these lipids are mixed with
the watery makeup of body fluids, the hydrophobic lipid “tails” cluster together inside the membrane, while the
hydrophilic phosphate “heads” are attracted to the water outside the cell. Thus, forming a lipid bilayer. A
sandwich is often used as an analogy of the bilayer. The hydrophilic heads line up together to form the bread
and the tails are the “fixins” of the sandwich. Draw what you think this might look like:
Title of this Section:
The cell membrane
functions to regulates what enters and exits the cell, and provides protection and support. In the digestive
system project the learning focused on the chemical break-down of four macromolecules. These molecules are
digested extracellularly into smaller monomers in the digestive system. Once these molecules digest into the
smaller monomer parts, like glucose, fatty acids, amino acids, and nucleotides- they are small enough to enter
the cells (with some help).
Title of this Section:
As mentioned,
the cell membrane regulates the entry and exit of molecules. Cell membranes are selectively or semipermeable,
meaning that some substances can pass across them and others cannot. There are two main categories of cell
transport- passive transport and active transport. Passive transport is the movement of molecules without the
use of cellular energy from an area of high concentration to an area of low concentration. In contrast active
transport requires cellular energy and moves molecules from an area of low concentration to an area of high
concentration or in other words, against a concentration gradient.
Title of this Section:
Some
molecules require chemical identification to allow entry. An analogy might be a cellular bouncer or doorman.
Often carbohydrates attached to the membrane perform this function. For example, insulin attaches to a
receptor molecule to allow glucose entry into the cells.
Title of this Section:
As mentioned passive transport is the
movement of molecules across the cell membrane without using cellular energy. There are three main types of passive
transport summarized below.
Diffusion is the process where molecules move from areas of higher concentration to an area of lower
concentration. The molecules move until equilibrium is reached where there is an equal number of molecules
on each side of the membrane. The most common examples of molecules entering by
passive diffusion are oxygen and carbon dioxide. Draw a 2 step picture of oxygen
entering the cell below. The first drawing should show excess oxygen (represent as
dots) on the outside the cell and the second should show equilibrium- equal number of dots inside and out.
Another type of passive transport is facilitated diffusion. The molecules moving do not require energy but must
move through protein channels or carriers. For example, the sugar glucose, which is the main source of cellular
energy passes through the lipid bilayer through specific protein channels or protein carriers. Glucose is an
example of a molecule that enters the cell through a protein carrier. Some ions (charged molecules such as
calcium, sodium, etc.) move into cells through protein channels. Draw the entry of glucose -make a channel and
draw an arrow showing glucose entering.
Osmosis is another type of passive transport. No energy is required but protein channels called aquaporin’s
allow the water to move from an area of high water concentration to an area of low water concentration. Or, as
mentioned in the Amoeba Sisters Video, from an area of low solute concentration to an area of high solute
concentration. Label each of the blood cells below as in a hypotonic, hypertonic, and isotonic solution.
List three types of passive transport 1)
2)
3)
As mentioned Active Transport allows the movement of materials against a concentration difference. This push to get
in or out by molecules requires energy. The two types of active transport are molecular transport and bulk transport.
The active transport of small molecules or ions across cell membrane is generally carried out by various
transport proteins- protein pumps- that are embedded in the membrane. This is called molecular transport.
Examples of ions moved across membranes by proteins pumps include sodium and potassium. A lot of the
energy from the food you eat is used in the active transport process- keeping molecules where they need to be.
Bulk Transport involves larger molecules and even solid clumps of material. This type of transport involves
movement of the cell membrane and the use of vesicles-small circular structures. Endocytosis is the process of
taking material into the cell through infoldings, or pockets and moving them into the cell via vesicles. Large
molecules, clumps of food, and whole cells can be taken up this way. Phagocytosis is a type of endocytosis in
which extensions of the cytoplasm surrounds the particle and engulfs it. Amoebas use this method for taking in
their food. White blood cells use this to engulf foreign invaders, like bacteria or viral cells. Cells can also “puke”
materials out using a process called exocytosis where they release large materials. Many hormones,
neurotransmitters, and digestive enzymes leave cells by exocytosis.
Summarize Cell Transport Below (there should be six types)
Type of Transport
Is it Active or Passive
Mechanisms – details – concentration
gradient, etc?
Example of
molecules