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Name _____________________________
Date_____________________
Human Anatomy & Physiology
Homework: Cells 2
SUMMARY OF CELL THEORY
1. All organisms are made up of one or more _____________.
2. All cells carry on their own ____________________ _______________.
3. New cells arise from __________________ ________________.
CELL STRUCTURE AND FUNCTION
Every cell is enclosed by a cell (plasma) membrane. Within the cell membrane are the nucleus
and the cytoplasm. The cytoplasm consists of all the material outside the nucleus and inside the
cell membrane. Within the cytoplasm are organized structures called organelles, which perform
specific functions.
A. Cell Membrane
The cell, or plasma, membrane surrounds the cell. It plays an active role in determining which
substances enter and which substances leave the cell. Because some substances can pass freely
through the cell membrane and others cannot, the cell membrane is said to be selectively
permeable or semipermeable. The permeability of the cell membrane varies from one cell type
to another and from time to time in the same type of cell, depending on the state of metabolic
activity.
The cell membrane is composed of lipids and proteins. The lipids form two layers of
molecules, and are arranged tail to tail. Protein molecules are embedded within the lipid
structure. This arrangement is known as the fluid mosaic model.
1. Describe the functions of the cell membrane.
______________________________________________________________________________
______________________________________________________________________________
2. The cell membrane is composed of ________________ and _____________________.
3. Protein molecules are _____________________ in the lipid structure.
4. Why is the cell membrane described as semipermeable?
______________________________________________________________________________
______________________________________________________________________________
5. What is the name of the model used to describe the physical structure of the cell membrane?
____________________________
B. Nucleus
The nucleus is the control center for cell functions. It is surrounded by a semipermeable
membrane called the nuclear membrane or nuclear envelope. Within the nucleus are the
chromosomes, which contain the genetic material. One of the responsibilities of the nucleus is to
make sure that a copy of each chromosome is replicated during the process of mitosis. Also
found within the nucleus is at least one nucleolus. The function of a nucleolus is involved with
the process of transcription, which is the first step in protein synthesis.
1. The _______________________ is involved with the production of new proteins.
2. The control center for the cell is the ______________________.
3. During cell division, the ______________________ replicate with one copy going to each
daughter cell.
C. Cytoplasm
The material within the cell but outside the nucleus is called cytoplasm. Although cytoplasm
contains thousands of substances, it consists mainly of water. The cytoplasm provides the proper
environment in which the organelles carry on the life processes of the cell, for example
glycolysis. Glycolysis is the first major step of cellular respiration.
1. What is the main function of cytoplasm?
______________________________________________________________________________
2. Cytoplasm consists mainly of ________________.
D. Mitochondria
Mitochondria are oval or rod-shaped organelles found in the cytoplasm. They are enclosed by
a double membrane, whose inner layer is highly folded so that it has a large surface area. The
remainder of the chemical reactions of cellular respiration occur within the mitochondria.
1. What is the function of the mitochondria?
______________________________________________________________________________
2. What is the advantage of having the inner membrane tightly folded?
______________________________________________________________________________
3. Which part of cellular respiration does not occur within the mitochondria?
________________
E. Endoplasmic reticulum
The endoplasmic reticulum (ER) is a membrane bound system of fluid-filled channels or tubes
through which materials are transported within the cell. The membranes of the ER may also
serve as sites of biochemical reactions. There are two types of ER: smooth and rough. The
rough, or granular, appearance os some ER is due to the presence of ribosomes on the surface of
its membrane. Rough ER is found mainly in cells involved in protein synthesis. Smooth ER,
which has no attached ribosomes, is found mainly in cells involved in the synthesis of nonprotein
substances.
1. What are the functions of the ER?
______________________________________________________________________________
______________________________________________________________________________
2. The two types of ER are ______________ and ___________________.
3. In what types of cells are each found?
______________________________________________________________________________
______________________________________________________________________________
4. What structures give certain types of ER a rough appearance? _____________________
F. Ribosomes
Ribosomes are tiny spheres that are either free floating within the cytoplasm or attached to the
endoplasmic reticulum. They provide the site for protein synthesis. Genetic information carried
from the nucleus to the ribosomes via messenger RNA determines the sequence of amino acids
for a specific protein. Proteins synthesized by free ribosomes perform their functions within the
cell (not secreted out of cell.)
1. What cellular process occurs at the ribosomes? ____________________________________
2. What happens to proteins synthesized by free ribosomes?
______________________________________________________________________________
G. Lysosomes
Lysosomes are packages, or sacs, filled with digestive enzymes. They keep the enzymes
separated from the rest of the cell contents until they are needed. Lysosomes are egg-shaped
structures enclosed by a membrane. They are thought to be produced by the Golgi complex.
1. What is the function of lysosomes?
______________________________________________________________________________
H. Golgi complex
The Golgi complex is a stack of 4 to 8 membranous sacs located near the nucleus. Newly
produced proteins and lipids are packaged for distribution within the cell or export from the cell.
1. What is the function of the Golgi complex?
______________________________________________________________________________
I. Centrioles and centrosomes
The centrosome is a dense area of cytoplasmic material near the nucleus that contains a pair of
cylindrical structures called centrioles. During cell division, the centrioles generate spindle
fibers, which are responsible for the separation of chromosomes into each new daughter cell.
1. What is the function of centrioles?
______________________________________________________________________________
J. Cell inclusions
Inclusions are substances produced by cells and stored within cytoplasm. Examples of
inclusions are 1) triglycerides, which are stored in adipose (fat) tissue and 2) melanin, a pigment
stored in cells of the hair, skin and eyes.
1. What substance is responsible for skin and eye coloration? ___________________________