SBI 4U
Name: ________________________
Cells and Organelles Assignment – Answer Key Guide
Date: ________________________
Cells
1. What does the term “eukaryotic cell” mean?
See http://www.diffen.com/difference/Eukaryotic_Cell_vs_Prokaryotic_Cell.
What features do all eukaryotic cells have in common? See page 58 of text.
2. Define the term “organelle”. See http://www.biology-online.org/dictionary/Organelles
3. Label the following diagrams. (You can label the diagrams using your textbook.)
The Nucleus
1. What important macromolecule is found in the cell nucleus? DNA What is its purpose? DNA stores and replicates the
genetic information of the cell. Each molecule of DNA in the nucleus is combined with an equal mass of protein to form
a chromosome. The number of chromosomes in the nucleus is species dependent. Chromosomes are visible in dividing
cells. In a non-dividing cells, chromatin, the unfolded state of chromosomes, is present. (pg. 59).
2. Define nucleoplasm, nuclear matrix, nucleolus, nuclear envelope and nuclear pore complex. (All of these terms are
defined at the top of page 60.)
3. In general, what is the function of the nucleus? The cell nucleus is a membrane bound structure that contains the cell's
hereditary information and controls the cell's growth and reproduction. It is the command center of a
eukaryotic cell and is commonly the most prominent organelle in a cell.
4. Label the diagrams below. (See text book.)
The Endoplasmic Reticulum
1. What is the endoplasmic reticulum made of? Endoplasmic reticulum is a composed of hollow membranes that are
connected to and a part of the nuclear envelope.
2. What are the two types of endoplasmic reticulum and what are their functions? Rough endoplasmic reticulum is studded
with ribosomes. Ribosomes are made up of two subunits – a larger one and a smaller one. These subunits consist of
masses of protein and RNA and are responsible for protein assembly. Proteins that are part of membranes or are
intended for export from the cell are assembled by the ribosomes on the rough ER and are then pushed into the lumen
(the hollow space) of the endoplasmic reticulum tubules. Proteins that function in the cytosol are made by ribosomes
that are not attached to endoplasmic reticulum but are instead freely suspended in the cytosol itself.
The other type of endoplasmic reticulum is the smooth ER. Smooth ER does not have bound ribosomes. Smooth ER
synthesizes lipids and lipid-containing molecules such as phospholipids that make up membranes. Smooth ER also
performs other cell specific functions. For example, smooth ER in the liver helps to detoxify drugs and alcohol and in the
testes and ovaries, smooth ER produces testosterone and estrogen.
3. What unique fact about ribosomes allows antibiotics to help fight infection and not kill the host cells? Ribosomes of
eukaryotes and prokaryotes have different structures and mechanisms so some antibiotics can target protein synthesis
in prokaryotic ribsomes without affecting protein synthesis in human cells.
4. Label the diagram of a ribosome below.
Large subunit
Small subunit
The Endomembrane System
1. Define endomembrane system. The endomembrane system is the system within the cell that acts to synthesize, modify
and transport proteins and other cell products. This system includes the nuclear envelope, the endoplasmic reticulum,
the Golgi apparatus, vesicles and the cell membrane among others.
2. Define and give the function of the Golgi apparatus, vesicles and lysosomes. Your textbook does a terrific job of defining
these terms on pages 61-63. Be sure you understand and can label and talk about Figure 2.6, page 61 which summarizes
much of the written text.
3. What is the general type of enzyme found in lysosomes? What do they catalyze? In animal cells, one of the products of
the Golgi apparatus are lysosomes which are membrane bound sacs containing digestive enzymes. Specifically,
lysosomes contain more than 40 enzymes that catalyze hydrolysis reactions (so, hydrolases) responsible for breaking
down macromolecules into smaller molecules the cell can use. The primary function of lysosomes is to break down
parts of the cell that are old or no longer needed. They also break down bacteria and ingested foreign particles. These
enzymes function best at an acidic pH of about 5. Since the cystol of the cell has a pH of about 7.2, this means that if
lysosomes break apart their enzymes are unlikely to break down the living cell.
4. What are the general functions of the endomembrane system? Your textbook does a terrific job of defining these terms
on pages 61-63. Be sure you understand and can label and talk about Figure 2.6, page 61 which summarizes much of the
written text.
5. Label the diagram of the endomembrane system below.
Peroxisomes
1. What are peroxisomes? What is their function? (page 63)
2. What type of enzymes are found in peroxisomes? What is their function? (page 63)
3. Explain the various functions of peroxisomes in cells. (page 63)
Vesicles and Vacuoles
1. What are vesicles and vacuoles. Do all cells have them? Explain.
2. What is turgor pressure?
3. What happens to the vacuoles of the plant cells that do not have enough water?
Page 63 of text.
Chloroplasts and Mitochondria
1. Explain the function of the chloroplast and of the mitochondrion. Chloroplasts are membrane bound organelles found
within cells that can undergo photosynthesis. Photosynthesis uses the pigment chlorophyll found within chloroplasts to
absorb light energy as part of the process that converts carbon dioxide and water, through redox reactions, into energyrich organic molecules. Mitochondria are organelles in eukaryotic cells which use redox reactions to oxidize high energy
organic molecules resulting in a net release of energy for the cell.
2. What is chlorophyll? What is its function? Where is it found? Chlorophyll is a pigment that absorbs light energy used in
part of the photosynthetic process. Chlorophyll is found in the membranes of thylakoids, which are flattened disks
inside chloroplasts.
3. What unique feature do mitochondria and chloroplasts have that other organelles do not? Both contain some of their
own DNA which encodes for some but not all of their own proteins.
[An aside: There is compelling evidence that mitochondria and chloroplasts were once primitive bacterial cells. This
evidence is described in the endosymbiotic theory. How did this theory get its name? Symbiosis occurs when two
different species benefit from living and working together. When one organism actually lives inside the other it's called
endosymbiosis. The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become
dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution,
mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.
http://learn.genetics.utah.edu/content/cells/organelles/]
The Cell Wall and the Cytoskeleton
1. What is the function of the cell wall? Can cell walls differ in terms of their composition? Explain. (See page 65)
2. What is the cytoskeleton? Explain its functions. (See page 65)
3. What are the three types of protein fibres in the cytoskeleton? Compare and contrast their structure and function by
filling in the table provided below. (See Table 2.1, page 66.)
Cilia and Flagella
1. What are cilia and flagella? Describe their structure and function. (See page 66.)
2. Give examples of where cilia and flagella can be found. (See page 66.)
The Cell Membrane
1. What are the functions of the cell membrane? The contents of cells are physically separated from the aqueous
environment in which they are found by the very thin cell membrane. The cell membrane is a selectively permeable,
dynamic boundary between the cell and its environment. The cell membrane controls which substances can go in and
out of the cell. It can allow a particular substance to pass through at a certain time, and then reject the same substance
at a later time. Its other main functions include cell adhesion, ion channel conductance, cell signaling,
and attachment point for cytoskeleton (which is important in keeping the shape of the cell). Another interesting feature
of the cell membrane is the presence of surface molecules (e.g. glycoproteins, glycolipids, etc.) that act like a ‘signature’
for a cell. Every cell has a different ‘signature’ or ‘marker’ that is thought to function in cell recognition, or in a sort of
cellular identification system.
http://www.biology-online.org/dictionary/Cell_membrane
2. What happens to cells when the cell membrane does not function properly? They die because cell processes fail.
3. Describe the arrangement of phospholipids in the cell membrane. We have covered the arrangement of the hydrophilic
heads and the hydrophobic tails of the phospholipid bilayer several times. It is described again, in detail, on page 69.
4. Label the diagram of a typical cell membrane shown below. (See Figure 2.12 page 69.)
Features of the Fluid Mosaic Model
1. Describe all the features of the fluid mosaic model of the cell membrane.
This material is covered in detail on pages 69-70
2. Describe the fluidity of the cell membrane.
in the text. It is important material for the
3. What factors affect the fluidity of the cell membrane? Explain.
coming evaluation. If you have difficulty with it,
4. Give an overview of the functions of proteins in a phospholipid bilayer.
please ask.
So, What Do I Need to Review from this Handout Before the Evaluation?
1. Be able to label all of the diagrams in this assignment.
2. Be able to distinguish between eukaryotic and prokaryotic cells.
3. Be able to define the term “organelle” and to explain the functions of all of the organelles in this assignment.
4. Be sure to review the parts and functions of the endomembrane system and the fluid mosaic model of a cell membrane in
detail.