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Biology
Teach Yourself Series
Topic 2: Cells
A: Level 14, 474 Flinders Street Melbourne VIC 3000
T: 1300 134 518 W: tssm.com.au E: [email protected]
© TSSM 2013
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Contents
Cells ................................................................................................................................................................... 3
Prokaryotic and Eukaryotic Cells ................................................................................................................... 3
As it appears in Unit 1 ................................................................................................................................ 3
Review Questions .................................................................................................................................. 5
Cells ................................................................................................................................................................ 7
As it appears in Unit 3 ................................................................................................................................ 7
Review Questions .................................................................................................................................. 8
Organelles ....................................................................................................................................................... 9
As it appears in Unit 1 ................................................................................................................................ 9
Review Questions ................................................................................................................................ 10
Organelles ..................................................................................................................................................... 12
As it appears in Unit 3 .............................................................................................................................. 12
Review Questions ................................................................................................................................ 12
Solutions to Review Questions ........................................................................................................ 13
© TSSM 2013
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Cells
Every living thing is composed of cells. A cell has an outer plasma membrane, which separates its contents
from the external environment. Cytosol, the fluid component of cells, consists predominantly of water but
also contains other dissolved substances. DNA contains the genetic material that controls the metabolism of
the cell.
Prokaryotic and Eukaryotic Cells
As it appears in Unit 1
Cells are classified into two key groups, prokaryotes and eukaryotes. Prokaryotes lack membrane-bound
organelles and contain a single, circular chromosome which floats free within the cytosol. Whilst they lack
membrane-bound organelles prokaryotes do possess ribosomes that are involved in the synthesis of proteins.
Eukaryotic cells do contain membrane-bound organelles, including a nucleus which holds numerous linear
chromosomes.
Prokaryotic organisms belong to the kingdoms Archaea and Bacteria. All are single celled organisms. The
plasma membrane of these organisms is surrounded by a cell wall which is primarily composed of the
complex carbohydrate murein. This differs from the cell wall of plant cells which is composed of the
carbohydrate cellulose and that of fungi, which is composed of the carbohydrate chitin. Prokaryotic cells
often possess flagella (as shown in the diagram below) or cilia to assist them in moving through their aquatic
environment.
Flagella
Cell Wall
DNA
Ribosome
Plasma Membrane
Eukaryotic cells can belong to any of the four remaining kingdoms: Fungi, Plantae, Animalia or Protista.
Whilst some Fungi are unicellular, most are multicellular and all are heterotrophic, meaning that they must
obtain organic material by digesting other organisms. Unlike the prokaryotic organisms, fungal cells never
have flagella or cilia and thus fungi are not able to move.
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Members of kingdom Plantae are multicellular and, like fungi, are unable to move. Plants, however, differ
from fungi as they are autotrophic. This means that they are able to produce organic compounds from
inorganic materials using light energy. Plant cells possess a large central vacuole, which is used to store
water and helps to provide the cell with rigidity.
Animals are multicellular organisms, which are heterotrophs and need to consume and digest organic
material. Animal cells possess membrane-bound organelles but they lack a cell wall.
Kingdom Protista is the most varied of the five kingdoms. Protists can be both unicellular such as Amoeba
or Paramecium and multicellular such as Sea Weed. They can be plant-like, animal-like or fungus-like but
they lack the dedicated characteristics of fungal, plant and animal cells.
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Review Questions
1. Use the diagram below to answer the following questions.
a. To which kingdom would this cell belong? Why?
b. Name one organelle that is visible in the above cell.
c. Would this cell be able to manufacture enzymes? Explain.
2. Outline the difference between a heterotroph and an autotroph
3. A prokaryotic cell
A. Has a circular chromosome
B. Contains chloroplasts
C. Lacks ribosomes
D. Possesses a cell wall composed of chitin
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Questions 4 and 5 refer to the following information.
W
X
Y
4. The cell above is likely to be from a:
A. plant
B. bacteria
C. fungus
D. animal
5. Which structure is labeled with an X?
A. nucleus
B. vacuole
C. ribosome
D. chloroplast
© TSSM 2013
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Cells
As it appears in Unit 3
Unit 3 Biology examines the functions of the cell. This includes cell death through either necrosis or
programmed cell death (apoptosis). Within healthy tissues, there is a balance between cell replication and
cell death. If this balance is disturbed and there is an unrestrained increase in cells a tumour results. A
tumour that continues to grow and impacts on healthy tissue is considered malignant or cancerous. The main
cause of tumours is a lack of apoptosis.
In apoptosis cells respond to signals. There are two main signal pathways that instigate apoptosis: the death
receptor pathway and the mitochondrial pathway. The death receptor pathway is activated when cells are no
longer required even though they are still able to function normally. For example, in the embryo fingers and
toes develop within groups of cells. The cells between the fingers and toes are not necessary and as a result
receive an external message to undergo apoptosis. Specific receptors are found on the surface of cells receive
the message to initiate apoptosis. When this message is received a chain reaction occurs:
Caspases (enzymes that slice proteins) are activated and phagocytes are stimulated.
The cells involved begin to shrink and caspases enter through the nuclear pores where they slice the
DNA.
Phagocytes consume the remaining organelles and release cytokines to inhibit the inflammation of
nearby cells. The release of cytokines does not occur in necrosis.
The mitochondrial pathway involves signals from inside a cell. These signals are initiated when major
damage occurs to a cell, for example, the breakdown of internal membranes. This triggers a chain reaction
within the cell, including the activation of caspases, which pass through the nuclear pores and dismantle the
DNA. The remainder of the mitochondrial pathway is similar to the death receptor pathway outlined above.
The mitochondrial pathway can also be activated by the cell itself when it becomes infected by a virus. This
action prevents the virus from spreading to other cells and causing further harm to the host.
Necrosis takes place when a cell becomes seriously damaged so that it is no longer able to control the
movement of substances through the plasma membrane. This causes the cell to swell and burst, spreading its
contents throughout nearby cells, causing the inflammation of surrounding tissue.
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Review Questions
6. When a cell’s DNA becomes damaged why does the cell undergo apoptosis rather than waiting for
necrosis to set in?
7. What role does apoptosis play in the formation of a tumour?
8. Outline the role played by phagocytes in apoptosis.
9. Apoptosis
A. Results in the production of new cells
B. Can results in the death of healthy cells
C. Is only triggered by external signals
D. Recycles each part of the dead cell.
© TSSM 2013
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Organelles
As it appears in Unit 1
Cells contain numerous organelles which are able to carry out a range of specific activities. A number of
organelles are found in most cells, however, a small range of organelles are unique to some kingdoms or cell
types. The following table details the function of a range of organelles.
Cytoplasm
The entire contents of a cell aside from the nucleus. It is composed of more than 90%
water and also includes salts, enzymes and organelles (other than the nucleus).
Cytosol:
The liquid transport medium of a cell.
Chloroplast:
A green organelle found in some plant cells that is the site of photosynthesis. It is made
up of numerous folded layers of membrane.
Endoplasmic
An interconnected network of membranes that connects the plasma membrane and
reticulum:
other organelles. It can be rough (with associated ribosomes) or smooth (lacking
ribosomes). It is involved with the production, transport and storage of materials
throughout the cell.
Golgi apparatus:
The site of the final synthesis and packaging of proteins into membrane-bound vesicles
in preparation for being secreted from the cell.
Mitochondria:
Organelle made up of folded membranes that are the site of cellular respiration.
Nucleus:
Surrounded by a double-layered nuclear membrane (nuclear envelope), which contains
pores that permit communication with the cytoplasm. The nucleus contains linear
chromosomes composed of DNA and proteins. It controls cellular activities.
Plasma
Composed of a phospholipid bilayer, which encloses the cytoplasm in all cells. It
membrane:
controls the movement of substances into and out of the cell. It is also responsible for
cell recognition and chemical communication between cells.
Ribosomes:
Small organelles that are not membrane-bound. They are either located in the cytosol or
associated with endoplasmic reticulum. They are sites of protein production.
Vacuole:
Plant cells generally contain large central vacuoles containing cell sap that provides
turgidity to the cell and acts as a depository for water and waste. Vacuoles are used by
other kingdoms for digestion (food vacuoles) or water balance (contractile vacuoles).
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Review Questions
A
B
10.
a. To which kingdom does the cell above, most likely belong? How can you tell?
Name and describe the function of organelles A and B.
b.
Organelle A
Function
c.
Organelle B
Function
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11. The following questions relate to the cell shown below.
A
B
a. Organelle A is a green coloured organelle, what is the function of this organelle?
b. Organelle B contains cellulose, what is the function of this organelle?
12. Which one of the following supplies a cell with energy?
A. A chloroplast
B. A mitochondria
C. A nucleus
D. A vacuole
13. Which of the following organelles would be the most difficult to view under a microscope?
A. Nucleus
B. Chloroplast
C. Mitochondria
D. Ribosome
© TSSM 2013
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Organelles
As it appears in Unit 3
Unit 3 explores a wider range of organelles, which are summarised in the table below and looks at the use of
organelles to determine the function and kingdom of the cell in question.
Plastids:
A group of organelles found only in plant cells. They include chloroplasts,
amyloplasts and tonoplasts.
Tonoplast:
The membrane of a plant cell vacuole that regulates the movement of substances into
and out of the vacuole.
Amyloplast:
Starch granules that allow the plant to determine up and down.
Centrioles:
Composed of microtubules. Involved in the separation of chromosomes during cell
division in protists and animal cells.
Lysosomes:
Membrane-bound vesicles that contain enzymes involved in the breakdown of foreign
material and are present in most animal cells.
Review Questions
14. Aside from a cell wall and a chloroplast, how could you differentiate between a plant and an animal
cell?
15. A plant cell can be distinguished from an animal cell by the presence of a
A. Nucleus
B. Chloroplast
C. Mitochondria
D. Cell wall
16. The role played by lysosomes within a cell is
A. Digestion of foreign material by enzymes
B. Site of cellular respiration
C. Site of water storage
D. Repair of cell structures such as the cell membrane
© TSSM 2013
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