Topic 2: Cells
Key facts
1. The cell theory states that living organisms are composed of cells, that cells are the
smallest unit of life, and that cells come from pre-existing cells.
2. Even unicellular organisms carry out the functions of life which include: metabolism,
response, homeostasis, growth, reproduction and nutrition.
3. A size hierarchy exists involving cells going from largest to smallest: cells (100
microns) – organelles (10 microns) – bacteria (1 micron) – viruses (100 nanometers) –
membrane thickness (10 nanometers) – molecules (1 nanometer).
4. Scale bars or stated magnifications allow one to determine the actual size of
specimens.
5. It is essential that there be a high surface area to volume ratio if a cell is going to
successfully exist. As a cell increases in size, the volume increases much faster than the
surface area thus decreasing the surface area to volume ratio. This decrease the chances
for the successful existence of the cell.
6. It is essential to note that cells show emergent properties. This means that the
interaction of the parts of the cell results in the fact that the whole is greater than the sum
of its parts.
7. In multicellular organisms, cells differentiate to carry out specialized functions. This
specialization occurs as a result of differential expression of genes in multicellular
organism’s genes.
8. Stem cells have yet to go through the differentiation process. Thus, they maintain the
ability to differentiate along different pathways. There appear to be stem cells in most
major types of tissues.
9. Stem cells have many therapeutic uses including the replacement of damaged bone
marrow cells in leukemia patients. In the future it may be possible to treat conditions
such as Alzheimer’s disease and Parkinson’s disease with stem cells. There is even hope
that some forms of diabetes may be treated with these undifferentiated cells. Plants show
large numbers of stem cells in meristematic (growth) areas.
10. Prokaryotic cells divide by binary fission.
11. Prokaryotic cells include ribosomes, a cell wall, a cell membrane, a nucleoid region,
and, in most cases, plasmids.
12. Some prokaryotic cells include an exterior layer of a complex sugar compound called
a capsule.
13. Ribosomes carry out protein production, and they do not include an exterior
membrane.
14. Bacteria are examples of prokaryotic cells and are between one and ten micrometers
in size.
15. Flagella occur in some bacteria and they allow organism mobility.
16. The nucleoid region is composed of a circular thread of pure DNA.
17. The cell wall is made of a material called peptidoglycan.
18. Eukaryotic cells are up to 100 micrometers in size.
19. Membrane bound organelles are characteristic of eukaryotic cells.
20. Common organelles include: endoplasmic reticulum, ribosomes, lysosomes, Golgi
apparatus, mitochondria, nucleus, chloroplasts, centrosomes, and vacuoles.
21. Animals cells contain centrioles but plant cells do not. Plant cells contain
chloroplasts, animal cells do not. Plant cells have cell walls, animal cells do not. Plant
cells have larger vacuoles than animal cells.
22. The extracellular matrix of the animal cell is produced by the secretion of
glycoproteins. This matrix functions in support, adhesion and movement.
23. The exterior of the plant cell involves the cell wall and it maintains cell shape,
prevents excessive water uptake, and holds the whole plant up against the force of
gravity.
24. Cell membranes include phospholipids and proteins. These proteins may be
classified as integral or peripheral proteins.
25. It is the hydrophobic and hydrophilic properties of phospholipids that maintain the
structure of cell membranes.
26. Functions of membrane proteins include hormone binding sites, enzyme activity, cell
adhesion, cell-to-cell communication, channels for passive transport, and pumps for
active transport.
27. Diffusion is the passive movement of particles along a concentration gradient.
28. Osmosis is the passive movement of water across a partially permeable membrane
along a concentration gradient.
29. Cells expend energy (ATP) during active transport. Passive transport does not
involve the expenditure of ATP by the cell.
30. Endocytosis and exocytosis are examples of active transport. It is essential that the
membrane has a degree of fluidity so that shape changes may occur to allow endocytosis
and exocytosis to occur.
31. Integrated proteins are embedded in the phospholipid bilayer of the plasma
membrane, whereas peripheral proteins are attached to the surface.
32. Vesicles are used to transport materials within the cell between the rough
endoplasmic reticulum, the Golgi apparatus, and the plasma membrane.
33. The cell cycle includes 4 phases: G1, S, G2, and M.
34. Interphase of the cell cycle includes G1, S, and G2.
35. Tumours (cancers) are the result of uncontrolled cell division and they may occur in
any organ or tissue.
36. Interphase is the phase in which the cell is carrying out its appointed activity or
activities. Metabolic activities such as protein synthesis, DNA replication and organelle
reproduction occur in this phase.
37. The phases of mitosis can be remembered in their proper order by the word shipmate.
If you remove “she” from shipmate you have interphase, prophase, metaphase, and
telophase.
38. It is essential to know the important events of these phases of mitosis.
39. During prophase and metaphase the chromosome is actually two molecules of DNA
attached together at the centromere. Each molecule of DNA is called a chromatid.
40. When the chromatids of the chromosomes split during anaphase, two separate
chromosomes appear and the term chromatid is not used anymore.
41. The kinetochore of the centromere allows attachment to the spindle microtubules.
42. The microtubules are made of a protein called tubulin.
43. Mitosis produces two genetically identical nuclei. However, the cytoplasm splitting
which occurs during cytokinesis does not result in identical halves. One half may have
more organelles of a particular type than the other.
44. Growth, embryonic development, tissue repair and asexual reproduction involve
mitosis.
45. The term plasma membrane, not cell surface membrane, should be used for the
membrane surrounding the cytoplasm.
Additional key facts:
Draw assessment statements from this topic
1. Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli), as an
example of a prokaryote. The drawing should include the cell wall, plasma membrane,
cytoplasm, pili, flagella, ribosomes, and nucleoid region (region containing naked DNA).
2. Draw and label a diagram of the ultrastructure of a liver cell as an example of an
animal cell. The diagram should show free ribosomes, rough endoplasmic reticulum
(rER), lysosome, Golgi apparatus, mitochondrion, and nucleus.
3. Draw and label a diagram to show the structure of membranes. The diagram should
show the phospholipid bilayer, cholesterol glycoproteins, and integral and peripheral
proteins.
Complete the following.
1. What happens to the relative rate of excretion of metabolic wastes from cells as the
surface area to volume ratio of the cell decreases? Explain why.
2. Complete the following statements:
a. One millimeter is a ___________ times smaller than a meter.
b. One micrometer (micron) is a __________ times smaller than a millimeter.
c. One nanometer is a ___________ times smaller than a micron.
3. What is a scale bar?
4. Order the following from largest to smallest: molecules, bacteria, membranes,
organelles, eukaryotic cell.
5. Discuss the evidence for the cell theory.
6. Explain how each of the following functions of life could be seen in the life of a cell:
a. metabolism
b. response
c. homeostasis
d. growth
e. reproduction
f. nutrition
7. What happens in cell differentiation?
8. What controls differentiation within a cell?
9. What is a stem cell?
10. Where in a plant would one most likely find stem cells?
11. Why would stem cells never entirely disappear from an organism’s tissue?
12. What is controversial about the use of stem cells?
13. What is the potential therapeutic value of stem cells in medicine? Use an example in
your explanation.
14. What would prevent stem cells from other species being successful in humans?
15. Name the function of the following prokaryotic cell parts:
a. cell wall
b. plasma membrane
c. cytoplasm
d. pili
e. flagella
f. ribosomes
g. nucleoid
16. By what mechanism do prokaryotic cells divide?
17. Study some electron micrographs of bacterial cells.
18. How do ribosomes differ in prokaryotic and eukaryotic cells?
19. Describe the DNA of a prokaryotic cell.
20. Compare the location of genetic material in prokaryotic and eukaryotic cells.
21. What are thought to have been the first cell types on this planet?
22. What polysaccharide is stored in plant cells?_______________ in animal
cells?______________
23. Explain why animal cells may change shapes while plant cells are less likely to do
so.
24. Describe the vacuole which occurs within plant cells.
25. Name three ways that animal and plant cells are similar.
26. Name three ways that animal and plant cells are different.
27. Explain why plants have mitochondria, even though they include chloroplasts.
28. How does the plant cell wall allow plants to maintain an upright position, not wilted?
29. Why would muscle cells have large numbers of mitochondria?
30. Name two organelles that are similar to prokaryotic cells.
31. What is the major component of plant cell walls?
32. Which major type of cell demonstrates compartmentalization?_________________
Why is this important?
33. What are the proteins that DNA is combined with in eukaryotic chromosomes?
34. Distinguish between the nucleolus and the nucleus.
35. In which organelle would one find grana, stroma, and thylakoids?
36. In which organelle would one find cristae and matrix?
37. Why would the Golgi apparatus have vesicles associated with it?
38. Name two functions of lysosomes.
39. Compare the structure and function of rough and smooth endoplasmic reticulum.
40. Why would liver cells have a large amount of sER?
41. Describe the major characteristics of the nuclear membrane.
42. What are the major components of a phospholipid which occurs in cellular
membranes?
43. Animal cell membranes contain cholesterol to maintain proper membrane fluidity.
Since plant cell membranes do not contain cholesterol, how do they maintain membrane
fluidity?
44. Differentiate between a peripheral and an integral protein when examining a cell
membrane.
45. Which end of a phospholipid is hydrophobic?_____________________Which is
hydrophilic?____________________
46. What general type of membrane proteins would make up channel proteins?
47. Name 6 general function of cell membrane proteins.
48. Explain what membrane glycoproteins are.
49. Compare and contrast passive and active transport.
50. State two examples of passive transport.
51. How does facilitated diffusion compare to diffusion?