UNIT 2 CELLS UNIT HOMEWORK GRADING RUBRIC
Chapter 6 , A Tour of the Cell
1. Identify several cell structures are common to both prokaryotic and eukaryotic cells.
- Cell membrane, ribosomes, DNA (genetic information), cytoplasm
2. Prepare a chart that gives the major parts of eukaryotic cells (excluding the cytoskeleton).
For each item in your chart give the following four items of information:
a) name of part, b) structure, c) function(s), d) found in (plants, animals or both).
7 pts total - 1 pt correct part matched with correct structure/function/occurrence
Chart could include the following: nucleus, ribosomes, rough ER, smooth ER, Golgi,
mitochondria, chloroplasts, lysosome or other structures. REFER TO TEXT!
3. Explain why mitochondria and chloroplasts not considered part of the endomembrane
System.
- They are not derived from the folding of cellular membranes (or similar answer)
4. Contrast and Compare the cell walls of plants and bacteria.
– similar – both are external to the cell and offer support/protection
– different – they are made of different polysaccharides (or similar answer)
5. Discuss why you would rather be hit by an object made of plant cells with primary cell walls
than an object made of plant cells with secondary walls.
– primary cells
– primary cells have a soft cell wall; second cells have hard and thick cell walls
such as found in wood. This would cause severe discomfort.
6. Several years ago, a meteorite was found from Mars. Upon SEM examination, objects that
looked like prokaryotic cells were found in the interior. This discovery caused a major
splash in the scientific community. Discuss why this was so.
– cells are the basic unit of life. If the objects were cells, this was evidence of
past life on Mars (or extra-terrestrial life).
7. The structure of cilia and flagella are the same in all eukaryotic cells? Discuss why this
might be so.
– the structure must have originated very early in evolutionary history and has been
inherited by all of the diverse types of eukaryotes.
Chapter 7, The Cell Membrane and Transport Across the Membrane
1. The most accepted model of membrane structure today is the fluid mosaic model.
Explain the meaning behind the terms “fluid” and “mosaic” in this model. 2 pts total
– fluid refers to the phospholipid bilayer. The molecules are not attached side to
side and are free to slide next to each other.
– mosaic refers to the proteins in the phospholipid bilayer. The move continually
and form changing patterns.
2. Are both sides of a cell membrane the same? Explain and give evidence to support your
Answer. 1 pt total
– no they are not the same
– the two sides differ in phospholipid composition or the outer membrane has
oligosaccharides attached while the inner membrane does not
3. Explain why integral proteins stay in place in the phospholipid bilayer.
- the proteins have polar amino acids to match the head areas and non-polar
amino acids in the fatty acid area
4. Identify what types of molecules have difficulty crossing the plasma membrane and explain
why. ½ pt – name, ½ pt – explanation, any two examples - 2 pts total
Hydrophilic molecules – can’t cross the hydrophobic fatty acids
Large molecules – too big AND Ions – charges prevent crossing hydrophobic fatty acids
5. Define aquaporins and discuss why are they important. 1 pt total
– channels that allow water to cross membranes by facilitated diffusion
– osmosis is too slow without these channels
6. Contrast and compare passive and active transport. What kind of molecules are moved by
each? Which direction do the materials move? 1 ½ pts total
– passive transport does not require cell energy, active transport does
– passive transport works with non-polar and small molecules, water. Active
transport works with polar molecules, ions and larger molecules
- passive is H->L, active is L-> H
7. Predict what will happen if some of your cheek cells were placed in the following solutions?
a) hypertonic b) isotonic c) hypotonic
a) hypertonic – cells shrink or crenate
b) isotonic – cells stay the same
c) hypotonic - cells swell and lyse
8. Predict what will happen to a cell with a rigid cell wall (e.g. bacteria or plant) if they a
are placed in the following solutions?
a) hypertonic – cells shrink or plasmolysis occurs
b) isotonic – cells are slightly flaccid
c) hypotonic – cells are turgid or swollen
9. A writer for a TV soap opera consults with you about their idea for killing off one of
the characters. Their idea is to have the villain replace the IV drip being give to the
character while they are unconscious in the hospital with a bag of distilled water.
Could murder most foul be accomplished this way? Explain.
– the distilled water is hypotonic to the cells and will cause them to swell and possible
lyse. The destruction of the blood cells might lead to death.
10. The Na+/K+ pump, the major electrogenic pump in animal cells, exchanges
sodium ions for potassium ions, both of which are cations. Describe how this exchange
generates a membrane potential or difference in electrical charge since both ions have
the same charge.
– the cations are not in equal concentration giving one side a more positive charge as
compared to the other.
11. One of the first signs of cell death is that ions such as Na+ and K+ start moving
down their concentration gradients. Explain why this occurs.
– movement down the concentration gradient indicates that active transport is no longer
working. The cell may no longer be able to generate energy for active transport.
Chapter 12, The Cell Cycle
1. Describe how are the three subphases of interphase are alike and how they are different.
- They are alike in that many of the cell’s metabolic processes occur in all three.
- They are different by if the DNA has not replicated (G1), is replicating (S) or has already
replicated (G2). The checkpoints are also different in each of phase.
2. Is binary fission the same as mitosis? Explain.
- Binary fission is the division of a prokaryotic cell which lacks a nucleus.
- Mitosis is the division of the nucleus of a eukaryotic cell. They are not the same thing.
3. During prometaphase, the nuclear envelope disappears. Where does it go?
- The components of the nuclear envelope are in the cytoplasm.
4. Imagine a cell that mutates and loses the function of its kinetochore proteins. Explain what
this might do to the cell the next time it divides.
- The kinetochores could not pull the replicated chromatids apart after the centromere
breaks. The chromosomes would stay together and the chromosome number would likely
double with each replication.
5. Is mitosis the same thing as Cytokinesis? Explain.
- No.
- Mitosis is the division of the nucleus while cytokinesis is the division of the cytoplasm.
6. Imagine another cell mutation that allows the cell to ignore anchorage dependency. Discuss
what might be the results of this mutation.
- The cells might divide and travel off. This is what happens when cancer undergoes
metastasis and spreads through the body.
7. Identify where in the cell cycle the three main checkpoints are located. What determines if the
cell moves past each checkpoint?
½ pt name, ½ pt event, 3 pts total
G1 checkpoint – cell must receive a go-ahead signal or exit into Go
G2 checkpoint – requires MPF activity to go-ahead to mitosis
M checkpoint – controls the onset of anaphase.
8. Chemicals, such as colchicine from the Autumn Crocus plant, are known to disrupt
spindle fibers. Speculate on what affect this will have on a cell undergoing mitosis.
Identify what ploidy level (N=?) of the cell resulting from this treatment.
- The spindle fibers will not form during mitosis and the chromatids cannot be pulled
apart.
- This tends to double the chromosome number (tetraploid).
9. Imagine that the enzyme that breaks down cyclin is on strike and refuses to work. Explain
what might be result from this situation.
- Cyclin would remain and active MPF would be constantly present. This would signal
the cell to continually divide.
10. Small cuts that open blood vessels and bleed often heal faster than cuts that don’t
bleed (e.g. paper cuts). Using your knowledge of factors that affect cell division,
speculate on a possible mechanism for why this occurs.
- Bleeding brings platelets to the area to form blood clots. The presence of platelets places
the cell division stimulate PDGF in the cut. PDGF would stimulate cell division and
close the wound faster.