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Virtual 2020 Essay 2

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Edgewood College
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Name: _________________________ UNIT 2 ESSAY
1. Paramecia are single-celled aquatic eukaryotes that can survive in a wide range of salinities. Paramecia use
contractile vacuoles to help maintain homeostasis under these varying salt conditions. The contractile
vacuoles fill with fluid and then contract to remove the fluid from the paramecia. Scientists wanted to
determine the effect of salinity on contractile vacuole activity. They maintained different groups of paramecia
in water of different salinities for one month. They then measured the average amount of fluid ejected from
the contractile vacuoles in each group of paramecia each time the vacuoles contracted. (Table 1)
Table 1. Contractile Fluid Output by Paramecia Adapted to Different Salinities
Salinity of Maintenance Water (milliosmoles of
solute/kg)
Average Fluid Output of Contractile Vacuole
(picoliters/minute)
10 (freshwater)
1.3
250
0.25
750
0.1
1000
0.05
a. Use the template provided to construct an appropriately labeled graph that represents the data in Table. 1. (5
pts)
b. Describe how increasing salinity affects the amount of fluid ejected each time a contractile vacuole contracts.
(1 pt)
Increasing salinity decreases the amount of fluid ejected.
Average Fluid
Output of
Contractile Vacuole
(picoliters/minute)
Salinity of Maintenance Water (milliosmoles of solute/kg)
1
2
1000
X-axis: each
increment is 50

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c. Describe how the phospholipids of a plasma membrane regulate the movement of large or polar molecules
across the membrane. (1 pt)
The phospholipids does not allow large or polar molecules to enter the plasma membrane. Polar and large
molecules can affect the cell through chemical signals that bind to receptors on the plasma membrane.
d. Explain how osmosis will affect animal cells when the cells are placed into an environment with a low water
potential (high solute potential) compared to the intracellular water potential. (1 pt)
When cells are placed in low water potential, osmosis will occur from cell to the surrounding and intracellular water
potential will decrease.
2. Estuaries are places where a river empties into the ocean. In these special environments there is a mixture of
freshwater and saltwater that depends upon tides and flow rate of the freshwater tributary. There are many
types of plant species that live in estuaries. One such plant species is called Smooth Cordgrass (Spartina
alterniflora). The pressure potential inside S. alterniflora’s cells is 3 bars. The solute potential inside the cells
is -7 bars.
a. What is the water potential of S. alterniflora? __________-4____________(1pt) Show work for
problem: (1pt) (Put your final answer in the space above with units)
Equation: Ψ = ΨS + ΨP
Water potential=pressure potential+solute potential
Water potential=-7+3= -4 water potential
The water surrounding S. alterniflora is 20 degrees Celsius and has a concentration of 0.2M NaCl (NaCl has an
ionization constant of 2).
What is the water potential of the estuary? _______-9.74_________ (1pt) Show work for problem:
(1pt) (Put your final answer in space above with units.)
s = -iCRT
Water potential= -2*0.2M*(20+273)*0.0831=-9.74
b. Which of the following statements is true about the situation above? Circle all that apply. (1 pt)
i. The grass is in a hypotonic environment
ii. The grass is in a hypertonic environment
iii. The grass and the water are in equilibrium
iv. Water would tend to flow into the grass from the environment
v. Water would there would be no net water movement
vi. Water would tend to flow out of the grass into the environment
3. A study was carried out to investigate the effect of passive protein channels on the movement of glucose into

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Name: _________________________ UNIT 2 ESSAY 1. Paramecia are single-celled aquatic eukaryotes that can survive in a wide range of salinities. Paramecia use contractile vacuoles to help maintain homeostasis under these varying salt conditions. The contractile vacuoles fill with fluid and then contract to remove the fluid from the paramecia. Scientists wanted to determine the effect of salinity on contractile vacuole activity. They maintained different groups of paramecia in water of different salinities for one month. They then measured the average amount of fluid ejected from the contractile vacuoles in each group of paramecia each time the vacuoles contracted. (Table 1) Table 1. Contractile Fluid Output by Paramecia Adapted to Different Salinities Salinity of Maintenance Water (milliosmoles of solute/kg) Average Fluid Output of Contractile Vacuole (picoliters/minute) 10 (freshwater) 1.3 250 0.25 750 0.1 1000 0.05 a. Use the template provided to construct an appropriately labeled graph that represents the data in Table. 1. (5 pts) 2 Average Fluid Output of Contractile Vacuole (picoliters/minute) 1 X-axis: each increment is 50 0 1000 Salinity of Maintenance Water ...
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