General Biology 193 Lab - Mosses and Ferns Worksheet Answers PDF

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Mosses and Ferns Worksheet Responses: Moss Gametophytes: 1. Examine the moss images shown. Why don’t moss plants grow taller than they do? ● Moss plants don’t grow taller than they do because true mosses lack a xylem and phloem which serve respectively to transport water, nutrients, and the products of photosynthesis. Due to this lack of a xylem and phloem, mosses cannot grow taller than they are because their biological systems would not be able to sustain the vertical plant growth and thus, must remain closer to the ground to distribute nutrients efficiently to all plant parts w/o high energy tradeoff. Additionally, because moss sporophytes remain nutritionally and structurally dependent upon the larger and more conspicuous gametophyte, the sporophyte cannot grow much taller away from its respective gametophyte. 2. Indicate which cells (1 or 2) on the Sphagnum “ leaf” shown store water, and which conduct photosynthesis. Explain how you were able to make this distinction. ● On the Sphagnum “ leaf”, we can discern that cell 1 is primarily used to store water while cell 2 serves primarily as the site to conduct photosynthesis. This distinction can be made as cell 2 green coloration is an indication of the presence of chlorophyll, a green pigment responsible for light energy absorption necessary in photosynthesis. Cell 1 is reminiscent of a vacuole; a space, cavity, or vesicle enclosed by a membrane that stores fluids like water. 3. Examine the moss gametangia shown. Indicate which label (1 or 2) denotes where eggs are formed, and which denotes where sperm are formed. ● Examining the moss gametangia shown, label 1, which pictures the Mnium archegonia, denotes where eggs are formed while label 2, which pictures the Mnium a ntheridia, denotes where sperm are formed. Moss Sporophytes: 4. Note which image (1 or 2) displays an entire sporangium and which displays the peristome. What is the role of the peristome? In what environmental conditions will it open to release spores? ● Image 1 displays an entire sporangium while Image 2 displays the peristome. The peristome is a “teeth-like” structure around the lip of a moss capsule or sporangium that serves to help disperse spores in a process known as gradual spore discharge. In environmental drier or dehydrated conditions, the peristome will open to release spores and help “rake” them out of the capsule. Fern Sporophytes: 5. Are fern fronds haploid or diploid? In what structure(s) does meiosis occur in ferns?

● Fern fronds are actually diploid structures of the fern plant, found on the sporophyte of the plant which happens to live independently of the haploid gametophyte. In ferns, meiosis occurs in the sori, which are clusters of sporangia on the lower surface of fern leaves. It is in sporangia that the production and protection of spores occurs through meiosis. 6. Note which label (1 or 2) indicates the annulus and which indicates a spore on the image of the sporangium shown. ● On the image of the sporangium shown, label 1 indicates the annulus while label 2 indicates a spore. In botany, an annulus is an arc or ring of specialized cells on the sporangium. Fern Gametophytes: 7. Note which label (1 or 2) indicates where archegonia and antheridia can be found on the hermaphrodite gametophyte. ● On the hermaphrodite gametophyte, label 1 indicates where the archegonia can be found whereas label 2 indicates where the antheridia can be located. 8. What gametophyte structure produces sperm? What structure produces the egg? ● The antheridia are the gametophyte structure that produce sperm while the archegonia are the gametophyte structure that produces the egg. 9. How do fern sperm sense the location of the egg? ● For fern sperm to sense the location of the egg, water first must be present for the sperm to use their flagella to swim to an egg and fertilize  it. Additionally, in the presence of water, female eggs release chemoattractants to help guide sperm to the egg in a process known as sperm chemotaxis. The fertilized egg remains in the archegonia. 10. What is required for the transport of sperm in mosses and ferns ● In correlation with answer 9, a thin film of water is required as a medium for the transport of sperm in mosses, ferns, and other nonvascular and seedless vascular plants. Sperm use their flagella in the water medium to swim to an egg and fertilize it. 11. From what structure does a fern sporophyte develop? ● Fern sporophytes develop from the process of mitosis of the zygote (made in fertilization of the sperm and egg, 2N) which grows to form the embryo which in turn, matures mitotically into fern sporophytes.

Sex Ratio Experiment: 12. Name three environmental factors that could influence sex determination. ● Nutrient Availability ● Light

● Temperature ● etc. 13. What is the Independent Variable in this experiment? What is the dependent variable? ● Independent Variable: Gametophyte density ● Dependent Variable: Fern sex ratio amongst a gametophyte population 14. What is the null hypothesis in this experiment? What is the alternative hypothesis? ● Null Hypothesis: There is no statistically significant relationship between gametophyte density and a resulting fern sex ratio amongst a gametophyte population. ● Alternative Hypothesis: There is a statistically significant relationship between gametophyte density and a resulting fern sex ratio amongst a gametophyte population. 15. Write a prediction of how density of gametophytes might affect sex ratios in this fern ● Prediction: Increasing the density of gametophytes within a C. richardii gametophyte population results in a greater sex ratio of male to hemaphroditic gametophytes.

F. Total # and % male gametophytes at each density: ● Total #: 14 ● % Male Gametophytes: 42.8% 16. Graph the data below, and label the x-axis and y-axis appropriately

Figure 1.1: Line Plot of the Percentage of Male Gametophytes present at Varying Densities. Table 2: Worksheet for Calculation of the Slope and Y-Intercept of the Regression Line 1

2

3

4

5

6

7

x

y

x-x

y-y

(x-x)(y-y)

(x-x)2

y’

A

540

57

383.5

6.7

2569.45

147072.25

58.99706215

B

180

54

23.5

3.7

86.95

552.25

50.83293607

C

116

55

-40.5

4.7

-190.35

1640.25

49.38153588

D

56

48

-100.5

-2.3

231.15

10100.25

48.0208482

E

33

45

-123.5

-5.3

654.55

15252.25

47.49925125

F

14

42.8

-142.5

-7.5

1068.75

20306.25

47.06836682

Σ

939

301.8

4420.5

194923.5

301.8

156.5

50.3

50.3

5.84

4.47769286

AVG SD

Statistical Analysis:

17. What is the slope of the regression line? m= 0.022678128 18. What is the y-intercept of the regression line? b= 46.75087303 19. Write the equation for the regression line below, and use a ruler to sketch it on the graph. y = 0.022678128x + 46.75087303 20. Do you reject or fail to reject the null hypothesis? Why or why not? ● We reject the null hypothesis. Our data and calculations show us that the obtained r2 value of 0.587872 indicates that about 58.79% of the observed variation in sex expression can be explained by density alone. Therefore, there appears to be a statistically significant relationship between gametophyte density and a resulting fern sex ratio amongst a gametophyte population. Interpretation of Data: 21. Describe the relationships between gametophyte population density and sex expression that is suggested by your data. ● According to data obtained in lab experimentation and the resulting calculations, there appears to be a statistically significant relationship between gametophyte density and a resulting fern sex ratio amongst a gametophyte population. As can be seen in Figure 1.1 , our linear regression determines a positive relationship exists between the percentage of male gametophytes present in a population as the total number of gametophytes in the overall population(density) rises. 22. How much of the observed variation in sex expression can be explained by density alone? ● 58.79% of the observed variation in sex expression can be explained by density alone. 23. Why don’t all fern gametophytes develop as hermaphrodites? From an evolutionary perspective, why is it beneficial to produce some male gametophytes? ● From an evolutionary perspective, is it beneficial to produce some male gametophytes in order to avoid unnecessary competition between hermaphrodites and high energy tradeoffs. From our data set, calculations, and graph(Figure 1.1 ) , a positive relationship exists between the percentage of male gametophytes present in a population as the total number of gametophytes in the overall population(density) rises. If all fern gametophytes were to develop as hermaphrodites, as density rises, the intraspecific competition between these larger form of gametophyte would significantly increase as hermaphroditic gametophytes(which are a lot larger in size than males) vie for resources, spaces, light, and nutrients. Intraspecific competition leads to a reduction in fitness for both individuals; however, the most fit individual survives and eventually reproduces. Resultantly, as the fitness significantly reduces for both hermaphrodites, one gametophyte eventually dies out. Repeated instances of intraspecific competition in high densities amongst hermaphrodites would cause a

significant loss within the “male” and “female” gametophyte populations as hermaphrodites are bisexual. Therefore, from an evolutionary perspective, is it beneficial to produce some male gametophytes amongst a population so as to support fern gametophytes populations in high AND low density systems. 24. Would it be more beneficial for an individual to be a hermaphrodite at low or high density? Why? Do the data support this prediction? ● It would be more beneficial for an individual to be a hermaphrodite at lower density systems. This is because hermaphrodites, which are significantly larger than their male gametophyte counterparts, require far more resources, space, light, and nutrients. As a result, being a hermaphrodite in a high density setting would greatly increase intraspecific competition which leads to a reduction in fitness for both individuals. This adversity is supported in our data which shows that ultimately a positive relationship exists between the percentage of male gametophytes present in a population as the total number of gametophytes in the overall population(density) rises. As the total number of gametophytes in the overall population(density) lowers, the percentage of male gametophytes present in a population also lowers which inherently means the percentage of hermaphroditic gametophytes increases at these lower densities....