28. Plants

What does it mean to say that a signal is transduced? a. The signaling molecule enters the cell directly and elicits a cellular response. b. The signal is generated by the production of proteins. c. The physical form of the signal changes between the outside of the cell and the inside. d. The signal is amplified.

Summarize the experimental evidence in sponges showing that animal cells adhere to each other selectively. Explain the molecular basis of selective adhesion.

What is the significance of the observation that many signal transduction pathways create a network, where they intersect or overlap?

Steroid hormones, like most lipid-soluble signaling molecules, are processed directly. How does the absence of a signal transduction cascade in the processing of steroid hormones affect (a) signal amplification?

Suppose you have an antibody that binds to the receptor tyrosine kinase illustrated in Figure 11.16. When you add this antibody to the cell, you find that it activates the cell response, even when no signaling molecule is present. Explain this result.

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more. Researchers hypothesized that small animals called springtails (a type of arthropod) facilitate sperm transfer in mosses. To test this hypothesis, the researchers grew patches of male and female mosses at varying distances from each other and in the presence or absence of springtails. They later checked to see how many sporophytes were found in each female patch (as an indicator that fertilization had occurred). Their results are shown in the graph here (** means P<0.01, * means P>0.05. What conclusions can be drawn about the role of the springtails during the reproductive cycle of the mosses?

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more. What structure do moss sperm use for motility, and how does that reflect the evolution of land plants from green algae?

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more. Beyond the results presented here, what other evidence would be useful when drawing conclusions about the role of springtails in moss reproduction?

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more. Besides springtails, are there other ways moss sperm may be transferred from male to female gametophytes?

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more. Animals are responsible for pollinating many flowering plants. Did animal-mediated fertilization originate with flowering plants, or was this mode of sperm dispersal likely in place before the origin of flowering plants? Explain.

Suppose an efficient conducting system evolved in a moss that could transport water and other materials as high as a tall tree. Which of the following statements about “trees” of such a species would be true?

a. Spore dispersal distances would probably decrease.

b. Females could produce only one archegonium.

c. Unless its body parts were strengthened, such a “tree” would probably flop over.

d. Individuals would probably compete less effectively for access to light.