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.

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 not be true?

a. Spore dispersal distances would probably increase.

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 more effectively for access to light.

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.