Problem set D answers

35) To grow, plant cells loosen their cell wall with enzymes (including expansins). Turgor pressure within the cell then drives cell growth.

36) The shoot apical meristem is at the top of the plant and produces leaves, lateral shoot meristems, and flower meristems. The lateral meristems also produce leaves, branches, and flower meristems. Flower meristems produce sepals, petals, stamens, and carpels. The root meristem is at the tip of the root. Lateral roots do not derive directly from the main root meristem, but instead derive from pericycle cells farther back along the root.

37) a) Cells at the top of the plant (the part removed by chopping) send the signal.

b) Lateral meristems respond to the signal.

c) The signal tells the lateral meristems not to grow (as long as the top of the plant is still present).

d) Chop off the top of the plant, and then supply auxin to the cut surface. If the lateral meristems fail to grow out, then auxin can substitute for the part of the plant that was removed.

38) a) The most rapidly dividing cells are in the peripheral zone of the meristem, flanking the central zone.

b) i) CLV1 recognizes its ligand and then probably phosphorylates intracellular target(s). ii) CLV3 is the ligand for CLV1.

c) In the mutants, the central zone of the meristem expands to a much larger size than normal.

d) The pathway inhibits proliferation of central zone cells, so that the central zone doesn't grow too big.

39) a) The synergids flank the egg at the micropylar end of the egg chamber. The central cell has two nuclei and is in the center of the egg chamber. The chalazal cells are the farthest from the micropyle. b) The egg and the central cell will be fertilized by male gametes. c) The fertilized egg will become the embryo, the fertilized central cell will become the endosperm, and maternal cells surrounding the egg chamber will become the seed coat.

40) a) The seed coat be in the F1 seed will be yellow, reflecting the maternal genotype.

b) The endosperm be in the same F1 seed will be purple because it will have a wild-type allele from the pollen.

c) The seed coat be in F2 seed derived from self-fertilization of the F1 plants in part a) will be brown, because the maternal tissue will be heterozygous.

d) The endosperm be in the F2 seed will segregate 3:1 purple:yellow.

41) genotype whorl 1 whorl 2 whorl 3 whorl 4

wild type sepals petals stamens carpels

agamous sepals petals petals new flower

pistillata sepals sepals carpels carpels