1 A) Enzymes diffuse away from the membrane, and thus they tend to have more activity farther away. B) The middle lamella, which causes plant cells to stick together, is responsible for the primary wall, while the cell membrane has the enzyme structures for making the secondary wall. C) Rosettes in the cell membrane lay down successive cell wall layers. Thus, the primary cell wall is formed first with the secondary wall pushing it outward over time. D) The primary cell wall is digested by the rosettes which eventually create the secondary wall in order to create room for the new material. E) Cellulose expands as it forms the semicrystalline wall, leading to older material being moved outward over time. 2 A) Root hairs are made from many cells extending from the epidermis. Trichomes are extensions of epidermal cells. B) The surface area of roots is increased by root hairs because they have no cross walls and can freely interface with the soil. Trichomes often break wind currents and shade shoot epidermal regions. C) Root hairs are glandular, providing nutrients for symbiotic associations with soil fungi, while trichomes cannot serve as glands. D) All of the above distinguish root hairs from trichomes. E) None of the above are differences between root hairs and trichomes. 3 mutant characteristics, which usually reflect a loss of function of the normal (wild-type) gene. Mutant alleles are written in lower case, while (normal) wild-type genes are written in capital letters. What are the roles of SCARECROW (SCR) and WEREWOLF (WER) in root development? (p. 728)A) SCR makes the roots grow in absurd directions (as if there's no "brain" controlling them). WER makes roots "hairy" because it stimulates excessive differentiation of hairs from root epidermal cells.B) The wer protein results in cells with lots of root hairs, while scr creates a skinny root. C) The scr allele creates a skinny root (like a scarecrow that has lost its stuffing), while the wer allele attacks neighboring cells, killing them. D) Protein from SCR "turns on" the WER genes. E) The WER protein suppresses root hair development in neighbors to a cell that has a hair, while SCR allows the ground meristem to create lateral cell divisions of endodermis and ground tissue. 4 A) An axillary bud, which reserves meristematic material from the shoot apical meristem. B) A petiole, which forms below the leaf and props up the tissue that joins the leaf to the stem. C) A terminal bud, which creates branching patterns in plants. D) Internodes, which split at each node to create more branches. E) Bundle scars, which allow the material above the node to slough off during seasons that don't favor growth. 5 A) The loose palisade layer allows gas exchange to occur rapidly. The stomata are on the bottom to allow diffusion of the air upwards. B) The stomata can only differentiate on the bottom because ultraviolet radiation impedes their development. The palisade layer helps shelter them. C) Palisade cells control development of stomata on the bottom of the leaf through gravitational dispersal of hormones. D) Tight-fitting palisade cells prevent water loss from the hot surfaces of the leaves. Stomata allow gas exchange on the bottom of the leaf, where it's cooler and therefore has less water loss. E) This is a trick question: stomata are on the top of the leaf while the palisade layer lines the bottom!
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