and the matrix is a network of polysaccharides and proteins.
(c) Both ECM and cell walls are important in maintaining cell shape
and in retaining water, thereby resisting compression.
(d) Roles unique to the ECM include regulation of cellular processes
such as adhesion, motility, and differentiation during embryonic development. Roles unique to cell walls include protection of the cell from mechanical injury and microbial invasion, as well as provision of the mechanical support necessary to withstand the turgor pressure that gives plant tissues their rigidity.
（2） 答：①细胞培养技术 ②离心分离技术 ③流式细胞分离技术 ④基因敲除技术 ⑤干细胞培养技术
（3）． Answer③The N-terminal and C-terminal propeptides present in newly synthesized collagen monomers as-ist in alignment of the peptides to form the triple helix. These propeptides are removed after the trimers are transported to the extracellular matrix, and thus are not available to perform the same function in denatured calf type I collagen. In addition, inappropriate disulfide bridges can be generated during renaturation; these will also inhibit the generation of a normal triple helix.
（4）ANSWER:
The binding of epinephrine to ?-adrenergic receptors causes a stimulation
of heart function, both in terms of heart rate and with respect to the amount of work done in pumping blood. The effect appears to be mediated by cyclic AMP. When an antagonist such as the beta blocker propranolol is given to patients with hypertension, the cellular response caused by the binding of epinephrine to beta receptors is partially inhibited. Heart function is gradually restored over a period of time, with a corresponding decrease in blood pressure.
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