Biology Paper 2 November 2008

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1. ASelecting the fastest-growing, largest colonies on ordinary nutrient agar, since plasmid uptake is assumed to speed up bacterial growth.
2. BExamining colonies under a light microscope for a visible change in cell shape or size, based on the assumption that taking up any recombinant plasmid physically alters the host bacterium's cell wall.
3. CCulturing the bacteria on a medium containing the antibiotic to which the plasmid's marker gene confers resistance; only bacteria that took up the plasmid will survive and grow.
4. DStaining bacterial colonies with Gram stain and selecting only the colonies that stain gram-negative, since this is assumed to indicate plasmid uptake.

1. AThe same enzyme produces complementary sticky (cohesive) ends on both the plasmid and the human gene, allowing them to base-pair and be joined together by DNA ligase.
2. BIt prevents the plasmid from being cut at more than one site, since an enzyme cannot cut its own recognition sequence twice.
3. CIt switches on the antibiotic resistance gene carried by the plasmid, which is otherwise assumed to stay permanently inactive and untranscribed until the plasmid DNA has actually been cut by the enzyme.
4. DIt ensures both DNA fragments are cut to exactly the same length, which DNA ligase requires before it can join them.

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Answer this when you sit the paper.

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Answer this when you sit the paper.

1. AEnabling cell recognition, by acting as receptor sites for hormones and antigens.
2. BCatalysing the hydrolysis of ATP to actively pump ions across the membrane.
3. CProviding structural support by forming covalent cross links between adjacent phospholipid molecules.
4. DActing as a store of chemical energy for active transport across the membrane.

1. AThe protein molecules form a continuous, immobile mosaic layer that anchors the phospholipids in place.
2. BThe membrane is completely rigid and fixed in overall shape, while only the carbohydrate chains on its outer surface form a repeating, tile-like mosaic pattern.
3. CThe phospholipids are arranged in a single, fixed layer that mimics the pattern of a mosaic tile.
4. DThe phospholipid molecules are free to move within the bilayer, and the protein molecules are scattered throughout it like tiles in a mosaic.

1. AThe presence of a specific shape recognised by carrier proteins in the membrane.
2. BThe concentration of the substance in the surrounding solution.
3. CThe size of the molecule relative to the membrane's pores and channels.
4. DIts solubility in fat, which affects how easily it dissolves in the phospholipid bilayer.