Describe the features of the structure of a cellulose molecule.
Researchers have found that adding nitrate to leaf tissue increases messenger RNA (mRNA) molecules of gene $NR$, which codes for nitrate reductase. State one advantage to leaf cells of an increase in mRNA molecules of gene $NR$ after nitrate is added.
One technique used to detect nitrite produced by the reduction of nitrate in leaf tissue involves: using an inhibitor to stop nitrite taking part in further reactions in the leaf tissue; placing the leaf tissue in a solution that contains a colourless test reagent. Nitrite from the leaf tissue moves into the surrounding solution, causing the solution to turn magenta (red-purple). Suggest why a colorimeter can improve this method for detecting nitrite.
Outline and explain the sequence of events that allows amino acids to be carried from the apoplast into the cytoplasm of a companion cell.
Suggest why amino acid transporters are not required to move amino acids from the companion cell into a phloem sieve tube element.
The nitrate uptake of excised maize roots was studied under a range of conditions. Table 4.1 gives the details and results for a control experiment and for four altered experiments, 1, 2, 3 and 4. The same nitrate-solution concentration was used in all experiments. All results were recorded after a fixed time period. The results for experiments 1, 2, 3 and 4 in Table 4.1 can be compared with the control experiment. Discuss how comparing each result with the control provides information about: - how nitrate ions are absorbed by the root cells - the factors that influence nitrate-ion uptake.