Nitrogen is part of many important substances in living organisms.

Draw labelled diagrams to show a condensation reaction between two amino acids.

Nitrogen is part of many important substances in living organisms.

Distinguish between transcription and translation.

Nitrogen is part of many important substances in living organisms.

Explain how insects excrete nitrogenous wastes.

a. at least one of the amino acid structures completely correct

b. peptide bond shown with N–C and C=O and N–H correct

c. release of water clearly shown

a. DNA is transcribed AND mRNA is translated

Disallow the first mark, if a candidate gets transcription and translation the wrong way round, but allow marks
after that up to [3 max]

b. transcription produces RNA AND translation produces polypeptide/protein

c. RNA polymerase used in only in transcription and ribosomes only in translation

d. transcription in the nucleus «of eukaryotes» and translation in the cytoplasm

e. tRNA needed for translation but not transcription

f. nucleotides linked in transcription and amino acids in translation

   OR

   sugar-phosphate/phosphodiester bonds in transcription and peptide bonds in translation

[Max 4 Marks]

a. excreted as uric acid

b. excretion by Malpighian tubules

c. nitrogenous waste/ammonia «accumulates» in hemolymph

d. nitrogenous waste/ammonia absorbed by Malpighian tubules

e. ammonia converted to uric acid

f. conversion to uric acid requires energy/ATP

g. high solute concentration in Malpighian tubules

    OR

    active transport of ions/Na+/K+ into Malpighian tubules

h. water absorbed by osmosis flushes uric acid/nitrogenous waste to «hind» gut

i. water/ions reabsorbed from the feces and returned to hemolymph

j. uric acid precipitates/becomes solid/forms a paste so can pass out with little water

k. uric acid excreted/egested with the feces

l. water conservation/osmoregulation

   OR

   reduces mass of water «in body»

m. uric acid is non-toxic

[Max 8 Marks]