Excretion Structured Questions | Cambridge O Level Biology

Biology 5090 · Question 1[11 marks]

Question 1

(a)

Fig. 1.1 illustrates the metabolic processing of surplus amino acids within human liver hepatocytes following protein digestion.

[5]

(i)

State what is meant by the term deamination.

[1]

(ii)

Explain why deamination is necessary in humans when excess protein is ingested.

[2]

(iii)

Name the organ where urea is produced and the primary organ where it is excreted from the human body.

[2]

(b)

Table 1.1 shows the daily dietary protein intake, volume of urine produced, and daily mass of urea excreted by three healthy adult volunteers maintained in identical ambient conditions ( $22^\circ\text{C}$ , $50\%$ humidity) with a fixed daily water consumption of $2.0\text{ dm}^3$ .

Volunteer Daily Protein Intake / $\text{g}$ Daily Urine Volume / $\text{cm}^3$ Daily Mass of Urea Excreted / $\text{g}$

Volunteer P 40 1500 12.0

Volunteer Q 90 1450 27.0

Volunteer R 160 1400 48.0

[3]

(i)

Describe the relationship shown in Table 1.1 between daily dietary protein intake and the daily mass of urea excreted.

[1]

(ii)

Calculate the percentage increase in the daily mass of urea excreted when protein intake increases from $40\text{ g}$ in Volunteer P to $160\text{ g}$ in Volunteer R. Show your working.

[2]

(c)

Carbon dioxide is another major metabolic excretory product in humans. Explain why carbon dioxide must be continuously excreted from the body and state two physiological consequences if it is allowed to accumulate in blood plasma.

[3]