(a) Biological molecules are made of chemical elements. Complete Table 2.1 by placing ticks (✓) in the boxes to show which chemical elements each biological molecule is made from
(b) Large molecules are made from smaller molecules. The boxes on the left show the names of some small molecules. The boxes on the right show the names of some large molecules. Draw a line from each small molecule to the large molecule that it makes. Draw four lines.
(c) (i) Complete the sentences about excretion. Choose the correct words to complete the sentences.
assimilation digestion faeces gain glucose
ions metabolism nitrogen plasma removal urea
Excretion is the ………… of the waste products of ……….. and substances in excess of requirements. A kidney excretes ………. , excess ………… and excess water.
(ii) State the name of an organ in the human body that excretes carbon dioxide.
(d) Fig. 2.1 is a diagram of part of the human excretory system and associated blood vessels.
(i) State the letter of a structure in Fig. 2.1 that excretes excess water.
(ii) State the letter in Fig. 2.1 that identifies the urethra.
(iii) State the name of the structure labelled C in Fig. 2.1.
(iv) State the name of the vein that removes blood from the kidneys.
(e) Excretion is one characteristic of living organisms. State two other characteristics of living organisms.
▶️ Answer/Explanation
Ans:
(a) Biological molecule elements:
Explanation: Carbohydrates and lipids contain C, H, O; proteins add N (sometimes S); nucleic acids include P.
(b) Molecule matching:
Explanation: Monosaccharides → starch (polymerization); fatty acids → lipids (ester bonds); amino acids → proteins (peptide bonds); nucleotides → DNA (phosphodiester bonds).
(c)(i) Excretion is the removal of the waste products of metabolism and substances in excess of requirements. A kidney excretes urea, excess ions, and excess water.
Key point: Metabolism produces urea (from proteins) and excess ions/water are regulated by kidneys.
(c)(ii) Lungs excrete carbon dioxide (a byproduct of respiration).
(d) Excretory system:
(i) A (kidney filters blood to excrete water)
(ii) D (urethra carries urine out)
(iii) Bladder (stores urine)
(iv) Renal vein (returns filtered blood to circulation)
(e) Two other characteristics: respiration (energy release) and growth (increase in cell number/size).