The four molecules of life: carbohydrates, lipids, proteins, nucleic acids

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   “Building-block chain, not to scale,” Ari studies a starch chain from bread flour. Bead X is one repeating unit of the chain. What is bead X?

   • A glucose unit
   • An amino acid
   • A nucleotide
   • A fatty acid
2. 2.

   no bead has a name. Bo reads about DNA, the molecule that carries genetic information. Bead Y is one repeating unit of one DNA strand. What is bead Y?

   • A glucose unit
   • A fatty acid
   • A nucleotide
   • An amino acid
3. 3.

   Building-block drawing, not to scale. Esme draws a fat from sunflower seeds. Bead X is joined to three fatty-acid beads. What is bead X?

   • Glycerol
   • An amino acid
   • A glucose unit
   • A fourth fatty acid

4. Read this first

   Class card (reference card)

   Class	Atoms	Building block	Job
   Carbohydrates	C, H, O	monosaccharides	energy and structure
   Lipids	mostly C and H	glycerol and fatty acids in fats	energy storage and insulation
   Proteins	C, H, O, N, often S	amino acids	enzymes, structure, transport
   Nucleic acids	C, H, O, N, P	nucleotides	genetic information

5. 4.

   Jun uses the class card. Which class has atoms of both nitrogen (N) and phosphorus (P)?

   • Carbohydrates
   • Nucleic acids
   • Lipids
   • Proteins
6. 5.

   Luz reads that cellulose fills plant cell walls. Using the class card, what do carbohydrates do?

   • They are sweet sugars that give no structure
   • They supply energy and give structure
   • They make enzymes and carry oxygen
   • They carry genetic information

7. Use this

   Two building-block drawings, not to scale. Protein: a chain of six identical beads labeled amino acid joined end to end by peptide bonds. Phospholipid: one bead labeled glycerol joined by ester bonds to two beads labeled fatty acid and by a covalent bond to one bead labeled phosphate.

8. 6.

   Noah compares two molecules from a cell. Which molecule is a polymer?

   • The phospholipid only
   • Both molecules
   • Neither molecule
   • The protein only

9. Use this

   Two building-block drawings, not to scale. Left drawing: six identical beads joined end to end by covalent bonds, each bead holding a sugar, a phosphate and a base. Right drawing: six identical beads joined end to end by peptide bonds, each bead holding an amino group, a carboxyl group and a side chain.

10. 7.

    Pia compares two drawings. Which drawing is built from amino acids?

    • Neither drawing
    • The right drawing
    • The left drawing
    • Both drawings

11. Results card (model data)

    Tube	Sample	Test	Result
    Tube A	potato extract	iodine solution	turned blue-black
    Tube B	plain water	iodine solution	stayed amber

12. 8.

    A teacher ran this iodine test while Ren’s class watched. What does the result in tube A show?

    • Protein, which is made of amino acids
    • No carbohydrate, since starch is not a sugar
    • A fat, which is a lipid
    • Starch, which is a carbohydrate
13. 9.

    A teacher ran this biuret test while Tala’s class watched. What does the result in tube C show?

    • DNA, which is a nucleic acid
    • Starch, which is a carbohydrate
    • Protein, which is made of amino acids
    • A fat, which is a lipid
14. 10.

    A teacher ran this brown paper test while Zee’s class watched. What does the spot at A show?

    • Protein, which is made of amino acids
    • A fat, which is a lipid
    • DNA, which is a nucleic acid
    • Starch, which is a carbohydrate