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 nucleotide
   • An amino acid
   • A fatty acid
   • A glucose unit
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 fatty acid
   • A glucose unit
   • 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?

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

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)?

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

   Kira uses the class card. Which class is mostly carbon (C) and hydrogen (H) atoms?

   • Carbohydrates
   • Lipids
   • Nucleic acids
   • Proteins
7. 6.

   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 carry genetic information
   • They make enzymes and carry oxygen
   • They supply energy and give structure

8. 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.

9. 7.

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

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

10. 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.

11. 8.

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

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

12. Results card (model data)

    Tube	Sample	Test	Result
    Tube C	bean extract	biuret reagent	turned violet
    Tube D	plain water	biuret reagent	stayed blue

13. 9.

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

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

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

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