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

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Building-block chain, not to scale. M is the storage form of glucose in people. Ari finds molecule M in a diagram of a person’s cell. M stores glucose for later. Which class is M, and why?

   • Not a carbohydrate: carbohydrates are single sweet sugars
   • Carbohydrate: a polysaccharide of glucose units
   • Protein: any long chain is made of amino acids
   • Lipid: it stores energy, so it is a fat
2. 2.

   Building-block drawing, not to scale. Bo reads about molecule M, which has four linked carbon rings and a short tail. Which statement about M is correct?

   • M is a steroid, a lipid that is a polymer of rings
   • M is a protein, because rings join like amino acids
   • M is a steroid, a lipid that is not a polymer
   • M is a nucleic acid, because bases are rings
3. 3.

   Every sample also contains carbon, hydrogen and oxygen. Jun reads a lab’s atom report. Which sample is most likely a nucleic acid?

   • Sample A: it has no nitrogen, phosphorus or sulfur
   • Sample D: it has phosphorus
   • Sample B: it has nitrogen and sulfur
   • Sample C: it has nitrogen and phosphorus
4. 4.

   Sample Z also contains carbon, hydrogen and oxygen. Kira reads the atom report for sample Z. Which pair of classes can be ruled out?

   • Proteins and nucleic acids
   • Lipids and nucleic acids
   • Carbohydrates and lipids
   • Proteins and carbohydrates
5. 5.

   Both samples also contain carbon, hydrogen and oxygen. Luz compares samples E and F in the atom report. Which statement is correct?

   • Neither can be a protein, since both lack phosphorus
   • E is a protein, but F cannot be one without sulfur
   • E is likely a protein, and F could be a protein too
   • E is likely a nucleic acid, since both have nitrogen
6. 6.

   Building-block chain, not to scale. Milo reads that hemoglobin carries oxygen through the body. Which statement about hemoglobin is correct?

   • It is a lipid that insulates the body
   • It is a protein that transports oxygen
   • It is a carbohydrate that stores energy
   • It is a food nutrient, not a molecule that works inside cells
7. 7.

   Noah studies molecule M, which makes up the outer layer of cell membranes. Which statement about M is correct?

   • M is a nucleic acid, since it contains phosphate
   • M is a polymer of many identical lipid units
   • M is a lipid with a phosphate-containing head
   • M is a protein that forms channels in membranes
8. 8.

   Pia learns that saliva contains amylase, an enzyme. Amylase is a folded chain of beads joined by peptide bonds. Which statement is correct?

   • It is a protein that works as an enzyme
   • It is a food nutrient, so it cannot work inside the body
   • It is a nucleic acid, because it directs a reaction
   • It is a carbohydrate, because it acts on starch
9. 9.

   Tube R holds potato extract. A teacher ran two tests on potato extract while Tala’s class watched. Which conclusion fits both results?

   • Starch and a simple sugar, since iodine changed
   • No carbohydrate, since Benedict’s stayed blue
   • Starch is present, but no simple sugar was found
   • Protein, since iodine changed color
10. 10.

    Sample S is a seed extract. A teacher ran two tests on a seed extract while Zee’s class watched. Which conclusion fits both results?

    • A lipid is present, and violet shows starch
    • Protein is present, and the spot shows a carbohydrate
    • A lipid is present, and violet shows DNA, a protein
    • Protein and a lipid are both present