How small molecules join into big ones

Answer Key - Grade 9 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   A cell builds one protein chain by dehydration synthesis and releases 49 water molecules. How many amino acids are in the chain, Ari?

   50 amino acids
2. 2.

   Bo's class reads that a starch piece was split completely into single glucose units by adding 11 waters. How many glucose units did the piece have?

   12 glucose units

3. Read this first

   Model data card: 5 beads joined into one chain

   item	mass (units)
   one bead	120
   one water	18

4. 3.

   Jun joins 5 amino-acid beads into one chain by dehydration synthesis. A bead has a mass of 120 units, and a water has 18 (model data). What is the chain's mass?

   528 units

5. Model data card: 4 beads joined into one chain

   item	mass (units)
   one bead	180
   one water	18

6. 4.

   Kira joins 4 glucose beads into one starch piece. A glucose bead has a mass of 180 units, and a water has 18 (model data). What is the piece's mass?

   666 units
7. 5.

   Milo's friend says a cell takes in one water at each peptide bond, so cells must supply water to join amino acids. Which response is best?

   • Disagree: no water is involved because amino acids just stick together
   • Agree: each peptide bond is built by adding one water
   • Disagree: forming a peptide bond releases a water molecule
   • Agree: the added water forms the peptide bond itself
8. 6.

   Noah's friend says a polymer built from 12 monomers releases 12 waters, one for each monomer. Which response is best?

   • Disagree: the first bond in the chain alone releases a water
   • Disagree: 12 monomers share 11 bonds, so 11 waters are released
   • Agree: each of the 12 monomers gives off one water as it joins the chain
   • Agree: 12 monomers form 12 bonds, so 12 waters are released
9. 7.

   Pia's friend says a chain and the pieces made by splitting it with water have the same total mass. Which response is best?

   • Disagree: the pieces also hold the added water, so they have more mass
   • Disagree: the pieces have more mass because splitting makes new atoms
   • Agree: splitting just separates the pieces, so the total mass stays the same
   • Disagree: the pieces have less mass, because water leaves as the chain splits
10. 8.

    Ren eats a sandwich. Hydrolysis splits its starch into glucose, and cells later use that sugar's carbon, hydrogen and oxygen with nitrogen to build amino acids. Which statement is supported?

    • Atoms from the sugar are rebuilt into amino acids with nitrogen added
    • Hydrolysis turns the starch's atoms into amino-acid atoms
    • The starch molecules are joined together directly into long protein chains
    • Cells create new carbon atoms to make the amino acids
11. 9.

    Tala grows a bean plant. Its leaves make sugar by photosynthesis, and cells then use that sugar to build amino acids for new protein. Where do the carbon atoms in the amino acids come from?

    • From the sugar, whose carbon atoms are rearranged into amino acids
    • The sugar's carbon atoms are destroyed and replaced by new ones
    • From the soil, which supplies the carbon directly
    • Cells create new carbon atoms when they build amino acids
12. 10.

    Building-block chain, not to scale. Zee's class models digestion: a 5-bead protein chain is split into single beads by hydrolysis, then the same beads are rebuilt into a new chain. Which statement fits both steps?

    • 5 new beads are made from the 4 waters when the chain is rebuilt
    • The same 5 beads are reused: 4 waters are used in splitting and 4 released in rebuilding
    • Rebuilding joins the beads with no water involved
    • Rebuilding releases 5 waters, one for each bead in the chain