The four molecules of life: carbohydrates, lipids, proteins, nucleic acids
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Both samples contain nitrogen. Ari reads that sample C is chitin, in the hard outer covering of insects and crabs. Why is C a carbohydrate and D a protein?
- The building blocks decide the class: sugar units against amino acids
- Nitrogen marks nucleic acids, so C must be a nucleic acid
- Both hold nitrogen, so C is a protein with a few sugar units attached to it
- A carbohydrate cannot hold nitrogen, so the label is wrong
Read this first
Atom list (model data)
Atom Found in sample Q? Carbon yes Hydrogen yes Oxygen yes Nitrogen no Phosphorus yes Sample Q has phosphorus but no nitrogen. Bo thinks any sample with phosphorus is a nucleic acid. Which class fits Q best, and why?
- Protein: phosphorus links the amino acids together
- Lipid: some phospholipids fit, and a nucleic acid would also hold nitrogen
- Carbohydrate: sugar units are made of carbon, hydrogen and oxygen atoms alone
- Nucleic acid: phosphorus marks the nucleotides
Reference card (reference card)
Molecule Made of Where it works Amylase amino acids in saliva Amylase works in saliva. Esme asks why it is called a protein if proteins are nutrients in food. What is the best answer?
- Amylase is a carbohydrate, since it acts on starch, which is a carbohydrate
- Amylase is a nucleic acid, since it carries instructions
- Proteins also act as enzymes the body makes, and amylase is one
- Protein is a food nutrient, so amylase must come from food
Protein card (reference card)
Protein Job Amylase helps digest starch Hemoglobin carries oxygen Keratin builds structures Insulin signals other cells Jun says protein is just a nutrient in beans. Which reply fits the card best?
- No: proteins also work as enzymes, carriers and building materials
- Yes: a protein is a nutrient that cells do not use as a tool
- Yes: enzymes and carriers are carbohydrates, not proteins
- No: proteins are the units that make up DNA
Comparison table (model data)
Molecule Building blocks Repeating chain? Starch glucose units yes Protein amino acids yes Fat glycerol and three fatty acids no Kira says every large biological molecule is a polymer. Which reply, with its reason, fits the table?
- Yes: a fat is a polymer made of many fatty acid units joined in a long chain
- No: a fat is glycerol with three fatty acids, not a repeating chain
- Yes: proteins are polymers, so lipids must be too
- No: starch is not a polymer, since it is not a sugar
Location table (model data)
Where Holds DNA? Nucleus yes Mitochondrion yes Chloroplast yes Cell wall no Bacterial cell (no nucleus) yes Luz says DNA is found in the nucleus and nowhere else. Which reply fits the table?
- No: DNA is a protein found throughout the cell
- No: mitochondria, chloroplasts and bacterial cells also hold DNA
- No: DNA is in the cell wall and the nucleus
- Yes: DNA stays in the nucleus, and the cell wall holds no DNA
Milo reads two figures. Molecule M is a chain joined by peptide bonds. Which sample most likely holds M?
- Sample H: it has nitrogen and turned violet
- Sample J: it has nitrogen, so it is a protein
- Sample G: it has nitrogen and phosphorus
- Sample F: it has no nitrogen or phosphorus
Use this
Two figures. Drawing (building-block drawing, not to scale): molecule V, one bead labeled glycerol joined by ester bonds to three beads labeled fatty acid. Table (model data), 4 rows. Columns: Sample | Paper spot | Iodine | Biuret. Sample X: translucent spot stayed | stayed amber | stayed blue; Sample Y: no spot left | turned blue-black | stayed blue; Sample Z: no spot left | stayed amber | turned violet; Sample U: no spot left | stayed amber | stayed blue.
Pia reads two figures. Molecule V is glycerol joined to three fatty acids. Which sample holds V, and is V a polymer?
- Sample Y; V is not a polymer
- Sample Z; V is a polymer of amino acids
- Sample X; V is a polymer of fatty acids
- Sample X; V is not a polymer
The sample is plant fiber, which is cellulose. Ren tested plant fiber, which is cellulose. Neither test changed color, so Ren says fiber is not a carbohydrate. What is the flaw?
- Both tests were negative, so they should have been repeated with more fiber
- There is no flaw, since carbohydrates must be sweet sugars like glucose
- Cellulose is a protein, which neither of these tests is able to find
- Cellulose is neither starch nor a simple sugar, so neither test finds it
Location table (model data)
Cell part DNA found? Nucleus yes Chloroplast yes Cell wall no Tala concludes that DNA stays in the nucleus because the nucleus had DNA. What is the flaw in this conclusion?
- The chloroplast row also shows DNA, so the conclusion ignores data
- The cell wall row shows DNA, so DNA is found everywhere
- DNA stays in the nucleus, so the chloroplast row must be an error
- The nucleus row shows no DNA, so the conclusion is false