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?
- Nucleic acid: phosphorus marks the nucleotides
- Carbohydrate: sugar units are made of carbon, hydrogen and oxygen atoms alone
- Lipid: some phospholipids fit, and a nucleic acid would also hold nitrogen
- Protein: phosphorus links the amino acids together
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?
- Yes: enzymes and carriers are carbohydrates, not proteins
- No: proteins also work as enzymes, carriers and building materials
- No: proteins are the units that make up DNA
- Yes: a protein is a nutrient that cells do not use as a tool
Milo reads two figures. Molecule M is a chain joined by peptide bonds. Which sample most likely holds M?
- Sample G: it has nitrogen and phosphorus
- Sample H: it has nitrogen and turned violet
- Sample J: it has nitrogen, so it is a protein
- Sample F: it has no nitrogen or phosphorus
Use this
Two figures. Drawing (building-block chain, not to scale): molecule W, a chain of six identical beads labeled glucose joined end to end by glycosidic bonds; W is starch. Table (model data), 4 rows. Columns: Sample | Iodine | Benedict's | Biuret. Sample K: stayed amber | stayed blue | stayed blue; Sample L: turned blue-black | stayed blue | stayed blue; Sample P: stayed amber | turned orange-red | stayed blue; Sample R: stayed amber | stayed blue | turned violet.
Noah reads two figures. Molecule W is starch, a chain of glucose beads. Which sample most likely holds W?
- Sample R: biuret turned violet
- Sample P: Benedict’s turned orange-red
- Sample L: iodine turned blue-black
- Sample K: no test changed color
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 X; V is a polymer of fatty acids
- Sample X; V is not a polymer
- Sample Z; V is a polymer of amino acids
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?
- There is no flaw, since carbohydrates must be sweet sugars like glucose
- Cellulose is neither starch nor a simple sugar, so neither test finds it
- Cellulose is a protein, which neither of these tests is able to find
- Both tests were negative, so they should have been repeated with more fiber
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 cell wall row shows DNA, so DNA is found everywhere
- DNA stays in the nucleus, so the chloroplast row must be an error
- The chloroplast row also shows DNA, so the conclusion ignores data
- The nucleus row shows no DNA, so the conclusion is false
Results card (model data)
Sample Nitrogen Phosphorus Biuret result Sample X yes yes stayed blue Zee sees nitrogen in sample X and says it must be a protein. What else on the card argues against this?
- A blue biuret result shows X holds no nitrogen
- Nothing: nitrogen is found in proteins, so X is a protein
- Phosphorus and a blue biuret result point to a nucleic acid
- The nitrogen and phosphorus show X is a triglyceride