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
- A carbohydrate cannot hold nitrogen, so the label is wrong
- Both hold nitrogen, so C is a protein with a few sugar units attached to it
- Nitrogen marks nucleic acids, so C must be a nucleic acid
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?
- Lipid: some phospholipids fit, and a nucleic acid would also hold nitrogen
- Protein: phosphorus links the amino acids together
- Nucleic acid: phosphorus marks the nucleotides
- Carbohydrate: sugar units are made of carbon, hydrogen and oxygen atoms alone
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 nucleic acid, since it carries instructions
- Amylase is a carbohydrate, since it acts on starch, which is a carbohydrate
- Protein is a food nutrient, so amylase must come from food
- Proteins also act as enzymes the body makes, and amylase is one
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: a protein is a nutrient that cells do not use as a tool
- No: proteins are the units that make up DNA
- Yes: enzymes and carriers are carbohydrates, not proteins
- No: proteins also work as enzymes, carriers and building materials
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?
- 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
- Yes: a fat is a polymer made of many fatty acid units joined in a long chain
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?
- Yes: DNA stays in the nucleus, and the cell wall holds no DNA
- No: mitochondria, chloroplasts and bacterial cells also hold DNA
- No: DNA is in the cell wall and the nucleus
- No: DNA is a protein found throughout the cell
Milo reads two figures. Molecule M is a chain joined by peptide bonds. Which sample most likely holds M?
- Sample J: it has nitrogen, so it is a protein
- Sample F: it has no nitrogen or phosphorus
- Sample G: it has nitrogen and phosphorus
- Sample H: it has nitrogen and turned violet
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 K: no test changed color
- Sample L: iodine turned blue-black
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?
- 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
- Cellulose is neither starch nor a simple sugar, so neither test finds it
- There is no flaw, since carbohydrates must be sweet sugars like glucose
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?
- DNA stays in the nucleus, so the chloroplast row must be an error
- The nucleus row shows no DNA, so the conclusion is false
- The chloroplast row also shows DNA, so the conclusion ignores data
- The cell wall row shows DNA, so DNA is found everywhere