The four molecules of life: carbohydrates, lipids, proteins, nucleic acids
Grade 9 Science Worksheet
Circle the best answer.
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?
- Carbohydrate: a polysaccharide of glucose units
- Not a carbohydrate: carbohydrates are single sweet sugars
- Protein: any long chain is made of amino acids
- Lipid: it stores energy, so it is a fat
Building-block chain, not to scale. Esme reads about molecule M, used when cells build proteins. M is a chain of beads, each with a sugar, a phosphate group and a base. What is M?
- Lipid, because it holds phosphate groups
- Nucleic acid, because its beads are nucleotides
- Protein, because it helps build proteins
- Carbohydrate, because each bead has a sugar
Every sample also contains carbon, hydrogen and oxygen. Jun reads a lab’s atom report. Which sample is most likely a nucleic acid?
- Sample D: it has phosphorus
- Sample A: it has no nitrogen, phosphorus or sulfur
- Sample B: it has nitrogen and sulfur
- Sample C: it has nitrogen and phosphorus
Sample Z also contains carbon, hydrogen and oxygen. Kira reads the atom report for sample Z. Which pair of classes can be ruled out?
- Lipids and nucleic acids
- Proteins and nucleic acids
- Proteins and carbohydrates
- Carbohydrates and lipids
Both samples also contain carbon, hydrogen and oxygen. Luz compares samples E and F in the atom report. Which statement is correct?
- E is a protein, but F cannot be one without sulfur
- E is likely a nucleic acid, since both have nitrogen
- E is likely a protein, and F could be a protein too
- Neither can be a protein, since both lack phosphorus
Building-block chain, not to scale. Milo reads that hemoglobin carries oxygen through the body. Which statement about hemoglobin is correct?
- It is a food nutrient, not a molecule that works inside cells
- It is a carbohydrate that stores energy
- It is a lipid that insulates the body
- It is a protein that transports oxygen
Noah studies molecule M, which makes up the outer layer of cell membranes. Which statement about M is correct?
- M is a lipid with a phosphate-containing head
- M is a protein that forms channels in membranes
- M is a polymer of many identical lipid units
- M is a nucleic acid, since it contains phosphate
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 carbohydrate, because it acts on starch
- It is a food nutrient, so it cannot work inside the body
- It is a protein that works as an enzyme
- It is a nucleic acid, because it directs a reaction
Read this first
Results card (model data)
Tube Sample Test Result Tube P glucose solution Benedict’s solution, heated by a teacher turned orange-red Tube Q plain water Benedict’s solution, heated by a teacher stayed blue A teacher ran this Benedict’s test while Ren’s class watched. What does the result in tube P show?
- A fat, which is a lipid
- A simple sugar, a carbohydrate
- Starch, which stores glucose
- Protein, which is made of amino acids
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 and a lipid are both present
- Protein is present, and the spot shows a carbohydrate
- A lipid is present, and violet shows DNA, a protein
