Grade 9 · Science · Biology

9th grade The four molecules of life: carbohydrates, lipids, proteins, nucleic acids worksheet

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The four molecules of life: carbohydrates, lipids, proteins, nucleic acids

Grade 9 Science Worksheet - Building Confidence

NameDate

Circle the best answer.

1.
“Building-block chain, not to scale,” Ari studies a starch chain from bread flour. Bead X is one repeating unit of the chain. What is bead X?
- A fatty acid
- An amino acid
- A glucose unit
- A nucleotide
2.
Building-block drawing, not to scale. Esme draws a fat from sunflower seeds. Bead X is joined to three fatty-acid beads. What is bead X?
- A glucose unit
- An amino acid
- Glycerol
- A fourth fatty acid

Read this first

Class card (reference card)

Class	Atoms	Building block	Job
Carbohydrates	C, H, O	monosaccharides	energy and structure
Lipids	mostly C and H	glycerol and fatty acids in fats	energy storage and insulation
Proteins	C, H, O, N, often S	amino acids	enzymes, structure, transport
Nucleic acids	C, H, O, N, P	nucleotides	genetic information

3.
Kira uses the class card. Which class is mostly carbon (C) and hydrogen (H) atoms?
- Lipids
- Nucleic acids
- Carbohydrates
- Proteins
4.
Luz reads that cellulose fills plant cell walls. Using the class card, what do carbohydrates do?
- They are sweet sugars that give no structure
- They make enzymes and carry oxygen
- They supply energy and give structure
- They carry genetic information
5.
Milo compares two drawings of molecules from a seed. Which drawing shows a polymer?
- Drawing 1 only
- Neither drawing
- Both drawings
- Drawing 2 only
Use this
Two building-block drawings, not to scale. Protein: a chain of six identical beads labeled amino acid joined end to end by peptide bonds. Phospholipid: one bead labeled glycerol joined by ester bonds to two beads labeled fatty acid and by a covalent bond to one bead labeled phosphate.
6.
Noah compares two molecules from a cell. Which molecule is a polymer?
- Neither molecule
- The protein only
- The phospholipid only
- Both molecules
Use this
Two building-block drawings, not to scale. Left drawing: six identical beads joined end to end by covalent bonds, each bead holding a sugar, a phosphate and a base. Right drawing: six identical beads joined end to end by peptide bonds, each bead holding an amino group, a carboxyl group and a side chain.
7.
Pia compares two drawings. Which drawing is built from amino acids?
- The right drawing
- The left drawing
- Both drawings
- Neither drawing
Results card (model data)
Tube Sample Test Result
Tube A potato extract iodine solution turned blue-black
Tube B plain water iodine solution stayed amber
8.
A teacher ran this iodine test while Ren’s class watched. What does the result in tube A show?
- Protein, which is made of amino acids
- Starch, which is a carbohydrate
- No carbohydrate, since starch is not a sugar
- A fat, which is a lipid
9.
A teacher ran this biuret test while Tala’s class watched. What does the result in tube C show?
- DNA, which is a nucleic acid
- A fat, which is a lipid
- Starch, which is a carbohydrate
- Protein, which is made of amino acids
10.
A teacher ran this brown paper test while Zee’s class watched. What does the spot at A show?
- Protein, which is made of amino acids
- A fat, which is a lipid
- Starch, which is a carbohydrate
- DNA, which is a nucleic acid

Tube	Sample	Test	Result
Tube A	potato extract	iodine solution	turned blue-black
Tube B	plain water	iodine solution	stayed amber

9th grade The four molecules of life: carbohydrates, lipids, proteins, nucleic acids worksheet – printable — Print: 1 2 3 4 5 6

About this worksheet

The four molecules of life: carbohydrates, lipids, proteins and nucleic acids. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

I can name the four classes of biological molecules and give each one's building block (monomer), main atoms, jobs and an example.
I can tell a polymer (a chain of repeating monomers: starch, protein, DNA) from a lipid, which is not a polymer.
I can use the atoms (N, P, S) and the building blocks together to identify a class, including odd cases (chitin has nitrogen but is a carbohydrate; a phospholipid has phosphorus but is a lipid).
I can read a model-data results card for four food tests (iodine, Benedict's, biuret, brown paper) and say what each result shows and what it leaves out.
I can correct four common mistakes: lipids are polymers, carbohydrates are only sugar, protein is only food, and DNA is only in the nucleus or is a protein.

Standard: HS-LS1-6

Words to know

monomer: One small building block that can join with others in a chain

polymer: A large molecule made of many repeating monomers joined together

carbohydrate: Sugar and starch-type molecules; atoms C, H, O in about 1 : 2 : 1

monosaccharide / polysaccharide: One sugar unit, such as glucose / a long chain of sugar units

lipid: Fats, oils, phospholipids and steroids; mostly carbon and hydrogen; water-fearing

triglyceride: A fat: glycerol joined to three fatty acids

phospholipid: A lipid with a phosphate head and two fatty acid tails; makes up membranes

steroid: A lipid with four linked carbon rings, such as cholesterol

Common mistakes

Your child treated a fat as a chain of repeating units, like starch or protein. Look at the drawing together: does one bead repeat along a chain, or does a glycerol bead hold three fatty-acid tails?

Your child thought carbohydrates are only sweet sugars, so starch or cellulose did not seem to count.

Your child thought protein is only a nutrient in food. Proteins also work inside the body as enzymes, carriers and building materials.

What to say

Ask: is a long chain of glucose units still a carbohydrate?

Ask: what job does this protein do?

Questions parents ask

What is the most common mistake with the four molecules of life: carbohydrates, lipids, proteins, nucleic acids?

Your child treated a fat as a chain of repeating units, like starch or protein. Look at the drawing together: does one bead repeat along a chain, or does a glycerol bead hold three fatty-acid tails?

Are these 9th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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