Question

1. the instructions for making proteins are held by a section of dna called ________.

\ta chromosome \t a gene \t mrna \t a nucleotide

1. when can mutations occur?

\ta) when new copies of dna are being made
\tb) when cells are dividing
\tc) when cells are exposed to harmful environmental factors
\td) all of these

1. in the cell, dna is copied to make rna which then is used to make proteins. what organelles do the work?

\tnucleus \t ribosome \t mitochondrion \t chloroplast \t rough er

Explanation:

1. For question 5: Genes are specific sections of DNA that contain the code to produce proteins. Chromosomes are larger structures holding many genes, mRNA is a RNA molecule that carries the gene's code, and nucleotides are the building blocks of DNA.
2. For question 6: Mutations can happen during DNA replication (when new DNA copies are made, which occurs during cell division), and harmful environmental factors like radiation or chemicals can also damage DNA and cause mutations.
3. For question 7: Transcription (DNA to RNA) happens in the nucleus, and translation (RNA to protein) is carried out by ribosomes. The rough ER is involved in protein processing but not the core DNA→RNA→protein synthesis steps, while mitochondria and chloroplasts handle energy production.

Answer:

1. a gene
2. D) all of these
3. nucleus, ribosome