How does mitosis produce two identical cells, and what happens when the cell cycle goes wrong?
Describe the cell cycle and mitosis as the process that produces two genetically identical cells for growth and repair, and relate uncontrolled cell division to cancer (Virginia 2018 Biology SOL BIO.3.c, BIO.3.d).
A SOL-level answer on the cell cycle for the Virginia Biology EOC: interphase and the stages of mitosis, why the two daughter cells are identical, the role of growth and repair, and how loss of control leads to cancer.
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What this topic is asking
Virginia Biology SOL standards BIO.3.c and BIO.3.d ask how cell division and differentiation produce and maintain organisms. This page covers mitosis: the part of the cell cycle that produces two genetically identical cells for growth and repair. The Biology EOC expects you to know the outcome of mitosis, why the cells are identical, and how losing control of the cycle leads to cancer. Keeping mitosis straight from meiosis (the next topic) is essential, because the test contrasts them directly.
The cell cycle
The single most important event before division is DNA replication during interphase. Because the DNA is copied first, each daughter cell can receive a complete, identical set. If you remember that replication comes before mitosis, the "identical cells, same chromosome number" outcome makes sense.
Mitosis and its outcome
The stages of mitosis (prophase, metaphase, anaphase, telophase) are the steps by which the duplicated chromosomes line up and are pulled apart so each new cell gets one complete copy. For the EOC the outcome matters most: two cells, identical to each other and to the parent. This is why mitosis can grow a whole organism from a single fertilized egg and replace worn-out or injured cells.
Why the cells are identical
The daughter cells are identical because the DNA is replicated during interphase and then divided equally during mitosis. Each new cell receives one exact copy of every chromosome, so it has the same genes as the parent cell. This is the opposite of meiosis, which deliberately produces variation, and the contrast is a favorite exam point.
Cell differentiation
A multicellular organism is built from many specialized cell types (muscle, nerve, skin), yet they all arose by mitosis from one cell and contain the same DNA. The difference comes from differentiation: different cells switch on different genes, so they make different proteins and take on different structures and functions. This is how identical cells become a complex organism with many tissues, and it links to gene expression in the genetics module.
When the cell cycle loses control: cancer
The cell cycle is normally controlled at checkpoints that decide whether a cell should divide. Mutations in the genes that regulate the cycle can disable this control, so the cell divides uncontrollably. The dividing cells pile up into a mass called a tumor. A tumor that invades and spreads is cancer. Risk factors that increase mutations, such as tobacco smoke, ultraviolet radiation, and certain chemicals (carcinogens), raise the chance of cancer. The EOC expects you to connect uncontrolled mitosis to tumor formation.
Try this
Q1. State the purpose of mitosis in a multicellular organism. [1]
- Cue. Growth, repair of tissues, and (in some organisms) asexual reproduction; it replaces and adds genetically identical cells.
Q2. Explain why the daughter cells of mitosis are genetically identical. [2]
- Cue. The DNA is replicated during interphase and then divided equally during mitosis, so each daughter cell receives one exact copy of every chromosome.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
VA Biology SOL (2023 released style)1 marksWhat is the result of mitosis? (A) four cells with half the chromosome number. (B) two genetically identical cells with the same chromosome number. (C) two cells with double the chromosome number. (D) one cell with a random chromosome number.Show worked answer →
A 1-point multiple-choice item on the outcome of mitosis.
The correct answer is B. Mitosis produces two genetically identical daughter cells, each with the same chromosome number as the parent cell, for growth and repair. A describes meiosis, and C and D are incorrect outcomes.
The test rewards the key result of mitosis: two identical cells, same chromosome number.
VA Biology SOL (2024 released style)2 marksCancer is sometimes described as uncontrolled cell division. (a) Name the part of the cell cycle that is faulty in cancer. (b) Explain how this leads to a tumor.Show worked answer →
A 2-point item linking the cell cycle to cancer.
(a) 1 point: the control or regulation of the cell cycle (the checkpoints that normally control when a cell divides) is faulty, often because of mutations in the genes that regulate division.
(b) 1 point: without normal control, the cells divide repeatedly and uncontrollably by mitosis, so they accumulate into a mass of cells called a tumor.
Markers reward identifying loss of cell-cycle control and explaining that uncontrolled mitosis builds up a tumor.
Related dot points
- Describe meiosis as the division that produces gametes with half the chromosome number, and explain how crossing over, independent assortment, and fertilization create genetic variation (Virginia 2018 Biology SOL BIO.3.d, supporting BIO.5).
A SOL-level answer on meiosis for the Virginia Biology EOC: producing haploid gametes, the contrast with mitosis, and how crossing over, independent assortment, and fertilization generate genetic variation.
- Identify the major cell organelles and relate each structure to its function, showing how organelles work together to support life processes (Virginia 2018 Biology SOL BIO.3.a).
A SOL-level answer on organelles for the Virginia Biology EOC: the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, chloroplasts, vacuoles, and cell wall, and how structure relates to function.
- Describe the structure of DNA (the antiparallel double helix and base pairing) and explain how complementary base pairing allows DNA to be replicated accurately (Virginia 2018 Biology SOL BIO.5.a).
A SOL-level answer on DNA for the Virginia Biology EOC: the double helix, base pairing, why DNA is a stable information store, and how complementary base pairing allows accurate replication.
- Explain that a mutation is a change in the DNA base sequence with harmful, beneficial, or neutral effects, and that genetic variation (from mutation and sexual reproduction) is important to the survival of a species (Virginia 2018 Biology SOL BIO.5.c).
A SOL-level answer on mutations for the Virginia Biology EOC: what a mutation is, its harmful, beneficial, or neutral effects, the difference between body-cell and gamete mutations, and why genetic variation matters for survival.
- State the cell theory and the evidence for it, and distinguish prokaryotic from eukaryotic cells and plant from animal cells (Virginia 2018 Biology SOL BIO.3.a).
A SOL-level answer on cell theory for the Virginia Biology EOC: the three parts of cell theory and its evidence, the difference between prokaryotic and eukaryotic cells, and how plant and animal cells compare.
Sources & how we know this
- 2018 Science Standards of Learning (Biology) — Virginia Department of Education (2018)
- SOL Practice Items (All Subjects) — Virginia Department of Education (2024)