How does one cell become a whole organism through cell division, and what are stem cells used for?
The cell cycle and mitosis producing two genetically identical cells, the role of mitosis in growth, repair and asexual reproduction, stem cells in embryos, adult tissue and plant meristems, and the use of stem cells in medicine and the ethics involved.
A focused answer to the OCR Gateway GCSE Combined Science A topic B2 on cell division, covering the cell cycle, mitosis producing genetically identical cells, growth and repair, stem cells in embryos, adults and plant meristems, and the medical uses and ethics of stem cells.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this topic is asking
OCR wants you to describe the cell cycle and mitosis, explain that mitosis makes two genetically identical cells for growth, repair and asexual reproduction, describe where stem cells are found, and discuss their medical uses and the ethics involved.
The cell cycle and mitosis
The cell cycle is the sequence a cell goes through to divide, and it has three stages. First, the cell grows and increases the number of sub-cellular structures such as ribosomes and mitochondria, and the DNA replicates so that there are two copies of each chromosome. Second, mitosis divides the nucleus: the chromosomes line up, and one copy of each is pulled to each end of the cell. Third, the cytoplasm and cell membranes divide to produce two new cells. Because the DNA was copied exactly, the two daughter cells are genetically identical to each other and to the parent. Mitosis is used for the growth of an organism, the repair of damaged tissue (replacing worn-out cells), and asexual reproduction, where organisms produce genetically identical offspring from one parent.
Stem cells
A stem cell is an undifferentiated cell that can divide to produce more stem cells and can differentiate into specialised cell types. The main sources to know are:
- Embryonic stem cells, found in early embryos, which can differentiate into any type of cell in the body.
- Adult stem cells, found in some tissues such as bone marrow, which can form a more limited range of cells (for example the different types of blood cell).
- Plant meristems, found at the tips of roots and shoots, where stem cells can form any plant tissue throughout the plant's life. This is why gardeners can grow whole new plants from cuttings.
The ethics and risks of stem cells
Using stem cells raises issues OCR expects you to discuss in a balanced way. Embryonic stem cells are the most flexible, but obtaining them destroys an embryo, which some people consider unacceptable because they believe the embryo has a right to life; others argue the embryos are often spare ones from fertility treatment that would otherwise be discarded, and that the potential to cure serious illness justifies their use. There are also practical risks: stem cells grown in the laboratory could be contaminated with a virus and pass it to the patient, and transplanted cells may be rejected by the patient's immune system. Adult stem cells avoid the embryo issue but are less flexible. A good exam answer weighs a benefit against a cost rather than just stating opinions.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksDescribe what happens during the cell cycle, including the role of mitosis, and state two uses of mitosis in the body.Show worked answer →
A Biology Paper 1 structured question. Reward a clear sequence: in the first stage the cell grows, makes more sub-cellular structures (such as ribosomes and mitochondria), and the DNA replicates so there are two copies of each chromosome. Mitosis is the stage when the nucleus divides, separating one copy of each chromosome to each end of the cell. Finally the cytoplasm and membranes divide to form two genetically identical daughter cells. Two uses in the body: growth, and repair of damaged tissue (replacing worn-out or damaged cells). Markers credit the DNA replication step, the production of two identical cells, and two valid uses.
OCR 20214 marksExplain what a stem cell is and discuss one benefit and one risk of using stem cells to treat a medical condition.Show worked answer →
A B2 question linking knowledge to an evaluation. Reward: a stem cell is an undifferentiated cell that can divide and differentiate into different specialised cell types. A benefit: stem cells could replace damaged cells and treat conditions such as diabetes (replacing insulin-producing cells) or paralysis (replacing nerve cells). A risk: stem cells may be rejected by the patient, there is a risk of viral contamination during culture, or (for embryonic stem cells) some people object on ethical grounds because an embryo is destroyed. Markers want a defined stem cell, a specific benefit and a specific risk, not just "they are useful but some people disagree".
Related dot points
- Eukaryotic and prokaryotic cells, the function of sub-cellular structures (nucleus, mitochondria, ribosomes, chloroplasts, cell wall, vacuole, plasmids), light and electron microscopy, the magnification equation, and the use of standard form and SI units for cell sizes.
A focused answer to the OCR Gateway GCSE Combined Science A topic B1 on cell level systems, covering eukaryotic and prokaryotic cells, sub-cellular structures, light and electron microscopy, the magnification equation, and using standard form for cell sizes.
- Diffusion, osmosis and active transport as ways substances move across membranes, the factors affecting the rate of diffusion, surface area to volume ratio, and the adaptations of exchange surfaces such as alveoli, villi and root hair cells.
A focused answer to the OCR Gateway GCSE Combined Science A topic B2 on transport across membranes, covering diffusion, osmosis and active transport, the factors affecting diffusion rate, surface area to volume ratio, and adaptations of exchange surfaces.
- DNA, genes and chromosomes, sexual and asexual reproduction, meiosis producing genetically varied gametes, dominant and recessive alleles, genotype and phenotype, Punnett squares and inheritance ratios, and inherited disorders.
A focused answer to the OCR Gateway GCSE Combined Science A topic B5 on genes and inheritance, covering DNA, genes and chromosomes, sexual reproduction and meiosis, dominant and recessive alleles, genotype and phenotype, Punnett squares and ratios, and inherited disorders.
- Genetic and environmental causes of variation, mutation, evolution by natural selection, evidence from fossils and antibiotic resistance, selective breeding, genetic engineering, and the work of Darwin.
A focused answer to the OCR Gateway GCSE Combined Science A topic B5 on variation and evolution, covering genetic and environmental variation, mutation, natural selection and Darwin, evidence from fossils and antibiotic resistance, selective breeding and genetic engineering.
- The human circulatory system (heart, blood vessels and blood), the double circulation, the structure of arteries, veins and capillaries, the components and roles of blood, and transport in plants by xylem and phloem with transpiration and translocation.
A focused answer to the OCR Gateway GCSE Combined Science A topic B2 on transport systems, covering the heart and double circulation, arteries, veins and capillaries, the components of blood, and transport in plants by xylem (transpiration) and phloem (translocation).