Cell proliferation
pp. 662–663Cells proliferate for growth (plant meristems, early animal embryos), replacement (skin cells made in the basal layer replace those lost at the surface) and repair (healing a wound).
Guiding questions
- How are large numbers of cells with identical genes produced?
- How do eukaryotes make genetically varied cells that can become gametes?
Slides
Notes
Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 662–669 of the course textbook. Image credits are on slide 12.
The cell cycle
Phases of the cell cycle
pp. 663–664The cycle is interphase (G1, S and G2), then mitosis and cytokinesis. DNA is replicated in S. Some cells leave the cycle and stay in G0.
Growth in interphase
pp. 664–665Interphase is metabolically active: the cell makes proteins and membranes, replicates its DNA, and its mitochondria and chloroplasts grow and divide so each daughter cell receives enough.
Cyclins
pp. 665–666
Concentrations of different cyclins rise and fall during the cycle. Each activates a cyclin-dependent kinase, and a threshold level of a specific cyclin is needed to pass each checkpoint. The cyclin is then broken down.
Cancer
Mutations in cell cycle genes
pp. 666–667Proto-oncogenes stimulate division when signalled; a mutation can turn one into an oncogene that is always active (for example Ras). Tumour suppressor genes stop the cycle if DNA is damaged; mutations that inactivate both copies (for example p53) remove this brake. Either way, cells divide without control.
Benign and malignant tumours
pp. 667–669Benign tumours grow slowly and stay in one place; they are not cancer. Malignant tumours grow fast, invade nearby tissue and can metastasize: cells from the primary tumour travel in blood or lymph and form secondary tumours elsewhere.
Videos
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Note-taking sheet
Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
Quick self-check
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Practice questions
A printable worksheet covering all six statements, from quick recall to data questions and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
Practical
Calculating a mitotic index
You will need: Prepared slide of root tip, or a micrograph, microscope, tally counter
- Find a field of view just behind the root tip
- Count the cells in mitosis and the total number of cells
- Calculate mitotic index
- Repeat in three fields, then discuss what a higher index in a tumour would suggest
Safety: Carry microscopes with two hands. Take care with glass slides.
Carry this out with your teacher's supervision and follow your school's lab rules.
Nature of science and TOK
Nature of science
Global impact of science
Cells taken from Henrietta Lacks in 1951, without her knowledge, became the HeLa line, which has supported countless discoveries about cell division.
Theory of knowledge
Does the value of knowledge justify how it was obtained?
HeLa cells have brought huge benefits, but consent was never given. Consider who should benefit from research and who should decide.
Syllabus statements
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
- D2.1.12Cell proliferation for growth, replacement and repairp. 662
- D2.1.13The stages of the cell cyclep. 664
- D2.1.14How cells grow during interphasep. 665
- D2.1.15How cyclins control the cell cyclep. 665
- D2.1.16What happens when genes controlling the cell cycle mutatep. 667
- D2.1.17How tumours differ in their division and growth rates, and in their ability to spread and invadep. 667
More of D2.1 in this course
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