Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 256–264 of the course textbook. Image credits are on slide 13.
After fertilization, repeated division forms unspecialized, genetically identical cells. These then differentiate, as different genes are expressed in each cell type. In an early embryo, gradients of signalling chemicals called morphogens show a cell its position and so affect gene expression.
Stem cells can divide endlessly, and can differentiate along different pathways.
A niche is a location that can maintain stem cells, or can promote their division and differentiation. Bone marrow produces all types of blood cell, and hair follicles produce new hair and help to repair skin.
| Type | Can become | Found in |
|---|---|---|
| Totipotent | Any cell type, including support tissues | Zygote and earliest embryo |
| Pluripotent | Any cell type of the body | Early embryo |
| Multipotent | A limited range of related cells | Adult tissue, such as bone marrow |
Red blood cells are small enough to pass through capillaries. Eggs are large because they store food, whereas sperm are small and able to swim. White blood cells are larger than red ones, while neurons and striated muscle fibres can be very long.
Exchange across the surface depends on area, whereas the need for exchange depends on volume. As a cell grows, volume rises faster than area, so the ratio falls. Materials then cannot enter or leave quickly enough, and the cell must stop growing or divide.
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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.
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A printable worksheet covering all six statements, from quick recall to data questions and a longer answer. It has 32 marks and takes about 30 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Agar cubes of three sizes containing a pH indicator, dilute hydrochloric acid, ruler, timer
Safety: Eye protection. Use acid no stronger than 0.1 M.
Carry this out with your teacher's supervision and follow your school's lab rules.
Stem cell research promises new treatments. In 2006 Yamanaka's team reprogrammed adult cells, easing some objections to using embryos.
New methods removed one objection while raising other questions. Consider whether ethical conclusions should depend on what is technically possible.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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