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QLDBiologyQuick questions
Unit 1: Cells and multicellular organisms
Quick questions on Hierarchy of organisation and stem cells (QCE Biology Unit 1)
9short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is hierarchy of organisation?Show answer
The structural levels of a multicellular organism, from simplest to most complex:
What is cell specialisation and division of labour?Show answer
Specialised cells are differentiated to perform one function efficiently, expressing only the subset of genes needed for that role.
What is stem cells?Show answer
Stem cells are unspecialised cells that have two properties: - Self-renewal. They can divide to produce more stem cells. - Potency. They can differentiate into one or more specialised cell types.
What is totipotent?Show answer
- The full set: can form every cell type of the body plus extra-embryonic tissues (placenta, yolk sac). - Found only in the zygote and the cells produced by the first few cleavage divisions.
What is pluripotent?Show answer
- Can form any cell type from the three primary germ layers (ectoderm, mesoderm, endoderm) and therefore any body cell type, but not extra-embryonic tissues. - Found in the inner cell mass of the blastocyst. - Can be produced from adult somatic cells by reprogramming (induced pluripotent stem cells, iPSCs), avoiding many of the ethical issues of embryonic stem cells.
What is multipotent?Show answer
- Can form a restricted set of related cell types in one lineage. - Examples: - Haematopoietic stem cells in bone marrow form all blood cell types. - Mesenchymal stem cells form bone, cartilage and fat.
What is skipping levels in the hierarchy?Show answer
Always include tissues between cells and organs; QCAA mark schemes penalise jumping straight from cells to organs.
What is calling all stem cells embryonic?Show answer
Adult tissues (bone marrow, brain, intestinal crypts, skin) contain multipotent or unipotent stem cells. iPSCs reprogram adult cells back to pluripotency.
What is treating pluripotent as totipotent?Show answer
Pluripotent cells cannot form a whole organism on their own because they cannot generate the placenta or yolk sac.