SL Content Statements

• D2.1.1

  Generation of new cells in living organisms by cell division

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  In all living organisms, a parent cell—often referred to as a mother cell—divides to produce two daughter cells.
  

• D2.1.2

  Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells

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  Students should appreciate that in an animal cell a ring of contractile actin and myosin proteins pinches a cell membrane together to split the cytoplasm, whereas in a plant cell vesicles assemble sections of membrane and cell wall to achieve splitting.
  

• D2.1.3

  Equal and unequal cytokinesis

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  Include the idea that division of cytoplasm is usually, but not in all cases, equal and that both daughter cells must receive at least one mitochondrion and any other organelle that can only be made by dividing a pre-existing structure. Include oogenesis in humans and budding in yeast as examples of unequal cytokinesis.
  

• D2.1.4

  Roles of mitosis and meiosis in eukaryotes

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  Emphasize that nuclear division is needed before cell division to avoid production of anucleate cells. Mitosis maintains the chromosome number and genome of cells, whereas meiosis halves the chromosome number and generates genetic diversity.
  

• D2.1.5

  DNA replication as a prerequisite for both mitosis and meiosis
  

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  Students should understand that, after replication, each chromosome consists of two elongated DNA molecules (chromatids) held together until anaphase.
  

• D2.1.6

  Condensation and movement of chromosomes as shared features of mitosis and meiosis
  

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  Include the role of histones in the condensation of DNA by supercoiling and the use of microtubules and microtubule motors to move chromosomes.
  

• D2.1.7

  Phases of mitosis
  

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  Students should know the names of the phases and how the process as a whole produces two genetically identical daughter cells.
  

• D2.1.8

  Identification of phases of mitosis
  

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  AOS: Students should do this using diagrams as well as with cells viewed with a microscope or in a micrograph.
  

• D2.1.9

  Meiosis as a reduction division
  

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  Students should understand the terms “diploid” and “haploid” and how the two divisions of meiosis produce four haploid nuclei from one diploid nucleus. They should also understand the need for meiosis in a sexual life cycle. Students should be able to outline the two rounds of segregation in meiosis.
  

• D2.1.10

  Down syndrome and non-disjunction
  

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  Use Down syndrome as an example of an error in meiosis.
  

• D2.1.11

  Meiosis as a source of variation
  

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  Students should understand how meiosis generates genetic diversity by random orientation of bivalents and by crossing over.
  

AHL Content Statements

• D2.1.12

  Cell proliferation for growth, cell replacement and tissue repair
  

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  Include proliferation for growth within plant meristems and early-stage animal embryos as examples. Include skin as an example of cell proliferation during routine cell replacement and during wound healing. Students are not required to know details of the structure of skin.
  

• D2.1.13

  Phases of the cell cycle

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  Students should understand that cell proliferation is achieved using the cell cycle. Students should understand the sequence of events including G1, S and G2 as the stages of interphase, followed by mitosis and then cytokinesis.
  

• D2.1.14

  Cell growth during interphase

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  Students should appreciate that interphase is a metabolically active period and that growth involves biosynthesis of cell components including proteins and DNA. Numbers of mitochondria and chloroplasts are increased by growth and division of these organelles.
  

• D2.1.15

  Control of the cell cycle using cyclins

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  Limit to the concentration of different cyclins increasing and decreasing during the cell cycle and a threshold level of a specific cyclin required to pass each checkpoint in the cycle. Students are not required to know details of the roles of specific cyclins.
  

• D2.1.16

  Consequences of mutations in genes that control the cell cycle

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  Include mutations in proto-oncogenes that convert them to oncogenes and mutations in tumour suppressor genes, resulting in uncontrolled cell division.
  

• D2.1.17

  Differences between tumours in rates of cell division and growth and in the capacity for metastasis and invasion of neighbouring tissue

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  Include the terms “benign”, “malignant”, “primary tumour” and “secondary tumour”, and distinguish between tumours that do and do not cause cancer.
  AOS: Students should observe populations of cells to determine the mitotic index.