D2.1  Cell and Nuclear Division

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How can large numbers of genetically identical cells be produced?
• How do eukaryotes produce genetically varied cells that can develop into gametes?

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What processes support the growth of organisms?
• How does the variation produced by sexual reproduction contribute to evolution?

D2.1.1—  Generation of new cells in living organisms by cell division.

• ​List implications of the idea that new cells are only produced from a pre-existing cell. ​

D2.1.2— Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells.

• Define cytokinesis.
• State the difference between mitosis and cytokinesis.
• Compare and contrast  cytokinesis in plant and animal cells. 
• Describe the formation of the cleavage furrow in animal cell cytokinesis.
• Describe the formation of the cell wall in plant cell cytokinesis.

D2.1.3- Equal and unequal cytokinesis.

• State that cytokinesis usually, but not always, results in equal division of the cytoplasm.
• State the reason why daughter cells must receive at least one mitochondria during cytokinesis.
• Outline unequal cytokinesis in yeast budding.
• Outline unequal cytokinesis during human oogenesis.

D2.1.4- Roles of mitosis and meiosis in eukaryotes.

• State that mitosis is nuclear division resulting in continuity of the chromosome number and genome.
• State that meiosis  is nuclear division that results in reduction of the chromosome number and diversity between genomes.
• Outline the cause and consequence of anucleate cells. ​

D2.1.5— DNA replication as a prerequisite for both mitosis and meiosis.

• State that DNA replication occurs before both mitosis and meiosis.  
• State that DNA replication occurs in S-phase of interphase. ​
  
• Explain how replicated DNA molecules are held together, with reference to chromatid, replicated chromosome, centromere and cohesin.​

D2.1.6- Condensation and movement of chromosomes as shared features of mitosis and meiosis.

• Explain how and why chromosomes condense during mitosis and meiosis.
• State the role of microtubules and kinetochore motor proteins. 

 ​​​​D2.1.7- Phases of mitosis.

• State the names of the four phases of mitosis.
• Draw typical eukaryotic cells as they would appear during the interphase and the four phases of mitosis.
• Outline four events that occur during prophase.
• Outline the process of metaphase, inclusive of the role of microtubules and the kinetochore.
• Outline the process of anaphase.
• Outline four events that occur during telophase.

D2.1.8- Identification of phases of mitosis.

• Determine the phase of mitosis of a cell viewed in a diagram, micrograph or with a microscope.

D2.1.9- Meiosis as a reduction division.

• Explain what it means for chromosomes to be “homologous.”
• Define diploid.
• State the human cell diploid number.
• Define haploid.
• State the human cell haploid number.
• List example haploid cells.
• Given a diploid number (for example 2n=4), outline the movement and structure of DNA through the stages of meiosis.
• Explain why meiosis I is a reductive division.
• State that cells are haploid at the end of meiosis I.
• Compare meiosis with mitosis.
• ​Outline the events of prophase, metaphase, anaphase and telophase in meiosis I and meiosis II.

D2.1.10- Down syndrome and nondisjunction.

• Define nondisjunction.
• State the result of nondisjunction during anaphase I and anaphase II.  
• Describe the cause and symptoms of Down syndrome.​

D2.1.11-  Meiosis as a source of variation.  

• Explain how meiosis leads to genetic variation in gametes.
• Define bivalent.
• Describe the process and result of crossing over  during prophase I of meiosis.
• Draw a diagram to illustrate the formation of new allele combinations as a result of crossing over.
• Describe the process and result of random orientation of bivalents during metaphase I of meiosis.
• Draw a diagram to illustrate the formation of different chromosome combinations that result from random orientation during meiosis. 
• State that the number of chromosome combinations possible due to random orientation is 2^n.​

AHL ​​​​​​D2.1.12- Cell proliferation for growth, cell replacement and tissue repair.

• Define cell proliferation.
• List three processes which require cell proliferation.
• Outline cell proliferation during growth at plant meristems and early-stage animal embryos. 
• Describe skin cell proliferation during cell replacement and tissue repair.​

AHL ​​​​​​D2.1.13- Phases of the cell cycle.

• List the phases of the cell cycle.
• Distinguish between interphase, mitosis and cytokinesis. 
• Outline events of the G1, S, and G2 phases of interphase.
• Outline the fate of cells that leave the cell cycle.​

AHL ​​​​​​D2.1.14- Cell growth during interphase.

• Outline the structures that must be produced by a cell as it grows prior to division.
• List example metabolic reactions occurring during cell interphase.​

AHL ​​​​​​D2.1.15- Control of the cell cycle using cyclins.

• State the functions of cell cycle checkpoints.  
• Outline events of the G1, G2 and M checkpoints.
• Outline the role of cyclins in controlling the cell cycle. 
• Interpret a graph of cyclin concentrations throughout the cell cycle.​

AHL ​​​​​​D2.1.16- Consequences of mutations in genes that control the cell cycle.

• Describe how cancer arises, referring to accumulation of mutations over time.
  
• Define and list mutagens.
• Explain how mutations to proto- oncogenes and tumor suppressor genes can lead to the development of cancer.​

AHL ​​​​​​D2.1.17- Differences between tumors in rates of cell division and growth and in the capacity for metastasis and invasion of neighboring tissue.

• Compare the rates of cell division and growth and the capacity for metastasis and invasion of neighboring tissues between normal cells and cancerous cells. 
• Define primary tumor, secondary tumor, benign, malignant, metastasis and cancer.
• State the formula for calculation of a mitotic index.
• Calculate the mitotic index of a tissue as seen in a micrograph.
• Outline the use of mitotic index calculations in diagnosis and treatment of cancer.​