D2.1  Cell and Nuclear Division

Theme:  Continuity and Change

The process of mitosis ensures continuity of the genetic sequence between generations of cells. 

• During the S-phase of interphase, DNA is replicated. The resulting sister chromatids are identical copies. The mechanical process of mitosis is designed specifically to separate these copies into two different nuclei, guaranteeing the consistency of the genetic message.
• During metaphase, microtubules ensure that chromosomes align at the equator. This ensures that each daughter cell receives exactly one copy of every chromosome.
• Cyclins and internal checkpoints ensure the cell does not proceed to division if the DNA is damaged or improperly copied, maintaining the integrity of genetic information.

DNA and cellular structures change dramatically over the course of cell division and errors in the cell cycle can lead to uncontrolled division and formation of tumors.

• During prophase, DNA undergoes a massive structural change. DNA, which exists as loose chromatin for most of the cycle, supercoils into condensed chromosomes. This allows the genetic material to be moved without tangling.
• The physical separation of the cytoplasm during cytokinesis is a permanent change in the cell’s identity from one unit to two.
• Mutations in proto-oncogenes or tumor suppressor genes can cause the cell to lose control of the cycle. This leads to primary tumors and, through metastasis (a change in location), secondary tumors.

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?

​
​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?

Key Terms to Know: * higher level only

Actin
Anaphase
Animal Cell
Anucleate Cell
Benign*
Bivalent
Cancer*
Cell Cycle*
Cell Cycle Checkpoint*
Cell Division
Cell Growth*
Cell Membrane
Cell Proliferation*
Cell Replacement*
Cell Wall
Chromatid
Chromosome Number
Condensation (of Chromosome)
Crossing Over
Cyclin*
Cytokinesis
Cytoplasm
Daughter Cell

Diploid
DNA Replication
Down Syndrome
Embryo*
Eukaryotes
G1 Phase*
G2 Phase*
Genetic Diversity
Haploid
Histone
Interphase*
Malignant*
Meiosis
Meristem*
Metaphase
Metastasis*
Microtubule Motors
Microtubules
Mitosis
Mitotic Index*
Mutation*
Myosin
Non-Disjunction

Nuclear Division
Oncogene*
Oogenesis
Organism Growth*
Parent Cell
Plant Cell
Primary Tumour*
Prophase
Proto-Oncogene*
Random Orientation
Reductive Division
S Phase*
Secondary Tumour*
Sexual Life Cycle
Supercoiling
Telophase
Tissue Repair*
Tumor Suppressor Gene*
Tumour*
Vesicle
Yeast Budding

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.​