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IB Biology SL D2.1 Cell and Nuclear Division Questions

Practise IB Biology SL D2.1 by identifying mitosis stages, explaining cytokinesis and interpreting cell-division evidence.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • link mitosis to new-cell production for growth, tissue replacement, repair or asexual reproduction
  • describe animal-cell cleavage-furrow cytokinesis and identify unequal division in yeast budding
  • compare mitosis and meiosis by cell number, chromosome number and genetic similarity
  • link pre-division DNA replication to sister chromatids and higher DNA quantity at G2 than G1
  • identify chromosome events shared by mitosis and meiosis, including sister-chromatid separation
  • sequence mitotic phases from chromosome/spindle events and identify them in diagrams or micrographs
  • explain how mitosis produces two genetically identical nuclei with the expected chromosome number
  • trace DNA replication through meiosis I/II, homologous then sister-chromatid separation to haploid nuclei
  • explain non-disjunction and interpret chromosome counts or karyotypes for trisomy 21
  • explain crossing over and random homologous-chromosome assortment as sources of genetic variation

Covered syllabus points

D2.1.1—Generation of new cellsD2.1.2—CytokinesisD2.1.3—Equal and unequal cytokinesisD2.1.4—Roles of mitosis and meiosisD2.1.5—DNA replication prerequisiteD2.1.6—Shared featuresD2.1.7—Phases of mitosisD2.1.8—Identification of mitosis phasesD2.1.9—Meiosis as reduction divisionD2.1.10—Down syndromeD2.1.11—Meiosis generates variation

Question 1

[Maximum number: 1]

Which process contributes to growth of a multicellular body?

A

Exocytosis

B

Meiosis

C

Mitosis

D

Osmosis

Question 2

[Maximum number: 3]

Both the genome and the environment of an organism affect its growth and development. Variation between individuals of a species can be continuous or discrete (discontinuous). Mitosis produces identical cells for growth and meiosis allows for variation.

The micrographs show onion and whitefish cells in mitosis.

Figure for Question 2 — IB Biology SL

Question (a)

(a)

Identify the phase of mitosis labelled X .

[ 1 ]

Question (b)

(b)

The process of cytokinesis is occurring in the whitefish embryo cells. Explain how cytokinesis occurs in this animal cell.

[ 2 ]

Question 3

[Maximum number: 2]

Ultraviolet (UV) light can penetrate cells, causing DNA damage. This effect can be reduced by using sunscreens or covering skin with clothing.

In an experiment to look at the effect of different treatments to reduce UV damage to DNA, yeast fungus (Saccharomyces cerevisiae) was used as the test organism. Six Petri dishes with agar were inoculated with yeast in sucrose solution. The Petri dishes were labelled according to the treatment applied to the lid, with sunscreen (Sun Protection Factors SPF15 or SPF50), cloth (polyester or cotton) or control (no treatment). Control 1 was placed in the dark and all the other Petri dishes were placed in direct sunlight for 6 hours. The dishes were then incubated for three days. The image shows yeast colonies that grew on the agar in one of the Petri dishes. The bar graph shows the number of yeast colonies present per Petri dish.

Figure for Question 3 — IB Biology SL
Figure for Question 3 — IB Biology SL

Describe how yeast cells reproduce.

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