The given diagram shows a stage during mitotic division in an animal cell: The given diagram shows a stage during mitotic division in an animal cell:
Identify the stage. Give a reason to support your answer.
Topic: Prophase
Answer
The stage is PROPHASE.
Reasons: the chromosomes have DUPLICATED and appear as paired CHROMATIDS joined at a CENTROMERE; the CENTROSOME has split into two CENTRIOLES which are moving to opposite poles; and the NUCLEAR MEMBRANE and NUCLEOLUS are DISAPPEARING.
Give the stage AND the visible reasons — the reasons must describe what can be SEEN in the diagram.
Each stage has one unmistakable feature: PROPHASE — chromosomes visible but SCATTERED; nuclear membrane BREAKING DOWN METAPHASE — chromosomes LINED UP at the equator ANAPHASE — chromatids SEPARATED, moving to the poles, V or J shaped TELOPHASE — two groups ARRIVED at the poles; nuclear membranes RE-FORMING
THE DISAPPEARING NUCLEAR MEMBRANE is the surest sign of prophase, and it is what separates it from telophase, where the membrane is re-forming instead. Prophase is also the LONGEST stage of mitosis.
Note that the chromosomes are already DOUBLE when they first appear — the DNA was replicated in the S phase of interphase, before prophase began.