Fig. 1 shows four stages observed in a time-lapse study of a human cell dividing in a culture dish. The student took photographs every 20 minutes. The cells...
Question 1 Report
Fig. 1 shows four stages observed in a time-lapse study of a human cell dividing in a culture dish. The student took photographs every 20 minutes. The cells had been removed from a small skin sample and were supplied with glucose and oxygen. The stages are not shown in the order in which they occurred.
(a) Use Fig. 1 to state which stage, W, X, Y or Z, shows two new cells almost completely formed. [1]
(b) Describe the correct sequence of stages, starting with W. [2]
(c) Explain how mitosis produces two cells with the same chromosome number as the original cell. [3]
(d) Use this information to explain one reason why cultured human cells must be supplied with glucose. [2]
Answer Details
(a) Stage Z shows two new cells almost completely formed. [1]
(b) Starting with W, the sequence is W, X, Y, Z. W shows an intact nucleus, X shows condensed chromosomes, Y shows chromosomes arranged during division, and Z shows division into two cells. [2]
(c) Before cell division, DNA is copied. The chromosomes, or sister chromatids, then separate into two groups. Each new nucleus receives one complete, identical set of chromosomes, so each daughter cell has the same chromosome number as the original cell. [3]
(d) Glucose is used in respiration. Respiration releases energy needed for cell division, growth and making new cell material. [2]
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