# 10.2 The cell cycle  (Page 4/40)

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## G 0 Phase

Not all cells adhere to the classic cell cycle pattern in which a newly formed daughter cell immediately enters the preparatory phases of interphase, closely followed by the mitotic phase. Cells in G 0 phase    are not actively preparing to divide. The cell is in a quiescent    (inactive) stage that occurs when cells exit the cell cycle. Some cells enter G 0 temporarily until an external signal triggers the onset of G 1 . Other cells that never or rarely divide, such as mature cardiac muscle and nerve cells, remain in G 0 permanently.

## Determine the time spent in cell cycle stages

Problem : How long does a cell spend in interphase compared to each stage of mitosis?

Background : A prepared microscope slide of blastula cross-sections will show cells arrested in various stages of the cell cycle. It is not visually possible to separate the stages of interphase from each other, but the mitotic stages are readily identifiable. If 100 cells are examined, the number of cells in each identifiable cell cycle stage will give an estimate of the time it takes for the cell to complete that stage.

Problem Statement : Given the events included in all of interphase and those that take place in each stage of mitosis, estimate the length of each stage based on a 24-hour cell cycle. Before proceeding, state your hypothesis.

1. Place a fixed and stained microscope slide of whitefish blastula cross-sections under the scanning objective of a light microscope.
2. Locate and focus on one of the sections using the scanning objective of your microscope. Notice that the section is a circle composed of dozens of closely packed individual cells.
3. Switch to the low-power objective and refocus. With this objective, individual cells are visible.
4. Switch to the high-power objective and slowly move the slide left to right, and up and down to view all the cells in the section ( [link] ). As you scan, you will notice that most of the cells are not undergoing mitosis but are in the interphase period of the cell cycle.

5. Practice identifying the various stages of the cell cycle, using the drawings of the stages as a guide ( [link] ).
6. Once you are confident about your identification, begin to record the stage of each cell you encounter as you scan left to right, and top to bottom across the blastula section.
7. Keep a tally of your observations and stop when you reach 100 cells identified.
8. The larger the sample size (total number of cells counted), the more accurate the results. If possible, gather and record group data prior to calculating percentages and making estimates.

Results of Cell Stage Identification
Phase or Stage Individual Totals Group Totals Percent
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Totals 100 100 100 percent

Analyze your data/report your results : To find the length of time whitefish blastula cells spend in each stage, multiply the percent (recorded as a decimal) by 24 hours. Make a table similar to [link] to illustrate your data.

Estimate of Cell Stage Length
Phase or Stage Percent (as Decimal) Time in Hours
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Draw a conclusion : Did your results support your estimated times? Were any of the outcomes unexpected? If so, discuss which events in that stage might contribute to the calculated time.

## Section summary

The cell cycle is an orderly sequence of events. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages. In eukaryotes, the cell cycle consists of a long preparatory period, called interphase. Interphase is divided into G 1 , S, and G 2 phases. The mitotic phase begins with karyokinesis (mitosis), which consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase. The final stage of the mitotic phase is cytokinesis, during which the cytoplasmic components of the daughter cells are separated either by an actin ring (animal cells) or by cell plate formation (plant cells).

## Art connections

[link] Which of the following is the correct order of events in mitosis?

1. Sister chromatids line up at the metaphase plate. The kinetochore becomes attached to the mitotic spindle. The nucleus reforms and the cell divides. Cohesin proteins break down and the sister chromatids separate.
2. The kinetochore becomes attached to the mitotic spindle. Cohesin proteins break down and the sister chromatids separate. Sister chromatids line up at the metaphase plate. The nucleus reforms and the cell divides.
3. The kinetochore becomes attached to the cohesin proteins. Sister chromatids line up at the metaphase plate. The kinetochore breaks down and the sister chromatids separate. The nucleus reforms and the cell divides.
4. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.

[link] D. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.

what is Economics?
Is the study of human behaviour as a relationship between ends and scares mean which have alternative use
Alhaji
yes
Tawa
what is monopoly
Alhaji
what is labour
LABOUR is a measure of work done by human being
Blessing
It is all form of human effort use to utilize in production
Alhaji
Why is scarcity a foundermental problem in economics
Alhaji
Why is scarcity a foundermental problem in economics
scarcity occur unbalance demand and supply at this time cost goods increase then inflation very increase
Tesfaye
scarcity is a foundermental problem because its a natural situation and it affects the world at Large.in other words,it's limit in supply relating to deman
Akwosih
'Economics is about making choices in the presence of scarcity"
. 'Economics is about making choices in the presence of scarcity" - Dscuss.
manoj
describe the producer's scarce resources.. I.e land,Labour,capital and enterprise
short in supply
Charles
What are human behaviour?
the rationality in decision making
Charles
how can you describe economic goods in a much better easier way?
any thing that have utility
Charles
what is deman and supply
Demand can be defined as the ability and willingness to buy commodities in a given price of goods and services in a particular period of time
Alasana
supply refers to the ability and willingness to offered commodities for sale in a given price of goods and services in a period of time .
Alasana
Demand can refer to the ability and willingness to purchase a commodity at a giving price and time.
habib
what must the producer do if total costs exceed total revenue
raise price
Nguyen
reduce cost
Charles
scarcity resources sample
land
Charles
what's scarcity
resources short in supply
Charles
hello
scarcity is excess against human wants.
Kennedy
scarcity is limit in supply relating to demand
Akwosih
students
Hamdu
shortge of resources .imbalance of wants to resources .
Hamdu
hlo
Yahya
limitation of supply in relation to their demand for commodity
Prince
what are the two types of economic theory's?
i thick it is microeconomic theory and macroeconomic theory. or it can be normative and positive economic theories.
Deep
yes^
Nguyen
with diagrams show thé change in prices in thé different time period that can result in an increase in demande
define momentary period
Fankam
What is a monopsony?
monopsony is a situation where only one buyer is available in the market
The
And with many sellers?
Allan
oligopsony
The
to be more specific, oligopsony is a situation with many sellers but few buyers
The
Thank you
Allan
economic is tha process of banking
Pls can u explain it into details
Praise
Cause I don't understand what you are saying
Praise
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