Cell Biology: Surface-Volume Ratio and Mitosis

Questions and Answers

What is the DNA amount in a cell at G2 phase compared to the original diploid amount?

It remains at 2C.

It decreases to 1C.

It is doubled to 4C. (correct)

It varies but averages at 3C.

During which phase does the synthesis of histone proteins occur?

M Phase

S Phase (correct)

G1 Phase

G2 Phase

What role do cyclins play in the cell cycle?

They activate kinases for cell cycle regulation. (correct)

They decrease DNA replication.

They facilitate RNA transcription.

They inhibit mitosis.

Which phase is characterized as the 'invisible phase' of the cell cycle?

S Phase Signup and view all the answers

What is the main activity that occurs during the G2 phase?

Synthesis of spindle tubulin and aster formation Signup and view all the answers

What happens to S-cyclin after its function is fulfilled?

It is destroyed. Signup and view all the answers

What is the average duration of the entire cell cycle in a human cell?

24 hours Signup and view all the answers

What are the key processes involved in the M phase of the cell cycle?

Karyokinesis and cytokinesis Signup and view all the answers

What is the longest stage of karyokinesis?

Prophase Signup and view all the answers

During which stage does the nuclear envelope completely disintegrate?

Metaphase Signup and view all the answers

What is the role of spindle fibers during metaphase?

To attach to chromosomes at kinetochores Signup and view all the answers

Which phase of karyokinesis has chromosomal fibers and supporting fibers arranged in the cell?

Metaphase Signup and view all the answers

What happens to the chromatids during anaphase?

Chromatids split lengthwise at the centromere Signup and view all the answers

Which of the following statements is true about prophase?

Chromatin condenses into chromosomes Signup and view all the answers

What feature is common at the metaphase stage?

Visible sister chromatids aligned on the metaphase plate Signup and view all the answers

What is the smallest stage of karyokinesis?

Anaphase Signup and view all the answers

What occurs when a cell's surface area becomes insufficient to draw necessary materials?

The cell begins division. Signup and view all the answers

Which factor is NOT responsible for cell division to occur?

Cell's age Signup and view all the answers

What is the term used for mitosis in plant cells?

Anastral division Signup and view all the answers

What do mitogens do?

Induce mitosis Signup and view all the answers

During which phase does karyokinesis occur?

M-phase Signup and view all the answers

What is the characteristic of amphiastral division in animal cells?

Presence of centrioles Signup and view all the answers

What is Eumitosis?

Mitosis occurring outside the nuclear membrane Signup and view all the answers

What does cytokinesis refer to?

Division of the cytoplasm Signup and view all the answers

What are darkly stained bead-like structures called that appear along the chromatin fibre?

Nucleosomes Signup and view all the answers

What is the term for the phase characterized by the absence of visible chromosomes during division?

Amitosis Signup and view all the answers

Which option best describes the process of amitosis?

Divides nucleus and cytoplasm simultaneously Signup and view all the answers

How many mitotic divisions are needed to form 'n' cells?

n-1 Signup and view all the answers

From the formula x = 2n, what does 'x' represent?

The final number of cells Signup and view all the answers

What characterizes the intrameiotic interphase?

Centrioles duplication happens in animals Signup and view all the answers

What type of organisms primarily utilize amitosis for cell division?

Prokaryotes Signup and view all the answers

What is a characteristic of a bivalent in meiosis?

Consists of four chromatids Signup and view all the answers

What is the primary purpose of cell division in unicellular organisms?

To increase population Signup and view all the answers

Which method of cell division is responsible for producing gametes?

Meiosis Signup and view all the answers

In multicellular organisms, what is a key function of cell division?

To ensure the body maintains and repairs itself Signup and view all the answers

Which of the following processes occurs during the cell cycle before cell division takes place?

Chromosome duplication Signup and view all the answers

How do multicellular organisms benefit from cell division?

By facilitating growth and specialized functions Signup and view all the answers

Which option correctly describes amitosis?

Direct division of the nucleus Signup and view all the answers

What is one key difference between mitosis and meiosis?

Mitosis leads to identical cells, while meiosis leads to genetic diversity Signup and view all the answers

What occurs during the cell cycle before a cell is ready to divide?

Preparation of cellular components Signup and view all the answers

Study Notes

Introduction to Cell Cycle and Cell Division

Cells serve as the basic unit and functioning component of all organisms, including both unicellular and multicellular types.
Cell division is essential for life, contributing to growth, repair, maintenance, and reproduction.
The process of cell division includes multiple methods: Mitosis, Meiosis, and Amitosis.
Unicellular organisms rely on cell division for population growth, while multicellular organisms depend on it for development and physiological functions.

Objectives of the Chapter

Understand and write about the various phases of the cell cycle.
Learn to sequence the phases of cell division correctly.
Distinguish the differences between mitosis and meiosis.

Cell Cycle Phases

G1 Phase: Initial phase with 2C DNA and 2n chromosomes. DNA replication preparation occurs here.
S Phase: DNA is replicated to 4C. Centrioles double, histones are synthesized, and chromosomes remain invisible until division.
G2 Phase: Pre-mitotic phase where organelles duplicate, RNA transcription, protein translation, and spindle preparations occur. Cyclin-dependent kinases (Cdks) regulate cell progression.

M-Phase (Mitosis)

Defined by the actual division of the cell, including both karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).
The human cell cycle averages 24 hours, with M-phase lasting about one hour.

Surface-Volume Ratio

As a cell grows, its volume increases more significantly than its surface area, leading to a stage where surface area becomes insufficient for material exchange.
Critical surface-area-to-volume ratio prompts cell division to maintain efficiency.

Mitosis Phases

Interphase: Preparing phase for cell division.
Factors influencing cell division include:
- Surface area-to-volume ratio
- Karyoplasmic index
Mitogens: Substances that induce mitosis, such as auxin and gibberellin.
Distinction between animal and plant mitosis: Animal cells exhibit amphiastral division, while plant cells undergo anastral division without centrioles.

Karyokinesis Stages

Prophase: Chromatin condenses into chromosomes; centrioles align at poles; spindle apparatus forms.
Metaphase: Nuclear envelope disassembles; spindle fibers bind to kinetochores; chromosomes align on the metaphase plate.
Anaphase: Centromeres split, and sister chromatids are pulled apart toward opposite poles.

Amitosis

A primitive form of cell division without visible chromosomes or spindle formation.
Involves simultaneous division of the cytoplasm and nucleus via constriction.
Typically faster than other division methods, completing in 20 to 30 minutes, and occurs in prokaryotes and some eukaryotes like budding yeast.

For ‘n’ cells, mitotic divisions required are n-1.
To produce ‘x’ cells, the number of generations (n) equals x = 2^n.
‘n’ meiosis events generate ‘n’ seeds or fruits.

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Description

Explore the critical concepts of surface-volume ratio in cells and the phases of mitosis. This quiz covers how cell growth impacts material absorption and the triggers for cell division. Test your understanding of these fundamental biological processes.