Cellular Reproduction—1

BIOL Class 10 Module 2 Mitosis and Cytokinesis

What structures are found in a typical bacterial cell?

Plasmid and chromosome

What two stages does prokaryotic cell division have?

1. Copy the DNA. (This process is called replication)

2. Split the cell in two to form daughter cells.( This process is called binary fission)

What happens during the binary fission stage of prokaryotic reproduction?

The cell splits in two, to form daughter cells.

What happens during the replication stage of prokaryotic cell reproduction?

The DNA is duplicated, ensuring that each daughter cell receives a complete copy of the genetic material.

Replication is..

The process in which a prokaryotic cell copies its DNA before dividing.

Binary fission is

The process in which a prokaryotic cell splits into two daughter cells after DNA replication.

Cell division in prokaryotes

A simple two-stage cycle involving DNA replication followed by binary fission to form two daughter cells.

Where is hereditary information stored in a prokaryote?

In DNA, the same as in any other organism.

What shape is the prokaryotic chromosome?

It is a single circle of DNA.

Where does DNA replication begin in a prokaryote?

It begins at a point called the origin of replication, where the double-stranded DNA unzips.

How is a new double helix formed during replication?

By adding complementary nucleotides to the exposed DNA strands that have been unzipped.

What happens after DNA replication in a prokaryote?

The cell grows and then splits in two; this process is called binary fission.

How does DNA differ between eukaryotic and prokaryotic cells?

Eukaryotic cells contain more DNA than prokaryotic cells, and their DNA is packaged differently.

How is DNA packaged in eukaryotic cells?

DNA in eukaryotic cells is linear and packaged into compact chromosomes.

How many chromosomes do humans have?

46 chromosomes, which are DNA macromolecules.

What are the two mechanisms of cell division in eukaryotic cells?

• Mitosis occurs in somatic cells.

• Meiosis occurs in germ cells.

Where are somatic and germ cells found?

• Somatic cells make up most body tissues and organs.

• Germ cells are found in reproductive organs and give rise to gametes.

What are the distinct phases of the eukaryotic cell cycle?

1. Interphase (G₁, S, and G₂ phases)

2. Mitosis (M phase)

3. Cytokinesis (C phase)

What do homologous chromosomes contain?

Homologous chromosomes contain the same genes, but may have different variations of those genes, called alleles. One homologous chromosome comes from each parent.

What are sister chromatids?

Sister chromatids are exactly the same and are the result of DNA replication.

The number of chromosomes does or does not determine the complexity of the organism?

Does not. Shrimp have 92!! and we only have 46

What happens to homologous chromosomes prior to cell division?

Each homologous chromosome replicates, forming two identical copies called sister chromatids.

What structure joins sister chromatids together?

Sister chromatids are joined together by a structure called a centromere.

How many pairs of homologous chromosomes do humans have?

23 pairs

How many chromatids are present when each chromosome in a human cell is replicated?

When each of the 46 chromosomes is replicated, the total number of chromatids is 92.

What do homologous chromosomes contain?

Homologous chromosomes contain the same genes, but they may have different variations of those genes, which are called alleles.

Where do homologous chromosomes come from?

One homologous chromosome is obtained from the father, and the other is obtained from the mother.

What structure joins sister chromatids?

They are joined together at a region called the centromere.

What is the difference between homologous chromosomes and sister chromatids?

• Homologous chromosomes: One from each parent; contain the same genes but may have different alleles.

• Sister chromatids: Identical copies of a single chromosome formed after replication.

What are the main stages of the eukaryotic cell cycle?

The steps of the cell cycle include G₁, S, G₂, mitosis (M phase), and cytokinesis.

What occurs during the G₁ phase?

It is the period of cell growth before the DNA replicates.

What occurs during the S phase?

It is the period when DNA replicates and chromosomal proteins are duplicated.

What occurs during the G₂ phase?

It is the period after DNA replicates, when the cell prepares for division.

What happens during mitosis (M phase)?

Mitosis is the division of the nucleus, consisting of prophase, metaphase, anaphase, and telophase.

What is cytokinesis?

Cytokinesis is the division of the cytoplasm, producing two separate daughter cells.

What is the G₀ phase?

The G₀ phase is a state of cell cycle arrest, where the cell is not actively dividing.

What are the main mechanisms that allow bacteria to acquire new DNA?

Bacteria can acquire new DNA through conjugation, transduction, and transformation.

What happens during bacterial conjugation?

A donor cell transfers DNA directly to a recipient cell through a structure called a pilus.

What happens during transduction in bacteria?

A virus (phage) transfers DNA from one bacterium to another.

What happens during transformation in bacteria?

A bacterium takes up DNA fragments from donor cells in its environment.

What process do bacteria use to divide?

Bacteria divide by binary fission, which involves DNA replication and splitting of the cytoplasm to form two identical cells.

What happens during DNA replication in binary fission?

The circular chromosome is copied beginning at the origin of replication.

What happens after DNA replication during binary fission?

The cell elongates, separating the DNA molecules, and then pinches in two to form daughter cells.

What is the end result of binary fission?

Two genetically identical daughter cells are produced.

What is a karyotype?

A karyotype is an arrangement or organization of all of a cell’s chromosomes.

How can chromosomes be compared in a karyotype?

Chromosomes can be compared based on their size, shape, and centromere location.

What does a human karyotype show?

The human karyotype shows 23 pairs of chromosomes, for a total of 46 chromosomes.

What do the pairs in a karyotype represent?

Each pair represents homologous chromosomes—one from the mother and one from the father.

What are sister chromatids in a karyotype?

Sister chromatids are two identical copies of a chromosome, closely aligned side by side.

What type of cell division occurs in somatic cells?

Mitosis, which produces two new identical cells.

What type of cell division occurs in germ cells?

Meiosis, which produces gametes (sperm or egg cells).

Do somatic cells have diploid or haploid chromosomes?

Diploid (2n) — they contain 46 chromosomes.

Do germ cells have diploid or haploid chromosomes before meiosis?

Diploid (2n) — they start with 46 chromosomes before producing haploid gametes.

What is the chromosome number of gametes (sperm or egg)?

Gametes are haploid (n) and contain 23 chromosomes.

What is the purpose of gametes?

To carry genetic information for fertilization, forming a diploid zygote.

What prepares the cell for division?

Interphase sets the stage for cell division.

What happens to chromosomes during interphase?

Chromosomes are duplicated, and although not visible, they begin to condense—winding up tightly in a process called condensation.

What is mitosis?

The division of the nuclear contents that follows interphase.

Is mitosis a single event or a continuous process?

Continuous process, but it is divided for study into four distinct stages.

What are the four stages of mitosis?

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

During which mitosis stage do condensed chromosomes first become visible?

During prophase, condensed chromosomes first become visible.

What happens to the nuclear envelope during prophase?

It begins to disintegrate.

What happens to the nucleolus during prophase?

The nucleolus disappears.

What is a kinetochore?

A disc of protein at the centromere where microtubules attach during cell division.

What do centrioles do during prophase?

They separate and migrate to opposite ends (poles) of the cell.

What structure do centrioles form during prophase?

They begin forming a network of spindle fibres.

What are spindle fibres made of?

Microtubules.

During which stage of mitosis do chromosomes align in the centre of the cell?

During metaphase, chromosomes attached to the spindle’s microtubules align in the centre of the cell.

What happens to the centromeres during metaphase?

They align along an imaginary plane that divides the cell in half, called the equatorial plane.

What is the equatorial plane?

The imaginary line in the centre of the cell where chromosomes align during metaphase.

What happens to sister chromatids during anaphase?

Sister chromatids separate.

What causes sister chromatids to separate during anaphase?

Enzymes break the cohesin and the kinetochores, allowing chromatids to separate.

What happens to the microtubules of the spindle during anaphase?

They are dismantled, starting at the poles.

What effect does dismantling the microtubules have?

It pulls the chromatids toward opposite poles of the cell.

What happens to the spindle during telophase?

It is dismantled.

What forms around each set of chromosomes during telophase?

A nuclear envelope forms around each set of chromosomes at the poles.

What happens to chromosomes during telophase?

Chromosomes begin to uncondense.

What happens to the nucleolus during telophase?

The nucleolus reappears.

What is cytokinesis?

Occurs at the end of mitosis and is the division of the cytoplasm into roughly equal halves.

How does cytokinesis occur in animal cells?

In animals, cytokinesis occurs when actin filaments contract, pinching the cell in two.

What visible feature shows cytokinesis in animal cells?

A cleavage furrow forms between the daughter cells where the cell membrane pinches inward.

When does cytokinesis occur in the cell cycle?

It occurs after mitosis, completing the process of cell division.

What structure causes cytokinesis in animal cells?

A contractile ring of microfilaments forms around the cell, tightening like a drawstring to divide it.

What is a cleavage furrow?

A cleavage furrow is an indentation that forms around the cell’s midpoint, created by the contraction of actin microfilaments.

How does the cleavage furrow deepen?

The furrow deepens as microfilaments contract, tightening around the cell and pulling the membrane inward.

When does cytokinesis end?

Cytokinesis continues until the daughter nuclei are completely enclosed in separate cells.

What is the final result of cytokinesis?

Two new, genetically identical daughter cells are formed.