Biology unit 11

Why do cells divide instead of continuing to grow?

To avoid DNA overload and maintain an efficient surface area-to-volume ratio.

What is the process by which one cell divides into two identical cells?

Mitosis.

What is the purpose of mitosis?

Growth, repair, and maintaining surface area-to-volume ratio.

What is asexual reproduction?

When a single organism produces offspring that are genetically identical.

What is sexual reproduction?

When two organisms produce offspring with DNA from both parents.

What is the main advantage of sexual reproduction?

Genetic variation.

How many cells does mitosis produce, and are they haploid or diploid?

2 diploid cells (2n), genetically identical.

What kind of cells does mitosis occur in?

Somatic (body) cells.

What is the goal of meiosis?

To produce 4 haploid gametes (sex cells) with genetic variation.

How many times does a cell divide during meiosis?

Twice.

What happens during crossing over in meiosis?

Homologous chromosomes exchange genetic information.

What do you get when male and female gametes combine?

A zygote with 46 chromosomes.

What is cancer?

Uncontrolled cell growth forming tumors.

What is the difference between benign and malignant tumors?

Benign grow slowly and don't spread; malignant grow quickly and spread.

Name a few causes of cancer.

Radiation (UV, x-rays), smoking, genetic factors, and environmental hazards.

What are some treatments for cancer?

Surgery, external and internal radiation.

What is a single-gene mutation?

A small change in the DNA sequence, such as a deletion or insertion.

What is a chromosomal mutation?

A large-scale change affecting whole sections of chromosomes.

What is nondisjunction?

When chromosomes fail to separate properly during meiosis.

What genetic disorder is caused by an extra 21st chromosome?

Trisomy 21 (Down Syndrome).

What is Klinefelter’s syndrome?

A male with an extra X chromosome (XXY).

What is Turner syndrome?

A person with only one X chromosome (no second sex chromosome).

What is chromatin?

Loosely coiled DNA present when the cell is not dividing.

What are chromosomes?

Tightly coiled DNA formed during cell division to protect the DNA.

When does DNA exist as chromatin?

During interphase (when the cell is not dividing).

What helps DNA fit inside the nucleus?

Coiling into nucleosomes to form chromatin and chromosomes.

Why do cells divide?

The cell grows to a size where it can no longer function efficiently, so it divides to maintain proper function.

What are the two main reasons cells divide?

DNA overload and surface area-to-volume ratio (exchange inefficiency).

What is DNA overload?

When a cell grows too large, its DNA cannot keep up with regulating all cellular activities.

How does DNA overload affect the cell?

The DNA struggles to control activities, make proteins, and respond to signals, causing the cell to divide.

What is the surface area-to-volume ratio problem?

As cells grow, volume increases faster than surface area, reducing efficiency of material exchange.

How do cells solve exchange inefficiency?

They divide to increase the surface area-to-volume ratio.

What is cell division?

The process by which one cell divides into two genetically identical daughter cells.

Why do multicellular organisms need cell division?

For growth, repair, and maintenance of tissues.

What process ensures each daughter cell gets a full set of DNA?

Mitosis

What is cytokinesis?

The division of cytoplasm and organelles after mitosis.

What are the phases of the cell cycle?

Interphase, Mitosis, Cytokinesis

What happens during interphase?

The cell grows, replicates DNA, and prepares for division.

What happens in G1 phase?

The cell grows and performs normal functions.

What happens in the S phase?

DNA is replicated in preparation for division.

What happens in G2 phase?

The cell grows more and prepares for mitosis.

What is mitosis?

Division of the nucleus into two genetically identical nuclei.

What are the four phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase (PMAT)

What happens in prophase?

Nuclear membrane dissolves and chromatin condenses into chromosomes.

What happens in metaphase?

Chromosomes line up in the middle and spindle fibers attach.

What happens in anaphase?

Sister chromatids are pulled apart to opposite sides of the cell.

What happens in telophase?

Nuclear membranes reform around chromosomes and spindle fibers disappear.

What happens in cytokinesis (animal cells)?

Cytoplasm pinches in to form two daughter cells (cleavage furrow).

What happens in cytokinesis (plant cells)?

A cell plate forms to divide the cytoplasm and build a new cell wall.

What are chromosomes?

Structures made of DNA that carry genetic information.

What is asexual reproduction?

Reproduction involving one parent that produces genetically identical offspring.

What is the purpose of meiosis?

To produce haploid gametes (sex cells) for sexual reproduction.

What is a haploid cell?

A cell with one set of chromosomes (n), like gametes.

How many chromosomes do humans have?

46 total (23 from each parent)

How is meiosis different from mitosis?

Meiosis involves two divisions and results in 4 unique haploid cells.

What happens in meiosis I?

Homologous chromosomes pair up, cross over, and are separated into two cells.

What is crossing over?

Exchange of genetic material between homologous chromosomes during prophase I.

What happens in meiosis II?

Sister chromatids are separated, resulting in four genetically different haploid cells.

Why does sexual reproduction lead to genetic variation?

It combines DNA from two parents and includes processes like crossing over.

What is the result of meiosis?

Four genetically unique haploid cells.

What is a diploid cell?

A cell with two sets of chromosomes (2n), like body cells.

What is the product of the cell cycle (mitosis)?

Two genetically identical diploid daughter cells.