1. Repair, Or Replace Old Or Worn out Cells

1. Repair, Or Replace Old Or Worn out Cells

Why do cells divide?

1. Repair, or replace old or worn out cells

2. "Reproduction" some organisms reproduce by simple cell division (Asexual Reproduction)

Mitosis: The process by which a cell reproduces to create two identical copies of itself. The cells formed are known as "daughter cells".

Steps involved:

  1. Genetic material must be copied
  2. Organelles must be distributed
  3. Cytoplasm splits in half

DNA replication: when the DNA of each chromosome is copied.

Chromatin: thin filaments of DNA. During most of Interphase the DNA is in this form

Chromosomes: when thin chromatin condenses to form thick rod like structures. During mitosis the DNA is in this form

Interphase: the stage of the cell cycle between cell division.

DNA Replication: EACH STRAND OF THE DOUBLE HELIX SERVES AS A TEMPLATE FOR THE FORMATION OF A COMPLIMENTARY STRAND.

How do cells increase in size? MITOSIS: The process of cell division which results in the production of two daughter cells from a single parent cell. The nucleus divides to form 2 identical nuclei. The daughter cells are identical

IPMAT: Interphase

Prophase

Metaphase

Anaphase

Telophase

Interphase:

DNA is actively duplicating, organelles are replicating and cell increase in size

Prophase:

Chromosomes are visible, nuclear membrane disappear and centrioles move to opposite ends.

Metaphase:

  • Chromosomes line up at the middle of the cell
  • Spindle fibers attach to chromosomes at the centromere.

Anaphase:

  • Spindle fibers pull chromosomes apart
  • The 2 strands (chromatids) move to each daughter cell.

Telophase:

Animal Cell

  • Chromosomes/DNA spreads out
  • 2 nuclei form
  • Cell membrane pinches in to form the 2 new daughter cells

Plant Cell

  • New cell wall forms between the nuclei to form the 2 new daughter cells

Asexual Reproduction

  • Offspring produced from one organism
  • Hereditary information is identical
  • Mitosis is one form of asexual reproduction

Types of Asexual Reproduction

  • Budding
  • Regeneration
  • Fission: (Binary Fission)

Budding: New organism develops as an outgrowth of the parent and then enlarges. Common in plants. Ex: yeast and hydra

Binary Fission: A one celled organism divides in half to form two daughter cells Ex: Ameoba, paramecium, Bacteria.

Regeneration: The ability to replace lost or damaged body parts. It is a common feature in invertebrates, like worms and starfish

Cancer: Out of control cell division

AIM: How do sexually reproducing organisms maintain their chromosome number?

All the body cells of the individual have the full chromosome number of the species Diploid (2n)

Gametes(sex cells): contain one half the number of chromosomes of the species. Haploid (n)

EX: Human Sperm Cells and Egg Cells contain 23 chromosomes

Homologous/pair Chromosomes:

Chromosomes come in identical looking pairs. These chromosomes have the same kind of genes along their length but the form of the gene (allele) on each might be different.

Sexual Reproduction

Type of reproduction

Union of 2 sex cells:

Egg + sperm: join to form a zygote, which will develop into a new organism with a unique identity.

The union of an egg and a sperm is called fertilization.

Meiosis is the type of cell division by which sex cells (eggs and sperm) are produced.

One parent cell produces 4 daughter cells.

Daughter cells have 1/2 the number of chromosomes: Haploid

Meiosis is also called reduction division.

The nucleus divides twice. DNA replicates once

Meiosis I and Meiosis II

First Division of Meiosis

  • Prophase I: Duplicated chromosomes remain closely, These are called sister chromatids.
  • Metaphase I: The pairs of duplicated chromosomes line up in the center of the cell.
  • Anaphase I: Chromosome pairs separate with sister chromatids remaining together.
  • Telophase I: Two daughter cells are formed with each daughter containing only one chromosome of the chromosome pair.

Second Division of Meiosis

  • Prophase II: DNA does not replicate.
  • Metaphase II: Chromosomes line up at the center of the cell
  • Anaphase II: Centromeres divide and sister chromatids move separately to each pole.
  • Telophase II: Cell division is complete.

Four haploid daughter cells are formed.

Mistakes can produce cells with too many or fewer chromosome number.

Differences in mitosis and meiosis

Mitosis

  • Asexual
  • Cell divides once
  • 2 daughter cells
  • Genetic information is identical

Meiosis

  • Sexual
  • Cell divides twice
  • 4 haploid daughter cells
  • Genetic information is different]
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