Science 9 - Reproduction Unit Study Guide

The Nucleus Controls the Functions of Life

Cell Theory & The Nucleus (4.1)

• The Three Components of Cell Theory:

  1. All living organisms are composed of one or more cells.

  2. The cell is the basic unit of life.

  3. All cells arise from pre-existing cells.

• What are organelles?

  • Small specialized structures within a cell that perform specific functions.

• Prokaryotic Cells vs. Eukaryotic Cells:

  • Prokaryotic Cells: No nucleus (e.g., bacteria).

  • Eukaryotic Cells: Have a nucleus and organelles (e.g., animal and plant cells).

• Structure & Function of the Nucleus:

  • Contains genetic material (DNA) and controls cell activities.

  • Surrounded by the nuclear envelope with nuclear pores.

  • Contains nucleolus, which makes ribosomes.

DNA - Deoxyribonucleic Acid (4.1)

• What is DNA?

  • The molecule that carries genetic information, determining traits and controlling cell functions.

• Structure of DNA:

  • Double helix (twisted ladder shape).

  • Sugar-phosphate backbone (sides) and paired nitrogenous bases (steps/rungs).

  • Base pair rule: A-T, C-G.

• What is a nucleotide?

  • The building block of DNA, made of:

    1. A sugar (deoxyribose)

    2. A phosphate group

    3. A nitrogenous base (A, T, C, G)

• Different Forms of DNA:

  • Uncoiled double helix (when not dividing).

  • Chromatin (loose DNA in the nucleus).

  • Chromosomes (condensed DNA for cell division).

• Karyotype:

  • A picture of chromosomes used to check for genetic disorders.

• Human Chromosomes:

  • 46 chromosomes (23 pairs).

  • Somatic (body) cells: 46 chromosomes.

  • Sex cells (gametes): 23 chromosomes.

• Genes & Proteins:

  • Genes: Segments of DNA that code for proteins.

  • Proteins: Perform essential functions (e.g., enzymes, hormones, transport proteins).

Mitosis is the Basis of Asexual Reproduction (5.1)

• Purpose of Cell Division:

  • Growth, repair, and reproduction.

• DNA Replication (S phase of Interphase):

  • Three Main Steps:

    1. Unwinding: Enzyme helicase unzips DNA.

    2. Base Pairing: DNA polymerase adds new bases.

    3. Two Identical DNA Strands: Semi-conservative process.

The Eukaryotic Cell Cycle & Mitosis

• Interphase:

  • G1 Phase: Cell growth, normal functions.

  • S Phase: DNA replication.

  • G2 Phase: Prepares for mitosis.

• Mitosis (PMAT):

  1. Prophase: Chromosomes condense, spindle fibers form, nucleus disappears.

  2. Metaphase: Chromosomes line up at the equator.

  3. Anaphase: Sister chromatids separate.

  4. Telophase: Two nuclei form in one cell.

• Cytokinesis:

  • Splitting of cytoplasm to form two identical daughter cells.

• Checkpoints & Cancer:

  • Checkpoints ensure proper cell division.

  • Cancer results from uncontrolled cell division.

• Asexual Reproduction Examples (5.2):

  • Binary Fission (bacteria), Budding (yeast), Fragmentation, Vegetative Reproduction, Artificial Cloning.

Meiosis is the Basis of Sexual Reproduction (6.1 & 6.2)

• Diploid vs. Haploid:

  • Diploid (2n): Full set of chromosomes (46 in humans).

  • Haploid (n): Half the chromosomes (23 in gametes).

• Meiosis Counterbalances Fertilization:

  • Meiosis creates haploid gametes → Fertilization restores diploid number.

• Meiosis I:

  • Homologous chromosomes separate.

• Meiosis II:

  • Sister chromatids separate.

  • Produces four genetically unique gamete cells.

• Spermatogenesis vs. Oogenesis:

  • Spermatogenesis (male) → 4 sperm cells.

  • Oogenesis (female) → 1 egg cell + 3 polar bodies.

• Genetic Variation Factors:

  1. Crossing Over (Prophase I)

  2. Independent Assortment (Metaphase I)

  3. Random Fertilization

Human Reproduction & Development

Trimesters of Human Development:

• First Trimester: Formation of organs, heart starts beating.

• Second Trimester: Growth, movement felt.

• Third Trimester: Final development, fat storage.