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.