Biology Notes on Reproduction, Inheritance, and Evolution

Reproduction: Sexual and Asexual (3.1 and 3.2)

  • Sexual Reproduction

    • Involves two parents and produces variation in offspring.
    • Allows for survival advantages in changing environments.
    • Decreases the chance of extinction.
    • Examples: Selective breeding enhances traits like meat production.

  • Asexual Reproduction

    • Involves only one parent and produces clones.
    • Is quicker and uses less energy (no mate needed).
    • Identical offspring can be produced rapidly under favorable conditions.

Reproduction in Plants (3.3-3.7)

  • Adaptations

    • Insect-pollinated Plants:
    • Feature bright, large petals and produce nectar.
    • Pollen is sticky in moderate amounts.
    • Wind-pollinated Plants:
    • Feature dull, small petals and do not produce nectar.
    • Pollen grains are smooth and light for easy dispersal.

  • Seed and Fruit Formation

    • Steps:
    1. Pollen grain lands on stigma (pollination).
    2. Pollen tube forms and moves down to the ovule.
    3. Male nucleus fuses with female egg nucleus, forming a zygote.
    4. The zygote divides to become a seed.
    5. Ovule becomes seed; ovarian wall becomes the fruit.

Germination Conditions

  • Conditions Required:

    • Water: Activates enzymes to break down starch reserves.
    • Oxygen: Necessary for aerobic respiration.
    • Warmth: Optimum temperature enhances growth rates.

  • Practical Experiment:

    • 4 boiling tubes with cress seeds under different conditions demonstrate the necessity of these factors.

Asexual Reproduction in Plants

  • Natural Runners: Example: Strawberry plants grow horizontally and form new plants.
  • Artificial Cuttings: Tissue samples grow into new plants when placed in nutrient agar.

Human Reproductive System (3.8-3.13)

  • Male Reproductive System:

    • Sex Gland: Produces semen containing sperm cells.
    • Testis: Produces sperm and testosterone.
    • Penis: Expels urine and semen.
    • Urethra: Carries urine/semen; prevents mixing.

  • Female Reproductive System:

    • Ovary: Contains ova and matures with FSH.
    • Oviduct: Pushes ovum toward the uterus.
    • Uterus: Thick lining for egg implantation.
    • Cervix & Vagina: Maintain pregnancy and lead to exterior.

Secondary Sexual Characteristics

  • Females (Oestrogen): Breast development, menstrual cycle, body hair growth.
  • Males (Testosterone): Growth of penis/testes, facial/body hair, muscle development.

Menstrual Cycle

  • Typically lasts 28 days with ovulation on day 14:
    • Oestrogen: Prepares uterus for egg.
    • Progesterone: Maintains uterine lining.

Development and Inheritance (3.14-3.27)

  • Key Terms:

    • Gamete: Half chromosome number (23).
    • Genome: Total DNA in an organism.
    • Chromosome: DNA structure in the nucleus.
    • Gene: DNA section coding for proteins.
    • Allele/Variant: Different gene forms.

  • Dominant & Recessive Alleles:

    • Alleles can be homozygous (same) or heterozygous (different).

DNA Structure & Protein Synthesis (3.16B-3.18B)

  • Structure:

    • Double helix from two strands made of nucleotides.
    • Complementary base pairing: A with T, C with G.

  • Protein Synthesis Steps:

    1. DNA unzips.
    2. mRNA forms from matched nucleotides (transcription).
    3. mRNA moves to ribosomes.
    4. Codons on mRNA translate into amino acids (translation).
    5. Amino acids form proteins, folding into unique structures.

Genetic Inheritance & Mitosis/Meiosis (3.28-3.32)

  • Mitosis:

    • One cell divides into two identical daughter cells.
    • Stages include interphase, chromosome alignment, and division.

  • Meiosis:

    • One cell divides to form four non-identical haploid gametes (23 chromosomes each).
    • Genetic variation due to crossing over and independent assortment.

Variation & Mutations (3.31-3.39)

  • Types of Variation:

    • Genetic: Eye color and blood type (inherited).
    • Environmental: Lifestyle, diet, climate changes.
    • Interaction: Gene-environment interaction affects traits.

  • Mutations: Rare changes in DNA that can be inherited.

    • Can affect protein synthesis and phenotype.
    • Mutagens: UV radiation and chemical substances increase mutation rates.

Evolution & Natural Selection

  • Darwin's Theory: Change in inherited characteristics over time via natural selection.

    • Variation arises through mutations; advantageous traits enhance survival.
    • Speciation occurs when populations diverge enough to prevent interbreeding.

  • Antibiotic Resistance in Bacteria:

    • Rapid reproduction allows advantageous traits to proliferate quickly.
    • Example: MRSA superbug emerged through selective pressures of antibiotic exposure.