Basic Principles of Reproduction and Growth

Basic Principles of Reproduction and Growth

• Reproduction is the biological process creating new organisms.
• Two forms of reproduction exist: asexual and sexual.

Types of Reproduction

• Asexual Reproduction: Involves one organism creating genetically identical copies without another organism.
  • Common in single-celled organisms like bacteria.
  • Also used by some multi-celled organisms (e.g., some plants).
  • Methods like budding, fragmentation, and parthenogenesis also fall under asexual reproduction.
• Sexual Reproduction: Requires two specialized cells (gametes) from different organisms to combine genetic material.
  • Creates genetic variation in offspring.
  • Involves meiosis (creating haploid gametes) and fertilization (combining gametes).

Growth Definition

• Growth is the irreversible increase in size, height, girth, volume, or weight of an organism.
• It results from increases in cell size and number.

Growth Phases

• Growth occurs in distinct phases, including a formative (lag) phase, an acceleration (exponential or log) phase, a maturity/developmental (stationary) phase, and a deceleration/aging (senescence) phase.
• The phases are typically illustrated by a sigmoid or S-shaped curve.

Growth Rates

• Growth can proceed by arithmetic progression (constant increase) or geometric progression (rapid, exponential increase).
• Arithmetic growth is common in root and shoot elongation in plants.
• Geometric growth is common from mitotic division when cells retain their ability to repeat division.

Planes of Cell Division

• Meristematic cells divide in different ways to form different tissues in an organism.
  • Anticlinal division occurs perpendicular to the surface of the plant.
  • Periclinal division occurs parallel to the surface.

The Cell Cycle

• The cell cycle consists of interphase and the M phase (mitosis).
  • Interphase is divided into G1, S, and G2 phases.
  • G1: Cell growth and recovery from division.
  • S (Synthesis): DNA replication.
  • G2: Preparation for mitosis.
• The M phase includes karyokinesis (division of the nucleus) and cytokinesis (division of the cytoplasm).

Mitosis

• Mitosis is a type of cell division that results in two identical daughter cells.
• It involves four phases: prophase, metaphase, anaphase, and telophase.
• Chromosomes condense, align, separate, and then two new nuclei form.
• This is an important process for growth and repair in organisms.

Cytokinesis in Plants

• Cytokinesis in plants involves the formation of a cell plate that divides the cytoplasm.
• The cell plate develops from vesicles that fuse to form new cell walls.

Sexual Reproduction

• Combines the genetic material of two organisms to produce new organisms.
  • Involves meiosis to produce haploid gametes.
  • Combines male and female gametes through fertilization to form a zygote.
  • Sexual reproduction may be isogamous (gametes similar) or anisogamous (gametes dissimilar - male and female).

Asexual Reproduction

• Organisms create genetically similar or identical copies of themselves.
• Different methods, including budding, fragmentation, and parthenogenesis.
• Usually takes place without the involvement of another organism.

Other Types of Asexual Reproduction

• Parthenogenesis: Development of an embryo from an unfertilized egg.
• Fragmentation: An organism splits into pieces, each capable of developing into a new organism.
• Spore Formation: Asexual reproduction using spores.

Growth Phases

• A cycle of phases that occur in the growth and development of an organism.
• Phases like growth (increasing size).
• The phases are illustrated by a Sigmoid Curve.