Biology Chapter: Cell Theory and Organelles

Cell Theory

• All living things are composed of cells.
• The cell is the fundamental unit of structure and function in living organisms.
• All cells originate from pre-existing cells.

Cell Organelles

• Nucleus: Houses DNA, directing cell activities.
• Mitochondria: The "powerhouse" of the cell, producing energy (ATP).
• Endoplasmic Reticulum (ER): Rough ER (with ribosomes) makes proteins; Smooth ER synthesizes lipids.
• Ribosomes: Sites of protein synthesis.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
• Lysosomes: Contain digestive enzymes for waste breakdown.
• Vacuoles: Store nutrients and waste, maintaining turgor pressure (in plant cells).
• Chloroplasts: Found in plant cells, conduct photosynthesis.
• Cell Membrane: Controls substance entry and exit.

DNA and Chromosomes

• DNA: Carries genetic instructions for organism development and function.
  • Located in the nucleus of eukaryotes, cytoplasm of prokaryotes.
• Chromosomes: Coiled DNA structures.
  • Humans have 46 chromosomes (23 pairs).
  • Each chromosome contains many genes.

DNA Structure

• Double Helix: DNA's twisted ladder shape.
• Nucleotides: The building blocks of DNA, composed of sugar, phosphate, and a nitrogenous base.
• Base Pairing: Adenine (A) with Thymine (T), Cytosine (C) with Guanine (G).
• Function: DNA stores and transmits genetic information.

Asexual Reproduction

• Binary Fission: Simple division of a cell into two identical cells (e.g., bacteria).
• Budding: New organism grows from the parent organism (e.g., yeast).
• Fragmentation: Parent organism splits into pieces, each forming a new organism (e.g., starfish).
• Vegetative Reproduction: New plants sprout from parent plant parts (e.g., runners in strawberries).

Binary Fission

• Process: DNA replicates, cell membrane pinches inwards, and two identical daughter cells form.
• Location: Prokaryotic cells (bacteria).

Mitosis

• Mitosis: Cell division producing two identical daughter cells.
• Interphase: Cell growth and DNA replication.
• Prophase: Chromosomes condense, nuclear membrane breaks down.
• Metaphase: Chromosomes align at the cell center.
• Anaphase: Sister chromatids separate to opposite poles.
• Telophase: Nuclear membranes reform around chromosomes.
• Cytokinesis: Cytoplasm divides, forming two daughter cells.

Sexual Reproduction

• Definition: Fusion of male and female gametes producing a zygote.
• Advantage: Genetic variation, enhancing adaptation to changing environments.

Gametes and Fertilization

• Gametes: Specialized reproductive cells (sperm and egg).
• Fertilization: Union of sperm and egg to create a zygote.

Meiosis

• Meiosis: Cell division producing four non-identical haploid cells (gametes).
• Meiosis I (Reduction Division):
  • Prophase I: Chromosome pairing, crossing over.
  • Metaphase I: Homologous chromosomes align.
  • Anaphase I: Homologous chromosomes separate.
  • Telophase I: Nuclear membranes form, producing two cells.
• Meiosis II (Similar to Mitosis):
  • Prophase II: Chromosomes condense, membrane dissolves.
  • Metaphase II: Chromosomes align.
  • Anaphase II: Sister chromatids separate.
  • Telophase II: Nuclei reform, generating four haploid cells.

Key Terms

• Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells).
• Haploid (n): Cells with one set of chromosomes (e.g., gametes).

Test your knowledge on cell theory, organelles, and their functions. This quiz covers important concepts such as the nucleus, mitochondria, and DNA. Perfect for students studying biology at any level!