Cell Biology and Genetics Overview

Cell Theory:
- All living organisms are composed of cells.
- The cell is the basic unit of life.
- All cells arise from pre-existing cells.
Types of Cells:
- Prokaryotic: No nucleus, smaller, unicellular (e.g., bacteria).
- Eukaryotic: Nucleus present, larger, can be unicellular or multicellular (e.g., plants, animals).
Cell Organelles:
- Nucleus: Contains genetic material; controls cell activities.
- Mitochondria: Powerhouse; site of ATP production.
- Ribosomes: Protein synthesis.
- Endoplasmic Reticulum: Rough (with ribosomes) and Smooth (lipid synthesis).
- Golgi Apparatus: Modifies, sorts, and packages proteins.
- Cell Membrane: Semi-permeable barrier; regulates entry and exit of substances.

DNA Structure: Double helix made of nucleotides; consists of adenine (A), thymine (T), cytosine (C), and guanine (G).
Gene: A segment of DNA that codes for a protein.
Chromosomes: Structures made of DNA and proteins; humans have 46 chromosomes (23 pairs).
Mendelian Genetics:
- Law of Segregation: Alleles separate during gamete formation.
- Law of Independent Assortment: Genes for different traits segregate independently.

Theory of Evolution: Descent with modification; organisms change over time through natural selection.
Natural Selection: Process where organisms better adapted to their environment tend to survive and reproduce.
Speciation: Formation of new and distinct species through evolution.

Ecosystem: A community of living organisms and their physical environment, interacting as a system.
Biotic Factors: Living components (plants, animals, bacteria).
Abiotic Factors: Non-living components (climate, soil, water).
Trophic Levels:
- Producers: Autotrophs (e.g., plants).
- Consumers: Heterotrophs (primary, secondary, tertiary).
- Decomposers: Break down dead organic matter.

Organ Systems:
- Circulatory System: Transports blood, nutrients, gases.
- Respiratory System: Facilitates gas exchange (oxygen and carbon dioxide).
- Digestive System: Breaks down food, absorbs nutrients.
- Nervous System: Controls and coordinates body functions through signals.
Homeostasis: The maintenance of stable internal conditions despite external changes.

Photosynthesis: Process by which plants convert light energy into chemical energy (glucose).
- Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
Plant Structures:
- Roots: Anchor and absorb nutrients/water.
- Stems: Support and transport nutrients/water.
- Leaves: Main site of photosynthesis.

Bacteria: Single-celled prokaryotes; can be beneficial (e.g., gut microbiota) or pathogenic.
Viruses: Non-cellular infectious agents; require a host to replicate.
Fungi: Eukaryotic organisms; decomposers that play a vital role in nutrient cycling.

Cell Theory: Foundation of biology; states all organisms consist of cells, cells are the basic life unit, and all cells originate from existing cells.
Types of Cells:
- Prokaryotic: Lack a nucleus, typically smaller in size, and mostly unicellular organisms like bacteria.
- Eukaryotic: Contain a nucleus, larger, can be unicellular or multicellular as seen in plants and animals.
Cell Organelles:
- Nucleus: Houses genetic material (DNA); regulates cell activities.
- Mitochondria: Known as the powerhouse of the cell; responsible for ATP energy production.
- Ribosomes: Sites of protein synthesis, crucial for cell function.
- Endoplasmic Reticulum (ER):
  - Rough ER: Studded with ribosomes; involved in protein synthesis.
  - Smooth ER: Lacks ribosomes; responsible for lipid synthesis.
- Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or use within the cell.
- Cell Membrane: A semi-permeable barrier that regulates the movement of substances in and out of the cell.

DNA Structure: Composed of a double helix formed from nucleotides; includes bases adenine (A), thymine (T), cytosine (C), and guanine (G).
Gene: A DNA segment coding for a specific protein.
Chromosomes: DNA-protein structures; humans possess 46 chromosomes arranged in 23 pairs.
Mendelian Genetics:
- Law of Segregation: Alleles from each parent segregate into gametes.
- Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Theory of Evolution: Suggests that species change over time through descent with modification; a cornerstone of biological sciences.
Natural Selection: Mechanism of evolution; organisms better suited to their environment have higher survival and reproduction rates.
Speciation: The evolutionary process by which new species arise.

Ecosystem: A system formed by the interaction of living organisms (biotic factors) with their physical environment (abiotic factors).
Biotic Factors: Include all living components like plants, animals, and bacteria.
Abiotic Factors: Encompass non-living elements such as climate, soil, and water.
Trophic Levels:
- Producers: Autotrophic organisms (e.g., plants) that create their own food.
- Consumers: Organisms that rely on others for energy, categorized into primary, secondary, and tertiary consumers.
- Decomposers: Organisms like fungi and bacteria that decompose dead organic matter, recycling nutrients.

Organ Systems:
- Circulatory System: Transports blood, nutrients, gases, and waste products throughout the body.
- Respiratory System: Enables gas exchange, primarily involving oxygen intake and carbon dioxide expulsion.
- Digestive System: Responsible for food breakdown and nutrient absorption.
- Nervous System: Coordinates body functions via signaling between different organs and systems.
Homeostasis: The ability to maintain stable internal conditions amid external changes.

Photosynthesis: The process where plants convert light energy into glucose; follows the equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
Plant Structures:
- Roots: Anchor plants and absorb essential nutrients and water from the soil.
- Stems: Provide support and facilitate the transport of nutrients and water.
- Leaves: The primary site for photosynthesis due to their large surface area and chlorophyll content.

Bacteria: Single-celled prokaryotes that can be beneficial (e.g., gut microbiota) or harmful (pathogens).
Viruses: Non-cellular entities that require a host organism to replicate and cause infections.
Fungi: Eukaryotic decomposers that play a crucial role in nutrient cycling and ecosystem balance.