Key Concepts in Biology

Cell Theory: All living organisms are composed of cells, the basic unit of life; cells arise from pre-existing cells.
Prokaryotic vs. Eukaryotic Cells:
- Prokaryotic: No nucleus, smaller, simpler (e.g., bacteria).
- Eukaryotic: Nucleus present, larger, complex (e.g., plants, animals, fungi).
Organelles:
- Nucleus: Control center, houses DNA.
- Mitochondria: Powerhouse, site of ATP production.
- Ribosomes: Protein synthesis.
- Endoplasmic Reticulum: Rough (protein synthesis) and Smooth (lipid synthesis).
- Golgi Apparatus: Modifies, sorts, and packages proteins.

DNA Structure: Double helix made of nucleotides (adenine, thymine, cytosine, guanine).
Gene: A segment of DNA that codes for a protein.
Mendelian Genetics:
- Dominant and recessive traits.
- Law of Segregation and Law of Independent Assortment.
Genotype vs. Phenotype:
- Genotype: Genetic makeup (e.g., Aa, AA, aa).
- Phenotype: Observable characteristics (e.g., tall or short).

Natural Selection: Mechanism of evolution; survival of the fittest leads to adaptation.
Species: A group of organisms capable of interbreeding and producing fertile offspring.
Common Descent: All species share a common ancestor.
Variation and Adaptation: Genetic variation leads to adaptive traits that enhance survival.

Systems:
- Circulatory: Transports blood and nutrients.
- Respiratory: Gas exchange (oxygen and carbon dioxide).
- Digestive: Breaks down food for energy.
- Nervous: Controls body functions and responses.
- Musculoskeletal: Movement and support.

Ecosystem Components:
- Producers (plants), consumers (animals), and decomposers (fungi, bacteria).
Energy Flow: Energy flows from producers to primary consumers to higher trophic levels.
Biomes: Large ecological areas with distinct climates and species (e.g., deserts, forests, tundras).
Biodiversity: Variety of life in an ecosystem; essential for resilience.

Macromolecules:
- Carbohydrates: Energy source (sugars, starches).
- Proteins: Building blocks; enzymes catalyze reactions.
- Lipids: Fats and oils; energy storage and cell membranes.
- Nucleic Acids: DNA and RNA; carry genetic information.

Homeostasis: The ability of an organism to maintain stable internal conditions (temperature, pH).
Feedback Mechanisms:
- Negative Feedback: Mechanism that counteracts a change (e.g., temperature regulation).
- Positive Feedback: Mechanism that amplifies a change (e.g., childbirth).

These notes cover the fundamental concepts necessary for understanding the field of biology and its various branches.

Cell Theory: All living things are composed of cells, the smallest unit of life. New cells arise from pre-existing cells.
Prokaryotic cells are simpler and smaller, lacking a nucleus and distinct organelles.
Eukaryotic cells are more complex, possessing a nucleus, a membrane-bound organelle containing DNA.
Organelles are specialized structures within cells, each with a specific function.
- Nucleus: Contains DNA, controlling cell activity.
- Mitochondria: Powerhouse of the cell, generates ATP (energy).
- Ribosomes: Sites of protein synthesis.
- Endoplasmic Reticulum (ER), a network of membranes. The rough ER is studded with ribosomes and involved in protein synthesis, while the smooth ER is responsible for lipid synthesis and detoxification.
- Golgi Apparatus: Modifies, sorts, and packages proteins for transport within the cell or secretion outside the cell.

DNA consists of two strands of nucleotides wound around each other in a double helix structure.
Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base: adenine (A), thymine (T), cytosine (C), or guanine (G).
A pairs with T and C pairs with G via hydrogen bonds.
A gene is a specific segment of DNA that codes for a specific protein.
Mendelian Genetics:
- Dominant traits mask recessive traits.
- Law of Segregation: Alleles (gene versions) separate during gamete formation.
- Law of Independent Assortment: Alleles of different genes assort independently of each other.
Genotype: The genetic makeup of an individual (e.g., Aa, AA, or aa), while phenotype refers to the observable characteristics of an organism.

Natural Selection: The process where organisms with traits better suited to their environment survive and reproduce more successfully.
Species: A group of organisms that can interbreed and produce fertile offspring.
Common Descent: All living organisms share a common ancestor which has diverged over time into the range of life we see today.
Variation and Adaptation: Genetic variation within a species leads to differences in traits, which in turn influence an organism's ability to survive and reproduce. These beneficial traits are then passed on to offspring, resulting in populations adapted to their environment.

Systems:
- Circulatory system: Transports blood, oxygen, nutrients, and waste products throughout the body.
- Respiratory system: Responsible for gas exchange, taking in oxygen and releasing carbon dioxide.
- Digestive system: Breaks down food into smaller molecules that can be absorbed and used by the body.
- Nervous system: Controls and coordinates body functions, receives and processes information from the environment.
- Musculoskeletal system: Provides support, movement, and protection for the body.

Ecosystem Components:
- Producers: Organisms (plants, algae) that make their own food through photosynthesis.
- Consumers: Organisms that get their energy by consuming other organisms.
- Decomposers: Organisms (fungi, bacteria) that break down dead organic matter.
Energy Flow: Energy flows from producers to primary consumers (herbivores) to secondary consumers (carnivores), and so on.
Biomes: Large-scale ecological areas characterized by distinct climates and communities of plants and animals. Some examples include deserts, forests, tundras, grasslands, and aquatic biomes.
Biodiversity: The variety of life within an ecosystem. Higher biodiversity contributes to ecosystem health and resilience.

Macromolecules: Large organic molecules essential for life.
- Carbohydrates: Primarily used as a source of energy (e.g., sugars, starches).
- Proteins: Complex molecules comprised of amino acids. They serve as building blocks and enzymes, acting as catalysts for biochemical reactions.
- Lipids: Include fats and oils. Lipids store energy, provide insulation, and form cell membranes.
- Nucleic Acids: DNA and RNA, responsible for carrying genetic information.

Homeostasis: The ability of an organism to maintain a stable internal environment despite external changes.
Feedback Mechanisms:
- Negative Feedback: Mechanisms counteract change, maintaining equilibrium.
- Positive Feedback: Mechanisms amplify change, driving a process further.

These notes provide a concise overview of key concepts in biology, offering a foundation for further exploration in this fascinating field.