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# Biology Cheatsheet ## Cell Biology ### Organelles | Organelle | Description | |-----------|-------------| | Nucleus | Contains genetic material (DNA) | | Mitochondria | Site of cellular respiration | | Ribosomes | Site of protein synthesis | | Endoplasmic reticulum (ER) | Network of membranes for protein folding and transport | | Golgi apparatus | Modifies, sorts, and packages proteins and lipids | | Lysosome | Contains enzymes for breaking down cellular waste | ### Cell Cycle 1. G1 (gap 1) phase: Growth and normal cell functions 2. S phase: DNA replication 3. G2 (gap 2) phase: Growth and preparation for cell division 4. M (mitotic) phase: Cell division (mitosis and cytokinesis) ## Genetics ### Mendelian Genetics - Law of segregation: Each individual has two alleles for each gene, and they segregate (separate) during gamete formation - Law of independent assortment: Genes on different chromosomes assort independently during gamete formation - Dominant alleles are expressed over recessive alleles ### DNA Structure - DNA (deoxyribonucleic acid) is composed of nucleotides - Nucleotides consist of a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine) - DNA is double-stranded and complementary (A-T, C-G) ### DNA Replication 1. Helicase unwinds and separates the DNA strands. 2. Primase adds RNA primers to the template strand. 3. DNA polymerase synthesizes a new strand of DNA in the 5' to 3' direction. 4. DNA ligase seals the gaps between Okazaki fragments on the lagging strand. ## Ecology ### Levels of Organization 1. Organism: An individual living thing 2. Population: A group of individuals of the same species in a particular area 3. Community: All the different species in a particular area 4. Ecosystem: The community and the abiotic factors (non-living components) in a particular area 5. Biome: A group of similar ecosystems with the same climate and dominant vegetation 6. Biosphere: The sum of all the biomes on Earth ### Symbiosis - Mutualism: Both organisms benefit from the interaction - Commensalism: One organism benefits, and the other is not affected - Parasitism: One organism benefits, and the other is harmed ### Succession - Primary succession: Succession on newly exposed surfaces that have no soil - Secondary succession: Succession that occurs after a disturbance (e.g., fire, flood) has removed some or all of the previous organisms ## Resources - Khan Academy: [https://www.khanacademy.org/science/biology](https://www.khanacademy.org/science/biology) - Crash Course Biology: [https://www.youtube.com/playlist?list=PL3EED4C1D684D3ADF](https://www.youtube.com/playlist?list=PL3EED4C1D684D3ADF) - Biology Dictionary: [https://www.biologydictionary.net/](https://www.biologydictionary.net/) - Biology Online: [https://www.biologyonline.com/](https://www.biologyonline.com/)