← TEAS Life & Earth Science Mastery

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TEAS Life & Earth Science Mastery: Study Guide


Overview

This study guide covers the core Life and Earth Science concepts tested on the TEAS exam, spanning cell biology, genetics, ecology, human physiology, and earth science. Mastery of these topics requires understanding not just isolated facts, but how systems interact and regulate themselves. Use this guide alongside active recall practice to maximize retention.


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Cell Biology


Summary

Cell biology focuses on the structure and function of cells — the basic units of life. The TEAS exam tests your ability to distinguish cell types, identify organelle functions, understand membrane transport, and explain energy production.


Key Concepts


#### Cell Types

  • • Prokaryotic cells — No membrane-bound nucleus; DNA floats freely in the cytoplasm (e.g., bacteria)
  • • Eukaryotic cells — Contain a true, membrane-bound nucleus and membrane-bound organelles (e.g., animal, plant, fungal cells)

    • #### Critical Organelles

    | Organelle | Function |

    |---|---|

    | Mitochondria | Produce ATP via cellular respiration ("powerhouse of the cell") |

    | Ribosomes | Protein synthesis in ALL cell types (prokaryotic and eukaryotic) |

    | Nucleus | Houses DNA; controls cell activities |

    | Cell membrane | Selectively permeable barrier; maintains homeostasis |


    #### Membrane Transport

  • • Osmosis — Passive movement of water across a semipermeable membrane from low solute → high solute concentration
  • • Phospholipid bilayer — Acts as a selectively permeable barrier; hydrophilic heads face outward, hydrophobic tails face inward

    • #### Cellular Respiration

    | Type | Final Electron Acceptor | ATP Yield |

    |---|---|---|

    | Aerobic | Oxygen (O₂) | ~36–38 ATP |

    | Anaerobic | Other molecules | ~2 ATP |


    #### Mitosis Phases (in order)

    1. Prophase — Chromosomes condense

    2. Metaphase — Chromosomes align at the metaphase plate (equatorial plate)

    3. Anaphase — Sister chromatids separate and move to poles

    4. Telophase — Two nuclei form; cell begins to divide


    Key Terms

  • • ATP (adenosine triphosphate) — The cell's primary energy currency
  • • Semipermeable membrane — Allows some substances to pass while blocking others
  • • Cytoplasm — Fluid-filled interior of a cell
  • • Homeostasis — The maintenance of a stable internal cellular environment

    • Watch Out For

    > ⚠️ Osmosis moves water, not solutes. Water moves toward higher solute concentration — this is counterintuitive for many students.

    >

    > ⚠️ Ribosomes are present in BOTH prokaryotic and eukaryotic cells — they are one of the very few structures shared by all cell types.

    >

    > ⚠️ Metaphase = "Middle" — use the alliteration trick: chromosomes line up at the middle during metaphase.


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    Genetics & Heredity


    Summary

    Genetics covers how traits are inherited, how DNA is structured, and how genetic information is expressed. The TEAS exam emphasizes Mendelian ratios, DNA structure, mutation types, and the central dogma.


    Key Concepts


    #### Fundamental Definitions

  • • Genotype — The organism's actual genetic makeup (allele combination, e.g., Aa)
  • • Phenotype — The observable, physical expression of the genotype (e.g., brown eyes)
  • • Dominant allele — Expressed when one or two copies are present (uppercase letter)
  • • Recessive allele — Only expressed when two copies are present (lowercase letter)

    • #### Inheritance Patterns

  • • Monohybrid cross (Aa × Aa)

    • - Genotypic ratio: 1 AA : 2 Aa : 1 aa

    - Phenotypic ratio: 3 dominant : 1 recessive

  • • Codominance — Both alleles are fully and equally expressed in the heterozygote (e.g., AB blood type)
  • • Incomplete dominance — A blended intermediate phenotype appears in the heterozygote

    • #### DNA Structure

  • • DNA is composed of nucleotides containing a sugar, phosphate group, and nitrogenous base
  • • Purines (double-ring): Adenine (A) and Guanine (G)
  • • Pyrimidines (single-ring): Thymine (T) and Cytosine (C)
  • • Base pairing rules: A–T and G–C

    • #### The Central Dogma

    ```

    DNA → (Transcription) → mRNA → (Translation) → Protein

    ```

  • • Transcription — DNA is copied into mRNA in the nucleus
  • • Translation — Ribosomes read mRNA to assemble amino acids into proteins

    • #### Cell Division Comparison

    | Feature | Mitosis | Meiosis |

    |---|---|---|

    | Purpose | Growth and repair | Sexual reproduction |

    | Daughter cells | 2 | 4 |

    | Genetic makeup | Identical (diploid) | Unique (haploid) |


    #### Chromosomal Mutations

  • • Trisomy — Three copies of a chromosome instead of two (e.g., Trisomy 21 = Down syndrome)

    • Key Terms

  • • Allele — A variant form of a gene
  • • Heterozygous — Two different alleles (Aa)
  • • Homozygous — Two identical alleles (AA or aa)
  • • Haploid — Half the normal chromosome number (n)
  • • Diploid — Full chromosome number (2n)
  • • mRNA — Messenger RNA; carries genetic instructions from DNA to ribosome

    • Watch Out For

    > ⚠️ Codominance ≠ Incomplete dominance. In codominance, BOTH traits show fully (like AB blood — both A and B antigens present). In incomplete dominance, a BLENDED trait appears (like red + white = pink flowers).

    >

    > ⚠️ The 3:1 ratio is a PHENOTYPIC ratio for a monohybrid cross. The genotypic ratio is 1:2:1.

    >

    > ⚠️ Purines are the BIGGER bases (double ring) and pair with the smaller pyrimidines. Memorize: "Pure As Gold" — Purines = Adenine and Guanine.


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    Ecosystems & Ecology


    Summary

    Ecology examines how organisms interact with each other and their environment. Key TEAS topics include energy flow through trophic levels, symbiotic relationships, nutrient cycles, succession, and the roles of different species.


    Key Concepts


    #### Energy Flow

  • • Autotrophs (producers) — Make their own food via photosynthesis (sunlight) or chemosynthesis (chemical reactions)
  • • Heterotrophs (consumers) — Obtain energy by consuming other organisms
  • • 10% Rule — Only ~10% of energy transfers from one trophic level to the next; 90% is lost as heat
  • • Energy pyramids always have producers at the base

    • #### Trophic Levels (Bottom to Top)

    1. Producers (plants, algae)

    2. Primary consumers (herbivores)

    3. Secondary consumers (carnivores/omnivores)

    4. Tertiary consumers (apex predators)


    #### Symbiotic Relationships

    | Relationship | Organism A | Organism B | Example |

    |---|---|---|---|

    | Mutualism | Benefits (+) | Benefits (+) | Bees and flowers |

    | Commensalism | Benefits (+) | Unaffected (0) | Barnacles on whales |

    | Parasitism | Benefits (+) | Harmed (−) | Tapeworm in a host |


    #### Ecological Succession

  • • Primary succession — Starts on bare substrate with NO soil (e.g., after a volcanic eruption); pioneer species (like lichens) colonize first
  • • Secondary succession — Occurs after disturbance where soil remains (e.g., after a forest fire); faster than primary

    • #### Nitrogen Cycle

  • • Nitrogen fixation — Bacteria (Rhizobium) convert atmospheric N₂ → NH₃ (ammonia), making nitrogen available to plants
  • • Nitrogen cannot be used directly from the atmosphere by most organisms

    • #### Keystone Species

  • • A keystone species has a disproportionately large ecological impact relative to its abundance
  • • Removal causes dramatic, cascading changes to the community structure

    • Key Terms

  • • Biotic factors — Living components of an ecosystem
  • • Abiotic factors — Non-living components (temperature, water, sunlight)
  • • Carrying capacity — Maximum population size an environment can sustain
  • • Pioneer species — First organisms to colonize a new environment
  • • Decomposers — Break down dead organic matter, recycling nutrients

    • Watch Out For

    > ⚠️ Energy is LOST, not gained, moving up trophic levels. The 10% rule means that a tertiary consumer has access to very little of the original energy fixed by producers.

    >

    > ⚠️ Primary succession requires NO existing soil. If soil is present, it's secondary succession — even if the area looks barren.

    >

    > ⚠️ Commensalism = one benefits, one is UNAFFECTED (not harmed). Do not confuse with parasitism, where one organism is harmed.


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    Human Biology & Physiology


    Summary

    Human physiology covers the organ systems that maintain homeostasis. The TEAS exam focuses on the digestive, urinary, circulatory, nervous, and endocrine systems, emphasizing the function and location of key structures.


    Key Concepts


    #### Circulatory System

  • • Hemoglobin — Iron-containing protein in red blood cells (RBCs); binds oxygen in the lungs and delivers it to body tissues

    • #### Digestive System

  • • Small intestine — Primary site of chemical digestion AND nutrient absorption
  • • Absorption is enhanced by villi and microvilli, which dramatically increase surface area
  • • Large intestine — Water reabsorption; no significant nutrient absorption

    • #### Urinary System

  • • Nephron — The functional unit of the kidney

    • - Filters blood

    - Reabsorbs useful substances (glucose, water, ions)

    - Produces urine as the waste product


    #### Nervous System

    | Division | Control Type | Function |

    |---|---|---|

    | Somatic | Voluntary | Controls skeletal muscle movement |

    | Autonomic | Involuntary | Controls heart rate, digestion, breathing |

  • • Autonomic system is further divided into sympathetic ("fight or flight") and parasympathetic ("rest and digest")

    • #### Endocrine System

  • • Insulin — Produced by beta cells of the islets of Langerhans in the pancreas

    • - Lowers blood glucose by promoting cellular glucose uptake

  • • Glucagon — Also from the pancreas (alpha cells); raises blood glucose (opposite of insulin)

    • Key Terms

  • • Villi/Microvilli — Finger-like projections in the small intestine that increase surface area for absorption
  • • Nephron — Kidney's filtering unit; includes the glomerulus, Bowman's capsule, and tubules
  • • Islets of Langerhans — Clusters of endocrine cells in the pancreas
  • • Homeostasis — Maintaining a stable internal environment despite external changes

    • Watch Out For

    > ⚠️ Most digestion and ALL absorption happen in the SMALL intestine, not the stomach. The stomach mainly breaks down food mechanically and chemically (with acid/pepsin), but very little absorption occurs there.

    >

    > ⚠️ Insulin LOWERS blood glucose. Students often confuse insulin and glucagon. Remember: Insulin In = glucose goes IN to cells (blood levels drop).

    >

    > ⚠️ The nephron filters blood; it does NOT just remove waste. It also actively reabsorbs water and nutrients — this is how the body conserves resources.


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    Earth Science


    Summary

    Earth science on the TEAS covers the rock cycle, plate tectonics, the atmosphere, and the distinction between weather and climate. Understanding the mechanisms that drive Earth's processes is key.


    Key Concepts


    #### The Rock Cycle

    | Rock Type | Formation Process | Example |

    |---|---|---|

    | Igneous | Cooling and solidification of magma or lava | Granite, basalt |

    | Sedimentary | Compaction and cementation of sediment layers | Limestone, sandstone |

    | Metamorphic | Heat and/or pressure transforms existing rock | Marble, slate |


    #### Plate Tectonics

  • • Driving force — Convection currents in the mantle

    • - Hot material rises → spreads → cools → sinks → repeats

  • • Divergent boundaries — Plates move apart; new crust forms
  • • Convergent boundaries — Plates collide; one may subduct
  • • Transform boundaries — Plates slide past each other

    • #### Earth's Atmosphere Layers (Bottom to Top)

    1. Troposphere — Where most weather occurs (0–12 km); temperature decreases with altitude

    2. Stratosphere — Contains the ozone layer

    3. Mesosphere — Meteors burn up here

    4. Thermosphere — Very high temperatures; auroras occur here

    5. Exosphere — Outermost layer; merges with space


    #### The Greenhouse Effect

  • • Atmospheric gases trap solar heat, warming Earth's surface
  • • Most abundant greenhouse gas — Water vapor (H₂O)
  • • Most discussed in climate change — Carbon dioxide (CO₂)
  • • Other greenhouse gases: methane (CH₄), nitrous oxide (N₂O)

    • #### Weather vs. Climate

    | | Weather | Climate |

    |---|---|---|

    | Time scale | Short-term (hours/days) | Long-term (decades) |

    | Scope | Specific location | Regional/global averages |

    | Example | "It is raining today" | "This region receives 40 inches of rain per year" |


    Key Terms

  • • Magma — Molten rock beneath Earth's surface
  • • Lava — Magma that has reached the surface
  • • Subduction — When one tectonic plate slides beneath another
  • • Convection — Heat transfer through circular movement of fluid/gas
  • • Ozone layer — Absorbs harmful UV radiation; located in the stratosphere

    • Watch Out For

    > ⚠️ Water vapor is the MOST ABUNDANT greenhouse gas, but CO₂ is the primary driver of human-caused climate change. Know both facts — the TEAS may ask about each specifically.

    >

    > ⚠️ Weather ≠ Climate. One cold day does not disprove climate trends. Weather is short-term; climate is long-term.

    >

    > ⚠️ All weather occurs in the TROPOSPHERE. Although other layers exist above it, the troposphere is where temperature inversions, precipitation, and storms happen.


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    Quick Review Checklist


    Use this checklist before your exam. Check off each item when you feel confident:


    Cell Biology

  • • [ ] I can distinguish prokaryotic from eukaryotic cells
  • • [ ] I know the function of mitochondria, ribosomes, and the cell membrane
  • • [ ] I can explain osmosis and the direction of water movement
  • • [ ] I can list the phases of mitosis and describe what happens in metaphase
  • • [ ] I can compare aerobic vs. anaerobic respiration by ATP yield

    • Genetics & Heredity

  • • [ ] I can work out a monohybrid cross and state the 3:1 phenotypic ratio
  • • [ ] I can distinguish codominance from incomplete dominance
  • • [ ] I know the difference between genotype and phenotype
  • • [ ] I can name the purine bases (A and G) and explain base pairing rules
  • • [ ] I can explain the central dogma: DNA → RNA → Protein
  • • [ ] I can compare mitosis and meiosis by purpose and daughter cell number

    • Ecosystems & Ecology

  • • [ ] I know that only 10% of energy transfers between trophic levels
  • • [ ] I can define and distinguish mutualism, commensalism, and parasitism
  • • [ ] I can compare primary and secondary succession
  • • [ ] I can explain nitrogen fixation and name a key bacterium involved
  • • [ ] I can explain why keystone species are ecologically critical

    • Human Physiology

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