Living Environment Regents Review Sheet

Life is chemistry with a purpose. Cells to systems to ecosystems, all obeying the same core rules.

Practice Living Environment free Reference & formulas

Big ideas

All living things maintain HOMEOSTASIS — a stable internal state. Every disease is a failure of homeostasis.
DNA → RNA → Protein. Proteins do everything. Change the DNA, you change the protein, you change the trait.
Every ecosystem is a nutrient cycle. Matter cycles, energy flows one-way (sun → producer → consumer → decomposer).

Cells & homeostasis

The cell is the basic unit of life. It's also a beautifully organized chemistry factory.

Cell parts

Nucleus stores DNA. Ribosomes make proteins. Mitochondria make ATP. Membrane controls what goes in/out. Chloroplasts (plants only) make sugar.

Example: Where is DNA? → Nucleus

Membrane transport

Passive: high to low concentration (no energy). Active: low to high (uses ATP). Osmosis = water diffusion.

Example: Cell in salt water — water goes which way? → OUT (high water inside → low water outside)

Homeostasis

Steady state despite change. Blood sugar, temperature, pH all regulated. Feedback loops = the mechanism.

Example: Sweating in heat? → Homeostatic response — cools the body

Enzymes

Protein catalysts. Lock-and-key with substrate. Denatured by heat, pH extremes.

Example: Fever above 105°F → Enzymes denature — deadly

Trap: Prokaryote vs eukaryote: prokaryote has no nucleus (bacteria). Eukaryote has a nucleus (plants, animals, us).

Tip: Enzyme names usually end in '-ase.' Lactase digests lactose. Amylase digests amylose (starch).

Photosynthesis & respiration

Photosynthesis stores sun energy in glucose. Respiration cashes it in for ATP.

Photosynthesis

6CO_2 + 6H_2O \xrightarrow{sunlight} C_6H_{12}O_6 + 6O_2

In chloroplasts. Uses CO₂, water, sunlight → makes glucose + oxygen.

Example: Source of O₂ we breathe? → Photosynthesis (plants + algae)

Cellular respiration

C_6H_{12}O_6 + 6O_2 \to 6CO_2 + 6H_2O + \text{ATP}

In mitochondria. Opposite of photosynthesis. Releases usable energy (ATP).

Example: Why do we breathe out CO₂? → Waste of cellular respiration

Aerobic vs anaerobic

Aerobic: with oxygen, lots of ATP. Anaerobic: without oxygen, less ATP + byproducts (lactic acid, alcohol).

Example: Sore muscles after sprinting? → Anaerobic → lactic acid

Trap: Plants ALSO do cellular respiration. They photosynthesize during day AND respire 24/7.

Tip: If ATP is asked about, respiration. If glucose creation, photosynthesis. If both, plants.

Genetics & protein synthesis

DNA is the instruction book. Proteins are what get built. Alleles come in pairs.

DNA vs RNA

DNA: double helix, T pairs with A, G with C. RNA: single strand, U replaces T.

Example: DNA strand ATG. Complementary strand? → TAC

Protein synthesis

Transcription: DNA → mRNA (in nucleus). Translation: mRNA → protein (at ribosome). Three-base 'codons' each specify one amino acid.

Example: Where does translation happen? → Ribosome

Mutations

Change in DNA. May be silent, harmful, or beneficial. Point (one base) or frameshift (add/remove a base — shifts everything).

Example: Insertion of one base in the middle of a gene? → Frameshift — usually disastrous

Punnett squares

Dominant (capital) mask recessive (lowercase). Cross parents' alleles, count offspring ratios.

Example: Cross Bb × Bb → 1 BB : 2 Bb : 1 bb → 3 dominant : 1 recessive

Trap: Genotype = actual alleles (Bb). Phenotype = what you see (brown eyes). Don't mix them up.

Tip: For 'sex-linked' traits (like color blindness), think X and Y. Males have XY — only one X, so recessive traits show up.

Evolution & classification

Descent with modification, driven by natural selection. Small changes, huge time, big diversity.

Natural selection

Variation exists → some traits help survival/reproduction → those alleles increase → population changes over generations.

Example: Antibiotic-resistant bacteria? → Selection: resistant survive, reproduce, take over

Evidence of evolution

Fossil record, homologous structures (similar bones, different jobs), embryology, molecular DNA similarities.

Example: Whale flipper and human arm share bones? → Homologous — common ancestor

Speciation

Two groups isolated → different selection pressures → gene pools diverge → can no longer interbreed.

Example: Two lizard populations on different islands → May evolve into separate species

Biodiversity

More species = more stable ecosystem. Diversity = insurance against disease and change.

Example: Monoculture farming — vulnerable to? → Disease wiping out the whole crop

Trap: Individuals don't evolve — populations do. Natural selection acts on the population's gene pool.

Tip: Structural adaptations (webbed feet), behavioral (migration), and physiological (making venom) are three types.

Ecology & cycles

Everything is connected. Energy flows one direction; matter cycles.

Food chain / web

Producer (photosynthesizer) → primary consumer (herbivore) → secondary (carnivore) → tertiary. Decomposers recycle everything.

Example: Grass → rabbit → fox. Fox is what? → Secondary consumer

10% rule

Only ~10% of energy passes to the next trophic level. Rest lost as heat.

Example: Why fewer top predators than herbivores? → Less energy makes it up the chain

Carbon cycle

Photosynthesis pulls CO₂ from air. Respiration/decomposition/combustion puts it back. Burning fossil fuels adds MORE — climate change.

Example: Main human contribution to climate change? → Burning fossil fuels (excess CO₂)

Symbiosis

Mutualism (both benefit), commensalism (one benefits, other neutral), parasitism (one benefits, other harmed).

Example: Bees and flowers? → Mutualism

Trap: Energy pyramids narrow going up. If a base has 10,000 kcal, top has ~10 kcal (3 levels × ÷10).

Tip: Regents loves the 4 mandated labs: Beaks of Finches (evolution), Diffusion, Relationships & Biodiversity (DNA & evolution), Making Connections (heart rate).

Human body systems

Every system has a job in maintaining homeostasis. Learn the job and the ORGANS follow.

Circulatory

Heart pumps blood. Arteries carry AWAY from heart, veins toward. Red cells carry O₂ (hemoglobin), white cells fight infection.

Example: Blood returning to heart from body? → In veins

Respiratory

Lungs exchange gases with blood. Alveoli = tiny air sacs where O₂ enters blood and CO₂ leaves.

Example: Where does gas exchange happen in lungs? → Alveoli

Digestive

Break food into absorbable pieces. Mouth → stomach (acid + enzymes) → small intestine (main absorption) → large intestine (water reabsorbed).

Example: Where are nutrients absorbed? → Small intestine

Nervous & endocrine

Nervous = fast signals (electrical). Endocrine = slow, long-lasting (hormones through blood).

Example: Insulin regulating blood sugar? → Endocrine (hormone)

Immune

White blood cells + antibodies fight infection. Vaccine = weakened pathogen → memory cells → future protection.

Example: Why does the flu shot work? → Memory cells 'recognize' the flu next time

Trap: Arteries carry AWAY from heart (both letter A). Veins carry back TO heart.

Tip: Pulmonary artery is the ONE artery that carries deoxygenated blood — it's going from heart to lungs.

Frequently asked questions

How should I study for the Living Environment Regents?

Work real past-exam questions by topic, review this one-page summary of the must-know concepts, and read the worked solution every time you miss one. The exam reuses the same ideas year after year.