NY Regents Life Science: Biology cheat sheet

Cell theory: all living things are made of cells, the cell is the basic unit of structure and function, and all cells come from preexisting cells.

Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells have a nucleus and membrane-bound organelles such as mitochondria and chloroplasts.

Cell membrane is a phospholipid bilayer with embedded proteins; it is selectively permeable, controlling what enters and leaves the cell.

Mitochondria carry out aerobic cellular respiration, converting glucose and oxygen into ATP, carbon dioxide, and water.

Chloroplasts carry out photosynthesis: light energy + CO2 + H2O yields glucose + O2, using chlorophyll to absorb light.

Ribosomes assemble proteins from amino acids using mRNA instructions; they are found free in the cytoplasm and on the rough endoplasmic reticulum.

Enzymes are proteins that lower activation energy; each has an active site whose shape determines specificity, and activity depends on temperature and pH.

Surface area to volume ratio decreases as cells grow larger, limiting diffusion efficiency and constraining cell size.

In multicellular organisms, cells differentiate and specialize into tissues, organs, and organ systems that work together to maintain homeostasis.

DNA is a double helix of nucleotides (sugar, phosphate, base); complementary base pairing is A-T and C-G.

DNA replication is semi-conservative: each new molecule contains one original strand and one newly synthesized strand.

Gene expression: DNA is transcribed to mRNA in the nucleus, then translated to protein at ribosomes using codons (three bases per amino acid).

Mutations are changes in DNA sequence; substitutions may alter one amino acid, while insertions or deletions can cause frameshifts.

Mendelian rules: alleles segregate during meiosis, and alleles for different genes assort independently when genes are on different chromosomes.

A monohybrid cross of two heterozygotes (Aa x Aa) yields a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

Genotype is the allele combination; phenotype is the observable trait, influenced by genotype and environment.

Sex-linked traits are carried on sex chromosomes; X-linked recessive traits appear more often in males, who have only one X.

Human chromosomes come in homologous pairs (46 total, 23 pairs); gametes are haploid (23) and form by meiosis, creating genetic variation through crossing over and independent assortment.

Natural selection requires heritable variation, competition for limited resources, and differential reproductive success across generations.

Fitness is measured by reproductive success, not strength or lifespan; traits that increase survival and reproduction become more common.

Evidence for evolution includes fossils, comparative anatomy (homologous structures), embryology, DNA and protein sequence comparisons, and observed change.

Homologous structures share ancestry but may differ in function; analogous structures share function but not ancestry (convergent evolution).

Speciation occurs when populations become reproductively isolated, often through geographic separation, accumulating genetic differences.

Genetic drift is random change in allele frequency, strongest in small populations; gene flow moves alleles between populations.

Classification hierarchy: domain, kingdom, phylum, class, order, family, genus, species; scientific names use binomial nomenclature (genus + species).

Organisms are grouped into three domains (Bacteria, Archaea, Eukarya) based largely on molecular and cell-structure evidence.

Antibiotic resistance spreads because resistant bacteria survive treatment and reproduce, increasing the proportion of resistant individuals.

In food chains, energy flows from producers to consumers; only about 10% transfers between trophic levels, so higher levels support fewer organisms.

Photosynthesis and cellular respiration form the carbon cycle: producers fix CO2 into organic matter, and respiration releases it.

Producers (autotrophs) make their own food; consumers (heterotrophs) obtain energy by eating other organisms; decomposers recycle nutrients.

Carrying capacity is the maximum population an ecosystem can sustain; limiting factors include food, water, space, and disease.

Population growth: exponential growth occurs with unlimited resources; logistic growth levels off at carrying capacity.

Symbiosis types: mutualism (both benefit), commensalism (one benefits, other unaffected), parasitism (one benefits, other harmed).

Ecological succession: primary succession begins on bare rock with pioneer species; secondary succession follows a disturbance where soil remains.

Biodiversity increases ecosystem stability; keystone species have effects on the community disproportionate to their abundance.

Burning fossil fuels releases carbon dioxide, a greenhouse gas that traps heat and drives global climate change.

Eutrophication: excess nitrogen and phosphorus runoff causes algal blooms, oxygen depletion, and dead zones in waterways.

Biological magnification concentrates toxins such as mercury and DDT in higher trophic levels.

Invasive species outcompete native species, disrupt food webs, and reduce biodiversity because they lack natural predators.

Habitat destruction and fragmentation are leading causes of species extinction and biodiversity loss.

Sustainable practices include renewable energy, recycling, reducing emissions, and managing resources so they can regenerate.

Ozone depletion is caused by chlorofluorocarbons (CFCs); the ozone layer shields organisms from harmful ultraviolet radiation.

Acid rain forms when sulfur and nitrogen oxides react with water vapor, lowering soil and water pH and damaging organisms.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant.

A valid experiment includes a control group for comparison and enough replicates to reduce the effect of random variation.

A hypothesis is a testable prediction; it is supported or rejected by data, never proven absolutely.

Reliable data come from repeated trials, large sample sizes, and objective measurement; bias is reduced by random sampling and blinding.

Graph choice: line graphs show continuous change, bar graphs compare categories, and scatter plots show correlation between two variables.

Correlation does not establish causation; a controlled experiment is needed to demonstrate cause and effect.

Engineering design cycle: define the problem, design a solution, build a prototype, test, evaluate, and iterate to improve.

Crosscutting concepts include cause and effect, structure and function, systems, patterns, energy and matter flow, and stability and change.

Scale and proportion matter: molecular, cellular, organismal, and ecosystem levels each reveal different patterns.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant.

A valid experiment includes a control group for comparison and enough replicates to reduce the effect of random variation.

A hypothesis is a testable prediction; it is supported or rejected by data, never proven absolutely.

Reliable data come from repeated trials, large sample sizes, and objective measurement; bias is reduced by random sampling and blinding.

Graph choice: line graphs show continuous change, bar graphs compare categories, and scatter plots show correlation between two variables.

Correlation does not establish causation; a controlled experiment is needed to demonstrate cause and effect.

Engineering design cycle: define the problem, design a solution, build a prototype, test, evaluate, and iterate to improve.

Crosscutting concepts include cause and effect, structure and function, systems, patterns, energy and matter flow, and stability and change.

Scale and proportion matter: molecular, cellular, organismal, and ecosystem levels each reveal different patterns.