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High School Biology: talk through cells, genetics, and ecology
This course covers a full year of high school biology aligned to the NGSS life science standards: the chemistry of life and DNA, cell structure and energy transformations, genetics and biotechnology, evolution, and ecosystems and matter cycling. It also includes engineering design practice applied to biology problems, like evaluating a solution for food security or building a simulation to test a biodiversity policy, the way HS-ETS1 asks.
A lesson works through one idea at a time. The tutor asks you to explain what you already know, for instance how diffusion might move oxygen across a membrane, then adjusts based on what you actually say. You get stopped before memorizing a definition you can't yet use, and pushed to say the reasoning out loud: why a Punnett square predicts a ratio, why fermentation yields less ATP than aerobic respiration, why a population graph bends into an S-curve.
Who it is for
- Students taking a first high school biology course, including NGSS-based curricula
- Students prepping for an end-of-course biology exam or AP Biology prerequisites
- Homeschooling families wanting a structured, discussion-based biology course
- Teachers looking for extra one-on-one practice material for students who need it
- Students who want to talk through genetics problems or evolution reasoning rather than just read about them
What you will be able to do
- Explain how DNA structure leads to proteins through transcription and translation
- Compare passive and active transport and predict which way substances move across a membrane
- Trace energy through photosynthesis, cellular respiration, and fermentation with the ATP accounting for each
- Work Punnett squares and probability problems for monohybrid, dihybrid, and non-Mendelian inheritance
- Explain natural selection as a mechanism and use Hardy-Weinberg equations to track allele frequencies
- Evaluate a proposed solution to a human impact on an ecosystem using prioritized criteria and trade-offs
A taste of a lesson on Cellular respiration
The tutor asks, you answer, and it works from what you actually said. No videos to sit through.
The 30 topics in Biology
Each topic builds on the ones before it. The tutor checks what you already know and starts there.
Engineering design and analyzing global challenges
Introduce the engineering design cycle as used in science courses. Teach how to analyze a major global challenge (e.g., food security, disease, water quality) and specify qualitative and quantitative criteria and constraints that account for societal needs and wants. Teach how to break a complex problem into smaller solvable sub-problems. Students should be able to state criteria, constraints, and sub-problems for a biology-related challenge.
Evaluating solutions with prioritized criteria and trade-offs
Teach how to evaluate a proposed solution against prioritized criteria and trade-offs, including cost, safety, reliability, aesthetics, and social, cultural, and environmental impacts. Students should be able to rank criteria, weigh trade-offs across a range of constraints, and justify a decision with evidence.
Builds on Engineering design and analyzing global challenges
Computer simulation of interacting systems and model limits
Teach how computer simulations model the impact of proposed solutions on interacting systems with numerous criteria and constraints. Students learn to identify variables, parameters, and outputs, run a simple simulation, and explain what a simulation can and cannot show, including its assumptions and limits.
Builds on Evaluating solutions with prioritized criteria and trade-offs
Water, macromolecules, and carbon-based molecules
Teach the key chemistry needed for biology: water's polarity and hydrogen bonding, the role of carbon's bonding versatility, and the four classes of biological macromolecules (carbohydrates, lipids, proteins, nucleic acids) with their monomers and linkages. Include how carbon, hydrogen, and oxygen from simple inorganic molecules such as methane, ammonia, water, and hydrogen sulfide can combine with nitrogen and sulfur to form amino acids and other large carbon-based molecules (as in the Miller-Urey experiment), and that this requires evidence such as the Miller-Urey experiment and meteorite amino acids, revised as understanding grows.
DNA structure and protein synthesis
Teach the double-helix structure of DNA (nucleotides, base pairing A-T and G-C, antiparallel strands), and the central dogma: transcription of DNA into mRNA and translation of mRNA into proteins using the genetic code and codons, with tRNA and ribosomes. Teach how the sequence of DNA determines the sequence of amino acids and therefore protein shape and function, and how proteins (enzymes, structural proteins, receptors) carry out essential life functions. Students should construct an evidence-based explanation linking DNA structure to protein structure.
Builds on Water, macromolecules, and carbon-based molecules
Enzymes and protein structure-function
Teach protein structure levels (primary through quaternary) and how shape determines function. Teach enzymes as biological catalysts: active site, lock-and-key/induced fit, lowering activation energy, and factors affecting rate (temperature, pH, substrate concentration, denaturation). Students should explain how a change in amino acid sequence can alter protein shape and function.
Builds on DNA structure and protein synthesis
Cell theory, cell types, and organelle functions
Teach cell theory, prokaryotic versus eukaryotic cells, and the functions of major organelles (nucleus, ER, Golgi, mitochondria, chloroplasts, lysosomes, cytoskeleton). Students should explain how cell structure relates to function, such as why mitochondria have folded membranes (inner membrane surface area for ATP production).
Builds on Enzymes and protein structure-function
Cell membranes and transport
Teach the phospholipid bilayer and fluid mosaic structure, the role of membrane proteins (channels, carriers, receptors), and passive transport (diffusion, osmosis, facilitated diffusion) versus active transport, with concentration gradients. Students should explain why membranes are selectively permeable and predict the direction of water and solute movement across membranes.
Builds on Cell theory, cell types, and organelle functions
Gene regulation and mutation
Teach basic gene regulation: operons in prokaryotes (lac operon as example) and selective gene expression in eukaryotes, including how transcription factors and chromatin state control which genes are expressed, and how regulation links to differentiation. Teach types of mutations (point substitutions, insertions, deletions, frameshifts, silent, missense, nonsense) and how they change protein structure and function, how environmental agents such as radiation and chemicals cause mutations, that most mutations are neutral or harmful, and that some are beneficial.
Builds on DNA structure and protein synthesis, Enzymes and protein structure-function
Cell cycle, mitosis, and cell differentiation
Teach the phases of the cell cycle (interphase G1, S, G2; mitosis PMAT; cytokinesis) and the purpose of mitosis in growth, repair, and replacement. Teach how cell differentiation occurs through selective gene expression so that one zygote produces many specialized cell types, and how checkpoints and errors relate to disease such as cancer. Students should use a model (diagram, flipbook, or physical model) to illustrate how division and differentiation produce and maintain complex organisms.
Builds on DNA structure and protein synthesis, Cell membranes and transport, Gene regulation and mutation
Hierarchical organization and homeostasis
Teach the hierarchy from cells to tissues, organs, organ systems, and organisms, and how the major organ systems (circulatory, respiratory, digestive, nervous, endocrine, immune, etc.) interact. Teach homeostasis and negative feedback (e.g., thermoregulation, blood glucose regulation by insulin and glucagon) versus positive feedback (e.g., childbirth, blood clotting). Students should develop and use a model of organ system interactions and plan a simple investigation providing evidence of feedback control, identifying variables, controls, and data to collect.
Builds on Cell cycle, mitosis, and cell differentiation
Photosynthesis
Teach photosynthesis as the transformation of light energy into stored chemical energy in glucose. Cover the light-dependent reactions (chlorophyll absorbing light, water split, ATP and NADPH produced, oxygen released) and the Calvin cycle (CO2 fixed into sugar using ATP and NADPH), chloroplast structure, and the overall equation. Students should use a model (diagram or energy flow model) to show light energy becoming chemical bond energy.
Builds on Water, macromolecules, and carbon-based molecules, Enzymes and protein structure-function, Cell theory, cell types, and organelle functions
Cellular respiration
Teach cellular respiration as the process breaking bonds of glucose and oxygen and forming bonds in CO2 and water, releasing energy captured as ATP. Cover glycolysis, the citric acid (Krebs) cycle, the electron transport chain and oxidative phosphorylation in mitochondria, and the role of oxygen as final electron acceptor. Teach net energy transfer and the overall equation, and contrast with photosynthesis as complementary processes. Students should use a model to show bond breaking and forming and net energy transfer.
Builds on Enzymes and protein structure-function, Photosynthesis
Fermentation and anaerobic energy release
Teach how cells make ATP without oxygen through fermentation (lactic acid and alcohol fermentation) and why it yields far less ATP than aerobic respiration. Students construct and revise an explanation of how aerobic and anaerobic conditions change energy yield and the products cells make, with examples such as human muscle during intense exercise and yeast in bread or fermentation.
Builds on Cellular respiration
Energy flow, food webs, and trophic levels
Teach producers, consumers, decomposers, trophic levels, food chains and webs, energy pyramids, and the 10 percent rule of energy transfer between trophic levels. Students use percent calculations and energy pyramids to support claims about how energy flows among organisms in an ecosystem and why energy, unlike matter, is not recycled.
Builds on Fermentation and anaerobic energy release
The carbon cycle and matter cycling
Teach the carbon cycle among biosphere, atmosphere, hydrosphere, and geosphere, including photosynthesis, respiration, decomposition, combustion, ocean exchange, and carbonate sediments and fossil fuels. Students develop a model of carbon cycling and explain how matter cycles while energy flows, including how anaerobic processes in wetlands and ocean sediments store carbon.
Builds on Energy flow, food webs, and trophic levels
Population growth, limiting factors, and carrying capacity
Teach exponential growth (J-curve) and logistic growth (S-curve) with carrying capacity, and density-dependent versus density-independent limiting factors. Students use mathematical and computational representations to explain how factors such as food, space, predators, disease, and climate affect carrying capacity at different scales (organism, population, ecosystem). Include the formula for growth rate and interpreting population graphs.
Builds on Energy flow, food webs, and trophic levels
Biodiversity, species interactions, and ecosystem stability
Teach how biodiversity is measured (species richness, evenness, and a simple diversity index) and why diverse ecosystems tend to be more stable. Teach how complex interactions (competition, predation, symbiosis, keystone species) maintain relatively consistent populations in stable conditions, and how changing conditions can shift an ecosystem into a new state through succession and invasive species.
Builds on The carbon cycle and matter cycling, Population growth, limiting factors, and carrying capacity
Group behavior and survival
Teach group behaviors such as herding, schooling, flocking, and cooperation, and why they can increase individual and species chances of survival and reproduction (predator dilution, cooperative hunting, vigilance, kin selection). Students evaluate evidence for these effects, weighing both benefits and costs such as competition for resources within groups.
Builds on Population growth, limiting factors, and carrying capacity
Human impacts on the environment and biodiversity
Teach major human impacts on ecosystems and biodiversity: habitat loss, pollution, climate change, overharvesting, invasive species, and the carbon footprint of fossil fuel use. Students use the engineering design cycle to design, evaluate, and refine a solution that reduces one such impact (e.g., wetland restoration, fish ladders, reducing emissions), applying the criteria and trade-offs approach from the engineering topics.
Builds on Evaluating solutions with prioritized criteria and trade-offs, Biodiversity, species interactions, and ecosystem stability
Meiosis and sources of genetic variation
Teach meiosis I and II, the production of haploid gametes, crossing over in prophase I, and independent assortment. Explain how meiosis creates new genetic combinations, how replication errors (viable errors) and environmentally caused mutations produce heritable variation, and contrast meiosis with mitosis. Students make and defend a claim, supported by evidence, about which mechanisms generate inheritable variation.
Builds on DNA structure and protein synthesis, Cell cycle, mitosis, and cell differentiation
Mendelian genetics and inheritance patterns
Teach Mendel's laws of segregation and independent assortment, alleles, dominant and recessive traits, genotype and phenotype, and Punnett squares for monohybrid and dihybrid crosses. Extend to incomplete dominance, codominance, and sex-linked traits. Students should explain how DNA and chromosomes code instructions for traits passed from parents to offspring and ask clarifying questions about these relationships.
Builds on Meiosis and sources of genetic variation
Genetic engineering and biotechnology applications
Teach how DNA technologies use heredity knowledge: restriction enzymes and gel electrophoresis, PCR, recombinant DNA and transgenic organisms, CRISPR gene editing, and selective breeding. Students ask questions about how DNA and chromosomes code traits and evaluate benefits and risks of biotechnology applications, such as insulin production, crop engineering, and gene therapy.
Builds on Gene regulation and mutation, Mendelian genetics and inheritance patterns
Probability and variation in populations
Teach the product and sum rules of probability as applied to genetics and binomial-type reasoning for offspring ratios. Compare observed and expected offspring counts with a simple difference or ratio comparison, noting that chi-square goodness-of-fit testing is an optional extension. Teach how polygenic and environmental influences produce continuous variation and how frequency distributions (histograms, normal curves) describe traits in a population. Students apply these statistics to explain the variation and distribution of expressed traits.
Builds on Mendelian genetics and inheritance patterns
Evidence for common ancestry and evolution
Teach the multiple independent lines of evidence for common ancestry and biological evolution: fossil record and transitional forms, homologous and vestigial structures, embryological similarities, biogeography, molecular evidence (shared DNA and protein sequences, cytochrome c comparisons), and direct observation (antibiotic resistance, peppered moths). Students communicate how these lines converge to support evolution.
Builds on Gene regulation and mutation
Natural selection and the four factors of evolution
Teach Darwin and Wallace's mechanism: potential for population increase exceeding resources, heritable variation from mutation and recombination, competition for limited resources, and differential survival and reproduction leading to adaptation. Students construct an evidence-based explanation of how natural selection leads to adaptation, using examples such as peppered moths, antibiotic resistance, and the beak of Darwin's finches.
Builds on Probability and variation in populations, Evidence for common ancestry and evolution
Allele frequencies and Hardy-Weinberg equilibrium
Teach how allele frequency (p and q) describes a gene pool, how to calculate genotype frequencies with p^2 + 2pq + q^2 = 1, and Hardy-Weinberg equilibrium as a null model with its five conditions. Teach that evolution is change in allele frequencies in populations and that departures from equilibrium indicate evolutionary forces. Students work simple calculations from data tables.
Builds on Probability and variation in populations, Natural selection and the four factors of evolution
Statistics of advantageous traits over generations
Students apply probability and statistics to show that organisms with an advantageous heritable trait increase in proportion to those without it over generations. Using simple calculations of allele and phenotype frequency change across generations and worked examples and data tables, students track how an advantageous allele's frequency rises under selection.
Builds on Allele frequencies and Hardy-Weinberg equilibrium
Speciation, extinction, and environmental change
Teach how changing environmental conditions can lead to increases in some populations, the emergence of new species through geographic isolation and reproductive isolation over time, and extinction of others. Teach mass extinctions and the role of rapid environmental change. Students evaluate the evidence supporting each of these three outcomes, citing fossil, genetic, and observational data such as Galapagos finches and the five major mass extinctions.
Builds on Human impacts on the environment and biodiversity, Statistics of advantageous traits over generations
Creating simulations to test biodiversity solutions
Teach how to create or revise a computer simulation that tests a proposed solution to reduce adverse human impacts on biodiversity (e.g., modeling the effect of a fishing quota or habitat corridor on a population over time). Students specify variables, parameters, and outputs, run the simulation, and revise the model based on results and its limitations.
Builds on Computer simulation of interacting systems and model limits, Population growth, limiting factors, and carrying capacity, Human impacts on the environment and biodiversity
Practice questions in Biology
A few of the kinds of questions you will work through, with answers.
Why can a water molecule form hydrogen bonds with neighboring water molecules?
See the answer
Because water is polar: oxygen pulls shared electrons more strongly, giving it a slightly negative charge and the hydrogens a slightly positive charge, so opposite partial charges attract.
This polarity, not a full ionic charge, is what lets water molecules hydrogen-bond to each other and to other polar molecules.
A cell is placed in a solution with a much lower solute concentration than its cytoplasm. Which way will water move, and what do we call this solution relative to the cell?
See the answer
Water moves into the cell; the solution is hypotonic.
Water moves by osmosis toward the side with more solute (lower water concentration), so it flows into the cell, which can cause the cell to swell.
Aerobic respiration from one glucose molecule yields roughly how much more ATP than fermentation of the same glucose?
See the answer
Roughly 15 to 18 times more (about 30-ish ATP versus about 2 ATP).
Fermentation only completes glycolysis (net 2 ATP), while aerobic respiration also runs the citric acid cycle and oxidative phosphorylation, extracting far more energy from the same glucose.
In a cross between two heterozygous pea plants (Tt x Tt) for tall (T, dominant) versus short (t), what fraction of offspring are expected to be short?
See the answer
1/4
A Tt x Tt cross gives genotype ratio 1 TT : 2 Tt : 1 tt, and only tt (recessive homozygous) is short, so 1 of 4 offspring.
In a population at Hardy-Weinberg equilibrium, the frequency of the recessive allele q is 0.2. What fraction of the population is expected to be heterozygous?
See the answer
0.32 (32%)
Heterozygote frequency is 2pq; with q = 0.2, p = 0.8, so 2(0.8)(0.2) = 0.32.
A deer population grows exponentially at first but then levels off near the carrying capacity of its habitat. What term describes this leveling-off growth pattern, and name one density-dependent factor that could cause it?
See the answer
Logistic growth (S-curve); a density-dependent factor such as food competition, disease spread, or predation.
As population size approaches carrying capacity, density-dependent factors like limited food intensify and slow growth, producing the characteristic S-shaped curve.
Questions about this subject
Does this course follow NGSS standards?
Yes, it's organized around HS-LS1 through HS-LS4 (molecules and organisms, ecosystems, heredity, and evolution) plus HS-ETS1 engineering design practices applied to biology problems.
Do I need a strong chemistry background first?
No. The course teaches the specific chemistry you need, like water's polarity and the four macromolecule classes, as part of the biology sequence, not as a separate prerequisite.
Does it cover genetics problems like Punnett squares and probability?
Yes, including monohybrid and dihybrid crosses, incomplete dominance, probability rules for offspring ratios, and Hardy-Weinberg calculations for allele frequencies.
Is human anatomy covered in depth?
No, organ systems are covered at the level of how they interact to maintain homeostasis, but detailed human anatomy is outside this course's scope.