Biology - StudyReady

Cell Biology

Key structures and processes

Mitochondria: The organelle that produces ATP (energy) through cellular respiration - often called the "powerhouse of the cell."
Nucleus: Contains the cell's DNA and controls gene expression; surrounded by the nuclear envelope.
Ribosomes: Sites of protein synthesis; read mRNA and assemble amino acids into proteins.
Cellular respiration: Glucose + oxygen → carbon dioxide + water + ATP. Occurs in the mitochondria and converts food energy into usable energy.
Photosynthesis: Carbon dioxide + water + light → glucose + oxygen. Occurs in chloroplasts of plant cells; the reverse of respiration in terms of inputs/outputs.
Mitosis: Cell division that produces two genetically identical daughter cells, used for growth and repair. Phases: prophase, metaphase, anaphase, telophase.
Meiosis: Cell division that produces four genetically distinct sex cells (gametes) with half the chromosome number - the basis of sexual reproduction.

Genetics

Inheritance vocabulary

Term	Meaning
Allele	A version of a gene (e.g., the brown-eye allele vs. the blue-eye allele)
Genotype	The genetic makeup of an organism (e.g., Bb)
Phenotype	The observable trait produced by a genotype (e.g., brown eyes)
Dominant / Recessive	A dominant allele masks a recessive one when both are present (Bb shows the dominant trait)
Homozygous / Heterozygous	Two identical alleles (BB or bb) vs. two different alleles (Bb)
Punnett square	A grid used to predict the probability of offspring genotypes from a genetic cross

DNA is transcribed into mRNA in the nucleus, then translated into a protein by ribosomes - the process is called the "central dogma": DNA → RNA → Protein.

Evolution

Natural selection concepts

Natural selection: Individuals with traits better suited to their environment survive and reproduce more, passing those traits to offspring over generations.
Adaptation: A trait that improves an organism's chance of survival and reproduction in its environment.
Speciation: The process by which populations evolve to become distinct species, often after geographic separation.
Common ancestor: A shared ancestor from which two or more species have evolved, evidenced by comparative anatomy and DNA.

Ecology

Ecosystem terms

Term	Meaning
Producer	Organism that makes its own food, usually via photosynthesis (e.g., plants, algae)
Consumer	Organism that eats other organisms for energy (herbivore, carnivore, omnivore)
Decomposer	Breaks down dead organic matter, recycling nutrients back into the ecosystem
Food web	A network of interconnected food chains showing energy flow through an ecosystem
Carrying capacity	The maximum population size an environment can sustain given its resources

Common Mistakes

Where students go wrong in biology

Patterns we see again and again in student work. Each one is fixable once you know to look for it.

Memorizing terms without the process: Knowing that "anaphase" is a phase of mitosis is worth very little. Knowing that sister chromatids separate during anaphase, and why that matters for producing two identical cells, is what tests ask. For every term, make sure you can say what happens and why it matters.
Confusing mitosis and meiosis: They share phase names and look similar in diagrams. The differences are the point: mitosis produces two identical diploid cells for growth and repair; meiosis produces four genetically different haploid cells for reproduction, with crossing over and two rounds of division. Make a two-column comparison and learn it as a pair.
Mixing up diffusion, osmosis, and active transport: Diffusion is any substance moving down its concentration gradient. Osmosis is specifically water across a membrane. Active transport moves substances against the gradient and costs ATP. The question to ask about any movement across a membrane is: which direction relative to the gradient, and does it use energy?
Treating natural selection as intentional: "Giraffes evolved long necks to reach leaves" is wrong in a way graders notice. Individuals with longer necks survived and reproduced more, so the trait became more common. Selection acts on variation that already exists; organisms do not evolve on purpose.
Skipping the diagrams: Biology exams are full of diagram questions. Cover the labels on every diagram in your notes and reproduce them from memory. Then try to draw the whole diagram unprompted. This takes minutes and is worth more than rereading the chapter.