Biology 11

The levels run: cell → tissue → organ → organ system → organism → population → community → ecosystem — each level is made of the one before it working together.

The nucleus stores DNA and controls the cell's activities; mitochondria break down food molecules to release usable energy (ATP); ribosomes build proteins.

Sexual reproduction combines genetic material from two parents through the fusion of sex cells (gametes), producing offspring that are a genetic mix of both — never identical to either parent.

Asexual reproduction comes from a single parent with no fusion of gametes, so offspring are genetically identical clones of that one parent.

Cellular respiration breaks down glucose in the presence of oxygen to yield usable energy (ATP) and carbon dioxide as a waste product — this is the process almost every cell uses to power its work.

Microevolution is change within a species that occurs over time in a population — driven by adaptation to changing environments and by changes in DNA (mutations) that create new genetic variation.

Speciation is the origin of new species, occurring when populations become reproductively isolated — they can no longer interbreed and produce fertile offspring — often after being geographically separated for many generations.

Artificial selection is humans choosing which individuals breed based on desired traits (like a farmer breeding the largest, fastest-growing canola plants) — it uses existing natural variation, just like natural selection, but humans pick the "winners" instead of the environment.

Adaptation happens at the population level, not to a single individual during its lifetime — individuals with traits suited to a NEW condition survive and reproduce more, so the population's traits shift over generations.

Neo-Darwinism (gradualism) describes slow, steady accumulation of small changes; punctuated equilibrium describes long periods of little change interrupted by relatively rapid bursts of speciation.

A single-celled (unicellular) organism performs every life function — feeding, moving, responding, reproducing — inside just one cell, and can be prokaryotic (like bacteria) or eukaryotic (like an amoeba).

Over deep evolutionary time, life has trended from simple single-celled organisms toward organisms showing greater symmetry, a body cavity (coelom), tissue development, cephalization (concentration of sensory organs and a "head" end), and vascularization (specialized transport tissues).

A phylogenetic tree is a diagram showing the evolutionary relationships between species, with branch points representing common ancestors.

Taxonomy classifies organisms into a nested hierarchy of ranks — kingdom, phylum, class, order, family, genus, species — from broadest group to most specific.

A phylogenetic tree (cladogram) is built from shared characteristics to show which species share more recent common ancestors, with each branch point representing a split.

Significant figures are the digits in a measurement that carry real meaning about its precision — all non-zero digits are significant, zeros between non-zero digits are significant, and leading zeros are never significant.

Every measurement carries some uncertainty — a range around the reported value showing how much it could reasonably vary, usually based on the smallest increment the measuring tool can read.

Scientific notation writes a number as a value between 1 and 10 multiplied by a power of 10, making very large or very small quantities compact and precise, like 8 × 10⁻⁶ m for a red blood cell's diameter.

A calculated result (e.g., a cell count divided by an area) cannot be more precise than the least precise measurement that went into it — the final answer must be rounded to match the smallest number of significant figures among the original measurements.

Accuracy means how close a measurement is to the true value; precision means how close repeated measurements are to each other — a set of measurements can be precise without being accurate, or accurate on average without being precise.