Armenia Biology Unified Exam cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; their DNA lies in a nucleoid region.

Eukaryotic cells compartmentalize functions into organelles bounded by membranes, enabling incompatible reactions to coexist.

Mitochondria and chloroplasts are double-membrane organelles; chloroplasts additionally contain thylakoid stacks (grana).

The plasma membrane follows the fluid-mosaic model: a phospholipid bilayer with embedded and peripheral proteins.

Ribosomes are non-membranous and are the site of protein synthesis; free ribosomes make cytosolic proteins, bound ribosomes make secreted or membrane proteins.

Plant cells possess a cellulose cell wall, a large central vacuole, and plastids; animal cells possess centrioles and lysosomes.

The cell theory states: all organisms are made of cells, the cell is the basic unit of life, and cells arise from pre-existing cells.

Osmosis is water movement across a semipermeable membrane from low to high solute concentration; plasmolysis occurs in hypertonic plant cells.

ATP is the universal energy currency; hydrolysis of one ATP to ADP plus Pi releases about 30–40 kJ/mol under cellular conditions.

Glycolysis occurs in the cytosol, converts one glucose to two pyruvate, and yields a net 2 ATP and 2 NADH.

The Krebs cycle runs in the mitochondrial matrix and yields per acetyl-CoA: 3 NADH, 1 FADH2, 1 GTP/ATP, and 2 CO2.

Oxidative phosphorylation on the inner mitochondrial membrane uses the electron transport chain and chemiosmosis; oxygen is the final electron acceptor.

Complete aerobic oxidation of one glucose yields about 30–38 ATP; anaerobic fermentation yields only 2 ATP per glucose.

Photosynthesis has light reactions in the thylakoid membrane (producing ATP, NADPH, O2) and the Calvin cycle in the stroma (fixing CO2).

Enzymes lower activation energy without altering reaction equilibrium; they are not consumed and are sensitive to pH and temperature.

Catabolic reactions release energy by breaking down molecules; anabolic reactions consume energy to build molecules.

Mendel's law of segregation: two alleles of a gene separate during gamete formation, so each gamete carries one allele.

Mendel's law of independent assortment applies to genes on different chromosomes or far apart on the same chromosome.

A monohybrid cross of two heterozygotes (Aa × Aa) gives a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio.

A dihybrid cross of double heterozygotes (AaBb × AaBb) gives a 9:3:3:1 phenotypic ratio with independent assortment.

A test cross (cross with a homozygous recessive) reveals whether a dominant-phenotype individual is homozygous or heterozygous.

Sex-linked traits are carried on sex chromosomes; X-linked recessive traits appear more often in males because males are hemizygous.

Codominance shows both alleles equally (AB blood type); incomplete dominance shows an intermediate phenotype.

Linked genes are on the same chromosome and tend to be inherited together; crossing over during meiosis separates them.

DNA is a double helix of antiparallel strands; adenine pairs with thymine (2 H-bonds) and guanine with cytosine (3 H-bonds).

DNA replication is semiconservative and proceeds 5' to 3' on the new strand via DNA polymerase.

Transcription copies DNA into mRNA using RNA polymerase; uracil replaces thymine in RNA.

Translation occurs on ribosomes: mRNA codons are read three bases at a time, and tRNA delivers matching amino acids.

The genetic code is degenerate (multiple codons per amino acid), non-overlapping, and nearly universal.

A mutation is a change in DNA sequence; substitutions may be silent, missense, or nonsense, while insertions/deletions can cause frameshifts.

The central dogma runs DNA → RNA → protein; retroviruses reverse-transcribe RNA back to DNA.

The lac operon is induced when lactose is present and glucose is absent, illustrating gene regulation in prokaryotes.

Asexual reproduction produces genetically identical offspring via mitosis (e.g., binary fission, budding, vegetative propagation).

Sexual reproduction combines haploid gametes to form a diploid zygote, generating genetic variation.

Meiosis halves the chromosome number, producing four haploid cells from one diploid cell over two divisions.

Crossing over occurs in prophase I between homologous chromosomes; independent assortment occurs in metaphase I.

Spermatogenesis yields four sperm per primary spermatocyte; oogenesis yields one ovum plus polar bodies.

Fertilization restores the diploid chromosome number; in humans this is 46 (23 from each parent).

In plants, the alternation of generations alternates a diploid sporophyte with a haploid gametophyte.

Double fertilization in angiosperms produces a diploid zygote and a triploid endosperm.

Fertilization is followed by cleavage, a series of mitotic divisions producing a blastula without growth in total size.

Gastrulation forms the three germ layers: ectoderm (outer), mesoderm (middle), and endoderm (inner).

Ectoderm gives rise to the nervous system and epidermis; mesoderm to muscle, bone, and blood; endoderm to the gut lining and internal organs.

Organogenesis follows gastrulation, in which germ layers differentiate into organs and tissues.

Direct development produces a juvenile resembling the adult; indirect development passes through a larval stage (metamorphosis).

Embryonic induction is the influence of one tissue on the differentiation of another (e.g., the notochord inducing the neural tube).

The notochord induces formation of the neural tube, whose failure to close can produce neural tube defects.

Postembryonic development includes growth, regeneration, and aging; apoptosis is programmed cell death essential to normal development.

The plant body has three basic organs: roots (absorption and anchorage), stems (support and transport), and leaves (photosynthesis).

Xylem transports water and dissolved minerals upward; phloem transports sugars bidirectionally.

Stomata, flanked by guard cells, regulate gas exchange and transpiration; they open when guard cells are turgid.

Transpiration pull drives water movement through xylem, driven by cohesion, adhesion, and evaporation from leaves.

Nonvascular plants (bryophytes) lack true vascular tissue; seedless vascular plants (ferns) have xylem and phloem but no seeds.

Gymnosperms bear naked seeds in cones; angiosperms bear seeds enclosed in fruit and reproduce via flowers.

Monocots have one cotyledon, parallel leaf veins, and scattered vascular bundles; dicots have two cotyledons, netted veins, and ring-arranged bundles.

Root hairs increase absorptive surface area; the root cap protects the growing tip.

Invertebrate groups include sponges (Porifera), cnidarians, flatworms, annelids, mollusks, arthropods, and echinoderms.

Arthropods have an exoskeleton of chitin, segmented bodies, and jointed appendages; they are the most species-rich phylum.

Vertebrate classes are fishes, amphibians, reptiles, birds, and mammals; all possess a vertebral column.

Open circulatory systems bathe organs in hemolymph (arthropods, most mollusks); closed systems keep blood in vessels (annelids, vertebrates).

Bilateral symmetry (with a head end) is associated with cephalization; radial symmetry appears in cnidarians and adult echinoderms.

Ectotherms rely on environmental heat; endotherms generate metabolic heat (birds and mammals).

Gas exchange occurs via gills in fish, skin and lungs in amphibians, and lungs in reptiles, birds, and mammals.

The amniotic egg, with membranes protecting the embryo, is a key adaptation allowing reptiles, birds, and mammals to reproduce on land.

The human body has 11 organ systems; blood is a connective tissue with plasma, red cells, white cells, and platelets.

The heart has four chambers; the left ventricle pumps oxygenated blood to the body via the aorta.

Gas exchange occurs in the alveoli, thin-walled sacs where oxygen diffuses into blood and carbon dioxide diffuses out.

Nephrons in the kidneys filter blood; the loop of Henle creates a concentration gradient enabling water reabsorption.

The nervous system has a central part (brain and spinal cord) and a peripheral part (somatic and autonomic divisions).

The autonomic nervous system splits into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) branches.

Hormones act via the endocrine system; insulin lowers blood glucose while glucagon raises it.

The small intestine is the main site of nutrient absorption; villi increase its surface area.

Natural selection requires heritable variation, differential reproductive success, and overproduction of offspring.

Darwin's mechanism is descent with modification from common ancestors.

Homologous structures share ancestry though they may differ in function (e.g., forelimbs of vertebrates); analogous structures share function but not ancestry.

Fossils, biogeography, comparative anatomy, and molecular data support common descent.

The Hardy-Weinberg principle states allele frequencies stay constant in a large, randomly mating population with no mutation, migration, or selection.

Speciation occurs when reproductive isolation arises between populations, often after geographic separation (allopatric speciation).

Genetic drift is random change in allele frequency, strongest in small populations; the founder effect is a form of it.

Directional, stabilizing, and disruptive selection are three modes of natural selection acting on phenotypic variation.

An ecosystem consists of a community of organisms and the abiotic environment interacting together.

Energy flows one way through trophic levels; only about 10% passes from one level to the next, forming a pyramid of energy.

Producers (autotrophs) capture energy; consumers (heterotrophs) obtain energy by eating other organisms.

Decomposers break down dead organic matter, recycling nutrients such as carbon and nitrogen.

A population's size is shaped by births, deaths, immigration, and emigration; carrying capacity limits growth in a given environment.

Interspecific interactions include competition, predation, parasitism, mutualism, and commensalism.

Primary succession begins on bare substrate (e.g., bare rock); secondary succession follows a disturbance that leaves soil intact.

Biodiversity includes genetic, species, and ecosystem diversity; it supports ecosystem stability and resilience.

The biosphere is the zone of life on Earth, spanning the lower atmosphere, hydrosphere, and upper lithosphere.

Biogeochemical cycles include the carbon, nitrogen, phosphorus, and water cycles, moving matter between living and nonliving reservoirs.

Burning fossil fuels releases stored carbon as CO2, driving the greenhouse effect and climate change.

Eutrophication occurs when excess nutrients (nitrogen, phosphorus) cause algal blooms and oxygen depletion in water bodies.

The greenhouse effect is natural and necessary; human-emitted greenhouse gases intensify it and raise global temperatures.

Ozone in the stratosphere shields life from ultraviolet radiation; ozone depletion is caused mainly by CFCs.

Conservation strategies include protected areas, sustainable resource use, and restoration of degraded habitats.

Sustainable development meets present needs without compromising the ability of future generations to meet theirs.