Taking the Test (05:47)
The AP Biology test is three hours long with multiple choice and free response sections. Multiple choice has 100 questions and wrong answers are not scored negatively; guessing is advised. Read directions, paying attention to "not," "least," or "most." To answer questions in less than a minute, keep moving and come back to unanswered questions.
Multiple Choice Topic Breakdown (00:53)
Twenty-five percent of the questions cover molecules and cells, including cellular energetics. Another quarter of the questions covers heredity and evolution. The remaining half of multiple choice questions ask about organisms and populations, including ecology and animal structure.
Free Response (06:33)
The free response section takes 90 minutes with a 10 minute reading period, and includes four questions. The questions cover molecules and cells, genetics and evolution, and organisms and populations. Often, a question will require a description of a laboratory experiment; all questions should be answered in essay form.
30 in 30: Water (01:40)
Water is the main component in cells and covers most of the Earth's surface. Water molecules form hydrogen bonds with each other, creating cohesion. Water is less dense in solid form and is a solvent for many substances.
Free Energy Changes (00:39)
Free energy is available energy in a system, and changes depending on temperature and pressure. An equation models and predicts this change.
Prokaryotic and Eukaryotic Cells (02:02)
Prokaryotic cells do not have a nucleus and have few organelles, while eukaryotic cells have a nucleus where genetic material is stored as chromosomes. Organelles perform various cell functions, and include endoplasmic reticulum, golgi apparatus, lysosomes, mitochondria, and cytoplasm. Unlike animal cells, plant cells have chloroplasts and a cell wall.
Plasma membranes are phospholipid bilayers that protect cells. Selectively permeable membranes control passage in and out of a cell. Diffusion and osmosis involve substances moving from an area of high concentration to one of low concentration. Transport requires proteins on the membrane.
Plants convert light energy to chemical energy. Sunlight activates chlorophyll, creating ATP and NADPH, which combine with CO2 to create glucose and oxygen.
Fermentation and Cellular Respiration (01:24)
Cells convert food into usable energy. Aerobic respiration involves glycolysis, Krebs cycle, and oxidative phosphorylation. Anaerobic respiration only involves glycolysis and fermentation.
Cell division in sex cells is called meiosis. A diploid cell divides into to four haploid cells, each with one set of chromosomes. Chromosomes duplicate to produce two attached chromatids, and in successive steps, these separate and cells divide.
Inheritance Patterns (01:46)
Gregor Mendel developed laws of inheritance through pea plant experiments. Learn the law of dominance, the law of separation, and the law of independent assortment.
RNA and DNA Structure and Function (02:41)
DNA is a double helix, with a sugar-phosphate backbone, and nitrogenous base pairs. DNA is transcribed to RNA and then translated into amino acids to become proteins; DNA replicates itself. In translation, codons on mRNA are translated into amino acids.
Gene Regulation (00:44)
All cells in the body have identical DNA, but a system of regulation controls which genes are expressed and where. Specialization depends on modes of gene expression, not different genes.
Mutations arise from changes in nitrogenous bases in a codon. See an example of a missense mutation; a nonsense mutation translates into a stop codon. A frameshift mutation adds or removes a base.
Viral Structure and Replication (01:56)
Viruses replicate and survive inside the cells of another organism. A double-stranded DNA virus has chromosomes protected by a protein capsid, surrounded by tegument. A virus forces the cell to make viral DNA and ribosomes translate viral proteins. The HIV retrovirus uses reverse transcriptase to make DNA from RNA.
Early Evolution of Life (00:57)
Proto-cells were the first prokaryotic cells and are the common ancestor of life on Earth. Prokaryotes include archaea and bacteria. Eukaryotic cells evolved through endosymbiosis.
Mechanisms for Evolution (01:37)
Alleles in a population change over time. In natural selection, organisms with traits well-suited to an environment pass these traits to offspring. Genetic drift occurs when part of a population is separated due to random chance, acting on genotype; gene flow also acts on genotype.
Evolutionary Patterns (00:54)
In divergent evolution, two or more related species become more distinct, while in convergent evolution, unrelated species become more similar. In parallel evolution, species evolve similarly, while in co-evolution, the species' evolutionary paths influence each other.
Taxonomic and Phylogenetic Classification (01:47)
Taxonomic classification organizes organisms based on similarities into domain, kingdom, phylum, class, order, family, genus, species. Domains include eukarya, bacteria, and archaea. Kingdoms include: monera, protista, plantae, fungi, and animalia. Phylogenetic trees show evolutionary relationships between groups of species.
Survey of the Diversity of Life (01:11)
Archaea obtain energy from organic or inorganic compounds, move with flagella, and reproduce asexually. Bacteria are asexual and are heterotrophs or autotrophs. Protists are photosynthetic or phagocytes, reproducing sexually or asexually. Fungi are heterotrophs, reproducing sexually or asexually.
Evolving from Water to Land (01:30)
Plants and animals originated in water. Plants began as algae, and evolved to vascular seed, and flowering plants. Animals adapted to the land to breathe oxygen; amphibians are born with gills and later develop lungs. Reptiles evolved from amphibians.
Plant Structure, Function, and Growth (01:39)
Plants make food and energy through photosynthesis, have cell walls, and reproduce sexually or asexually. Root systems anchor the plant and draw nutrients and water from soil. The vascular tissue moves nutrients between roots and shoots via xylem and phloem.
Angiosperm Reproduction (01:27)
The flowers and fruits of angiosperms are reproductive structures; flowers contain sexual organs and fruits contain seeds. The carpel is the female reproductive organ; the stamen is the male organ. Pollen is carried by natural forces to a stigma on the carpel of another plant, growing a pollen tube to the ovary; as the seed develops, the ovule develops into a fruit.
Plant Response to the Environment (00:57)
Plants respond to environmental stimuli with growth and development through various tropisms. A phototropism is a response to light; a thigmotropism is growth in response to touch. Tropisms are activated through plant hormones like auxin and cytokinins.
Animal Reproduction, Growth, and Development (01:53)
Animals reproduce sexually through the joining of two gametes in external or internal fertilization. The zygote divides during cleavage, a blastocyst forms and then a gastrula forms. In organogenesis, organs begin to form.
Animal Response to the Environment (00:52)
Homeostasis involves regulation of body temperature and processes to maintain balance. Through a negative feedback loop, the body remains in stable condition.
Human Physiology: Nervous and Muscular Systems (01:31)
The brain and spinal cord make up the central nervous system, while the peripheral nervous system includes somatic and autonomic nerves throughout the body. Neurons carry electrical signals. Muscles create force and motion through contraction of the sarcomere.
Human Physiology: Endocrine and Excretory Systems (02:08)
The endocrine system consists of seven glands which produce hormones or chemical signals. The pancreas secretes insulin and glucagon to regulate blood glucose levels. The liver and kidneys process waste products.
Human Physiology: Immune System (01:35)
The body has specific and general defenses. White blood cells include phagocytes which eat invaders. Lymphocytes include T-cells and B-cells which have reaction sites to respond to specific antigens; T-cells become natural killer cells after their receptors bind to an antigen.
Population Dynamics (01:17)
A population of species in a location can change over time due to birth or death rate changes, or movement. A growth curve models a population change; carrying capacity is the population size a certain environment can support. Limiting factors like food affect a population's size.
Communities and Ecosystems (02:47)
Ecosystems depend on energy and nutrient cycles. The food chain includes photosynthesizing producers, consumers, and decomposers. Energy is a one-way process, summarized in an energy pyramid; nutrients like water and carbon cycle through the ecosystem continuously. An ecological community develops according to succession, and diversity varies on species competition.
Global Issues (01:14)
Since the industrial revolution, humans have had an increasing effect on ecosystems and the Earth as a whole. This includes mining, dams, and deforestation. Emissions have increased atmospheric CO2, causing global warming.
Credits: Teaching Systems Advanced Placement Biology (00:10)
Credits: Teaching Systems Advanced Placement Biology
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