ASVAB

The General Science (GS) subtest measures your knowledge of life science, earth and space science, and physical science at the level taught in high school. The CAT-ASVAB has 15 questions in 12 minutes, and the paper version has 25 questions in 11 minutes, so most questions must be answered from recall in under a minute.

Cells and Organelles

All living organisms are made of cells, the basic structural and functional units of life. Prokaryotic cells lack a membrane- bound nucleus and include bacteria and archaea. Eukaryotic cells contain a nucleus and membrane-bound organelles and include plants, animals, fungi, and protists.

The cell membrane is a selectively permeable phospholipid bilayer that controls what enters and leaves the cell. Movement across it is either passive transport (no energy required) or active transport (energy required).

Structure	Function
Nucleus	ContainsDNAorganizedintochromosomes;controlscellactivities Thenucleolusinsideit .
	producesribosomes
Mitochondria	The"powerhouseofthecell":produceATPthroughcellularrespiration
Ribosomes	Sitesofproteinsynthesis freeinthecytoplasmorattachedtotheendoplasmicreticulum ,
Roughendoplasmicreticulum	Studdedwithribosomes;processesproteins
Smoothendoplasmicreticulum	Synthesizeslipidsanddetoxifiessubstances
Golgiapparatus	Modifies packages andshipsproteinsandlipids , ,
Lysosomes	Containdigestiveenzymesthatbreakdownwastematerials
Vacuoles	Storewater nutrients andwaste , ,
Cellwall(plants)	Rigidcelluloselayerthatsupportstheplantcell
Chloroplasts(plants)	Containchlorophyllandcarryoutphotosynthesis
Centralvacuole(plants)	Largestoragevacuolethatmaintainsturgorpressure

glucose + oxygen → carbon dioxide + water + ATP

Occurs in three stages: glycolysis, the Krebs cycle, and the electron transport chain.

DNA, RNA, and Protein Synthesis

DNA (deoxyribonucleic acid) is the molecule of heredity: two strands twisted into a double helix. Each strand is made of nucleotides containing a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases. Adenine pairs with thymine, and guanine pairs with cytosine.

RNA (ribonucleic acid) is single-stranded and uses uracil in place of thymine. Messenger RNA (mRNA) carries genetic information from DNA to the ribosomes, transfer RNA (tRNA) brings amino acids to the ribosomes, and ribosomal RNA (rRNA) forms part of the ribosomes.

Dna

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Genetic code in the nucleus

DNA is copied into mRNA in the

Ribosomes read mRNA, one

Amino acids joined in order

nucleus

codon (3 bases) per amino acid

Heredity

Gregor Mendel established the basic principles of heredity. Genes are units of heredity located on chromosomes, and alleles are different forms of a gene. Dominant alleles mask recessive alleles. Genotype is the genetic makeup; phenotype is the observable trait. Homozygous individuals have two identical alleles (AA or aa); heterozygous individuals have two different alleles (Aa). A Punnett square predicts the genotypes and phenotypes of offspring.

CompleteDominance					IncompleteDominance					Codominance
Thedominantallelecompletelymasks					Theheterozygousphenotypeis					Bothallelesarefullyexpressedatthe
therecessiveallele .					intermediatebetweenthetwoparents .					sametime .

Sex-linked traits are carried on the sex chromosomes, usually the X chromosome. Males (XY) are more likely to express X-linked recessive traits, such as color blindness and hemophilia, because they have only one X chromosome.

Cell Division

Mitosis produces two identical daughter cells for growth and repair, in four phases followed by cytokinesis, which divides the cytoplasm.

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Chromosomes condense;

Chromosomes line up at the

Sister chromatids separate to

Nuclear membranes re-form;

nuclear membrane breaks down

cell's equator

opposite poles

chromosomes relax

Meiosis produces four haploid gametes (sex cells) through two divisions: meiosis I separates homologous chromosomes, and meiosis II separates sister chromatids. Crossing over during prophase I increases genetic variation. Human body cells have 46 chromosomes (diploid); gametes have 23 (haploid).

Evolution and Classification

Evolution is the change in allele frequencies in a population over time. Charles Darwin proposed natural selection as its mechanism: individuals with favorable traits survive and reproduce more successfully, passing those traits to their offspring. Evidence includes fossils showing transitional forms, homologous structures (similar structure, different function), analogous structures (different structure, similar function), similarities in embryonic development, and comparisons of DNA and protein sequences.

Taxonomy classifies organisms from broadest to most specific: domain, kingdom, phylum, class, order, family, genus, species. The three domains are Bacteria, Archaea, and Eukarya. Binomial nomenclature names each species by genus and species, as in Homo sapiens.