HESI A2 Biology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cell theory

Three principles: all living organisms are composed of one or more cells, the cell is the basic unit of structure and function, and new cells arise from existing cells by division.

Prokaryotic cell

A cell with no membrane-bound nucleus or membrane-bound organelles. It has a single circular chromosome, 70S ribosomes, and a cell wall; bacteria are the primary example.

Eukaryotic cell

A cell containing a nucleus enclosed by a double membrane plus membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Found in plants, animals, fungi, and protists.

Mitochondrion function

The organelle where aerobic cellular respiration produces most of the cell's ATP. Its inner membrane folds into cristae to increase surface area for the electron transport chain.

Ribosome function

The site of protein synthesis, where messenger RNA codons are translated into amino acid chains. Found free in the cytoplasm or attached to the rough endoplasmic reticulum.

Golgi apparatus

A stack of flattened membranous sacs that modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum for secretion or delivery to other organelles.

Lysosome

A membrane-bound vesicle containing digestive enzymes that break down worn-out organelles, ingested food particles, and foreign material inside the cell.

Chloroplast

The plant organelle where photosynthesis occurs. It contains the green pigment chlorophyll, and its internal stacks of thylakoids carry out the light-dependent reactions.

Fluid mosaic model

Describes the plasma membrane as a phospholipid bilayer studded with proteins, cholesterol, and carbohydrates that move laterally, giving the membrane a fluid, mosaic-like structure.

Osmosis

The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration until equilibrium is reached.

Hypertonic solution

A solution with a higher solute concentration than the cell. Water leaves the cell by osmosis, causing the cell to shrink, a process called crenation in animal cells.

Hypotonic solution

A solution with a lower solute concentration than the cell. Water enters the cell by osmosis, causing it to swell and potentially burst, a process called lysis.

Mitosis

Nuclear division producing two genetically identical diploid daughter cells. It supports growth, repair, and asexual reproduction and includes prophase, metaphase, anaphase, and telophase.

Meiosis

Two successive nuclear divisions that produce four genetically unique haploid gametes. Crossing over and independent assortment during meiosis create genetic variation.

DNA structure

A double helix of two antiparallel strands held together by hydrogen bonds. Each nucleotide has deoxyribose, a phosphate group, and a base pairing A with T and G with C.

RNA versus DNA

RNA is usually single-stranded, contains ribose sugar, and uses uracil instead of thymine. DNA is double-stranded, contains deoxyribose, and uses thymine.

Enzyme properties

Biological catalysts, usually proteins, that lower activation energy and are not consumed by the reaction. They are substrate-specific and denature at extreme temperature or pH.

Punnett square

A grid used to predict offspring genotypes by combining parental alleles. It shows expected ratios such as 3:1 phenotype from a cross of two heterozygotes.

Genotype versus phenotype

Genotype is the actual combination of alleles an organism carries, such as Aa. Phenotype is the observable trait expressed, such as brown eyes.

Incomplete dominance

A pattern in which neither allele is fully dominant, so the heterozygote shows a blended intermediate phenotype, such as pink flowers from red and white parents.

Codominance

A pattern in which both alleles are expressed fully and simultaneously in the heterozygote, as in AB blood type where both A and B antigens appear.

Photosynthesis equation

Six carbon dioxide molecules plus six water molecules plus light energy produce one glucose molecule and six oxygen molecules. It occurs in chloroplasts of plant cells.

Cellular respiration

The process that converts glucose and oxygen into carbon dioxide, water, and ATP. Glycolysis occurs in the cytoplasm; the Krebs cycle and electron transport occur in mitochondria.

Aerobic versus anaerobic

Aerobic respiration uses oxygen and yields roughly 36 to 38 ATP per glucose. Anaerobic fermentation yields only 2 ATP and produces lactate or ethanol.

ATP function

Adenosine triphosphate is the cell's main energy currency. Breaking its terminal phosphate bond releases energy that powers cellular work such as transport and synthesis.

Binomial nomenclature

The two-part scientific naming system in which the genus is capitalized and the species is lowercase, with both italicized, for example Homo sapiens.

Taxonomic hierarchy

The classification order from broadest to most specific: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Each level groups organisms sharing more specific traits.

Natural selection

The mechanism of evolution in which individuals with heritable traits better suited to their environment survive and reproduce more, increasing those alleles in later generations.

Negative feedback

A control mechanism in which a change triggers a response that reverses the original change, returning the body to its set point, as in insulin lowering high blood glucose.

Diffusion

The passive movement of particles from an area of higher concentration to lower concentration. It requires no energy and continues until concentrations are equal.

Active transport

Movement of substances across a membrane against their concentration gradient, requiring energy from ATP and usually a carrier protein, as in the sodium-potassium pump.

Cell cycle order

Interphase (G1, S, DNA replication, G2) followed by mitosis and cytokinesis. Interphase occupies most of the cycle and prepares the cell for division.