Subject
Biology study guides
Cells, genetics, ecology, and the systems of living things — answered with worked explanations and diagrams.
16 explained questions, each with the answer, a worked explanation, and something interactive to help it stick.
- Which of the following correctly organizes these genetic terms in order from smallest to largest?From smallest to largest: nucleotide -> gene -> DNA molecule -> chromosome. A nucleotide is the single building block, a gene is a stretch of nucleotides, a DNA molecule contains many genes, and a chromosome is one long DNA molecule coiled with proteins.Read the guide
- Which statement accurately describes the relationship between cytokinesis and mitosis?Cytokinesis follows mitosis: mitosis divides the nucleus (the genetic material) and cytokinesis divides the cytoplasm. Together they complete cell division, producing two genetically identical daughter cells. Cytokinesis usually begins in late mitosis and finishes after it.Read the guide
- Which of the Following Does Not Occur During Mitosis?Synapsis and crossing over of homologous chromosomes do not occur during mitosis — those are unique to meiosis. DNA replication also does not occur during mitosis; it happens earlier, in the S phase of interphase. Mitosis itself only separates already-copied chromosomes into two identical nuclei.Read the guide
- The Endosymbiotic Theory Helps to Explain the Origin of Which Structures?Mitochondria and chloroplasts. The endosymbiotic theory proposes these double-membrane organelles descended from free-living prokaryotes — aerobic bacteria and cyanobacteria — that were engulfed by an ancestral eukaryotic cell and became permanent internal symbionts rather than being digested.Read the guide
- What is the role of a pioneer species in primary succession?Pioneer species create soil. Organisms like lichens and mosses colonize bare rock, secrete acids that weather it into particles, and add organic matter when they die — forming the first thin soil that allows grasses, shrubs, and trees to grow later.Read the guide
- How Are Proteins and Nucleic Acids Related?Proteins and nucleic acids are related because nucleic acids (DNA and RNA) store and carry the genetic instructions that determine a protein's amino-acid sequence. Information flows DNA to RNA to protein, so DNA ultimately specifies which protein a cell builds.Read the guide
- What is the most likely reason that horses and mountain goats have hooves?Because they share a common ancestor. Horses and mountain goats are both hoofed mammals (ungulates), and their hooves are homologous structures inherited from a shared ancestral foot, later adapted for their different terrains rather than evolving independently.Read the guide
- Which three processes are methods of genetic recombination?In sexually reproducing eukaryotes, the three processes are crossing over, independent assortment, and fertilization. Together they shuffle and combine alleles to create genetically unique offspring. (In prokaryotes, the equivalent trio is transformation, transduction, and conjugation.)Read the guide
- What is most likely to result immediately after a rainforest in Brazil is clear-cut?Secondary succession. Because clear-cutting leaves soil, roots, seeds, and some organisms intact, the community regrows through secondary succession rather than starting from bare rock, which would be primary succession.Read the guide
- Which is the best definition of directional selection?Directional selection is a process by which one extreme of a trait is favored, shifting the population's trait distribution toward that extreme over successive generations. The average value of the trait moves in one direction as the favored phenotype becomes more common.Read the guide
- Which structural characteristic is seen in RNA but not in DNA?RNA contains the nitrogenous base uracil (which replaces thymine) and the sugar ribose, which has a hydroxyl (–OH) group on its 2′ carbon. RNA is also typically single-stranded. DNA instead uses thymine, deoxyribose (no 2′ –OH), and is double-stranded.Read the guide
- What is the end result of mitosis?The end result of mitosis is two genetically identical diploid daughter cells, each containing the same number of chromosomes as the original parent cell. Mitosis produces exact copies used for growth, repair, and asexual reproduction.Read the guide
- Homologous pairs of chromosomes are lined up independently of other such pairs during _____.During metaphase I of meiosis. Homologous chromosome pairs (tetrads) line up at the metaphase plate, and each pair orients randomly and independently of every other pair. This independent assortment shuffles maternal and paternal chromosomes, creating genetic variation in the resulting gametes.Read the guide
- Is It Advantageous for a Predator to Prey Exclusively on a Single Prey Species?False. Specializing on one prey species is generally risky: if that prey declines, the predator has no fallback and may starve. Dietary flexibility (generalist foraging) buffers against prey fluctuations, so a broad diet is usually more advantageous for survival.Read the guide
- Which of These Is Not a Carcinogen?Fat is not a carcinogen. Among the usual options (fat, UV light, cigarette smoke, testosterone), fat does not directly damage DNA or trigger malignant change; it is linked to cancer only indirectly. The other three are established carcinogens or tumor promoters.Read the guide
- Glucose + glucose → _____ by _____.Glucose + glucose → maltose by dehydration synthesis (also called condensation). Two glucose monosaccharides bond through an α-1,4 glycosidic linkage, and one water molecule is removed to form the disaccharide maltose.Read the guide