HESI A2 Biology flashcards
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What counts as alive, and how biologists sort living things
- Name the eight properties of life.
- Order, response to stimuli, reproduction, adaptation, growth and development, regulation (homeostasis), energy processing and evolution.
- Why are viruses not considered living?
- Viruses are not made of cells. The cell is the smallest unit of structure and function in a living thing.
- Order from smallest to largest: ecosystem, population, community.
- Population (one species in an area), community (all populations there), then ecosystem (the community plus its nonliving surroundings).
- List the taxonomic ranks from broadest to most specific.
- Domain, kingdom, phylum, class, order, family, genus, species.
- How is a scientific name such as Canis lupus written?
- Genus then species, both in italics. Only the genus is capitalized.
- What is the key difference between prokaryotes and eukaryotes?
- Prokaryotes have no nucleus; their DNA sits in the nucleoid. Eukaryotes keep their DNA inside a nucleus.
Why water behaves the way it does
- Why is a water molecule polar?
- Oxygen is more electronegative, so it pulls shared electrons harder. Oxygen ends up slightly negative and the hydrogens slightly positive.
- What is a hydrogen bond between water molecules?
- A weak attraction between the slightly positive hydrogen of one molecule and the slightly negative oxygen of a neighbor.
- How do cohesion and adhesion differ?
- Cohesion is water sticking to water, which causes surface tension. Adhesion is water sticking to another surface, such as glass.
- Why does water warm up and cool down slowly?
- It has a high specific heat: 1 calorie per gram per °C, about five times that of sand.
- Why does ice float on liquid water?
- Hydrogen bonds hold the molecules in ice farther apart, so ice is less dense than liquid water.
- A solution goes from pH 6 to pH 4. By what factor does H⁺ change?
- 100 times. Each pH unit is a tenfold change in H⁺ concentration, so two units is a hundredfold change.
The four macromolecules of life and how cells build them
- Which reaction releases water: dehydration synthesis or hydrolysis?
- Dehydration synthesis releases water when monomers join. Hydrolysis uses water to split a polymer into monomers.
- How do plants and animals each store glucose?
- Plants store it as starch. Animals store it as glycogen, mainly in the liver and muscles.
- What is a triglyceride made of?
- One glycerol attached to three fatty acids.
- What happens to an enzyme heated far above its ideal temperature?
- It denatures. Its shape changes but its amino acid sequence stays, and the lost shape stops it from working.
- What type of molecule are almost all enzymes, and what job do they do?
- Proteins. They act as catalysts, speeding up reactions, and come out unchanged so they can be used again.
- Which sugar does DNA contain, and which does RNA contain?
- DNA contains deoxyribose. RNA contains ribose.
How cells build, break down, and speed up reactions
- How do anabolic and catabolic pathways differ?
- Anabolic pathways build complex molecules and use energy. Catabolic pathways break molecules down and release energy.
- What happens when ATP loses its last phosphate?
- ATP becomes ADP plus a free phosphate, and energy is released for the cell to use.
- What do enzymes do to activation energy, and are they used up?
- They lower activation energy. They come out of the reaction unchanged, so one enzyme can be reused many times.
- What is an enzyme's active site, and what is induced fit?
- The active site is the pocket where the substrate binds. In induced fit, the enzyme shifts shape slightly as the substrate binds.
- What happens to an enzyme heated far above its optimum temperature?
- It denatures. The active site loses its shape, and activity drops.
- Why does more substrate overcome competitive but not noncompetitive inhibition?
- A competitive inhibitor blocks the active site, so extra substrate can outcompete it. A noncompetitive inhibitor binds elsewhere and changes the enzyme's shape, so substrate cannot.
How a cell is built, fed, and copied
- What do prokaryotic cells lack that eukaryotic cells have?
- A nucleus and membrane-bound organelles. Prokaryotes still have DNA and ribosomes; their DNA sits in the nucleoid.
- A red blood cell is dropped into pure water. What happens, and why?
- Water moves in, so the cell swells and can burst. Pure water has less solute than the cell, so it is hypotonic.
- How does active transport differ from diffusion?
- Active transport moves substances against their gradient and uses energy, usually ATP. Diffusion moves them down the gradient with no cell energy.
- What route does a protein take when a cell exports it?
- Ribosomes on the rough ER build it, a vesicle carries it to the Golgi, which modifies it, and another vesicle releases it.
- Which division separates homologous pairs, and which separates sister chromatids?
- Meiosis I separates homologous pairs. Sister chromatids separate in mitosis and in meiosis II.
- Do plant cells have mitochondria, and what do they add?
- Yes. Plant cells add a cell wall, chloroplasts and a large central vacuole. Chloroplasts do not replace mitochondria.
How cells turn glucose into ATP
- What is the overall equation for cellular respiration?
- C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, with part of the released energy captured as ATP.
- Where does glycolysis happen, and what is its net ATP per glucose?
- In the cytoplasm, without oxygen. It nets 2 ATP and makes two pyruvate.
- Where does the Krebs cycle run, and how often per glucose?
- In the mitochondrial matrix. It turns twice per glucose and releases CO₂.
- What does oxygen do in the electron transport chain?
- It is the final electron acceptor. It picks up spent electrons and H⁺ and becomes water.
- Which stage of respiration makes most of the ATP?
- The electron transport chain with chemiosmosis, where H⁺ flows through ATP synthase. It makes about 90 percent of the ATP.
- A muscle runs short of oxygen. What happens to pyruvate, and why?
- Lactic acid fermentation makes lactate. This regenerates NAD⁺, so glycolysis can keep making its 2 ATP.
How plants turn light into sugar
- What is the overall equation for photosynthesis?
- 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
- Where do the light-dependent reactions happen, and what do they make?
- In the thylakoid membrane. They make ATP, NADPH and oxygen.
- Which molecule is the source of the oxygen photosynthesis releases?
- Water, not carbon dioxide. Photosystem II splits water to replace its energized electrons.
- Where is the Calvin cycle, and what does it do?
- In the stroma. It uses ATP and NADPH to turn CO₂ into the three-carbon sugar G3P, starting with RuBisCO.
- Why is the Calvin cycle called light-independent if it depends on light?
- Light does not drive it directly. It still runs on the ATP and NADPH made by the light reactions.
- How are photosynthesis and cellular respiration linked?
- The products of one are the reactants of the other. Plants do both, since plant cells have chloroplasts and mitochondria.
How one cell becomes two, or four
- In which phase is DNA copied, and what does each chromosome look like afterward?
- S phase of interphase. Each chromosome becomes two sister chromatids joined at a centromere.
- Give the order of mitosis, and name the step that follows.
- Prophase, metaphase, anaphase, telophase. Cytokinesis then divides the cytoplasm.
- How do the cells made by mitosis and by meiosis compare?
- Mitosis makes 2 genetically identical diploid cells. Meiosis makes 4 genetically different haploid cells.
- What does meiosis I separate?
- Homologous chromosomes. Sister chromatids stay joined until meiosis II.
- When does crossing over happen, and why does it matter?
- In prophase I of meiosis. Nonsister chromatids swap segments, which helps make the four cells genetically different.
- A cell with 2n = 8 finishes meiosis. Chromosomes per new cell?
- 4. Meiosis halves the chromosome number, so each new cell is haploid.
How traits pass from parents to children
- What ratios result from crossing two heterozygotes, Yy × Yy?
- Genotype 1 YY : 2 Yy : 1 yy. Phenotype 3 dominant : 1 recessive.
- Can you read a genotype from a dominant phenotype?
- No. YY and Yy look the same. A test cross with a recessive (yy) plant can reveal the genotype.
- How do incomplete dominance and codominance differ?
- Incomplete dominance gives a blend, like pink snapdragons. Codominance shows both alleles at once, like type AB blood.
- Can a type A parent and a type B parent have a type O child?
- Yes, if they are Iᴬ i and Iᴮ i. Type O is ii, so each parent passes i.
- Why can a father with an X-linked trait not pass it to his son?
- A son gets his father's Y chromosome. A father passes his X only to his daughters.
- Does a 3:1 ratio mean exactly 1 of every 4 children shows the recessive trait?
- No. The ratio is a probability: each child has a 1 in 4 chance, not a guarantee.
How a gene in DNA becomes a protein
- What does semiconservative replication mean?
- Each new DNA molecule keeps one original strand and gets one new strand.
- Where do transcription and translation happen in a eukaryotic cell?
- Transcription happens in the nucleus. Translation happens at ribosomes in the cytoplasm.
- During transcription, the DNA template strand has A. Which RNA base is added?
- Uracil (U). RNA uses U where DNA would use T.
- Which codon starts translation, and which three codons stop it?
- AUG starts it and codes for methionine. UAA, UAG and UGA are the stop codons.
- How does a silent mutation differ from a nonsense mutation?
- Silent: the codon still means the same amino acid. Nonsense: the codon becomes a stop codon and the protein ends early.
- Why does deleting one base usually harm a protein more than swapping one base?
- A deletion causes a frameshift, so every codon after it is misread. A swap changes only one codon.
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