DAT Organic Chemistry (Natural Sciences) Practice Questions Answers

Answers and Explanations

1. C: The hydrogen bonds between water molecules cause water molecules to attract each other (negative pole to positive pole. and “stick” together. This gives water a high surface tension, which allows small living organisms, such as water striders, to move across its surface. Since water is a polar molecule, it readily dissolves other polar and ionic molecules such as carbohydrates and amino acids. Polarity alone is not sufficient to make something soluble in water, however; for example, cellulose is polar but its molecular weight is so large that it is not soluble in water.

2. D: An exothermic reaction releases energy, whereas an endothermic reaction requires energy. The breakdown of a chemical compound is an example of a decomposition reaction (AB → A + B). A combination reaction (A + B →AB) is the reverse of a decomposition reaction, and a replacement (displacement) reaction is one where compound breaks apart and forms a new compound plus a free reactant (AB + C →AC + B or AB + CD → AD + CB).

3. B: Some RNA molecules in extant organisms have enzymatic activity; for example the formation of peptide bonds on ribosomes is catalyzed by an RNA molecule. This and other information has led scientists to believe that the most likely molecules to first demonstrate enzymatic activity were RNA molecules.

4. A: Osmosis is the movement of water molecules (not solutes) across a semi-permeable membrane. Water moves from a region of higher concentration to a region of lower concentration. Osmosis occurs when the concentrations of a solute differ on either side of a semi-permeable membrane. For example, a cell (containing a higher concentration of water) in a salty solution (containing a lower concentration of water) will lose water as water leaves the cell. This continues until the solution outside the cell has the same salt concentration as the cytoplasm.

5. D: Both prokaryotes and eukaryotes interact with the extracellular environment and use membrane-bound or membrane-associated proteins to achieve this. They both use diffusion and active transport to move materials in and out of their cells. Prokaryotes have very few proteins associated with their DNA, whereas eukaryotes’ DNA is richly studded with proteins. Both types of living things can have flagella, although with different structural characteristics in the two groups. The most important differences between prokaryotes and eukaryotes are the lack of a nucleus and membrane-bound organelles in prokaryotes.

6. D: The ovary houses the ovules in a flower. Pollen grains fertilize ovules to create seeds, and the ovary matures into a fruit.

7. C: Alternation of generations means the alternation between the diploid and haploid phases in plants.

8. B: Anthers produce microspores (the male gametophytes of flowering plants), which undergo meiosis to produce pollen grains.

9. C: In flowering plants, the anthers house the male gametophytes (which produce sperm) and the pistils house the female gametophytes (which produce eggs). Eggs and sperm are haploid. All other tissues are solely diploid.

10. C: In birds and reptiles, the yolk sac contains the yolk, the main source of nutrients for the embryo. In humans, the yolk sac is empty and embryos receive nutrition through the placenta. However, the yolk sac forms part of the digestive system and are where the earliest blood cells and blood vessels are formed.

11. D: At the lowest trophic level are the producers, followed by primary consumers. Primary carnivores follow consumers, followed by secondary carnivores.

12. A: Vultures eat carrion, or dead animals, so they are considered scavengers. Detritivores are heterotrophs that eat decomposing organic matter such as leaf litter. They are usually small.

13. D: Type I curves describe species in which most individuals survive to middle age, after which deaths increase. Dolphins have few offspring, provide extended care to the young, and live a long time.

14. B: The growth rate is equal to the difference between births and deaths divided by population size.

15. A: Transportation by humans or human-associated means is not considered a natural dispersal process.

16. B: Density-dependent limiting factors on population growth are factors that vary with population density. Pollution from a factory, volcanic eruptions, frosts, and fires do not vary as a function of population size. Waste products, however, increase with population density and could limit further population increases.

17. B: Character displacement means that, although similar, species in the same habitat have evolved characteristics that reduce competition between them. It occurs as a result of resource partitioning.

18. D: Natural selection was Darwin’s idea, not Lamarck’s. Mendel discovered that genes are the basic units of inheritance. Lamarck’s observation about use and disuse is true, although he did not connect it with the underlying mechanism of natural selection.

19. C: Disruptive selection occurs when the environment favors alleles for extreme traits. In the example, seasonal changes can make different types of food available at different times of the year, favoring the large or short bills, respectively.

20. C: Hybridization between two different species would result in more genetic variation than sexual reproduction within a species.

DAT Biology (Natural Sciences) Practice Questions