The Introduction to Theory of Evolution

- Darwin developed his theory of evolution by natural selection by carefully observing nature, especially during his voyage around the world on the Beagle.

- Darwin based this theory on well-known facts and some key inferences.

- Modern genetics has discovered the mechanisms of inheritance which Darwin did not understand.

- Darwin had no examples of the action of natural selection, so he based his arguments on artificial selection.

- For a population to evolve, its members must possess heritable genetic variation, which is the raw material on which agents of evolution act.

- A single individual has only some of the alleles found in the population of which it is a member.

- Considerable genetic variation characterizes most natural populations.

- Allele frequencies measure the amount of genetic variation in a population. Biologists estimate allele frequencies by measuring a sample of individuals from a population. The sum of all allele frequencies at a locus is equal to 1.

- Genotype frequencies show how a population’s genetic variation is distributed among its members. Populations that have the same allele frequencies may nonetheless have different genotype frequencies.

- Several conditions are required for a population to be at Hardy–Weinberg equilibrium: mating is random, the population is very large, there is no migration, there is no mutation, and natural selection is not acting on the population.

- In a population at Hardy–Weinberg equilibrium, allele frequencies remain the same from generation to generation. In addition, genotype frequencies will remain in the proportions p2 + 2pq + q2 = 1.

- Biologists can determine whether an agent of evolution is acting on a population by comparing the genotype frequencies of that population with Hardy–Weinberg expectations.

- Changes in the genetic structure of populations are caused by several evolutionary agents: mutation, gene flow, genetic drift, nonrandom mating and natural selection.

- The origin of genetic variation is mutation. Most mutations are harmful or neutral to their bearers but some are advantageous, particularly if the environment changes.

- Movement of individuals or gametes from one population to another, followed by reproduction in the new location, produces gene flow. Gene flow may add new alleles to a population or may change the frequencies of alleles already present.

- The random loss of alleles, known as genetic drift, produces changes in allele frequencies, which may be especially dramatic in small populations. Organisms that normally have large populations may pass through occasional periods (bottlenecks) when only a small number of individuals survive.

- New populations established by a few founding immigrants also have gene frequencies that differ from those in the parent population.

- If individuals mate more often with other individuals of a certain genotype than would be expected on a random basis—that is, when mating is not random—genotype frequencies differ from Hardy–Weinberg expectations.

- Self-fertilization, an extreme form of nonrandom mating, reduces the frequencies of heterozygous individuals below Hardy–Weinberg expectations without changing allele frequencies.

- Natural selection is the only agent of evolution that adapts populations to their environments.

- The reproductive contribution of a phenotype to subsequent generations relative to the contributions of other phenotypes is

its fitness. The fitness of a phenotype is determined by the average rates of survival and reproduction of individuals with that phenotype.

- Stabilizing selection reduces variation and preserves the average characteristics of a population.

- Directional selection changes a character by favoring individuals that vary in one direction from the population mean. If directional selection operates over many generations, an evolutionary trend may result.

- Disruptive selection changes a character by favoring individuals that vary in both directions from the population mean.

- Sexually selected traits may evolve because females prefer tomate with males having those traits.

- Possessing resistance to toxic chemicals may involve tradeoffs, such as reduced reproductive output.

- Sexually selected traits may result in higher parasite loads and mortality rates in males.

- Genetic drift, stabilizing selection, and directional selection all tend to reduce genetic variation, but most populations are genetically highly variable.

- Sexual recombination increases the evolutionary potential of populations, but it does not influence the frequencies of alleles.

Rather, it generates new combinations of genetic material on which natural selection can act.

- Genetic variation within a population may be maintained by frequency-dependent selection.

- Much genetic variation is maintained geographically.

- Natural selection acts by modifying what already exists.

- Learned traits can spread rapidly via cultural evolution.

- Patterns of long-term evolutionary change can be strongly influenced by events that occur so infrequently or so slowly that they are unlikely to be observed during short-term evolutionary studies. Additional types of evidence must be gathered to understand why evolution in the long term took the particular course it did.

Test questions 1

1. Coenzymes differ from enzymes in that coenzymes are

a. only active outside the cell.

b. polymers of amino acids.

c. smaller, such as vitamins.

d. specific for one reaction.

e. always carriers of high-energy phosphate.

2. Which statement about thermodynamics is true?

a. Free energy is used up in an exergonic reaction.

b. Free energy cannot be used to do work, such as chemical

transformations.

c. The total amount of energy can change after a chemical

transformation.

d. Free energy can be kinetic but not potential energy

e. Entropy tends always to a maximum.

3. In a chemical reaction,

a. the rate depends on the value of G.

b. the rate depends on the activation energy.

c. the entropy change depends on the activation energy.

d. the activation energy depends on the value of G.

e. the change in free energy depends on the activation energy.

4. Which statement about enzymes is not true?

a. They consist of proteins, with or without a nonprotein

part.

b. They change the rate of the catalyzed reaction.

c. They change the value of G of the reaction.

d. They are sensitive to heat.

e. They are sensitive to pH.

5. The active site of an enzyme

a. never changes shape.

b. forms no chemical bonds with substrates.

c. determines, by its structure, the specificity of the enzyme.

d. looks like a lump projecting from the surface of the enzyme.

e. changes G of the reaction.

6. The molecule ATP is

a. a component of most proteins.

b. high in energy because of the presence of adenine (A).

c. required for many energy-producing biochemical reactions.

d. a catalyst.

e. used in some endergonic reactions to provide energy.

7. In an enzyme-catalyzed reaction,

a. a substrate does not change.

b. the rate decreases as substrate concentration increases.

c. the enzyme can be permanently changed.

d. strain may be added to a substrate.

e. the rate is not affected by substrate concentration.

8. Which statement about enzyme inhibitors is not true?

a. A competitive inhibitor binds the active site of the enzyme.

b. An allosteric inhibitor binds a site on the active form of the enzyme.

c. A noncompetitive inhibitor binds a site other than the active site.

d. Noncompetitive inhibition cannot be completely overcome

by the addition of more substrate.

e. Competitive inhibition can be completely overcome by the addition of more substrate.

9. Which statement about feedback inhibition of enzymes is not true?

a. It is exerted through allosteric effects.

b. It is directed at the enzyme that catalyzes the first committed step in a branch of a pathway.

c. It affects the rate of reaction, not the concentration of enzyme.

d. It acts very slowly.

e. It is an example of negative feedback.

10. Which statement about temperature effects is not true?

a. Raising the temperature may reduce the activity of an enzyme.

b. Raising the temperature may increase the activity of an enzyme.

c. Raising the temperature may denature an enzyme.

d. Some enzymes are stable at the boiling point of water.

e. All enzymes have the same optimal temperature.

Test questions 2

1. In noncyclic photosynthetic electron transport, water is used to

a. excite chlorophyll.

b. hydrolyze ATP.

c. reduce chlorophyll.

d. oxidize NADPH.

e. synthesize chlorophyll.

2. Which statement about light is true?

a. An absorption spectrum is a plot of biological effectiveness

versus wavelength.

b. An absorption spectrum may be a good means of identifying

a pigment.

c. Light need not be absorbed to produce a biological effect.

d. A given kind of molecule can occupy any energy level.

e. A pigment loses energy as it absorbs a photon.

3. Which statement about chlorophylls is not true?

a. They absorb light near both ends of the visible spectrum.

b. They can accept energy from other pigments, such as

carotenoids.

c. Excited chlorophyll can either reduce another substance

or fluoresce.

d. Excited chlorophyll may be an oxidizing agent.

e. They contain magnesium.

4. In cyclic electron transport,

a. oxygen gas is released.

b. ATP is formed.

c. water donates electrons and protons.

d. NADPH + H+ forms.

e. CO2 reacts with RuBP.

5. Which of the following does not happen in noncyclic electron

transport?

a. Oxygen gas is released.

b. ATP forms.

c. Water donates electrons and protons.

d. NADPH + H+ forms.

e. CO2 reacts with RuBP.

6. In the chloroplasts,

a. light leads to the pumping of protons out of the thylakoids.

b. ATP forms when protons are pumped into the thylakoids.

c. light causes the stroma to become more basic than the

thylakoids.

d. protons return passively to the stroma through protein

channels.

e. proton pumping requires ATP.

7. Which statement about the Calvin–Benson cycle is not true?

a. CO2 reacts with RuBP to form 3PG.

b. RuBP forms by the metabolism of 3PG.

c. ATP and NADPH + H+ form when 3PG is reduced.

d. The concentration of 3PG rises if the light is switched off.

e. Rubisco catalyzes the reaction of CO2 and RuBP.

8. In C4 photosynthesis,

a. 3PG is the first product of CO2 fixation.

b. rubisco catalyzes the first step in the pathway.

c. four-carbon acids are formed by PEP carboxylase in

bundle sheath cells.

d. photosynthesis continues at lower CO2 levels than in

C3 plants.

e. CO2 released from RuBP is transferred to PEP.

9. Photosynthesis in green plants occurs only during the day.

Respiration in plants occurs

a. only at night.

b. only when there is enough ATP.

c. only during the day.

d. all the time.

e. in the chloroplast after photosynthesis.

10. Photorespiration

a. takes place only in C4 plants.

b. includes reactions carried out in peroxisomes.

c. increases the yield of photosynthesis.

d. is catalyzed by PEP carboxylase.

e. is independent of light intensity.

Test questions 3

1. Which is present in both prokaryotic cells and in eukaryotic

Plant cells?

a. Chloroplasts

b. Cell walls

c. Nucleus

d. Mitochondria

e. Microtubules

2. The major factor limiting cell size is the

a. concentration of water in the cytoplasm.

b. need for energy.

c. presence of membranous organelles.

d. ratio of surface area to volume.

e. composition of the plasma membrane.

3. Which statement about mitochondria is not true?

a. Their inner membrane folds to form cristae.

b. They are usually 1 nano-m or smaller in diameter.

c. They are green because they contain chlorophyll.

d. Energy-rich substances from the cytosol are oxidized in them.

e. Much ATP is synthesized in them.

4. Which statement about plastids is true?

a. They are found in prokaryotes.

b. They are surrounded by a single membrane.

c. They are the sites of cellular respiration.

d. They are found in fungi.

e. They are of several types with different functions.

5. If all the lysosomes within a cell suddenly ruptured, what would be the most likely result?

a. The macromolecules in the cytosol would begin to break

down.

b. More proteins would be made.

c. The DNA within mitochondria would break down.

d. The mitochondria and chloroplasts would divide.

e. There would be no change in cell function.

6. The Golgi apparatus

a. is found only in animals.

b. is found in prokaryotes.

c. is the appendage that moves a cell around in its

environment.

d. is a site of rapid ATP production.

e. packages and modifies proteins.

7. Which organelle is not surrounded by one or more membranes?

a. Ribosome

b. Chloroplast

c. Mitochondrion

d. Peroxisome

e. Vacuole

8. The cytoskeleton consists of

a. cilia, flagella and microfilaments.

b. cilia, microtubules and microfilaments.

c. internal cell walls.

d. microtubules, intermediate filaments and microfilaments.

e. calcified microtubules.

9. Microfilaments

a. are composed of polysaccharides.

b. are composed of actin.

c. provide the motive force for cilia and flagella.

d. make up the spindle that aids the movement of chromosomes.

e. maintain the position of the chloroplast in the cell.

10. Which statement about the plant cell wall is not true?

a. Its principal chemical components are polysaccharides.

b. It lies outside the plasma membrane.

c. It provides support for the cell.

d. It completely isolates adjacent cells from one another.

e. It is semirigid.

Test questions 4

1. Which statement about eukaryotic chromosomes is not true?

a. They sometimes consist of two chromatids.

b. They sometimes consist of a single chromatid.

c. They normally possess a single centromere.

d. They consist of proteins.

e. They are clearly visible as defined bodies under the light microscope.

2. Nucleosomes

a. are made of chromosomes.

b. consist entirely of DNA.

c. consist of DNA wound around a histone core.

d. are present only during mitosis.

e. are present only during prophase.

3. Which statement about the cell cycle is not true?

a. It consists of mitosis and interphase.

b. The cell’s DNA replicates during G1.

c. A cell can remain in G1 for weeks or much longer.

d. Proteins are formed throughout all subphases of interphase.

e. Histones are synthesized primarily during S phase.

4. Which statement about mitosis is not true?

a. A single nucleus gives rise to two identical daughter nuclei.

b. The daughter nuclei are genetically identical to the parent nucleus.

c. The centromeres separate at the onset of anaphase.

d. Homologous chromosomes synapse in prophase.

e. Mitotic centers organize the microtubules of the spindle

fibers.

5. Which statement about cytokinesis is true?

a. In animals, a cell plate forms.

b. In plants, it is initiated by furrowing of the membrane.

c. It generally immediately follows mitosis.

d. In plant cells, actin and myosin play an important part.

e. It is the division of the nucleus.

6. Apoptosis

a. occurs in all cells.

b. involves the cell membrane dissolving.

c. does not occur in an embryo.

d. involves a series of programmed events for cell death.

e. is not involved with cancer.

7. In meiosis,

a. meiosis II reduces the chromosome number from diploid to haploid.

b. DNA replicates between meiosis I and II.

c. the chromatids that make up a chromosome in meiosis II are identical.

d. each chromosome in prophase I consists of four chromatids.

e. homologous chromosomes separate from one another in anaphase I.

8. In meiosis,

a. a single nucleus gives rise to two daughter nuclei.

b. the daughter nuclei are genetically identical to the parent nucleus.

c. the centromeres separate at the onset of anaphase I.

d. homologous chromosomes synapse in prophase I.

e. no spindle forms.

9. A plant has a diploid chromosome number of 12. An egg cell of the plant has 5 chromosomes. The most probable