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The theory that mitochondria and chloroplasts originated as free-living bacteria and evolved into energy-producing organelles in eukaryotic organisms millions of years ago. This theory is considered an example of evolutionary evidence.



occurs when a modifier gene suppresses an expressed phenotype of another gene


vegetative segregation

the random replication of mitochondria, chloroplasts, and other organelles during cell divisions that results in daughter cells with random samples of these organelles



a form of nondisjunction that results in an extra chromosome being added to a cell during meiosis, leading to genetic disorders such as Down Syndrome



a chromosomal abnormality that occurs when non-homologous chromosomes exchange information, which alters the structure of the chromosome



an x-linked recessive genetic disorder, expressed primarily in males, that occurs when a gene that produced blood-clotting proteins is deleted


gene pool

the complete set of genetic information in a population


What are Mendelian genetics?

Three Laws: Segregation, Independent assortment, and dominance

The Law of Segregation states that genes separate into distinct alleles during meiosis.
The Law of Independent states that genes separate and recombine independently of one other.
The Law of Dominance states that offspring will express the dominant allele.


What occurs during the process of recombination?

Crossing over occurs during Prophase I of meiosis. As duplicated chromosomes separate into chromatids, the chromatids intertwine and exchange alleles in random patterns. The resultant chromosome therefore carries the same genes but has a combination of both parent's alleles.


Why are recessive X-linked traits expressed primarily in males, but not females?

If a female inherits a recessive X-linked allele, it has a greater chance of being masked by a dominant X-linked allele. Males only inherit one X allele so the trait will be expressed whether it is recessive or dominant.


Why are height and weight considered examples or traits that display continuous variation?

Height and weight are traits that exist along a continuum (unlike eye color that does not have a set number of varieties).


How is extranuclear DNA passed on from parent to offspring?

Some organelles, including chloroplast and mitochondria, contain DNA that does not replicate during gamete formations because it is not located within the nucleus. DNA in these organelles is duplicated from the maternal cell when two gametes fertilize, and the offspring inherits extranuclear DNA exclusively from the mother.


How do prokaryotic organisms increase genetic variation during reproduction?

Bacteria and archaea increase variation by exchanging genetic information through transduction, transformation, and conjugation.
Transduction occurs when a cell is infected by a virus that absorbs genetic material and transfers it to another host cell.
Transformation occurs when prokaryotic cells absorb genetic material from a source outside the cell.
Conjunction occurs when two prokaryotic cells exchange plasmids (gene-carrying structures in the cell).


How do chromosomal abnormalities increase genetic diversity and drive evolution around a population of organisms?

Some chromosomal abnormalities introduce new genes and changes to phenotypes that are expressed among a population. In sexually reproducing eukaryotes, these phenotypes can give organisms an ecological advantage and are more likely to be selected for and passed on in a population.


Why is cystic fibrosis considered an autosomal recessive disorder?

It is an inherited recessive disorder that results from a mutation of an autosomal gene (not linked to a sex chromosome).


Which mechanisms allow alleles to be distributed and move within and between populations of species?

Gene flow, Migration, Genetic drift, and nonrandom mating


What are the five conditions of the H-W equilibrium?

Large population, isolated, no genetic mutations, random mating, and no natural selection


How do evolutionary mechanisms lead to change in populations of sexually reproducing organisms?

They alter the variation of genetic information and allele frequency within the population, which alter the reproductive patterns of the population. Certain traits survive while others don't. Over time, this results in change.


Which conditions must be met for natural selection to occur?

variation in traits that can be inherited by offspring, overproduction of offspring, and differential reproduction


How do random events drive genetic drift in a population?

They can wipeout large portions of populations or isolate small populations from the larger population which leads to loss of diversity and causes genetic drift.


What is the role of stasis in the theory of punctuated equilibrium?

Theory: species remain in long periods of equilibrium with no major evolutionary changes (stasis) the majority of the time.

This stasis is punctuated by short, rapid bursts of evolution that drive species change and speciation.


What is the difference between convergent and divergent evolution?

Convergent: two unrelated species evolve similar traits (analogous structures) due to similar environments
Divergent: two species descended from a common ancestor evolve non-similar traits in response to different environments/niches


How does reproductive isolation play a central role in speciation?

Populations of species that become isolated will see reduction in gene flow between the two groups. Overtime, as they both experience evolutionary changes, they become incapable of inbreeding which may lead to speciation.


What are the different types of pre-zygotic isolation?

Habitat, temporal, behavioral, mechanical, and gamete isolation.


Why do hybrid organisms experience infertility?

They do not have a full set of compatible chromosomes.


In that absence of physical barriers, which factors can lead to parapatric speciation?

Populations share the same habitats, but they become isolated due to behavior or timing of breeding.


Why do homologous structures in living organisms indicate evidence of evolutionary relationships?

They indicate that the species shared a common ancestor at some point in its evolutionary history.


What distinguishes evolutionary trends from random trait fluctuation?

Trends: changes to a trait or structure that occur in one linage or across the lineage of multiple organisms. Occurs over and over with increasing quantities, sizes, or complexities.
Random fluctuation: does not show a distinct pattern across linages, and doesn't it display increasing complexity overtime



a kingdom found in the original five-kingdom system and consisted of prokaryotic, unicellular organisms. Now is subdivided into Bacteria and Archaea



animals that do not have an internal body cavity lined with a mesoderm
Includes: Porifera, Cnidaria, and Platyhelminthes



a subclass of fish distinguished by bony skeletons and fins supported by ray-like structures; they are also the largest group of fish in the world


The zone of maturation

a sections of a plant's root system where cells differentiate into specialized cells, such as vascular cells. Located at the tip of the root



(cork tissue) a layer of cells located in the periderm (bark). Compromised of nonliving cell tissue and waxy suberin within the cell walls.



a type of ground cell found in plants that is an abundant, undifferentiated cell that can divide rapidly and specialize to fill multiple roles in the plant.



root-like appendages found in the bryophytes (a nonvascular group of plants that includes mosses). Rhizoids absorb water from the soil and transport it from cell to cell.


nonvascular plants

the group of plants that lack xylem and phloem tissue, which is used to transport materials such as food and water throughout the plant



though scaly structures that enclose and protect the reproductive structures of gymnosperms



the seed leaf found in the seeds of developing plant embryos that store nutrients for future absorption; monocots have one of these while dicots have two



the life cycle of plants
plants alternate between a diploid sporophyte generation and a haploid gametophyte generation



mechanisms of seed dispersal that depend on secondary agents, such as wind, water, and animals


estuary biome

where oceans meet fresh water
Constant water movement stirs up nutrient-rich material from the benthic areas and supports large amount of vegetation and animal life


interspecific competition

two or more different species that occupy the same habitat and whose niches overlap causing an increased competition


opportunist species

tend to be small in size, reproduce rapidly, generalize rather that specialize, and have short life cycles.



the process in which an individual consumes a pollutant faster than it loses the pollutant through metabolizaiton or excretion, leading to increased amounts of the pollutant in the body


What are the 8 taxons of the domain classification system?

Kingdom, Phylum, Class, Order, Family, Genus, Species


How do unicellular colonies differ from multicellular organisms?

Each cell in a unicellular colony can survive independently of the colony.
Multicellular organisms have many specialized cells that are dependent on each other for survival.


How do the different kingdoms differ in terms of reproduction and replication?

Bacteria and Archaea only reproduce asexually through binary fission.
All other kingdoms (eukaryotic) reproduce asexually or sexually.


What is the order of biological organizations in multicellular eukaryotes, from simplest to most complex?

Organelles, cells, tissues, organs, organ systems


Why do more complex organ systems arise in Coelomates than in Pseudocoelomates or Acoelomates?

Coelomates have a coelom (a fluid filled body cavity that is derived from the mesoderm) that allow for separation and specialization of distinct organ systems through compartmentalization.


How do hermaphroditic organisms reproduce?

(have both male and female organs)
They either self-fertilize or mate with another member of their species


What are some advantages of ectothermy?

Do not use high amounts of energy to generate body heat, so they don't require as much food as endotherms. They can survive for long periods of time without eating and the food they do eat provides energy for growth.


What are the 2 stages of the Cnidarian life cycle?

The sissile polyp - free-swimming larvae become sissile and produce buds (asexual reproduction).
The motile medusa - buds from sissile stage are released as motile medusas and are free-swimming or floating


How do organisms that lack organ systems obtain oxygen?

through air or water diffusion


How does the Annelida phylum differ from other worm-like phyla (like Nematoda and Platyhelminthes)?

(most complex of the three worm phyla)
Display segmentation, a coelom, and a closed circulatory system unlike the Nematoda and Platyhelminthes.


Why is the circulatory system in Molluscs considered an open circulatory system?

Blood pumps from a two-chambered heart into body spaces, where an exchange of materials occurs as blood surrounds tissues. Blood is not delivered to organs via vessels as in closed circulator systems.


What are the functions of the 3 main body segments in Arthropods?

Head: contains eyes, mouthparts, and antennae
Thorax: middle section that contains legs and wings
Abdomen: contains most major organs


What distinguishes a notochord from a backbone among members of the Chordata phylum?

Notochord: flexible, rod-shaped structure that extends from head to tail in Chordates. All Chordates have a notochord during development, which may become the spinal cord. Not all Chordates develop a backbone.


Which groups of animals in the Chordata phylum lay amniotic eggs?

Reptiles, birds, and some mammals lay amniotic eggs (enclosed by fluid-filled membranes and a protective shell)


What are the parts and functions of plant leaves?

Blades: broad sections of a leaf, upper side contains chloroplasts and initiates photosynthesis
Petioles: thin part, connects the blade to the stem and play vital role in transporting sugars to the stem for farther distribution


What is the path water travels from the soil through the root system?

Water is absorbed by root hairs from the soil > cortex > endodermis > pericycle > vascular tissue > other parts via vascular cylinder


What is the difference between primary and secondary growth in a plant?

Primary: growth in the roots and shoots, increasing plant height and extending roots father into the ground
Secondary: widening that occurs as the vascular cambium produces more tissue


Why do dicots experience secondary growth but monocots don't?

Dicot have vascular cambium but monocots do not.


What distinguishes ferns and fern allies from other types of vascular plants?

They don't reproduces via seeds like gymnosperms and angiosperms. Instead, they reproduce via spore cells.


Which mechanisms do plants use to disperse seeds?

Gravity, wind, water, internal animal, external animal, and self-ejection


What is the function of plant meristem?

Meristematic tissues in plants contain undifferentiated cells that can give rise to multiple different types of cells in order to aid plant growth and replace destroyed or damaged cells.


What are the major vertical zones of the ocean biome?

Benthic zone: ocean floor
The Pelagic zone: open ocean
The photic zone: surface layer


What are two defining characteristics of populations that are examined by the field of population ecology?

Density and dispersion


What is the difference between a habitat and a niche?

Habitat: physical space
Niche: the organism's role and behavior


Compared to the exponential growth model, why is the logistic growth model appropriate for real-world populations?

Exponential growth models don't consider limiting factors, but logistic growth models do.


What are the ecological advantages of asexual reproduction?

occurs at rapid pace which helps occupy new habitats, adapt to ecosystem change, and recover from population loss


What are the three types of symbiotic relationships that occur between species?

Parasitic: one benefits and the other is harmed
Communalistic: one benefits and the other is unaffected
Mutualism: both species benefit


Which of the following cellular processes normally produces ATP from glucose in the absence of oxygen?



A unicellular organism that has cell walls containing chitin and that reproduces by budding is most likely

a fungus


By which of the following mechanisms does feedback inhibition most likely occur in a metabolic pathway?

The end product of a pathway regulates an enzyme early in the pathway


Which of the following best describes the pathway of a protein from its manufacture to its secretion from the cell?

Endoplasmic reticulum → Golgi apparatus → secretory vesicle


Red blood cells (RBCs) are placed in a sucrose solution that is hyperosmotic with respect to the cells. Which of the following will most likely occur immediately?

Water will diffuse out of the RBCs


Which of the following events signals the end of the M and S phases of the cell cycle?

Degradation of cyclins bound to cyclin-dependent kinases


A segment of mouse genomic DNA encoding gene X is inserted into an expression plasmid containing a promoter sequence, and the plasmid is introduced into bacteria. The bacteria transcribe mRNA from the recombinant plasmid and produce protein X, but the protein differs in sequence from the protein normally produced by mice. Which of the following is the most likely reason for the different protein sequence produced?

Gene X contains exons and introns, and bacteria cannot remove introns from mRNAs.


A visual representation of an individual's chromosomes that have been stained, photographed, enlarged, and arranged in order of size from largest to smallest is known as a



The diversity of the finches on the Galápagos Islands is an example of which of the following?

Adaptive radiation


Males of a certain species of small mammal have either fluffy tails or furless tails. Those with fluffy tails have been observed to attract significantly more mates than those with furless tails. The phenomenon described is an example of

sexual selection because selection is based on a physical feature is sexual selection


What happens during contraction of skeletal muscle?

The sarcomere shortens, but the actin and myosin filaments do not change in length.


A female squirrel sounds an alarm call to warn other squirrels of an approaching predator despite the increased risk to herself. The squirrel's behavior is an example of which of

Altruistic behavior


Which of the following are believed to be factors that are involved in causing or exacerbating hypertension (high blood pressure)?

Atherosclerosis, High cholesterol levels, High dietary salt intake


Bacterial samples were counted every hour from a flask being incubated at 37°C on a shaker. Which of the following was most likely being studied?

The growth rate of bacteria


The changes in turgor pressure that cause the stomata of leaves to open and close result primarily from the reversible uptake and loss of what ions by the guard cells?



Which of the following is a true statement about the disposal of aluminum soda cans?

Aluminum cans should be recycled because processing of aluminum ore requires a lot of energy.

Explanation: Aluminum is refined from bauxite in a process that requires a tremendous amount of energy and also releases a lot of CO2 into the atmosphere. Recycling aluminum cans saves energy, reduces CO2 emissions, and decreases the amount of waste entering landfills.


In a germinating seedling, the shoot grows upward toward the light while the root grows downward into the soil. Which of the following correctly explains these phenomena?

The shoot exhibits positive phototropism; the root exhibits positive gravitropism.

Explanation: Phototropism - growth toward or away from light; gravitropism - growth toward or away from the force of gravity on Earth.


Which of the following statements about the acrosome of a human sperm is correct?

It contains enzymes to help the sperm penetrate the egg.


What was Antoni van Leeuwenhoek's major contribution to biology?

Advancing the field of microscopy through the discovery of bacteria and protists


Which of the following statements about the stratospheric ozone layer is accurate?

Accumulation of chlorofluorocarbons (CFCs) in the atmosphere has led to depletion of the ozone layer.


A researcher collects what appears to be a new species in a freshwater stream. Microscopic analysis shows the presence of chloroplasts, mitochondria, a defined nucleus, and a cellulose-based cell wall. Individual cells cluster to form colonies, but the colony lacks any true tissue or organ formations. This new species most likely belongs in which of the following kingdoms?


Explanation: The characteristics described are those of green algae, which are protists. Although many of the features are also common to members of kingdom Plantae, plants all possess some level of tissue specialization and features that allow their adaptation to a terrestrial environment. Fungi also have cell walls, but their primary component is chitin rather than cellulose.


If the cerebellum of a vertebrate becomes irreversibly damaged, the organism will have significant impairment of which of the following functions?

Coordination of movement and balance


Behavioral biologist Konrad Lorenz noticed that baby geese considered him to be their mother if he was the first image they saw immediately upon hatching. The baby geese were exhibiting which of the following behaviors?



In flowering plants, the seed leaves that may store carbohydrates for the embryonic plant are called



Investigators have immunized a rabbit with Substance P. They are studying the effect of the immunization on production of anti-Substance P antibodies over a two-week period following the immunization. Which of the following is the best hypothesis for the experiment?

Antibody production by the rabbit in response to Substance P will increase over a two-week period.


Using DNA technology, researchers are engineering nitrogen-fixing bacteria that can live in the tissues of nitrogen-demanding plants, which would reduce the need to use chemical fertilizers. Which of the following crops would most likely benefit from this kind of research?


Explanation: Nitrogen is the most limiting nutrient in corn production. The root nodules of all legumes, which include soybeans, alfalfa, and green beans, contain nitrogen-fixing bacteria that supply nitrogen to the plants. No such bacteria are associated with the roots of corn plants, so farmers generally turn to nitrogen-containing fertilizers.


Molecular geneticists have created fruit varieties that will not ripen naturally, allowing the fruit to be shipped over long distances without being damaged. They do so by inactivating genes for the production of a hormone that causes the fruit to ripen. Which of the following practices will cause the fruit to ripen once it is received?

Introducing ethylene gas into shipping containers or storage rooms

Explanation: Ripening in fruits and senescence (aging) are caused by the production and release of ethylene gas by the fruits. The reason that fruit ripens more quickly in a shipping container or a storage room is because the container or room prevents the escape of ethylene, concentrating it and speeding up the ripening process.


Male stickleback fish have a characteristic red belly coloration. To defend its territory, a male stickleback fish will attack other male sticklebacks or a model that has a red mark on its belly, even if the model does not look like a fish. Attacking a model that does not look like a fish is an example of which of the following?

Fixed action pattern

Explanation: Fixed action patterns are a sequence of behaviors that are triggered by an external sensory stimulus and that are basically unchangeable. Male sticklebacks act aggressively toward anything that bears a red marking on its underside.


A researcher identifies a new species within the moist soil of a wooded area. The species exhibits bilateral symmetry, has internal body segmentation, and uses metanephridia to remove wastes from its blood and coelomic fluid. Based on these characteristics, the new species should be categorized in which of the following animal phyla?


Explanation: The characteristics exhibited by the new species are all features of the phylum Annelida (i.e., segmented worms).


Aphids are small insects that rest on the stems and leaves of plants and insert their needlelike mouthpiece directly into the phloem of the plants. Which of the following is the primary reason that an aphid infestation will kill a plant?

Aphids deplete the sugars normally available for the plant.

Explanation: Phloem transports the products of photosynthesis (sugars) to growing parts and storage areas of the plant. By removing the sap from the phloem, aphids reduce the nutrients available to the plant.


Which of the following structures will most likely be damaged if there is an injury to the cells of the endoderm during embryogenesis?

Stomach lining

Explanation: The endoderm layer gives rise to the epithelial lining of many organs and body systems, including the liver, pancreas, thyroid gland, urinary bladder, digestive tract, respiratory system, and the reproductive system.


The role of denitrifying bacteria in the nitrogen cycle is to

convert nitrate, NO3–, to atmospheric nitrogen, N2

Explanation: Plants primarily acquire nitrogen in the form of NO3– that is formed in the soil by nitrifying bacteria. Denitrifying bacteria are facultative anaerobes that generally live deep in the soil or in stagnant water and return nitrogen to the atmosphere by converting nitrogen oxides to atmospheric nitrogen, N2.


Which of the following will most likely occur when two species in a habitat have overlapping niches?

Interspecific competition will increase.


The presence of which chemical compound in the atmosphere, resulting from the burning of fossil fuels, is a major factor in the formation of acid precipitation (acid rain) ?

Sulfur dioxide

Explanation: The formation and acidity levels of precipitation have been greatly affected by the release of nitrogen oxides and sulfur oxides during the burning of fossil fuels (coal, oil, and gas).


Which of the following describes the primary function of bone marrow in humans?

It is the source of new blood cells.


Which of the following pairs of scientists used bacteriophages, which are composed of only DNA and protein, to demonstrate that DNA is the heritable macromolecule that carries genetic information?

Alfred Hershey and Martha Chase


What are the major reservoirs of carbon?

soils, fossil fuels, the sediments of aquatic ecosystems, plant and animal biomass, the oceans, and the atmosphere. The largest reservoir is sedimentary rocks such as limestone.


Which of the following structures pumps blood out of the mammalian heart?


Explanation: Blood returning to the heart enters the atria, passes through valves into the ventricles, and is pumped out by the ventricles. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the rest of body.


Humans, reptiles, birds, and fish all belong to the same


Explanation: Humans, reptiles, birds, and fish are all members of the phylum Chordata


In an attempt to understand human diversity, scientists are studying slight variations in individual DNA sequences from people around the world. This type of research is known as