Deoxygenated blood enters the heart from the rest of the body via the anterior vena cava and then enters the right atrium. From there, blood is pumped into the right ventricle and into the lungs to become reoxygenated. Reoxygenated blood is then pumped into the left atrium from the lungs and into the left ventricle, where it is then pumped out into the rest of the body via the aorta.

Crossing over takes place in prophase I of meiosis. Homologous chromosomes must be joined by exchanged DNA sequences before they can align at the metaphase plate.

Salamanders (along with frogs and snake-like caecilians) are tetrapods that lack water tight, amniotic eggs. Amphibians must lay their eggs in moist environments. Sharks are not tetrapods, and ostriches, rattlesnakes, and kangaroos are all amniotes. (Note that mammals are considered amniotes because they evolved from an ancestor with an amniotic egg.)

Because its evolutionary history is elsewhere, milfoil has adapted to an environment that lacks the natural predators and pathogens of North America, making it less susceptible to them and therefore more competitive than native plants in North America.

The production of urea serves to chemically join ammonia and carbon dioxide, thereby converting it to a relatively harmless compound. This prevents ammonia, which is toxic, from accumulating in the bloodstream and allows it to be eliminated without releasing large quantities of water.

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E The other choices do not describe substrate binding sites on an enzyme.

The nucleic acid in mRNA carries genetic information from the nucleus to the ribosomes in the cytoplasm, where it is translated into a polypeptide.

Both parents must be homozygous recessive, thus rendering them incapable of producing a dark-haired baby displaying the dominant trait. In Choice B, if both parents are heterozygous, they can display dark hair but still produce a light-haired baby. In Choice C we know that the mother is homozygous recessive, but we do not know whether the paternal genotype is homozygous dominant or heterozygous. If the father is heterozygous, it is possible that the couple could produce a light-haired child, making this an incorrect answer. Choice D is the same scenario as Choice C, but with the parents' genotypes reversed. In Choice E, no matter the woman's genotype, the couple may produce a dark-haired baby.

The pancreas secretes glucagon in response to low blood glucose levels. This causes the liver to release glucose into the bloodstream.

Centipedes belong to the phylum Arthropoda. Arthropods feature a ventral nerve cord, segmented body plan, jointed appendages, and possibly an exoskeleton of chitin. Mollusks (such as snails) secrete a calcium-rich shell.

While hyenas often feed on carrion, they are not considered decomposers. Decomposers convert molecules into substrates that may be used by producers to create organic compounds.

C For this question, you really have to know the definition of translate and know which type of nucleic acid gets translated. Eliminate choice E first, because it is not a nucleic acid (it's an enzyme). You should also be able to eliminate choice A fairly easily, if you know that RNA, and not DNA, is the nucleic acid that is translated. Finally, you should know that mRNA (messenger RNA) is the nucleic acid that is read (translated) to synthesize protein.

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The Calvin cycle fixes carbon dioxide, converting it, via a series of reactions, to a three-carbon sugar.

Only in bryophytes is the haploid gametophyte the dominant generation.

Nucleic acids are formed from mononucleotide polymers. A mononucleotide is one unit that is composed of three components: a sugar; a phosphate, which binds to the sugar in order to create the phosphodiester bond that unites nucleotides into a nucleic acid chain; and a nitrogen base, which pairs with other bases to form a readable sequence.

Genome marker maps are assembled using gene linkage informa-tion. Gene linkage occurs when genes are located next to each other in the genome and do not assort independently.

B Start by eliminating structures that are not layers, such as choices A, D, and E. Because humans do not have a cuticle as an outer layer (that's a plant layer), choice C can also be eliminated.

B Remember your LEAST/EXCEPT/NOT technique. Lizards, turtles, alligators, and snakes are all members of the class Reptilia. Frogs, however, are members of class Amphibia.

NPP is not equal to the total biomass of producers, but to the amount of biomass that is added. In a stable lake, the added phytoplankton biomass will equal that consumed by zooplankton.

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E Again, the human is being harmed by the tapeworm, so eliminate choices in which no harm is done (choices B and D). The human is not preyed on by the tapeworm (choice A is eliminated), and neither are the human and tapeworm competing (choice C is eliminated).

Phloem is the plant vascular tissue responsible for conducting water and dissolved sugars throughout the plant, downward from the leaves. It is always exterior to xylem, from which it is separated by the vascular cambium.

E Decomposers take organic material and break it down into its individual compounds, thus returning these compounds back to the earth. The other processes listed are carried out by other organisms: nitrogen fixing bacteria (choice A), heterotrophs and autotrophs (choice B), and other soil bacteria (choices C and D).

Hormones are secreted into the bloodstream, while neurotransmitters are released into the synapses between neurons.

According to Chargoff's rule, equal amounts of adenine and thymine, and of guanine and cytosine, will be present in a DNA sample. Therefore, the amount of cytosine will be equal to the amount of guanine, 32%. The percentages of adenine and thymine will total 36%, or 18% each.

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Polygenic inheritance describes traits that are influenced by multiple genes. Epistasis is an interaction between two genes, both affecting a phenotype. In contrast, pleiotropy occurs when a single gene influ-ences multiple traits.

In order for there to be interspecific competition, each organism must occupy the same niche to some degree. Of all the listed examples, a deer and a hare are most likely to share food resources and habitat space, which would create competition between them.

The nerve is outside the CNS and so belongs to the peripheral nervous system (PNS). Because it is not under voluntary control, it must belong to the autonomic system. Because it promotes “rest and digest” functions, it must belong to the parasympathetic (rather than sympathetic) nervous system. Finally, because it innervates the intestines, it is likely part of the enteric nervous system.

D This question is intimidating because it seems so complex. Remember to take the question apart piece by piece-don't guess at an answer until you are sure what the question is asking! The best way to tackle this question is to draw a diagram of the interactions of the populations with one another. It might look something like this:

The concept of inclusive fitness states that altruism can increase an individual's fitness by increasing the number of offspring produced by genetically similar individuals, such as siblings or parents. Alarm calls and care for the offspring of others are examples of altruistic acts.

Action potentials are transmitted from input at the dendrites of a neuron, travel down the axon, and release neurotransmitters into the synapse between adjacent cells. These neurotransmitters bind to receptors on the dendrite of the second neuron, helping to produce a new action potential. Action potentials cannot travel through synapses.

Females with Turner's syndrome lack an X chromosome. If females with this syndrome have a high rate of hemophilia, they must not have the second X to mask the expression of the disease.

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D Remember: "Dumb King Philip Came Over From Germany-So?" or make up your own!

A hypertonic solution has a higher osmotic pressure, meaning it has a higher concentration of dissolved solutes. A blood cell in this environment will lose water into the solution and shrivel because there is a pressure gradient across the cell membrane.