STAAR Biology Review

Which of these explains the relationship between the leaf-cutter ants and the fungi?

• Predation, because the ants feed on the fungi

• Mutualism, because both the ants and the fungi benefit from

  each other

• Competition, because both organisms consume the same resource for energy

• Commensalism, because the ants receive energy from the fungi and the fungi are unaffected

Answer explanation

The relationship between the leaf-cutter ants and the fungi is mutualism. Both the ants and fungi benefit from each other.

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NGSS.MS-LS2-2

Some relationships between species found in the Texas Gulf Coast are shown in the food web.

Which energy pyramid best models energy flow in the Texas Gulf Coast community?

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Answer explanation

Stone crabs consume gulf pipefish, and gulf pipefish consume aquatic plants.

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In some coral reefs, a symbiotic relationship exists between pygmy seahorses and sea fans. The pygmy seahorse can wrap its tail around the branches of the sea fan. This allows the pygmy seahorse to be camouflaged within the sea fan, protecting it from predators. The pygmy seahorse does not harm or benefit the sea fan while it grasps the branches with its tail. What is the correct classification of this symbiotic relationship?

• Predator/prey

• Mutualism

• Commensalism

• Parasite/host

Answer explanation

Commensalism is the symbiotic relationship that exists. The pygmy seahorse does not harm or benefit the sea fan while it grasps the branches with its tail.

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NGSS.HS-LS2-6

After a wheat field is cleared, wild grasses and weeds begin growing. This process is considered —

• primary succession because pioneer species appear

• primary succession because there are no large trees

• secondary succession because soil is already present

• secondary succession because the field contains inorganic matter

Answer explanation

After a wheat field is cleared, wild grasses and weeds begin growing due to secondary succession, since soil is already present. Primary succession can only occur in areas where life was not previously present e.g., newly formed volcanic rock.

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During an extended dry season in an area, the majority of the ground cover dried up. Which description best explains how this would affect the ecosystem in that area?

• The ecosystem would become less stable because the ranges of many organisms would expand and overlap.

• The ecosystem would become more stable because there would be less competition among canopy plants.

• The ecosystem would become less stable because less energy would be available to it from the decrease in producers.

• The ecosystem would become more stable because organisms in higher trophic levels would be able to find prey more easily.

Answer explanation

The ecosystem would become less stable if most of the ground cover dried up. Less energy would be available to the ecosystem due to a decrease in the number of producers.

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Which of these shows an example of an insertion mutation?

• A

• B

• C

• D

Answer explanation

An insertion mutation is a result of inserting new nitrogenous bases into DNA. In this model, new “K” and “L” genes have been inserted into the chromosome.

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NGSS.HS-LS3-2

A model of the genetic control of coat color in rabbits is shown.

Which Punnett square represents a cross that would produce albino offspring?

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Answer explanation

The albino allele (c) is recessive to all other alleles, so expression of the albino phenotype requires two copies of the allele. This option is the only option where two albino alleles would result.

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Which amino acid would be coded first from the DNA strand being transcribed?

• Cys

• Phe

• Ile

• Met

Answer explanation

The first mRNA codon is AUG. AUG on the codon chart codes for the amino acid Met.

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A cellular process is shown.

Which of these is the most likely result of the process shown in the diagram?

• Chromosome replication will cease to avoid errors that result in mutations.

• Offspring will no longer express traits from previous generations.

• Gametes will contain new allele combinations.

• Chromatids will have less genetic variety.

Answer explanation

In meiosis, during the cellular process of crossing over, homologous chromosome pairs exchange parts with each other creating new allele combinations on each chromosome.

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E. coli has three genes that each code for different enzymes that break down lactose. Scientists conducted investigations about the production of these enzymes using samples of E. coli. Their results are shown in the table. Which conclusion about the production of the enzymes can be determined by analyzing the scientists’ results?

• Gene expression for the enzymes was controlled by the temperature of lactose.

• The genes for the enzymes were expressed in equal amounts during both experiments.

•  Gene expression for the enzymes was controlled by the presence of lactose.

• The genes for the enzymes were mutated before being expressed by the presence of lactose.

Answer explanation

The scientists’ results indicate that gene expression for the enzymes was controlled by the presence of lactose because enzyme concentration was high when lactose was present and low when lactose was not present.