Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building?

The food chain describes who eats whom in the wild. Every living thing—from one-celled algae to giant blue whales—needs food to survive. Each food chain is a possible pathway that energy and nutrients can follow through the ecosystem.

For example, grass produces its own food from sunlight. A rabbit eats the grass. A fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants like grass.

Of course, many different animals eat grass, and rabbits can eat other plants besides grass. Foxes, in turn, can eat many types of animals and plants. Each of these living things can be a part of multiple food chains. All of the interconnected and overlapping food chains in an ecosystem make up a food web.

Trophic Levels

Organisms in food chains are grouped into categories called trophic levels. Roughly speaking, these levels are divided into producers (first trophic level), consumers (second, third, and fourth trophic levels), and decomposers.

Producers, also known as autotrophs, make their own food. They make up the first level of every food chain. Autotrophs are usually plants or one-celled organisms. Nearly all autotrophs use a process called photosynthesis to create “food” (a nutrient called glucose) from sunlight, carbon dioxide, and water.

Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcanoes use sulfur compounds to produce their own food. This process is called chemosynthesis.

The second trophic level consists of organisms that eat the producers. These are called primary consumers, or herbivores. Deer, turtles, and many types of birds are herbivores. Secondary consumers eat the herbivores. Tertiary consumers eat the secondary consumers. There may be more levels of consumers before a chain finally reaches its top predator. Top predators, also called apex predators, eat other consumers.

Consumers can be carnivores (animals that eat other animals) or omnivores (animals that eat both plants and animals). Omnivores, like people, consume many types of foods. People eat plants, such as vegetables and fruits. We also eat animals and animal products, such as meat, milk, and eggs. We eat fungi, such as mushrooms. We also eat algae, in edible seaweeds like nori (used to wrap sushi rolls) and sea lettuce (used in salads).

Detritivores and decomposers are the final part of food chains. Detritivores are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures eat dead animals. Dung beetles eat animal feces.

Decomposers like fungi and bacteria complete the food chain. They turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. Decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new food chain.

In one marine food chain, single-celled organisms called phytoplankton provide food for tiny shrimp called krill. Krill provide the main food source for the blue whale, an animal on the third trophic level.

In a grassland ecosystem, a grasshopper might eat grass, a producer. The grasshopper might get eaten by a rat, which in turn is consumed by a snake. Finally, a hawk—an apex predator—swoops down and snatches up the snake.

In a pond, the autotroph might be algae. A mosquito larva eats the algae, and then perhaps a dragonfly larva eats the young mosquito. The dragonfly larva becomes food for a fish, which provides a tasty meal for a raccoon.

Which of the following is the smallest biological structure that would most likely be visible with a standard research-grade light microscope?

The CFTR protein is made up of 1,480 amino acids linked together in a chain. Some humans produce a version of the CFTR protein in which phenylalanine (an amino acid) has been deleted from position 508 of the amino acid chain. Which of the following best predicts how the amino acid will affect the structure of the CFTR protein?

It will affect the primary, secondary, and tertiary structures of the CFTR protein.

Which of the following statements best explains how a modern transmission electron microscope (TEM) can achieve a resolution of about 2.0 nanometers, whereas a standard light microscope has a maximum resolution of about 200 nanometers?

The wavelengths of electron beams are much shorter than the wavelengths of visible light.

Which of the following structures is common to plant and animal cells?

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product. Which of the following statements best helps explain how the enzyme speeds up the reaction?

The enzyme's active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.

Which of the following structures are found in plant, animal, and bacterial cells?

Which of the following areas in bacterial cells best describes where chromosomal DNA is generally localized?

Which of the following statements best describes the function of the nuclear pore complex found in eukaryotic cells?

It regulates the movement of proteins and RNAs into and out of the nucleus.

Disruption of nuclear pore complexes in a eukaryotic cell will most likely interfere with the transport of which of the following molecules out of the nucleus?

Which of the following best predicts the effect of not having ATP available to supply energy to this process?

H+ ions will stop moving through the protein.

Which of the following terms most precisely identifies the cellular process of breaking down large molecules into smaller ones?

In which reactions of cellular respiration does substrate-level phosphorylation occur?

in both glycolysis and the citric acid cycle

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body. Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Substrate-level phosphorylation accounts for approximately what percent of the ATP formed by the reactions of glycolysis?

Glycolysis results in the net production of which of the following sets of molecules per glucose molecule?

2 NADH, 2 pyruvate, and 2 ATP

What of the following reactions produces the majority of the CO2 released by the complete oxidation of glucose?

If glucose is the sole energy source for cellular respiration in an animal, what proportion of the carbon dioxide exhaled is derived from oxidation of pyruvate to acetyl CoA?

Researchers claimed that a particular organelle originated from a free-living prokaryotic cell that was engulfed by a larger cell, as shown in Figure 1. Which of the following provides evidence to best support the researchers' claim?

The organelle has a double membrane

Which of the following events takes place in the electron transport chain?

Which two cellular organelles in eukaryotes have both electron transport systems and chemiosmotic mechanisms?

Chloroplasts and mitochondria

Which of the following processes is driven by chemiosmosis?

Oxidative phosphorylation

Which two cellular organelles in eukaryotes have both electron transport systems and chemiosmotic mechanisms?

Chloroplasts and mitochondria

What are the products of the electron flow in the light dependent reactions of photosynthesis?

Which of the following processes would be most directly affected if a thylakoid membrane is punctured (has a hole in it) so that the interior of the thylakoid is no longer separated from the stroma?

Which of the following best describes the process by which the bacteria are breaking down the glucose to produce lactic acid?

The bacteria are breaking down sugars in the absence of oxygen

In chloroplasts, the photosynthetic electron transport chain acidifies which of the following cellular compartments?

In a plant, which of the following reactions produces molecular oxygen (O2)?

The light reactions alone

Graphs I-IV depict the effect of pH on the activity of four different hydrolytic enzymes The most likely explanation for the results shown in Graph I is that...

The oxygen released by photosynthesis is produced by which of the following processes?

splitting water molecules

What is the name of the region on duplicated chromosomes where the sister chromatids are most closely attached to each other?

Which of the following best describes the process by which the bacteria are breaking down the glucose to produce lactic acid?

Which of the following was the dependent variable in the researcher's experiment?

In a diploid cell with four chromosome pairs (2n=8),how many centromeres will be found in a nucleus at G2 of the cell division cycle?

The diagram above represents a typical rod-shaped bacterium. Which of the following best describes a feature shown in the diagram that is unique to archaea and bacteria?

The organism does not have a nuclear membrane surrounding its genetic material.

Which of the following statements about reproduction is correct?

In sexual reproduction, individuals transmit half of their nuclear genes to each of their offspring.

Which of the following statements is true of a species that has a chromosome number of 2n=16?

Each diploid cell has eight homologous pairs of chromosomes.

Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building biological molecules?

Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

The researchers calculate a chi-square value of 4.6 and choose a significance level of p = 0.05. Which of the following statements best completes the chi-square goodness-of-fit test?

The null hypothesis cannot be rejected because the chi-square value is less than the critical value

A triploid cell contains three sets of homologous chromosomes. Which of the following describes the chromosomes in a triploid cell where n = 6?

Which of the following statements about the law of independent assortment is correct?

It describes the inheritance of different genes relative to one another.

Which of the following statements about the law of segregation is correct?

It describes the inheritance of different alleles relative to one another

In Table II, the F1 offspring of the cross between broad-leaved, white-flowered plants with narrow-leaved, purple-flowered plants have a phenotype that differs from that of either parent. However, many testcross offspring have the same phenotype as one of the two plants in the parental cross, but relatively few testcross offspring have the same phenotype as the F1 offspring. Which of the following best explains the observation?

Recombination between the leaf shape and flower color genes resulted in chromosomes carrying a dominant allele of both genes

According to chemiosmotic theory (chemiosmotic coupling), the energy required to move protons from the mitochondrial matrix to the intermembrane space against a concentration gradient comes most directly from

Based on the information presented, which of the following is the most likely explanation for a buildup of cholesterol molecules in the blood of an animal?

The animal's body cells are defective in endocytosis

Based on Figure 2, which of the following best supports the claim that drug X inhibits oxygen consumption?

A researcher measured the temperature at which two different samples of double-stranded DNA (separate into single strands) Sample 1 denatured at a significantly lower temperature than 2 did. Based on the data, the researcher claims that the DNA in sample 2 is composed of a higher percentage of guanine and cytosine than the DNA in sample 1 is. Which of the following best supports the researcher's claim?

Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do.

Based on the data in Figure 1, which of the following most likely represents the change in energy that occurs when ATP hydrolysis is coupled with the phosphorylation of a substrate?

Line 1 represents ATP hydrolysis, and line 4 represents phosphorylation of a substrate.

Organelles such as mitochondria and the endoplasmic reticulum have membranes that compartmentalize reactions and other metabolic processes. To function properly, the organelles must move substances across their membranes. Which of the following statements describes a feature shared by mitochondria and the endoplasmic reticulum that increases the efficiency of their basic functions?

They have highly folded membranes

Which of the following is the best explanation for the pattern of change in mass of the organisms over time?

Saccharomyces cerevisiae is a diploid yeast species that can reproduce either sexually or asexually. An experiment was performed to induce mitotically dividing S. cerevisiae cells in G2 to undergo meiosis. Which of the following best describes the steps these cells will follow to form gametes?

The first division will reduce the number of chromosomes by half for each daughter cell, and the second division will move single chromatids to each daughter cell

A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell?

Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

Some green sea turtle female deposit their eggs in nests that are dug on warm, tropical beaches. Researchers have studied the effects of temperature on the hatching rate and the proportion of female to male hatchlings produced at different average nest temperatures in Suriname (Figure 1). At temperatures below 23 C or above 33 C, the eggs do not develop. Which of the following best describes the results shown in Figure 1?

Which of the following statements correctly explains the fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment?

All of the genes controlling the traits were on different chromosomes

The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?

Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype?

A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the process will be in the cell?

Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

Pigeons demonstrate ZW sex determination, such that a ZZ genotype produces a male and a ZW genotype produces a female. The gene for feather color is located on the Z chromosome, and the red allele is dominant over the brown allele. Three crosses between brown male pigeons and red female pigeons were performed, and the results are shown below. Which of the following is the mean number of male offspring produced by the three crosses?

Why did all of the F1 offspring of Mendel's purple and white flowered pea cross always look like one of the two parental varieties?

Black fur in mice (b) is dominant to brown fur (b). Short tails (S) are dominant to long tails (s). What fraction of the progeny of crosses BbSs x BBss will be expected to have black fur and long tails?

Which of the following best supports the claim that organisms of different domains share a common ancestor?

Glycolysis occurs in both prokaryotic cells and eukaryotic cells

Which of the following conclusions is most clearly supported by the representations of nucleic acid #1 and nucleic acid #2?

Nucleic acid #1 contains adenine-thymine base pairs, whereas nucleic acid #2 does not

Having polydactyly (extra digits on hands and feet) is a dominant trait. A man has polydactyly. His wife and oldest daughter do not have polydactyly. The couple's second child has polydactyly. What is the probability that their next (third) child will have extra digits?

Which of the following statements justifies the claim that the conditions in the experiment above could generate the molecular building blocks essential for life?

What best describes the structure of carbohydrates?

What best describes the hydrolysis of carbohydrates?

Which of the following best describes a structural difference between DNA and RNA responses?