AP Biology Unit 3

Energy can be taken in as glucose, then has to be converted to a form that can be easily used to perform work in cells. What is the name of the latter molecule?

ATP contains potential for a quick burst of energy that can be harnessed to perform cellular work.

A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (Pi) is essential to cellular function. Which of the following statements best helps justify the researcher's claim?

ATP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy.

Which of the following comparisons or contrasts between endergonic and exergonic reactions is false?

Both endergonic and exergonic reactions require a small amount of energy to overcome an activation barrier.

Describe the connection between anabolic and catabolic chemical reactions in a metabolic pathway.

Catabolic reactions release energy and simpler compounds, whereas anabolic reactions involve the use of energy to make more complex compounds.

How do chemical reactions play a role in energy transfer?

Energy must be stored in a cell in the form of a bond between two molecules; it cannot be stored in the cell as free energy. The energy is attached to a chemical such as ATP, which transfers the energy from one reaction to another and from one area of a cell to another safely. Energy never exists in the living cells as free energy. These ATP molecules are obtained from the metabolism of glucose.

Which chemical reaction is more likely to occur?

Exergonic reactions can occur spontaneously, and free energy is released from the reaction.

What does it mean for a system to be in a higher level of entropy? How can it be reduced?

Higher level of entropy refers to higher state of disorder in the system and it can be reduced by input of energy to lower the entropy.

Energy transfers take place constantly in every day activities. Think of two scenarios: cooking on a stove and driving. Explain how the second law of thermodynamics applies to these scenarios.

In both examples, there is an input of energy that results in work being done—cooking and moving the car—and loss of heat as a result. The heat loss travels into the room during cooking and into the metal of the engine during gasoline combustion. Energy must be continuously put into the systems to maintain the activities. Run out of natural gas or propane, and the cooking stops. Run out of gasoline, and the car stops. The second law of thermodynamics states that no energy transfer is efficient, and some form of energy in the form of heat is released. While cooking, heat is lost and travels into the room. The engine metal heats up during gasoline combustion. If propane or gas runs out, then both of the activities would stop.

What counteracts entropy?

Input of energy lowers the entropy of the system and decreases the disorder. Thus, input of energy counteracts high entropy and makes the system stable.

Name two different cellular functions that require energy.

Phagocytosis helps amoebae in uptake of nutrients, and pseudopodia help the amoebae move.

Does physical exercise involve anabolic processes, catabolic processes, or both? Give evidence for your answer.

Physical exercise involves both catabolic and anabolic processes. Glucose is broken down into simpler compounds during physical activity to provide energy for forming molecules in anabolic pathway. Those molecules are then used to provide energy to the muscles for contraction.

Which of the following molecules is likely to have the most potential energy?

Sucrose is a disaccharide molecule made of glucose and fructose. The stored potential energy in it would be the greatest.

Which of the following best describes energy?

The ability to do work or cause some change is called energy.

Which of the following is the best way to judge the relative activation energies between two given chemical reactions?

The activation energy of a particular reaction determines the rate at which it will proceed. The higher the activation energy, the slower the chemical reaction will be. Thus, relative activation energies between two chemical reactions can be judged by comparing their reaction rates.

Imagine an elaborate ant farm with tunnels and passageways through the sand where ants live in a large community. Now imagine that an earthquake shook the ground and demolished the ant farm. In which of these two scenarios, before or after the earthquake, was the ant farm system in a state of higher or lower entropy? Why?

The ant farm is in the state of high entropy after the earthquake and energy must be spent to bring the system to low entropy.

Consider a pendulum swinging. Which type(s) of energy is/are associated with the pendulum in the following instances: 1. the moment at which it completes one cycle, just before it begins to fall back towards the other end; 2. the moment that it is in the middle between the two ends; 3. just before it reaches the end of one cycle (before step 1)

The energy possessed by the pendulum after completion of one cycle would be potential since it is at some elevation and energy is in stored form. When the pendulum is in between the two ends, then it is in motion and thus possesses kinetic energy.

Label each of the following systems as high or low entropy: 1. perfume the instant after it is sprayed into the air; 2. an unmaintained 1950s car compared with a brand new car; 3. a living cell compared with a dead cell

The entropy in case (1) would be low, since the disorder of the perfume is low immediately after it is sprayed; (2) would be high because, over time, the disorder in a 1950s car would increase; and (3) would be low because a living cell would have less disorder in comparison to dead cell.

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.

What is the difference between the first and second laws of thermodynamics?

The first law of thermodynamics states that energy can neither be created nor destroyed. It is just transformed from one state to other. The second law of thermodynamics states that every energy transfer involves some loss of energy in an unusable form, such as heat energy, resulting in a more disordered system.

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes. Which of the following must remain the same for all trials of this experiment?

The initial concentration of the substrate

What is the ultimate source of energy on this planet?

The main source of energy for this planet is the sun. Solar energy includes light, radio waves, and X-rays, all of which provide energy on Earth.

Explain the conversion of energy that takes place when the sluice of a dam is opened.

The potential energy of the water held in the reservoir behind the dam converts to kinetic energy as it falls through the opening of the sluice. Potential energy is referred to the energy stored in a system due to its position. Therefore, water held in a dam possesses potential energy, whereas kinetic energy is referred to as energy possessed by the motion of the object. When the sluice of the dam is opened, the potential energy is converted to kinetic energy.

Which of the following statements best helps explain the reaction specificity of an enzyme?

The shape and charge of the substrates are compatible with the active site of the enzyme.

Describe the position of the transition state on a vertical energy scale, from low to high, relative to the position of the reactants and products, for both endergonic and exergonic reactions.

The transition state of the reaction exists at a higher energy state than the reactants and, thus, activation energy is always positive regardless of whether the reaction is an exergonic or endergonic reaction.

Which of the following is the best example of the first law of thermodynamics?

A power plant burning coal and producing electricity is an example of the first law of thermodynamics. Energy is transformed from one form to another.

Explain the difference between a spontaneous reaction and one that occurs instantaneously.

A spontaneous reaction occurs without the input of energy and decreases the free energy of a system, making the system more stable and releasing that energy to do work. An instantaneous reaction occurs very rapidly with a sudden release of energy. A spontaneous reaction does not require energy to carry out the reaction. It releases free energy that is used by the system to move to a stable state. The difference lies in the duration of reactions: spontaneous reactions can take seconds to years, while instantaneous reactions occur right away.

When the air temperature drops and rain turns to snow, which law of thermodynamics is exhibited?

first law of thermodynamics

What food molecule used by animals for energy and obtained from plants is most directly related to the use of sun energy?

glucose

Which pair of descriptors of chemical reactions go together?

hydrolysis and exergonic

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students' results are shown in graph 1. If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be____

lower than the level at pH 9

What is an anabolic pathway? Which of these is an example of an anabolic pathway used by cells in their metabolism?

Anabolic pathways build new molecules out of the products of catabolic pathways. An example is the linkage of nucleotides to form a molecule of mRNA.

A researcher claims that only a portion of the light energy captured by green plants is available for growth and repair. (The researcher is thinking about the Second Law of Thermodynamics here.) Which of the following observations best helps justify the researcher's claim?

As light energy is converted to chemical energy by metabolic processes, some of the energy is lost as heat.

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.

Which of the following is a catabolic process?

Digestion of sucrose is a catabolic process because sucrose, being a disaccharide, is a complex molecule.

DNA replication involves unwinding two strands of parent DNA, copying each strand to synthesize complementary strands and releasing the resulting two semi-conserved strands of DNA. Which of the following accurately describes this process?

This is an anabolic process.

Which best describes the effect of inputting energy into a living system?

This is the best answer because inputting energy into a living system will allow cells to perform a variety of functions that decrease entropy, such as moving substances against their concentration gradient, repairing damage to cells and molecules, and storing energy as ATP.

Which of the terms in the Gibbs free energy equation denotes enthalpy?

Total energy change in a system is called enthalpy and is denoted by Delta H .