Eukaryotic cells first appeared billions of years ago and were marked by the presence of membrane-bound organelles (organelles with a lipid bilayer surrounding them) similar to the outer and inner membranes of prokaryotes like bacteria. One of these membrane bound organelles is called the mitochondrion, which is responsible for helping generate energy in the form of a nucleotide-sugar molecule called adenosine triphosphate (also known as ATP).

By using only oxygen and glucose (a type of sugar composed of a single molecule) as reactants, the mitochondrion is responsible for generating ATP and water. In order to make ATP, animals must eat food products that contain sugars, such as potatoes, which contain molecules called starches that have many sugar molecules linked together. Once the sugar has been processed in the cell by an enzyme called amylase, it undergoes a process called glycolysis, which breaks down glucose into a molecule called pyruvate and provides 2 ATP molecules in the process.

After glycolysis, the pyruvate molecule is transported to the mitochondrion, carried across its membrane and then enters a process called the Kreb’s cycle, where a net of 34 ATP are produced. However, the process of transporting the pyruvate molecule into the mitochondrion requires 1 ATP. The ATP produced from both glycolysis and the Kreb’s cycle serves to allow the cell to carry out its housekeeping functions.

The passage implies that eukaryotes may have:

Ecological succession refers to the observable change of the species composition of an ecological community over a period of time. This phenomenon is also known as forest succession. It is a process that begins with the colonization of a habitat by robust pioneer species that can survive inclement and harsh environments. Pioneer species are characterized by small size and rapid reproduction of many offspring. Over successive generations these species are replaced with increasing complexity until the ecosystem reaches a self-perpetuating climax community that ceases to vary in composition.

Researchers decide to quantify the ecological succession of a particular deciduous forest. Figure 1 is a representation of an ecological community over a forty-year period. The bars on the graph represent the percentage of the forest community that is made up by a particular species.

What are the pioneer species in the study?

Ecological succession refers to the observable change of the species composition of an ecological community over a period of time. This phenomenon is also known as forest succession. It is a process that begins with the colonization of a habitat by robust pioneer species that can survive inclement and harsh environments. Pioneer species are characterized by small size and rapid reproduction of many offspring. Over successive generations these species are replaced with increasing complexity until the ecosystem reaches a self-perpetuating climax community that ceases to vary in composition.

Researchers decide to quantify the ecological succession of a particular deciduous forest. Figure 1 is a representation of an ecological community over a forty-year period. The bars on the graph represent the percentage of the forest community that is made up by a particular species.

What is the order, from smallest to greatest, of the percentages of species present in the climax community?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

Based on the figures, which enzyme functions best at temperature extremes?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

Based on the figures, which enzyme is most likely to function in the blood?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

Based on the figures, which enzyme is most likely to function in the small intestine?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

Based on the figures, which enzyme is most likely to function in the stomach?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

Based on the figures, which enzyme functions optimally at body temperature (about 37ºC)?

Amino acids, when strung together in extensive chains, serve as the building blocks of muscles and proteins. At around 37ºC, these amino acid chains allow the body to carry out both macroscopic processes, like moving arms and legs, and microscopic processes, like increasing the rate of chemical reactions. A special class of proteins called enzymes assists in combining reactants to produce products by speeding up the rate of a reaction in one of three ways.

The first way enzymes increase reaction rate is by lowering the activation energy of a reaction. This is done by balancing positively charged amino acids with negatively charged amino acids, creating an electrically neutral environment. This process is called electrostatic interaction. Another way enzymes increase reaction rate is through the use of non-charged amino acids, such as valine and isoleucine, in a process called Van der Waals interactions. In Van der Waals interactions, the non-charged amino acids become temporarily polarized, similar to the permanent polarity of positively and negatively charged amino acids. This interaction brings non-charged amino acids together to stabilize the reactants. The final way enzymes increase reaction rates is by sharing the electrons in its hydrogen atoms with nitrogen, oxygen, or fluorine on the reactant molecules to trap them at the active site. The active site is the part of an enzyme where molecules bind and undergo a chemical reaction.

Enzymes are designed to work in specific parts of the body depending on their functions. For example, an enzyme in the stomach responsible for breaking down food would work most effectively at low pH while an enzyme in the small intestine responsible for absorbing food would work most effectively at high pH. Some enzymes, such as those that function in the blood, work best at intermediate pH. Some enzymes function better at lower temperatures while others require higher temperatures. All enzymes have exponential relationships between their rates of reactions and both pH and temperature, meaning that they function best in narrow pH and temperature windows. Graphs of four enzymes and their rates of reaction at various pH levels and temperature are presented below.

A certain enzyme in plants allows for improved conversion of sunlight and carbon dioxide into glucose and oxygen during photosynthesis. As temperature increases, the enzyme is able to help produce more oxygen. According to the figures, which enzyme is most likely to exist in plants?

Hormones are biochemical messengers utilized by multicellular organisms to coordinate development and behaviors. Hormones are secreted by the endocrine system and are key components in signal cascades that result in various essential activities. Plants, like animals, depend on hormonal signals for physiological adaptation and development.

There are several hormones that are primarily involved with seed germination and sprout formation. Abscisic acid, in high concentrations, prevents seed germination. Auxins are compounds that positively influence cell enlargement, the formation of buds, and the development of roots. Cytokinins influence cell division and shoot formation. Gibberellins promote seed germination as well as flowering and growth post-germination.

Study 1

Several scientists soaked Zea mays (corn) seeds in solutions rich in certain plant hormones. They observed and recorded seed germination and development over a three week period. At the end of the three week period, they measured coleoptile (the protective extension of sprout) and radicle (the primary root) growth of the seeds and plotted them in a graph (Figure 1).

Figure 1

Study 2

Scientists exposed Zea mays (corn) seeds to several hormonal treatments and measured coleoptile growth over a 14-day period and recorded their observations in a line graph (Figure 2). The groups consisted of a control exposed to saline solution, a treatment group exposed to a 0.15 millimolar solution of abscisic acid, and a treatment group exposed to a solution that included 0.15 millimoles of abscisic acid and 0.20 millimoles of gibberellins.

Figure 2

In Study 1, which of the treatments most positively facilitated seed growth and germination?