Ch. 5: The Working Cell – Essay Questions Study Guide

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Ch. 5: The Working Cell

Essay Questions – Key Concepts and Explanations

1. Potential Energy in Molecules

The amount of potential energy stored in molecules depends on their structure and the types of chemical bonds they contain. Large, complex molecules like polysaccharides or lipids generally store more potential energy than smaller, simpler molecules.

Key Point: Energy is stored in the chemical bonds of molecules; breaking these bonds releases energy that can be used by cells.
Example: Glucose contains more potential energy than carbon dioxide and water, which are its breakdown products after cellular respiration.
Additional info: Endergonic reactions absorb energy, while exergonic reactions release energy.

2. Chemical Reactions in Human Cells

Most chemical reactions in cells do not occur spontaneously at body temperature. Instead, they require enzymes to lower the activation energy and allow reactions to proceed efficiently.

Key Point: Enzymes are biological catalysts that speed up chemical reactions without being consumed.
Example: The breakdown of hydrogen peroxide by the enzyme catalase.

3. Enzyme Specificity and Substrate Interaction

Enzymes are highly specific for their substrates due to the unique shape of their active sites. This specificity ensures that enzymes catalyze only particular reactions.

Key Point: The induced fit model describes how enzymes change shape slightly to fit their substrates.
Example: Sucrase only catalyzes the hydrolysis of sucrose, not other disaccharides.

4. Effects of Environmental Factors on Enzyme Activity

Enzyme activity can be affected by temperature, pH, and the presence of inhibitors or activators. Each enzyme has optimal conditions under which it functions best.

Key Point: High temperatures or extreme pH can denature enzymes, reducing their activity.
Example: Pepsin works best in the acidic environment of the stomach.

5. Energy Conversion in Cells

Cells convert energy from one form to another, such as light energy to chemical energy during photosynthesis, or chemical energy to kinetic energy during muscle contraction.

Key Point: The first law of thermodynamics states that energy cannot be created or destroyed, only transformed.
Equation: (Change in energy equals heat added minus work done)
Example: Plants convert sunlight into glucose via photosynthesis.

6. Thermoregulation and Energy Balance

Organisms must regulate their internal temperature and energy balance to survive. Homeostasis involves maintaining stable internal conditions despite changes in the external environment.

Key Point: Endotherms generate heat internally, while ectotherms rely on external sources.
Example: Humans sweat to cool down when overheated.

7. ATP: The Energy Currency of the Cell

Adenosine triphosphate (ATP) is the primary energy carrier in cells. ATP stores energy in its high-energy phosphate bonds and releases it when these bonds are broken.

Key Point: ATP is produced during cellular respiration and used for cellular work.
Equation:
Example: Muscle contraction uses ATP to power movement.

8. Enzyme Inhibition and Regulation

Enzyme activity can be regulated by inhibitors, which decrease activity, or activators, which increase it. Inhibition can be competitive (blocking the active site) or noncompetitive (changing enzyme shape).

Key Point: Feedback inhibition is a common regulatory mechanism in metabolic pathways.
Example: The end product of a pathway inhibits the first enzyme in the pathway.

9. Energy Flow in Ecosystems

Energy flows through ecosystems from producers to consumers and decomposers. Only a fraction of energy is transferred between trophic levels; the rest is lost as heat.

Key Point: The second law of thermodynamics states that energy transformations increase entropy (disorder).
Example: Food chains illustrate energy transfer from plants to herbivores to carnivores.

10. Cellular Work and Energy Use

Cells use energy to perform work, including mechanical, transport, and chemical work. Energy from ATP is used to drive these processes.

Key Point: Cellular work includes muscle contraction, active transport, and biosynthesis.
Example: Sodium-potassium pumps use ATP to maintain ion gradients across membranes.