Unit 2 Ap Bio Review

AP Biology Unit 2 Review: Cellular Structure and Function – A Deep Dive

This comprehensive review covers AP Biology Unit 2, focusing on the structure and function of cells. Mastering this unit is crucial for success in the AP Biology exam, as it lays the foundation for understanding more complex biological processes. We'll delve into the intricacies of cell biology, exploring prokaryotic and eukaryotic cells, membrane structure and function, cell transport mechanisms, and cellular respiration. Prepare to solidify your understanding and boost your confidence for the upcoming exam!

I. Introduction: The Cell – The Fundamental Unit of Life

Biology, at its core, is the study of life. And the fundamental unit of life? The cell! Unit 2 in AP Biology delves into the fascinating world of cells, exploring their structures, functions, and the intricate processes that keep them alive. Understanding the cell is key to understanding all higher levels of biological organization, from tissues and organs to entire organisms and ecosystems. This review will cover the essential concepts you need to master for the AP exam, focusing on both prokaryotic and eukaryotic cells and the various processes that occur within them. We'll dissect the key differences between these cell types, explore membrane transport mechanisms, and delve into the powerhouse of the cell – cellular respiration.

II. Prokaryotic vs. Eukaryotic Cells: A Tale of Two Cell Types

The first critical distinction in cell biology is between prokaryotic and eukaryotic cells. These two cell types differ dramatically in their structure and complexity:

Prokaryotic Cells:

• Simplicity: These cells are significantly simpler and smaller than eukaryotic cells. They lack a membrane-bound nucleus and other membrane-bound organelles.
• Genetic Material: Their genetic material (DNA) is located in a region called the nucleoid, which is not enclosed by a membrane.
• Organelles: Prokaryotic cells possess ribosomes, but lack other complex organelles like mitochondria, chloroplasts, or endoplasmic reticulum.
• Examples: Bacteria and archaea are examples of organisms composed of prokaryotic cells.
• Cell Wall: Most prokaryotes have a rigid cell wall outside the plasma membrane, providing structural support and protection. The composition of this cell wall differs between bacteria and archaea.

Eukaryotic Cells:

• Complexity: Eukaryotic cells are significantly more complex and larger than prokaryotic cells. They possess a membrane-bound nucleus and a variety of other membrane-bound organelles.
• Membrane-Bound Nucleus: The genetic material (DNA) is enclosed within a double membrane-bound nucleus.
• Organelles: Eukaryotic cells contain a wide array of organelles, each with specialized functions, including mitochondria (for cellular respiration), chloroplasts (in plants, for photosynthesis), endoplasmic reticulum (for protein synthesis and lipid metabolism), Golgi apparatus (for protein modification and sorting), lysosomes (for waste breakdown), and vacuoles (for storage).
• Examples: Animals, plants, fungi, and protists are all composed of eukaryotic cells.
• Cell Wall: Plant cells and fungal cells have cell walls, but animal cells do not. Plant cell walls are primarily composed of cellulose, while fungal cell walls are composed of chitin.

III. Cell Membranes: The Gatekeepers of the Cell

The cell membrane, also known as the plasma membrane, is a selectively permeable barrier that surrounds the cell, regulating the passage of substances into and out of the cell. Its structure is crucial to its function.

Fluid Mosaic Model: The cell membrane is best described by the fluid mosaic model. This model depicts the membrane as a fluid bilayer of phospholipids, with embedded proteins and other molecules.

• Phospholipids: These amphipathic molecules form a bilayer, with their hydrophilic (water-loving) heads facing the aqueous environment (inside and outside the cell) and their hydrophobic (water-fearing) tails facing each other in the interior of the membrane.
• Proteins: Membrane proteins have diverse functions, including transport, enzymatic activity, signal transduction, cell adhesion, and intercellular communication. These proteins can be integral (embedded within the membrane) or peripheral (associated with the membrane surface).
• Cholesterol: In animal cells, cholesterol molecules are embedded within the phospholipid bilayer, influencing membrane fluidity.

IV. Membrane Transport: Moving Molecules Across the Membrane

The cell membrane's selective permeability ensures that only certain substances can cross it. This transport can be passive (requiring no energy) or active (requiring energy).

Passive Transport:

• Simple Diffusion: Movement of substances from an area of high concentration to an area of low concentration, directly across the membrane. This process is driven by the concentration gradient. Small, nonpolar molecules like oxygen and carbon dioxide diffuse readily across the membrane.
• Facilitated Diffusion: Movement of substances across the membrane with the assistance of membrane proteins. This is used for larger or polar molecules that cannot easily cross the membrane on their own. Channel proteins and carrier proteins facilitate this type of transport.
• Osmosis: The diffusion of water across a selectively permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration). Osmosis is crucial for maintaining cell turgor pressure and preventing cell lysis.

Active Transport:

• Primary Active Transport: Movement of substances against their concentration gradient, requiring energy directly from ATP hydrolysis. The sodium-potassium pump is a classic example.
• Secondary Active Transport: Movement of substances against their concentration gradient, utilizing the energy stored in an electrochemical gradient created by primary active transport. This often involves co-transport of two molecules.
• Endocytosis: The process of bringing substances into the cell by engulfing them in a vesicle. This includes phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis.
• Exocytosis: The process of releasing substances from the cell by fusing vesicles with the plasma membrane.

V. Cellular Respiration: Energy Production in the Cell

Cellular respiration is the process by which cells break down glucose to generate ATP, the primary energy currency of the cell. This process occurs in several stages:

Glycolysis:

• Location: Cytoplasm
• Input: Glucose
• Output: 2 pyruvate, 2 ATP, 2 NADH
• This is an anaerobic process (does not require oxygen).

Pyruvate Oxidation:

• Location: Mitochondrial matrix
• Input: 2 pyruvate
• Output: 2 acetyl-CoA, 2 NADH, 2 CO2

Krebs Cycle (Citric Acid Cycle):

• Location: Mitochondrial matrix
• Input: 2 acetyl-CoA
• Output: 2 ATP, 6 NADH, 2 FADH2, 4 CO2

Electron Transport Chain (ETC) and Oxidative Phosphorylation:

• Location: Inner mitochondrial membrane
• Input: NADH, FADH2, O2
• Output: ~34 ATP, H2O
• This is an aerobic process (requires oxygen). The ETC generates a proton gradient across the inner mitochondrial membrane, which drives ATP synthesis through chemiosmosis.

Total ATP Production: The theoretical maximum ATP yield from the complete oxidation of one glucose molecule is approximately 38 ATP. However, the actual yield is often slightly lower.

VI. Other Important Cellular Structures and Processes

Beyond the core concepts already discussed, several other cellular components and processes are important for a thorough understanding of Unit 2:

• Ribosomes: The sites of protein synthesis. Ribosomes can be free in the cytoplasm or bound to the endoplasmic reticulum.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein synthesis and lipid metabolism. Rough ER (with ribosomes) is involved in protein synthesis, while smooth ER is involved in lipid synthesis and detoxification.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
• Lysosomes: Membrane-bound organelles containing digestive enzymes that break down waste materials and cellular debris.
• Vacuoles: Storage compartments in cells, often larger in plant cells.
• Mitochondria: The "powerhouses" of the cell, where cellular respiration occurs.
• Chloroplasts (in plant cells): The sites of photosynthesis, where light energy is converted into chemical energy.
• Cytoskeleton: A network of protein filaments that provides structural support and facilitates cell movement.
• Cell Junctions: Specialized structures that connect adjacent cells, providing communication and structural integrity.

VII. Frequently Asked Questions (FAQs)

Q: What's the difference between diffusion and osmosis?

A: Diffusion is the movement of any substance from an area of high concentration to an area of low concentration. Osmosis is specifically the diffusion of water across a selectively permeable membrane.

Q: What is the role of ATP in cellular respiration?

A: ATP (adenosine triphosphate) is the primary energy currency of the cell. Cellular respiration generates ATP, which is then used to power various cellular processes.

Q: How does the sodium-potassium pump work?

A: The sodium-potassium pump is a primary active transporter that uses ATP to pump sodium ions out of the cell and potassium ions into the cell, against their concentration gradients. This creates an electrochemical gradient across the membrane.

Q: What is the significance of the fluid mosaic model?

A: The fluid mosaic model describes the structure of the cell membrane as a fluid bilayer of phospholipids with embedded proteins. This structure allows for the membrane's selective permeability and dynamic nature.

Q: How do plant cells maintain turgor pressure?

A: Plant cells maintain turgor pressure (the pressure of the cell contents against the cell wall) through osmosis. Water enters the cell by osmosis, creating pressure against the cell wall.

VIII. Conclusion: Mastering Cellular Structure and Function

Understanding the intricacies of cellular structure and function is paramount for success in AP Biology. This review has covered the key concepts, from the fundamental differences between prokaryotic and eukaryotic cells to the detailed processes of membrane transport and cellular respiration. By thoroughly grasping these concepts, you'll be well-prepared to tackle the challenges of the AP Biology exam and build a strong foundation for future studies in biology. Remember to utilize practice questions and review materials to solidify your understanding and identify any areas requiring further study. Good luck!