Chapter 6.2: Cell Transport Mechanisms

Types of Cell Transport

Cells use various mechanisms to move substances across their membranes. Understanding these processes is essential for grasping how cells maintain homeostasis and interact with their environment.

• Osmosis: The passive movement of water molecules across a selectively permeable membrane from an area of low solute concentration to high solute concentration.

• Diffusion: The passive movement of molecules from an area of higher concentration to lower concentration.

• Facilitated Diffusion: Passive transport of molecules across membranes via specific transmembrane proteins.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

Primary vs. Secondary Active Transport:

• Primary Active Transport: Direct use of ATP to transport molecules (e.g., Na+/K+ ATPase).

• Secondary Active Transport: Uses the energy from the movement of one molecule down its gradient to drive another molecule against its gradient.

Transport Proteins and Energy Requirements

• Na+/K+ ATPase: Pumps 3 Na+ ions out and 2 K+ ions into the cell per ATP hydrolyzed.

• Aquaporins: Channel proteins that facilitate water movement across membranes.

• Carrier Proteins: Bind and transport specific molecules across the membrane.

• Does passive transport require energy? No, passive transport does not require cellular energy.

• Does active transport require energy? Yes, active transport requires energy, typically from ATP.

Example: The Na+/K+ pump is crucial for maintaining cellular ion gradients and is an example of primary active transport.

Chapter 7: Cell Structure and Function

Prokaryotes vs. Eukaryotes

Cells are classified as prokaryotic or eukaryotic based on their structural features. Comparing these cell types helps understand their functions and evolutionary relationships.

• Prokaryotes: Lack a nucleus and membrane-bound organelles; DNA is located in the nucleoid region. Examples: Escherichia coli, Bacillus subtilis.

• Eukaryotes: Have a nucleus and membrane-bound organelles. Examples: animal cells, plant cells, fungi, protists.

• Comparison: Eukaryotes are generally larger and more complex than prokaryotes.

Cell Specialization: Cells may be specialized for particular functions, such as muscle contraction or photosynthesis.

Organelles and Their Functions

• Ribosomes: Sites of protein synthesis. In eukaryotes, ribosomes can be free in the cytoplasm or bound to the rough endoplasmic reticulum (RER).

• Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Organelles that contain DNA: Nucleus, mitochondria, and chloroplasts (in plants).

Example: Proteins synthesized by ribosomes on the RER are often destined for secretion or for use in the cell membrane.

Endocytosis and Exocytosis

Cells transport large molecules and particles via endocytosis and exocytosis.

• Endocytosis: The process by which cells engulf external substances, forming vesicles.

• Types of Endocytosis: Phagocytosis (cell eating), pinocytosis (cell drinking), receptor-mediated endocytosis.

• Exocytosis: The process by which cells expel materials in vesicles that fuse with the plasma membrane.

Example: White blood cells use phagocytosis to engulf pathogens.

Chapters 9 and 10: Cellular Metabolism and Photosynthesis

Oxidation and Reduction

Redox reactions are fundamental to cellular metabolism, involving the transfer of electrons between molecules.

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• Exergonic Reaction: Releases energy.

• Endergonic Reaction: Requires energy input.

Example: The oxidation of glucose during cellular respiration is an exergonic process.

Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose and other organic molecules.

• Catabolic Pathways: Break down molecules to release energy.

• Anabolic Pathways: Build complex molecules from simpler ones, requiring energy.

• Stages of Cellular Respiration: Glycolysis, Krebs cycle (citric acid cycle), electron transport chain.

• ATP Production: Most ATP is produced during oxidative phosphorylation in the mitochondria.

• Equation for Cellular Respiration:

• Oxygen Requirement: Aerobic respiration requires oxygen; anaerobic respiration does not.

• Purpose: To generate ATP for cellular activities.

Example: Muscle cells use aerobic respiration during prolonged exercise.

Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Light Reactions: Occur in the thylakoid membranes; convert solar energy to chemical energy (ATP and NADPH).

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to fix carbon dioxide into glucose.

• Equation for Photosynthesis:

• Relationship to Cellular Respiration: Photosynthesis stores energy in glucose; cellular respiration releases energy from glucose.

Example: Chloroplasts in plant cells carry out photosynthesis, providing energy for the plant and oxygen for other organisms.

Comparison Table: Prokaryotes vs. Eukaryotes

Comparison Table: Cellular Respiration vs. Photosynthesis

Additional info: Some context and definitions have been expanded for clarity and completeness.