Biological Transport

Cell Membrane Structure and Function

The cell membrane is a selectively permeable barrier that regulates the movement of substances into and out of the cell. It is primarily composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Selective Permeability: Allows certain molecules to pass while restricting others, maintaining homeostasis.

• Fluid Mosaic Model: Describes the dynamic and flexible nature of the membrane.

• Functions: Protection, communication, transport of materials, and cell recognition.

Diffusion and Factors Affecting Rate

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration.

• Factors Affecting Diffusion Rate:

  • Molecule Size: Smaller molecules diffuse faster than larger ones.

  • Charge: Uncharged (nonpolar) molecules diffuse more easily than charged (polar) molecules.

  • Temperature: Higher temperatures increase the kinetic energy of molecules, speeding up diffusion.

Osmosis is the diffusion of water across a selectively permeable membrane.

Osmotic Behavior in Plant and Animal Cells

• Isotonic Solution: Solute concentration is equal inside and outside the cell; no net water movement.

• Hypotonic Solution: Lower solute concentration outside; water enters the cell.

  • Animal Cells: May burst (lysis).

  • Plant Cells: Become turgid (normal state due to cell wall).

• Hypertonic Solution: Higher solute concentration outside; water leaves the cell.

  • Animal Cells: Shrivel (crenation).

  • Plant Cells: Undergo plasmolysis (cell membrane pulls away from cell wall).

Enzymes

Function and Regulation

Enzymes are biological catalysts that speed up chemical reactions without being consumed. They lower the activation energy required for reactions.

• Active Site: Region where substrate binds and reaction occurs.

• Specificity: Each enzyme acts on a specific substrate.

• Regulation: Enzyme activity can be regulated by inhibitors (competitive and noncompetitive) and by allosteric regulation.

Effects of Temperature and pH

• Temperature: Each enzyme has an optimal temperature. High temperatures can denature enzymes, reducing activity.

• pH: Each enzyme has an optimal pH. Deviations can alter enzyme structure and function.

Photosynthesis

Basic Principles and Requirements

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

• Requirements: Water (H2O), carbon dioxide (CO2), and light energy.

• General Equation:

• Products: Glucose (C6H12O6) and oxygen (O2).

Photosynthetic Pigments

• Chlorophyll a: Main pigment, absorbs blue-violet and red light.

• Chlorophyll b: Accessory pigment, broadens the spectrum of absorbed light.

• Carotenoids: Accessory pigments, absorb excess light energy and protect chlorophyll.

Leaf Structure: Stomata and Associated Cells

• Stomata (Stomates): Pores on the leaf surface for gas exchange.

• Guard Cells: Surround stomata and regulate their opening and closing.

• Epidermal Cells: Outermost layer of cells, provide protection.

Cellular Respiration

Reactants and Products

Cellular respiration is the process by which cells extract energy from glucose.

• Aerobic Respiration: Requires oxygen.

  • Equation:

• Anaerobic Respiration (Fermentation): Occurs without oxygen.

  • In yeast: Produces ethanol and CO2.

  • In animal cells: Produces lactic acid.

Comparison Table: Aerobic vs. Anaerobic Respiration

Mitosis

Stages of the Cell Cycle

The cell cycle consists of interphase (cell growth and DNA replication) and mitosis (nuclear division).

• Interphase: Cell grows, performs normal functions, and duplicates DNA.

• Mitosis: Division of the nucleus into two genetically identical daughter nuclei. Stages include:

  • Prophase: Chromosomes condense, spindle forms.

  • Metaphase: Chromosomes align at the cell equator.

  • Anaphase: Sister chromatids separate to opposite poles.

  • Telophase: Nuclear envelopes reform, chromosomes decondense.

• Cytokinesis: Division of the cytoplasm, forming two separate cells.

Application: Recognizing stages of mitosis in diagrams or microscope images is essential for understanding cell division and its regulation.

Additional info: Academic context and definitions have been added to expand on the brief review guide points and ensure the notes are self-contained for exam preparation.