Biology Chapter: Cell Structure

Cell Organelles and Their Functions

• Mitochondria: Known as the "Powerhouse of the cell," responsible for producing most ATP through aerobic respiration. They are about 0.2 µm in diameter and 2-6 µm long, featuring double membranes with inner cristae that increase surface area for cellular respiration.

• Lysosomes: Digestive organelles that act as vesicles to break down ingested material. Slightly smaller than mitochondria, they contain about 60 enzymes that facilitate chemical reactions and the disposal of degraded material.

• Centrioles: Rod-shaped structures that occur in pairs (Diplosomes/Centrosome), positioned at right angles to each other. They play a crucial role in chromosome movement during cell division, forming the mitotic spindle.

• Cytoskeleton: An extensive network of protein structures providing internal support, cell shape, and facilitating intracellular transport and cellular movement. Comprised of three types of filaments.

Cell Division Process

• Interphase: The phase between cell divisions that includes metabolic activity and DNA replication. There are three distinct phases within interphase:

  • G1 Phase: The cell grows and metabolizes, but there is no DNA replication.
  • S Phase: Chromosomal replication occurs, resulting in identical genetic copies.
  • G2 Phase: Pre-Mitotic phase where cell growth continues and proteins are synthesized.

• Mitosis: The nuclear division process yielding two identical daughter cells, divided into four stages:

  • Prophase: Chromatin condenses into chromosomes; centrioles move to opposite poles of the cell.

Transport Mechanisms

• Filtration: Movement of liquid through a filter, driven by hydrostatic pressure, separating larger molecules from smaller ones in a solution.

• Dialysis: Involves selective permeable membrane allowing small molecules to pass while retaining larger ones.

• Active Transport: Requires metabolic energy (ATP) to move substances against a concentration gradient, occurring via processes like:

  • Endocytosis: Absorbing extracellular substances into cells by engulfing them.
    • Phagocytosis: "Cell eating," engulfing solid particles for immune defense.
    • Pinocytosis: "Cell drinking," taking in liquids with dissolved nutrients.

• Exocytosis: The process of moving substances out of the cell, including the secretion of hormones and removal of waste.

Structure of the Cell

• Cell Components:
  • Plasma Membrane: Encloses cytoplasm, provides a selective barrier for substance movement.
  • Nucleus: Control center of the cell, containing nucleolus responsible for rRNA synthesis and gene regulation.
  • Cytoplasm: Factory area containing organelles and cytosol where cellular activities occur.

Cell Life Cycle

• Cell Division: The process for cell reproduction, including mitosis and meiosis.
• Mitosis: Results in two identical daughter cells through one nuclear division and chromosomal duplication.
• Meiosis: Reduces chromosome number by half, crucial for gamete formation; involves cytokinesis post-division.

Summary of Transport Mechanisms

• Passive Transport: Movement without energy expenditure, classified into:
  • Diffusion: Movement from higher to lower concentration.
  • Osmosis: Diffusion of water across membranes.
  • Filtration and Dialysis: Specialized processes for separating substances in a liquid.

Explore the fundamental components of a cell in this quiz, focusing on the plasma membrane, nucleus, and cytoplasm. Understand how organelles function and learn about the crucial role of the cell membrane in regulating substance movement. Test your knowledge on cell structure and function.