Biology Chapter 2.3: Tissues Overview

Cell Theory

• Cells require a microscope for visualization due to their small size.
• A high surface area to volume ratio facilitates efficiency in cellular processes.
• Functions of cells include internal environment regulation, energy acquisition and utilization, environmental responsiveness, and providing protection and support.
• Key contributors to Cell Theory:
  • Zacharias Janssen: created the first primitive microscope.
  • Robert Hooke: observed cork cells.
  • Francesco Redi: disproved spontaneous generation through experiments with maggots.
  • Anton Van Leeuwenhoek: discovered bacteria.
  • Matthias Schleiden: concluded that all plants are made of cells.
  • Theodor Schwann: concluded that all animals are composed of cells.
  • Rudolf Virchow: stated that all cells arise from pre-existing cells.
• Principles of Cell Theory assert:
  • Living organisms consist of one or more cells.
  • The cell is the basic unit of life.
  • Cells originate from pre-existing cells.
• Spontaneous Generation Theory proposed that life could arise from non-living matter, later debunked.

Major Parts of the Cell

• Cells mainly consist of three divisions: Plasma Membrane, Cytoplasm, and Nucleus.
• Plasma Membrane serves as the barrier separating the cytoplasm from the external environment, consisting of phospholipids, cholesterol, membrane proteins, glycoproteins, and glycolipids.
• The phospholipid bilayer is fundamental, with hydrophilic phosphate heads facing the cytoplasm and hydrophobic fatty acid tails sandwiched.
• The fluid mosaic model describes the membrane structure as a flexible, dynamic assembly.
• Nervous tissues comprise astrocytes, microglial cells, ependymal cells, oligodendrocytes, satellite cells, and Schwann cells.

Structure of Plant Cell

• Meristematic tissues are found in growing areas, allowing for apical (primary) and lateral (secondary) growth.
• Permanent tissues are responsible for photosynthesis, support, and transport of water and nutrients.
• Key components of simple permanent tissues include cuticles (water retention), root hairs (absorption), trichomes (water loss prevention), and guard cells (stomata regulation).
• Ground tissues consist of parenchyma (food storage), collenchyma (flexible support), and sclerenchyma (strengthening).
• Xylem transports water; phloem transports nutrients throughout plants.

Structure of Modified Cell

• Specialized animal cells include microvilli (nutrient absorption), cilia (mucus clearance), stereocilia (sensation), and flagella (motility).
• Basal infoldings increase surface area for ion and fluid transport while hemidesmosomes provide cell attachment.
• Cell junctions (tight junctions, adherens junctions, desmosomes, gap junctions) connect adjacent cells.
• Red blood cells facilitate gas diffusion and lack a nucleus, aiding oxygen transport.
• Hydra reproduce asexually through budding.

Significance of Meiosis

• Meiosis reduces genetic material and enables sexual reproduction, contributing to genetic diversity and inheritance for survival.
• This process produces gametes, restores chromosome number during fertilization, and increases survival probability.

Disorders and Diseases Related to Cell Malfunction

• Mitotic and meiotic errors include nondisjunction, where chromosomes fail to separate properly.
• Disorders like polyploidy and aneuploidy result from abnormal chromosome numbers.
• Cancer signifies uncontrolled cell growth, while nondisjunction disorders include Down Syndrome (Trisomy 21), Patau's Syndrome (Trisomy 13), and Turner Syndrome (monosomy X).

Structure and Functions of the Cell Membrane

• The phospholipid bilayer acts as a selective barrier for molecule and ion passage.
• Cholesterol stabilizes membrane fluidity across temperature variations.
• Membrane proteins serve functions in transport, adhesion, recognition, and receptor signaling.
• Carbohydrates form glycolipids and glycoproteins, enhancing cellular communication.

Cell's Transport Mechanism I: Diffusion and Osmosis

• Diffusion involves movement from high to low solute concentration (simple and facilitated).
• Osmosis refers to water movement toward low solute concentration, impacted by tonicity (isotonic, hypotonic, hypertonic).
  • Isotonic: equal solute concentration inside and outside the cell.
  • Hypotonic: lower solute concentration outside, causing swelling.
  • Hypertonic: higher solute concentration outside, leading to cell shrinkage.

Cell's Transport Mechanism II: Active and Facilitated Transport

• Active Transport moves molecules against concentration gradients, requiring energy (e.g., sodium-potassium pump).
• Facilitated Transport utilizes membrane proteins for moving molecules down concentration gradients (e.g., glucose transporters).

Bulk or Vesicular Transport

• Vesicles are cytoplasmic sacs enclosed by a lipid bilayer formed by Golgi Bodies.
• Processes include budding, scission, uncoating, translocation, tethering, and fusion.
• Types of vesicular transport: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (cell regulation).

Endocytosis and Exocytosis

• Exocytosis can be constitutive (continuous vesicle transport) or regulated (triggered transport).
• Endocytosis brings molecules into the cell:
  • Phagocytosis: ingestion of food molecules.
  • Pinocytosis: uptake of liquids or small molecules.
  • Receptor-mediated endocytosis: selective molecule regulation via receptors.

Enzyme Structure and Function

• Enzymes catalyze chemical reactions, reducing activation energy and speeding up reaction rates.
• Substrates are molecules acted upon by enzymes; products are resultant from substrate-enzyme interaction.
• Mechanisms include the lock and key model and induced fit theory.
• Enzymes play crucial roles in digestion, cell division, nervous function, and DNA replication.

Enzyme in Biological Systems

• Anabolism builds complex molecules; catabolism breaks down molecules.
• Redox reactions involve electron transfer, with redox enzymes facilitating these processes.
• Free radicals are uncharged atoms/molecules associated with cellular damage.

Factors that Affect Enzyme Regulation and Metabolism

• Reaction rates depend on the saturation level; the saturation point signifies the maximum achievable reaction rate.
• Temperature increases generally boost enzyme activity rates, optimizing biochemical reactions.

Explore the main types of tissues in animals and plants, including skeletal, smooth, and cardiac muscle tissues, as well as nervous tissues like astrocytes and microglial cells. Additionally, learn about meristematic and permanent tissues in plants and their roles in growth. This quiz will test your understanding of tissue structures and functions.