Cell Biology Overview

Functions of the Cell

Structure

  • Organelle: Specialized structures within a cell that perform distinct functions.
  • Cell membrane:
    • Composition: Double membrane made of lipids.
    • Function: Allows selective movement of particles in and out of the cell, facilitating various cellular functions.
  • Cytoplasm:
    • Description: Semi-solid, gel-like fluid within the cell, where many chemical reactions occur.
  • Nucleus: Enclosed by a double membrane; contains DNA and controls all cellular activities.

Components

Mitochondria
  • Description: Enclosed by a double membrane; site of aerobic respiration.
  • Function: Releases energy for the cell’s activities using glucose and oxygen.
  • DNA Presence: Contains its own DNA, indicating a degree of autonomy.
Ribosome
  • Composition: Not enclosed by a membrane; made of proteins and RNA.
  • Function: Protein synthesis.
Cell Wall
  • Composition: Made of cellulose in plant cells.
  • Function: Provides support and protection to the cell; helps regulate the movement of substances in and out.
Chloroplast
  • Description: Enclosed by a double membrane.
  • Function: Site of photosynthesis; converts light energy into chemical energy.
  • DNA Presence: Contains its own DNA.
Vacuole
  • Description: Enclosed by a single membrane, filled with cell sap.
  • Function: Storage of substances; contributes to rigidity in plant cells.

Cell Functions

Movement

  • Plants: Roots grow toward moisture.
  • Animals: Movement toward food and away from danger.

Reproduction

  • R: Cellular respiration denoted by the equation:
    • Chemical Reaction: ext{Glucose} + ext{Oxygen}
      ightarrow ext{Energy} + ext{Carbon Dioxide} + ext{Water}
    • Process: Involves the release of energy during metabolic processes.

Sensitivity

  • Definition: The ability to respond to environmental signals through senses (sight, smell, touch, taste, and hearing).
  • Homeostasis: Process of taking in signals from the environment to react and maintain body temperature.

Growth

  • Description: Involves cell division, where one cell divides into multiple cells, leading to the growth of an organism.
  • Types of Organisms:
    • Unicellular: Made up of one cell.
    • Multicellular: Comprises numerous diverse cells.

Excretion

  • Definition: Removal of metabolic waste from the body.
  • Details: Urine is a method of excretion, while defecation (pooping) is not considered excretion.
  • Plants: Primarily intake water and minerals and respire through their roots.

Nutrition

  • Definition: Converting chemical energy from sunlight into energy usable by the cell.
  • Plants: Leaves capture light and convert it into chemical energy through photosynthesis.

Cellular Organization

Levels of Biological Organization

  • Cell → Tissue → Organ → Organ System → Organism

Types of Cells

9.4 Bacterial, Virus, Fungi, and Protist Cells

Pathogens
  • Definition: Microorganisms that carry diseases.
Bacterial Cells (Prokaryotic)
  • Components:
    • Cell Wall: Provides structure and protection.
    • Ribosomes: Sites of protein synthesis.
    • Flagella: For movement.
    • Plasmid: Small, circular DNA molecule.
    • Lack: Mitochondria and chloroplasts; no true nucleus.
Viruses
  • Description: Consist of strands of DNA or RNA encapsulated in a protein coat.
  • Reproduction Requirement: Need host cells for reproduction, hence often not classified as living organisms.
Fungi**
  • Cell Wall Composition: Made of chitin.
  • Nutrition Mode: Saprotrophic nutrition – absorbs nutrients externally by secreting digestive enzymes that break down surrounding food.
Protists
  • Characteristics: Diverse group; often eukaryotic and can be unicellular or multicellular.

Specialised Cells

Types of Specialised Cells

Root Hair Cell
  • Function: To absorb water and minerals from the soil.
  • Structure: Long root hair increases surface area for absorption.
  • Chloroplast Presence: Absent due to underground location.
Palisade Cell
  • Function: Conduct photosynthesis to produce glucose for the plant.
  • Structure: Contains numerous chloroplasts; tall and thin to maximize light absorption.
Sperm Cell
  • Function: To fertilize an egg cell.
  • Structure: Long tail aids in swimming; many mitochondria for energy.
Egg Cell
  • Function: To be fertilized by a sperm cell.
  • Structure: Nutrient-rich cytoplasm; membrane changes post-fertilization to prevent further sperm entry.
Muscle Cell
  • Function: Movement of the body.
  • Structure: Contains protein bands that contract and relax; many mitochondria provide energy.
Nerve Cell
  • Function: Transmit nerve impulses throughout the body.
  • Structure: Long fibers; branching dendrites connect to other nerves or muscles.
Ciliated Epithelial Cell
  • Function: Remove dust and microorganisms from the lungs.
  • Features: Tiny hair-like structures called cilia help waft mucus along airways; energy from mitochondria facilitates cilia movement.
Red Blood Cell
  • Function: Transport oxygen throughout the body.
  • Structure: No nucleus, optimizing space for hemoglobin; biconcave shape enhances oxygen diffusion.
White Blood Cell
  • Function: Combat pathogens causing disease.
  • Features: Produce antibodies; change shape to engulf pathogens or squeeze out of blood vessels to reach affected areas.

Overview of Cell Types

Eukaryotic Cells

  • Categories: Plant, Animal, Fungi, Protist.
  • Nature: Generally multicellular.

Prokaryotic Cells

  • Characteristics: Lack a nucleus and other membrane-bound organelles; usually unicellular.

Nutrition Types in Organisms

  • Autotrophic: Organisms that produce their own food (e.g., plants through photosynthesis).
  • Heterotrophic: Organisms that consume food (e.g., animals).
  • Saprotrophic: Organisms that absorb nutrients externally (e.g., fungi).