Biology Chapter: The Cell and Its Functions

The Cell

• The cell is the fundamental unit of life.
• All living things are composed of one or more cells.
• Cells carry out essential functions like nourishment, environmental interaction, and reproduction.

Types of Cells

• Eukaryotic cells contain a nucleus.
• Prokaryotic cells lack a nucleus.

Organisms and Cell Number

• Unicellular organisms consist of a single cell.
  • Examples include bacteria and protozoa.
• Multicellular organisms are formed from two or more cells.
  • Examples include animals and plants.

Parts of the Cell

• Most cells share three basic components:
  • Nucleus (excludes prokaryotic cells)
  • Cytoplasm
  • Plasma membrane
• Additional structures include:
  • Cytoskeleton
  • Organelles
  • Cell wall (present in specific cell types)

Cytology

• Cytology is the biological study of cells and their functions.
• All living organisms rely on cells.
• Cells execute all life processes.

The Nucleus

• The nucleus is an internal structure exclusive to eukaryotic cells.
• It houses the genetic material of multicellular organisms.
• It's enveloped by cytoplasm and a membrane.
• It manages the activities of organelles within the cytoplasm.
• It directs cell reproduction.
• It holds the organism's genetic information.

Nucleus Structure

• Nuclear membrane: The outer layer of the nucleus.
• Nucleoplasm: The nucleus's internal fluid, containing various structures.
• Nucleolus: A dense region within the nucleus, responsible for ribosome production.
• Chromatin: Structures of proteins and DNA (deoxyribonucleic acid).
  • Chromatin packages into chromosomes.

Cytoplasm

• Cytoplasm is the watery, gel-like substance within the cell.
• Cytoskeleton: A dynamic filament network in all cell types.
  • The cytoskeleton gives the cytoplasm and membrane their shape, consistency, and dynamism.
  • It's continuously changing.
• Organelles: Small, specialized structures within the cytoplasm performing varied functions.
  • Their number and type change based on the cell's function.

Organelles

• Ribosomes: Present in all cells.
  • Composed of two RNA subunits.
  • Synthesize enzymes and proteins.
• Endoplasmic reticulum (ER): A membrane network transporting proteins.
  • Rough ER: Receives proteins.
  • Smooth ER: Creates new membranes.
• Golgi apparatus: Sacs near the nucleus, processing and packaging molecules from the ER into vesicles for cell export.
• Lysosomes: Membranous sacs digesting cellular material.
• Mitochondria: Two-membraned sacs generating energy for the cell through chemical reactions.
  • Each mitochondrion contains its own DNA (mitochondrial chromosome).

Organelles Found Only in Plant Cells

• Vacuoles: Compartments in eukaryotic plant cells storing fluids (like water) and potentially enzymes and nutrients.
• Plastids: Involved in photosynthesis, starch storage or synthesis of various materials.
  • Chloroplasts: Carry out photosynthesis.
  • Amyloplasts: Store starch.
  • Leucoplasts: Synthesize materials.

Peroxisomes

• Vesicle-shaped organelles for hydrogen peroxide oxidation and disposal.

Centrioles

• Barrel-shaped organelles aligned at right angles, crucial for cell division.

Flagella

• A single, elongated cellular projection for cell movement.

Cilia

• Multiple, thin cellular projections facilitating cell and fluid movement.

Plasma Membrane

• Plasma membrane (cell membrane/plasmalemma): The cell's outer boundary.
  • Functions include:
    • Maintaining cell stability.
    • Controlling molecule entry/exit.
    • Facilitating cell-cell communication.

Cell Wall

• Cell wall: Present in prokaryotes, plant cells, and fungi.
  • A rigid outer layer covering the plasma membrane.
  • Functions include:
    • Protecting the plasma membrane from osmotic stress.
    • Maintaining cell shape.
    • Preventing dehydration.