The Cell

The cell is the basic structural and functional unit of all known organisms. It is the smallest unit of life that can replicate independently.

Plant Cell: Cell Organelles and their Functions

Plant cells are eukaryotic cells that differ from animal cells in several key aspects, primarily due to the presence of a cell wall, chloroplasts, and a large central vacuole.

• Cell Wall:
  • Structure: A rigid, outer layer made primarily of cellulose, located outside the cell membrane.
  • Function: Provides structural support, protection, and maintains the shape of the plant cell. It also prevents excessive water uptake.
• Cell Membrane (Plasma Membrane):
  • Structure: A thin, semi-permeable membrane composed of a lipid bilayer with embedded proteins, located just inside the cell wall.
  • Function: Controls the movement of substances into and out of the cell. It is selectively permeable.
• Plastids:
  • Structure: Membrane-bound organelles, including chloroplasts (containing chlorophyll), chromoplasts (pigmented), and leucoplasts (storage).
  • Function: Chloroplasts are the sites of photosynthesis, where light energy is converted into chemical energy. Other plastids are involved in pigment synthesis and storage of food (starch, oils, proteins).
• Nucleus:
  • Structure: A large, spherical or oval organelle, usually located centrally, containing the cell's genetic material (DNA) organized into chromosomes. It is enclosed by a double membrane called the nuclear envelope.
  • Function: Controls all the activities of the cell, including growth, metabolism, and reproduction. It is the control center of the cell.
• Vacuole:
  • Structure: Plant cells typically have one large, central vacuole that can occupy up to 90% of the cell volume. It is surrounded by a membrane called the tonoplast.
  • Function: Stores water, nutrients, waste products, and maintains turgor pressure against the cell wall, providing support to the plant.
• Cytoplasm:
  • Structure: The jelly-like substance that fills the cell, enclosed by the cell membrane, and surrounds the organelles. It consists of the cytosol (the fluid portion) and the organelles suspended within it.
  • Function: Site of many metabolic reactions and cellular processes. It provides a medium for the movement of organelles and substances within the cell.

Animal Cell: Cell Organelles and their Functions

Animal cells are eukaryotic cells that lack a cell wall, chloroplasts, and a large central vacuole, which are characteristic of plant cells.

• Cell Membrane (Plasma Membrane):
  • Structure: A thin, flexible, outer boundary composed of a lipid bilayer with embedded proteins.
  • Function: Controls the passage of substances into and out of the cell. It is selectively permeable and plays a role in cell communication.
• Plastids:
  • Structure: Absent in animal cells.
  • Function: Not present, as animal cells do not perform photosynthesis.
• Nucleus:
  • Structure: A large, spherical or oval organelle, often located centrally, containing the cell's genetic material (DNA) in chromosomes. Enclosed by a nuclear envelope.
  • Function: Controls all cellular activities, including growth, metabolism, and reproduction. It is the control center of the cell.
• Vacuole:
  • Structure: Animal cells typically have several small, temporary vacuoles, if present at all.
  • Function: Involved in temporary storage of water, ions, and waste products, and sometimes in transport.
• Cytoplasm:
  • Structure: The jelly-like substance filling the cell, enclosed by the cell membrane, and surrounding the organelles. It includes the cytosol and suspended organelles.
  • Function: Site of many metabolic reactions and cellular processes. Provides a medium for the movement of organelles and substances within the cell.

Diagrams of Plant and Animal Cell

(Note: Diagrams cannot be generated in this format. Please refer to your textbook for labeled diagrams of plant and animal cells to visualize the organelles mentioned above.)

Differences between Plant and Animal Cells