Understanding Cells: Anatomy, Function, and Division

Posted on Mar 25, 2025 in Biology

Cell Structure and Function

A cell is the smallest functional and anatomical unit of living beings. Some organisms consist of a single cell (unicellular), while others have multiple cells (multicellular). Cells perform the following vital functions:

  • Nutrition: Taking in molecules from the environment and transforming them into energy.
  • Relationship: Communicating with the external environment.
  • Reproduction: Forming new cells from existing ones, with the same genetic information.

The cell theory, developed in part by Robert Hooke, who was among the first to analyze cells, states:

  • All living organisms are composed of cells.
  • The cell is the smallest and simplest unit of life.
  • Cells arise from pre-existing cells.
  • Each cell in a multicellular organism has its own activity but functions in coordination with others.

Cells share a common basic structure:

  • Cell membrane: A bilayer composed of proteins and lipids.
  • Cytoplasm: The liquid medium inside the cell where cellular organelles are located.
  • Genetic material: Dispersed throughout the cytoplasm in prokaryotes, and contained within the nucleus in eukaryotes.

Animal Cell

Its form varies depending on its function. It comprises:

  • Plasma membrane: Outlines the cell, regulates the input and output of substances, shapes the cell, and facilitates communication with other cells.
  • Mitochondria: Responsible for cellular respiration and energy production in the form of ATP.
  • Golgi apparatus: Processes and distributes proteins.
  • Nucleus: Located inside the cell, surrounded by the nuclear membrane. Its interior, called the nucleoplasm, contains genetic material, ribosomes, and the nucleolus.
  • Ribosomes: Consist of two subunits, formed in the nucleolus, and cross the nuclear membrane to reach the cytoplasm.
  • Lysosomes: Vesicles containing enzymes capable of digesting large molecules.
  • Vacuoles: Structures that store substances, smaller than those in plant cells.
  • Centrioles: Participate in the formation of flagella and cilia, and in cell division.
  • Cytoplasm: Contains nutrients and cellular organelles.
  • Endoplasmic reticulum: A network of flattened tubes responsible for synthesizing various substances. There are two types: smooth ER (lacking ribosomes, synthesizes lipids) and rough ER (containing ribosomes, synthesizes proteins).

Plant Cell

Contains the same components as animal cells, but also includes:

  • Chloroplasts: Organelles containing chlorophyll, enabling plants to perform photosynthesis, the process of converting inorganic matter into organic matter.
  • Cell wall: Composed of cellulose, providing protection to the cell.
  • Vacuole: Larger than in animal cells, often displacing the nucleus to the side.

Haploid cells contain half the genetic information of diploid cells, which contain the full complement of genetic information.

Cells can move through:

  • Cilia: Short and numerous.
  • Flagella: Longer and less numerous.

Chromosomes

  • Located in the nucleus of cells.
  • When the cell is not dividing, DNA is dispersed throughout the nucleus as chromatin.
  • When the cell is about to divide, the genetic material condenses and forms chromosomes.

Mitosis

The process by which a cell divides into two identical daughter cells. It has four phases (prophase, metaphase, anaphase, telophase):

  • Prophase: The genetic material condenses, forming chromosomes, and the nucleolus disappears. The centrioles and nuclear envelope appear and disappear.
  • Metaphase: The mitotic spindle forms, and chromosomes attach to it through the centromere, aligning in the center to form the equatorial plate.
  • Anaphase: The mitotic spindle breaks down, and the chromosomes are separated at the centromere, with each sister chromatid moving to opposite poles of the cell.
  • Telophase: The sister chromatids reach the poles, and the cell divides. The nuclear envelope reforms.

Meiosis

Meiosis is divided into two stages:

  1. Meiosis I: Similar phases to mitosis.
  • Prophase I: Homologous chromosomes pair up. Genetic material exchange (recombination) occurs.
  • Metaphase I: The mitotic spindle attaches to the pairs of homologous chromosomes, and they align in the center of the cell.
  • Anaphase I: Each pole receives a complete chromosome.
  • Telophase I: No significant events occur.
Meiosis II: Consists of the same phases:
  • Prophase II: Chromosomes form.
  • Metaphase II: Chromosomes align on the equatorial plate.
  • Anaphase II: Sister chromatids separate.
  • Telophase II: New daughter cells form.