Cell Types, Structures, and Division: A Comprehensive Overview

Posted on Mar 11, 2025 in Biology

Cell Types and Characteristics

Protoctists

Algae

  • Cell wall: Present
  • Healthy cell: Cytoplasm contains one or more chloroplasts and performs photosynthesis.

Protozoa

  • Actively move using flagella or cilia.

Fungi

  • Thick cell wall made of chitin.
  • Heterotrophic nutrition.

Plant Cells

  • Cell wall composed of cellulose.
  • Membrane contains chloroplasts (green).
  • Do not move if vacuoles are present.

Animal Cells

  • Some have flagella, many organelles in the cytoplasm.

Multicellular Organisms

Animal Tissues

  • Epithelial: Covers internal and external surfaces of the body.
  • Connective: Fills the space between organs.
  • Nervous: Facilitates communication.
  • Germ: Haploid cells.

Plant Tissues

  • Dermal: Wraps stems, leaves, and roots.
  • Vascular: Transports water through the plant’s vessel system.

Cellular Components

Cell Membrane

  • Structure: Phospholipid bilayer, cholesterol, proteins, and glycids.
  • Location: Plasma membrane delimits the cell and its intracellular organelles in the cytoplasm.
  • Function: Delimits the aqueous environment, facilitates transportation, exocytosis, and cell recognition.

Cell Wall

  • Surrounds the plasma membrane, formed by expelled substances.

Cytosol

  • Location of chemical reactions within the cell.
  • Dynamic structure that facilitates cell movement.

Endoplasmic Reticulum (ER)

  • Extensive network of cytoplasmic tubules, branched and interconnected sacs.
  • Function: Biosynthesis.

Golgi Apparatus

  • Processes and packages products, produces secretory vesicles, and directs traffic.

Lysosomes

  • Vesicles containing hydrolytic enzymes.
  • Function: Intracellular digestion.

Exocytosis

  • Process by which the cell carries substances that are manufactured.

Endocytosis

  • Captures and transports nutrients from outside the cell.

Nucleus

  • Site of DNA synthesis, separated by the nuclear envelope.

Chromosomes

  • Composed of DNA associated with proteins.
  • Sister chromatids: Doubled and joined by a centromere.
  • Diploid: Two copies of each chromosome.
  • Karyotype: Set of chromosomes.
  • Bacterial chromosome: Double-stranded, circular, and closed.

Ribosomes

  • Involved in RNA and protein synthesis.

Cell Division

Cell Cycle

  • Series of cellular events leading to cell duplication and division.

Types of Cellular Division

  • Binary Fission: Division into two daughter cells.
  • Gemmation (Budding): Formation of a large cell with many small buds.
  • Sporulation: Formation of spores.

Animal Cell Division (Mitosis)

  • Interphase: Cell size increases, chromatids are duplicated, and two centromeres form.
  • Prophase: Chromosomes become visible, the mitotic spindle forms, the nuclear envelope breaks down, and microtubules pull sister chromatids toward the spindle poles.
  • Metaphase: Chromosomes align at the equator, forming the equatorial plate.
  • Anaphase: Microtubules shorten, and sister chromatids separate into individual chromosomes, moving toward opposite poles.
  • Telophase: New nuclear envelopes form around the separated chromosomes, and chromosomes condense.
  • Cytokinesis: The cytoplasm divides into two via a contractile ring.

Meiosis

  • Process to create haploid cells from a diploid cell.
  • Interphase: Chromatids and centrosomes are duplicated.
  • Prophase I: Duplicated chromosomes form.
  • Metaphase I: Each bivalent is positioned on the equatorial plate.
  • Anaphase I: Homologous chromosomes are pulled toward opposite poles, separating the bivalent.
  • Telophase I: Daughter nuclei form.
  • Cytokinesis: The cytoplasm divides, leading to Meiosis II.

Centrosome

  • Main organizer of microtubules, contains a pair of centrioles.

Viruses

Structure

  • Composed of nucleic acid, capsid, and envelope (in some viruses).

Classification

  • Based on genetic material, cell types they infect, and shape (helical, icosahedral, complex).

Infection Process

  • Attachment to the cell surface.
  • Penetration into the cell.
  • Replication of viral components.
  • Assembly of new viruses.
  • Release of new virions.