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• Levels of organization


  • Chemical
  • Cellular
  • Tissue (primarily in animals)
  • Organ
  • Organ system
  • Organism
• Chemical level


  • Consists of atoms and molecules essential for life, such as DNA, proteins, carbohydrates, lipids, and water
  • These molecules form the building blocks of cells and are crucial for various biochemical reactions
• Cellular level


  • Cells are the basic unit of life
  • In protists, the single cell performs all the functions necessary for life
  • In animals, cells are specialized to perform specific functions
• Tissue level (primarily in animals)

  • Tissues are groups of similar cells that work together to perform a specific function
  • Four basic types of tissues: epithelial, connective, muscle, and nervous
• Organ level


  • Organs are structures composed of two or more different types of tissues that work together to perform specific functions
  • Animal-like protists do not form organs due to their simplicity and unicellular nature
• Organ system level


  • Groups of organs working together to perform complex functions
  • Does not apply to protists
• Organism level


  • The complete animal or protist as a whole, capable of carrying out all of life's processes
  • In animals, this includes the integration of various organ systems to maintain homeostasis and reproduce
  • In protists, the single cell performs all necessary functions for survival and reproduction
• Epithelial tissue


  • Closely packed cells with minimal extracellular matrix, forming continuous sheets
  • Functions include protection, absorption, secretion, and filtration
  • Serves as a barrier against microbial invasion and physical harm
• Connective tissue


  • Characterized by sparse cells scattered within an abundant extracellular matrix
  • Supports, binds together, and protects tissues and organs
  • Roles in storage, transport, and immune responses
• Muscle tissue


  • Composed of long, excitable cells called muscle fibers that can contract
  • Three types: skeletal, cardiac, and smooth
  • Primary function is contraction, enabling movement, pumping of blood, and movement of substances
• Nervous tissue


  • Consists of neurons, which transmit electrical impulses, and neuroglia, which support and protect neurons
  • Primary function is to receive stimuli and send impulses to the brain and spinal cord, facilitating communication and control
• Asymmetry


  • Absence of any plane of symmetry
  • Commonly seen in simpler organisms or those with a sessile (stationary) or a very simple lifestyle
• Radial symmetry


  • Body has a central axis, and any plane cut through the central axis divides the organism into roughly mirror-image halves
  • Advantageous for sessile or planktonic organisms that interact with their environment in all directions equally
• Bilateral symmetry


  • Presence of a single plane of symmetry that divides the body into two mirror-image halves
  • Associated with cephalization, the development of a head region where sensory organs and nerve cells are concentrated
  • Advantageous for mobility and directional movement
• Protostomes


  • Exhibit spiral cleavage, where cells divide at oblique angles to one another
  • The coelom (body cavity) forms by splitting the mesoderm
  • The blastopore develops into the mouth
• Deuterostomes


  • Display radial cleavage, with cells dividing parallel or perpendicular to the axis of the embryo
  • The coelom forms through enterocoely, where folds of the archenteron (primitive gut) form and then pinch off
  • The blastopore develops into the anus
• Protostomes include major groups such as mollusks, annelids, and arthropods
• Deuterostomes include echinoderms and chordates
• Unicellular organisms


  • Composed of a single cell that performs all the necessary functions for life
  • Exhibit a remarkable range of diversity in shape, size, and method of movement
  • Can live independently, each cell carrying out all life processes on its own
• Unicellular organisms


  • Amoebae
  • Paramecia
  • Euglena
• Cellular aggregates


  • Loose associations of individual cells that function more as a group of independent cells rather than as a true multicellular organism
  • Cells show very little specialization, each maintaining its ability to survive independently
  • Advantages include increased efficiency in feeding, movement, and protection
• The lack of significant cellular specialization in unicellular organisms and cellular aggregates means that the same structures within the cell must carry out a wide variety of functions
• Protists encompass a wide range of organism types, including algae, protozoa, and slime molds
• Protists play critical roles in their ecosystems, such as producing a significant portion of the world's oxygen through photosynthesis, serving as a primary food source in aquatic food webs, and decomposing organic material
• Diploblastic organization


  • Cells are organized into rudimentary tissues, and the body is derived from two primary embryonic cell layers: the ectoderm and the endoderm
  • Characteristic of the phylum Cnidaria and the phylum Ctenophora
• Ectoderm


  • Forms the outermost layer of the organism and gives rise to the epidermis (outer skin) and structures such as nerves and, in some animals, the outer portion of sensory organs
  • Serves as a protective layer against the environment, involved in sensory reception and has roles in secretion in some cnidarians
• Endoderm


  • Forms the innermost layer and gives rise to the gastrodermis, the lining of the gut
  • Involved in digestion and absorption of nutrients
• Diploblastic


  Organisms that develop from two primary germ layers: the ectoderm and the endoderm
• Diploblastic organisms


  • Have bodies made up of just the ectoderm and endoderm layers, plus a gelatinous substance called mesoglea that lies between them
  • Lack the third layer (the mesoderm) found in more complex organisms
• Two Embryonic Cell Layers

  • Ectoderm
  • Endoderm
• Ectoderm


  The outermost layer of the organism, gives rise to the epidermis (outer skin) and structures such as nerves and, in some animals, the outer portion of sensory organs. It serves as a protective layer against the environment, involved in sensory reception and has roles in secretion in some cnidarians.
• Endoderm


  The innermost layer, gives rise to the gastrodermis, the lining of the gut. This layer is involved in digestion and absorption of nutrients. In cnidarians, the gastrovascular cavity serves both for digestion and distribution of nutrients, as well as a hydrostatic skeleton to aid in movement.
• Mesoglea


  A gelatinous substance between the ectoderm and endoderm that in some cnidarians can be quite thick, providing the animal with structural support, buoyancy, and, to some extent, a means to transmit signals. It's not considered a true tissue layer as it lacks cellular complexity in many diploblastic organisms, though in others, it can contain some cells and fibers.
• Diploblastic organisms


  • Have rudimentary tissues, allowing for more specialized functions and interactions with the environment
  • Lack the complex organs seen in more advanced animals, but their simplicity allows for efficient nutrient distribution and gas exchange directly through their tissues
  • Many exhibit radial symmetry, which is advantageous for their sessile or planktonic lifestyles, allowing them to interact with their environment from all directions
• Triploblastic organization


  Represents a significant evolutionary advancement in the complexity of animal life, with three primary germ layers forming during embryonic development: the ectoderm, endoderm, and mesoderm. This development allows for greater complexity in structure and function, including the formation of internal organs and systems.
• Three Embryonic Cell Layers

  • Ectoderm
  • Endoderm
  • Mesoderm
• Ectoderm


  Develops into the epidermis (outer skin layer) and the nervous system. It forms the external protective covering of the body and is involved in sensory reception.
• Endoderm


  Gives rise to the gastrodermis (lining of the digestive tract) and organs associated with digestion and respiratory systems. It is responsible for the absorption and digestion of nutrients, as well as gas exchange in some animals.
• Mesoderm


  Forms the bulk of body tissues, including muscles, bones, the circulatory system, reproductive organs, and much of the excretory system. It fills the space between the ectoderm and endoderm and is pivotal for the formation of complex structures and organs.
• Coelom


  A body cavity completely surrounded by mesoderm. The coelom serves as a protective cushion for internal organs, allows for the development of more complex organ systems, and provides a space for organ movement and growth.