Learning Unit 1
Architectural patterns of Animals
Five major grades of organization
1. Protoplasmic grade of organization.
‣ Protoplasmic grade characterizes unicellular organisms
‣ All life functions are confined within boundaries of a single cell, the fundamental unit of life
...
ZOL1501 Exam
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ZOL1501 Exam Prep
1
, Learning Unit 1
Architectural patterns of Animals
Five major grades of organization
1. Protoplasmic grade of organization.
‣ Protoplasmic grade characterizes unicellular organisms
‣ All life functions are confined within boundaries of a single cell, the fundamental unit of
life
‣ Within Cell, protoplasm is differentiated into organelles capable of performing
specialized functions
2. Cellular grade of organization
‣ Cellular grade of organization is an aggregation of cells that are functionally
differentiated
‣ A division of labor is evidence, so that some cells are concerned with, for example,
reproduction and other nutrition. Some flagellates, such as volvox, that have a distinctive
somatic and reproductive cells are placed at cellular level of organization. Many authorities
also place sponges at this level.
3. Cell-tissue grade of organization
‣ A step beyond the preceding in an aggregation of similar cells into patterns or layers and
organized to perform a common function, to form a tissue. Sponges are considered by the
authorities to belong to this grade, although jellyfish and their relatives(Cnidaria) more
clearly demonstrates the tissue plan. Both groups are still largely of cellular grade of
organization because most cells are scattered and not organized into tissues.
‣ An excellent example of a definite tissue in Cnidarians is nerve net, in which nerve cells
and their processes form a definite tissue structure with the function of coordination.
4. Tissue-organ grade of organization
‣ An aggregation of tissues into organs is a further stage in complexity.
‣ Organs are usually composed of more than one tissue and have a more specialized
function than tissues.
‣ This is the organization level of Platyhelminthes(flatworms), in which well defined organs
such as eyespots, proboscis, and reproductive organs occur.
ZOL1501 Exam Prep
1
, ‣ In Platyhelminthes, the reproductive organs transcend the tissue-organ grade are
specialized into a reproductive system.
5. Organ-system grade of organization
‣ When organs work together to perform some function, we have the highest level of
organization, an organ system.
‣ Systems are associated with the basic body functions such as circulation, respiration,
and digestion.
‣ The simplest animals having this type of organization are Nemertean worms, which have a
complete digestive system distinct from the circulatory system.
‣ Most animal phyla demonstrates this type of organization.
Distinguish amongst spherical, radial, bilateral and biradial symmetry and refer to one
representative example for each
1. Spherical symmetry means that any plane passing through the body into equivalent or
mirrored halved. E.g Volvox
2. Radial symmetry forms that can be divided into similar halves by more than two planes
passing through the longitudinal axis. E.g Hydra
3. Biradial symmetry only lanes passing through the oral-aboral axis will produce
mirrored halves. E.g Sea walnut
4. Bilateral symmetry applies to animals that can be divided along a sagittal plane into
two mirrored portions-right and left halves. E.g Tapeworm
Learning
University 2
Classification and Phylogeny
1. Monophyletic group is a group that includes the most recent common ancestor of a
group of organisms, and all of its descendants
2. plesiomorphic (plƒ sƒ-‰-m|r k). An ancestral condition of a variable character
ZOL1501 Exam Prep
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