(Summary) BIOL 114 Exam 3 (Answered) 93
Questions and Correct Answers With Verified
Solution. Updated Fall 2024/2025.
Cambrian explosion
The radiation of animals began around 550 MYA during an event called the Cambrian explosion. After a
slow start, diverse animals suddenly appeared in the fossil record with shells, exoskeletons, internal
skeletons, legs, heads, eyes, tails, antennae, jaw-like mandibles, segmented bodies, muscles, and brains.
Animal
Animals are eukaryotes that share key traits.
- All animals are multicellular, with cells that lack cell walls but have an extensive ECM.
- All animals are heterotrophs, meaning they obtain the carbon compounds they need from other
organisms. Most ingest ("eat") their food, rather than absorbing it across their exterior body surfaces.
- All animals move under their own power at some point in their life cycle.
- All animals other than sponges have (1) neurons that transmit electrical signals to other cells; and (2)
muscle cells that can change the shape of the body by contracting.
*Difference between animals and fungi: digestion in animals typically occurs within the space, or lumen,
of the digestive tract rather than in the open exterior, as occurs with fungi.
*Animals are the larges predators, herbivores, and detrivores on earth.
Extracellular matrix
Includes proteins specialized for cell-cell adhesion and communication.
Phyla
Biologists currently recognize 30-35 phyla, or major lineages, of animals.
Body plan
- Comparative morphology (in addition to the fossil record and comparative genomics used in
establishing phylogenies) provides information about which embryonic, larval, or adult morphological
characteristics are common among groups of animals and which are unique to individual lineages
(synapomorphies).
- These data can be used to define the fundamental architecture, or BODY PLAN, of each animal lineage.
In a phylogenetic context, these data can be used to infer which characteristics arose first during the
evolution of animals, and which animal groups are more closely related
Sessile
Both choanoflagellates (single-celled animal outgroup) and sponges are sessile, meaning that adults live
permanently attached to a substrate.
Choanocytes
,- Both choanoflagellates and sponges feed in a similar way, using cells with nearly identical morphology.
The beating of flagella creates water currents that bring debris toward the feeding cells of
choanoflagellates and sponges.
- Sponge feeding cells are called CHOANOCYTES. Within these choanocytes, food particles are trapped
and ingested.
Epithelium
Recent research has shown that some sponges have true epithelium--a layer of tightly joined cells that
covers the interior and/or exterior surface of the animal. Epithelium is essential to to animal form and
function.
Tissue
Groups of similar cells that are organized into tightly integrated structural and functional units.
Diplo & triploblastic
Animals whose embryos have two types of tissue are called diploblasts ("two-buds"); animals who have
three types of tissue are called triploblasts ("three-buds").
Germ layers
The embryonic tissues are organized in layers, called germ layers. In diploblasts these germ layers are
called ectoderm (outer) and endoderm (inner). In triploblasts, however, there is a germ layer called
mesoderm (middle) between the ecto- and endoderm.
Ecto, meso, & endoderm
The embryonic tissues found in animals develop into distinct adult tissues, organs, an organ systems. In
triploblasts:
- Ectoderm gives rise to skin and the nervous system.
- Endoderm gives rise to the lining of the digestive tract.
- Mesoderm gives rise to the circulatory system, muscle, and internal structures such as bone and most
organs.
*In general, the ectoderm produces the covering of the animal and endoderm generates the digestive
tract. Mesoderm gives rise to the structures in between.
- The same pattern holds in diploblasts, except that (1) muscle is simpler in organization and is derived
from the ectoderm, and (2) reproductive tissues are derived from endoderm.
Radial v bilateral symmetry
Radial symmetry ("spoke-symmetry") means that an animal has at least two plans of symmetry.
Organisms with bilateral symmetry ("two-sided symmetry") have only one plane of symmetry and tend
to have a long, narrow body.
*Radial symmetry appears to have arisen earlier than bilateral symmetry, which occurs in all triploblastic
lineages.
Nerve net v CNS v brain
, - Sponges generally lack both nerve cells and symmetry.
- Ctenophores and cnidarians have nerve cells that are organized into a diffuse arrangement called a
NERVE NET. These generally radially symmetrical animals either float in water or live attached to a
substrate. Radially symmetric organisms are more likely to encounter prey and other aspects of the
environment in any direction. As a result, a diffuse nerve net can receive and send signals effectively.
- All other animals have a CNS. In a CNS, some neurons are clustered into one or more large tracts or
cords that project throughout the body; others are clustered into masses called ganglia. Most of the
bilaterally symmetric animals living today move through their environment. Bilaterally symmetric
organisms tend to encounter prey and other aspects of the environment at the leading end. As a result,
it is advantageous to the animal to have many neurons concentrated at that end, with nerve tracts that
carry information down the length of the body.
Cephalization
- CEPHALIZATION is he evolution of the head, or anterior region, where structures for feeding, sensing
the environment, and processing information are concentrated. - The large mass of neurons that is
located in the head, and that is responsible for processing information to and from the body, is called the
cerebral ganglion or BRAIN.
Body cavity, coelom
- The "tube-within-a-tube" body plan can pose a potential biomechanics and physiological challenge if
the inner tube is attached to the outer tube via the mesoderm.
- One bypass to this physical constraint is a fluid-filled cavity between the inner and outer tubes, called a
COELOM.
- The coelom provides a space for the circulation of oxygen and nutrients. It also enables the internal
organs to move independently of each other.
coelomate v pseudocoelomate v
acoelomate
Phylogenetic evidence suggests that the coelom arose in the common ancestor of protostomes and
deuterostomes.
- The bilaterians that possess a coelom that is completely lined in mesoderm are known as true
COELOMATES.
- The bilaterians that subsequently lost their coelom, such as flatworms, are called ACOELOMATES.
- The bilaterians that retained a coelom but lost the mesodermal lining in parts of their coelom, such as
nematodes, are known as PSEUDOCOELOMATES.
*The coelom was a critically important innovation during animal evolution, in part because an enclosed,
fluid-filled chamber can act as an efficient hydrostatic skeleton. Soft-bodied animals with hydrostatic
skeletons can move effectively even if they do not have fins or limbs.
No body cavity
Acoelomate
Body cavity lined on the inner side by endoderm-derived tissue and on the outer side by mesoderm-
derived tissue
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