Animal Characteristics and Body Plans

• Learning objectives include defining animals, describing body plans, understanding tissue/organ organization, and explaining homeostasis.

What is an Animal?

• Animal body plans are diverse.
• Features differentiating animals from other organisms include multicellularity, heterotrophy, unique embryological development, and lack of cell walls.
• Choanoflagellates are unicellular protists closely related to animals because of their similarity to sponge choanocyte cells.
• Sponge choanocyte cells and choanoflagellates share a single flagellum surrounded by microvilli.
• The beating flagellum creates a water current, and microvilli filter food particles.
• Choanoflagellates with microvilli also filter/capture bacteria to ingest via phagocytosis.
• Choanoflagellates are unicellular, whereas animals are multicellular, setting them apart.
• Animals are heterotrophs, obtaining energy and carbon from preformed organic molecules.
• Animal cells lack cell walls, distinguishing them from plants and fungi.
• Early embryological development in animals includes a blastula stage, which is a hollow ball of cells.
• The development continues with cell movement to form a gastrula, a multicellular embryo having three cell layers.
• Animals are multicellular, heterotrophic eukaryotes, exhibiting a distinctive embryological development, progressing from blastula to gastrula

Animal Body Plans - Symmetry

• Symmetry is the quality of being made up of exactly similar parts around an axis.
• Animals are divided into groups based on body symmetry:
  • Porifera - Irregular form
  • Cnidaria - Radial symmetry
  • Bilateria - Bilateral symmetry
• Radial symmetry involves a body axis running from mouth to base with many symmetry planes around the axis, examples include jellyfish and sea anemones
• This adaptation enables jellyfish to move up and down in the water column, using muscle fibers around the "bell."
• This adaptation enables sea anemones to move numerous tentacles in all directions at the same time.
• Bilateral symmetry has a single symmetry plane from mouth to tail, with distinct anterior, posterior, dorsal, and ventral sides; seen e.g., in crabs.
• The adaptation for Horizontal movement is enabled in such species to capture prey, find shelter, and escape enemies.

Animal Body Plans - Cephalization

• Cephalization is the concentration of nervous tissue and sensory organs at the "front" of an organism.
• Cephalization is an adaptation for locomotion and avoiding predation in bilateral animals.
• Sensory organs at the front enable efficient navigation, quick responses, protection of sensory organs, and better predator/prey detection.

Animal Body Plans - Segmentation

• Segmentation is the organization of the body into repeated units from front to back along the anterior-posterior axis.
• Body units are modified depending on their position and occur across Annelida, Arthropoda and Vertebrata.
• Insects' bodies are divided e.g., into head, thorax, and abdomen, and are made up of multiple segments
• Segmentation allows for differentiation into distinct body parts, evolves as an adaptation for higher mobility, and leads to specialized body part potential.
• In mammals, segmentation is obvious in the vertebral column and peripheral nervous system, where each segment of the spinal cord serves a specific body region

Animal Body Plans - Embryology

• Animals share patterns of early embryological development, even if adults are different.
• Diploblastic organisms such as cnidarians, have inner endoderm and outer ectoderm layers give rise to the adult body.
• Mesoderm develops into more complex tissues, like muscles and circulatory systems.
• The Mesoderm develops into enabling new locomotion, feeding, and behavior which evolved.
• Bilaterians are grouped as protostomes (mouth forms first) or deuterostomes (mouth forms second), depending on what the blastopore becomes.

Tissues

• Tissues are collections of cells performing a specific function.
• Animals have four tissue types: epithelial, connective, muscle, and nervous.

Tissues - Epithelial

• Epithelial tissue provides a lining inside and outside the body.
• Cells are closely packed, forming a continuous sheet for protection and absorption.
• Epithelial tissues are classified by layering (simple or stratified) and shape (flat, round, square, or tall).

Tissues - Connective

• Connective tissue has few cells within an extracellular matrix (ECM).
• The ECM is a network of proteins and polysaccharides produced, secreted, and modified by cells.

Tissues - Muscle

• Body support and movement is achieved by body tissues and organs (bone, cartilage, tendons and ligaments)
• The Blood matrix for body support and movement, plasma transports oxygen and tissue.
• Adipose tissue is made from tissue and fibre matrixes which then organize and support fat cells for storage of energy and insulation.

Tissues - Muscle

• Muscle tissue consists of elongated cells called muscle fibers that contain contractile proteins which cause movement.
• Skeletal muscle attaches to bone for movement.
• Smooth muscle lines the gut and blood vessels, performing waves of contraction and relaxation.
• Cardiac muscle, found in the heart, contracts to create heartbeat.

Tissues - Nervous

• Cnidarians contain nervous tissues located in the nerve net.
• Vertebrates nervous tissues may be found in the brain, spinal cord and peripheral nerves.
• The structural and functional unit of nerve tissue is the neuron.
• Communication is done quickly and specifically by neurons.
• The communication allows for decision making and complex behaviour.

Organs

• Multiple tissues combine to make an organ in bilaterians.
• The process has epithelial, connective, muscular and neural tissues

More on Sponges and Cnidarians

• Sponges have simple epithelia.
• Jellyfish, corals, and sea anemones (Cnidarians) possess several tissue types, but not true organs.
• Cnidarians contain a set of nerves called a nerve-net.
• Cnidarian nerve-nets are not organized like a brain or central nervous system.
• Cnidarians have muscle cells, but contain undeveloped muscle tissues; they exchange gases by diffusion in a central cavity.

Box Jellyfish Learning

• Box jellyfish are capable of learning and retain details
• These creatures contain 24 eyes, which enable them to preceive much detail of their environment.
• Jellyfish can associate different patterns with harmful stimuli for avoidance that are otherwise referred to as associative learning.

Homeostasis

• Homeostasis is the active maintenance of stable internal conditions, despite the external environment.
• It is critical for cell and organismal function.
• Specifically, chemical reactions and protein folding is best when performed within a small range of conditions.
• Parameters include temperatures, heart-rate, blood pressure etc, and they need to be maintained within their set and agreed-upon conditions
• Negative feedback is often a mechanism to achieve with homeostasis.
• The feedback is an effect of stimulus on a sensor that communciates with an effector which provides a initial stimulus.

Plant Hormones - Auxin

• Auxin is synthesized in rapidly dividing shoot apologies.
• Formation starts when new leaf prinordia trigger high levels.
• Cell expansion takes place with the promotoions given to enable growth for young levels

Light-Based Contexts

• Plants often depend on three types of receptors sensitive to light (photo), physical (mechanical) and chemical levels in their environments.
• Plants can also orient light by orienting light from sterns and roots.
• If plants are only exposed to light from one side, their illuminated sides activate.
• More cell exapnsion happens due to activation, triggering bending at a certain point.

Gravity Sensitive Context

• When moving plants, carbohydrates store as starch results in transport for Auxin in lower sides.
• The accumulation of plants causes stems to then bend up towards the light and gravity.
• Roots also have gravity critical regarding their orientation.