Earthworm Dissection

Earthworm Systems and
Homeostasis
Pre-lab Presentation
Objectives:
1. Become familiar to all major earthworm systems for
maintaining homeostasis.
2. Understand how the earthworm fits into the world.
3. Use this informative presentation to design and
conduct a well designed experiment to test
homeostasis in an Earthworm.
All living things must maintain a relatively stable
internal environment to survive.
• The term used to describe this is "homeostasis."
Living things carry out different essential functions
in order to accomplish this task.
• Multi-cellular organisms have “systems” that work
together to maintain this stable environment. For
example when you run your body is placed under
severe stress. Various systems will start to work
overtime keeping your body alive
• Your heart starts beating faster and your
breathing increases. Your body is trying to
deliver oxygen and take away carbon dioxide
(respiratory waste) from working muscles etc.
Your skin starts to sweat reducing the excess
body heat created by the activity.
• Without your body systems working together
your systems will fail and death would ensue.
There are many more system accommodations
that occur as you run or engage your body in
different activities.
• Multicellular organisms maintain
homeostasis differently. Compare the
differences between warm blooded and
cold blooded organisms. To adjust body
temperature insects or reptiles will move
their body to a location that will ether warm
or cool their body depending on their
needs.
Regulation and Conforming
• A regulator uses internal control
mechanisms to moderate internal change
in the face of external, environmental
fluctuation.
• A conformer allows its internal conditions
to vary with certain external changes.
• Animals may regulate some environmental
variable while conforming to others.
Feedback control maintains the internal
environment in many animals.
• Organisms use homeostasis to maintain a
“steady state” or internal balance
regardless of external environment.
• In mammals body temperature, blood pH,
and glucose concentration are each
maintained at a constant level.
• Animals manage their internal
environment by regulating or conforming
to the external environment.
Maintenance of homeostasis
• The dynamic equilibrium of homeostasis is
maintained by negative feedback, which
helps to return a variable to a normal range.
• Most homeostatic control systems function by
negative feedback, where buildup of an end
product shuts the system off.
• Positive feedback amplifies a stimulus and
does not usually contribute to homeostasis in
animals.
Regulator response to cold
Regulator response to warmth
Adjusting to seasonal changes
• Organisms can use homeostasis to adjust
to changes in external environment, a
process called acclimatization.
• Acclimatization to seasonal temperatures
in some animals may include changes in
insulation layers, such as thicker fur in
winter and shedding in summer.
• In ectotherms, cellular adjustments can
occur. Concentrations of lipids in cellular
membranes can increase or decrease..
• Some species produce antifreeze.
compounds that prevent freezing of
cellular tissues.
• Antifreeze proteins are a class of proteins
that interact with cellular membranes to
prevent freezing, allowing survival in
subzero temperatures.
Coordination and Control
• Control and coordination within a body
depend on the endocrine and nervous
systems.
• The endocrine system transmits chemical
signals called hormones to receptive cell
throughout the body.
• A hormone may affect one or more
regions throughout the body.
• Hormones are relatively slow acting, but
can have long-lasting effects.
• The nervous system by contrast carries
messaged to specific regions in an
organism via specialized nervous cells.
Below are a few examples of various systems found in
multicellular organisms under homeostatic control.
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Digestive /Feeding
Response /Nervous
Movement
Circulatory
Respiratory
Reproductive
Excretion
• Single celled organisms do not have systems because
they are only made of one cell. Thus each cell must
carry out all of these functions without relying on tissues,
organs and organ systems (ex. bacteria, yeast, and most
protists).
Classification of Earthworm
Kingdom Animalia: Multicellular eukaryote, heterotrophic
Phylum Annelida: body made of many segments separated by a septum. Two body openings and a
closed circulatory system. Ex. Earthworms, marine worms, leeches etc.
Class Oligochaeta: lack appendages and very few bristles. The can be terrestrial or found
in fresh water
External
Anatomy
The setae are structures we cannot visualize with
the naked eye. If you rub your fingers along the
ventral surface it feels like sand paper. This
sensation is a result of the little bristle like
structures called setae. These bristles give them
traction as they move through their tunnels and
along the surface of the soil.
Feeding (digestive), Earthworms have a fleshy projection on the anterior end called the
prostomium. This structure covers the mouth. The mouth leads into a muscular pharynx that
pumps food into a storage organ called the crop. Just posterior to the crop is a thick-walled, highly
muscularized gizzard. Small rocks (grit) in the gizzard help to grind food before it is moves into the
intestine where the nutrients from the food is absorbed. After absorption solid waste is eliminated
through the anus. The solid waste of earthworms are called castings. Worm castings are highly
sought after because of their concentrations of nitrogen, phosphorus, potassium, micronutrients and
beneficial bacteria. Worm feces is a fantastic fertilizer and very expensive. Earthworms also help to
till / mix the soil as they burrow through the ground. As a result they leave a network of tiny holes
and spaces that help water and air get to plant roots. These spaces are critical niches for bacteria to
colonize and decompose organic debris as well as fix nitrogen (nitrogen fixation).
The intestine extends from the posterior end of the gizzard and continues until it reaches the anus.
Respiration, (respiratory system)
Earthworms secrete a thin surface film of mucus to keep them
moist so oxygen and carbon dioxide can diffuse through the body
wall. Worms do not have lungs or gills like some organisms.
Remember that living things accomplish each of the tasks
necessary to maintain homeostasis differently. All living things
MUST have a way to deal with these requirements
Circulation, (circulatory) Earthworms have five simple hearts located just anterior to the crop
and posterior to the pharynx. These are very simple hearts / vessels that pump blood
throughout the earthworm. Earthworm blood is red because it has hemoglobin. Remember that
hemoglobin is a protein that binds oxygen. There are two relatively large blood vessels that run
along the top (dorsal) and along the bottom (ventral). There are small vessels that connect the
two. The earthworms circulatory system is considered to be a closed system because the blood
circulates within a network of vessels. An open system has spaces or cavities filled with blood
that surrounds body organs. The blood in these cavities is picked up by vessels and circulated
throughout the organism. Don’t forget that earthworms have a closed circulatory system.
Hearts
Excretion (excretory system) Solid waste passing though the intestine is eliminated
through the posterior opening called the anus. Cellular waste is excreted in a different way.
Remember all cells excrete cellular waste (nitrogenous). When waste products
accumulate inside body tissues they become toxic and must be removed or the creature
will die. To eliminate cellular waste metanephridia remove toxins keeping the cellular
landscape free of excess garbage. The metanephridia are connected to openings called
nephridiopores. The cellular waste is excreted from these openings.
Response (nervous)
The earthworm, as well as most annelids,
have a well developed nervous system
consisting of a brain and many nerve
cords. You can see from this image that
the ventral nerve cord is connected to the
brain
Movement (skeletal and muscular)
Earthworms alternately contract
their longitudinal (shortens) and
circular (elongates) muscles to
move.
Reproduction, (reproductive system) Although earthworms are
monecious, they undergo cross-fertilization during copulation. During
copulation sperm cells are released from the seminal vesicles and stored
in the seminal receptacles of the opposite earthworm. The clitellum slides
over the anterior segments and picks up eggs from the oviducts in the
14th segment and sperm as it slides over the anterior end of the worm to
form the egg cocoon.