Download 35 Arthropods and Echinoderms AP Biology

33 Arthropods: insects/invertebrates
AP Biology
Pages 664-675
Name: ___________________________ Date: _______________ Periods: ________
The transition from the Annelids to the Arthropods may be the fusion of various
segments during evolution (driven by environmental pressures) to produce specific
appendages. (Appendages are any specializations or outgrowth from the main body.) If
we look at the repeating segments of an earthworm, we see an animal that has managed
to create a primitive circulatory system with five hearts. Presumably the idea behind
such a circulatory system, why it is more complex than absorbing gasses directly through
the skin to try and reach each cell; is that is allows the animal to grow bigger (and
therefore more complex). We also address two other very important concerns: (a.) the
need to conserve water, (b.) the need to be more complex (i.e. isolate functions) so that it
is more difficult to be killed. If we look at different parts of the earthworm, we know that
there are the beginnings of specialized cells that are isolation of functions. Sex cells for
instance are specialized cells and have their own opening in the earthworm (to release
eggs and sperm). Moreover, earthworms are not so specialized that they cannot
regenerate large parts of their bodies that might get ripped away. As we move up the
evolutionary ladder, animals become more complex, with more specialized cells, harder
to kill, and we begin to see the loss of the ability to regenerate all or parts of the body.
The fusion of segments to form body parts (tagmatization), appendages, and
specialized cells, required that some animals were able to move away from an
environment where constant contact with water was not necessary. This “loss of touch”
with water was by no means universal in arthropods; yet may have simply been driven by
environmental pressures (the gradual drying up of water sources). The first modification
for the descendent(s) of the earthworm might have been to build a covering that would
limit the loss of water. The earthworm secretes a kind of mucous-like fluid (made of a
modified sugar) that helps it exchange gasses and move through the soil with less
friction. Modifying these secretions to be a thick tough exoskeleton made of chitin
(again a modified sugar) was perhaps successful in the water (crustaceans) and out of
the water (insects). There need not be a tight line drawn between these two classes of
animals-they have a lot in common. Their difference lies in their need for constant
contact with water. The hard exterior “shell” called an exoskeleton has several
desirable features:
1.) They help protect the organism from physical damage.
2.) They provide anchors (levers) for attachment of muscles-allows movement
3.) They help give the organism shape
4.) They “may” help limit the loss of water (depending on how “water-tight” the
exoskeleton is.
However- there are drawbacks to the formation of an exoskeleton:
1.) Limited range of motion (simply compare the range of motion of insects to
let’s say an octopus)
2.) Limits growth- the exoskeleton must be shed (molting) if the animal is to
grow larger- this leaves the animal more vulnerable during the molting stage
3.) Requires modifications for exchanging gasses(when not in contact with water)
Page 2 (Cont. #33 A/P Bio.)
4.) Requires that the animal modify its excretory system to limit water loss if the
animal does not have constant contact with water.
Tagmatization may take the form of repeating body units- as in the centipede and
millipede. (centipedes and millipedes are NOT insects- rather they are invertebrates)
Centipede- notice only one pair of legs per body
segment. These animals have poison fangs just
below the head and in rare cases can cause an
uncomfortable “bite” to humans. They eat other
smaller insects.
Millipedes have two pairs of legs per
body section- eat only decomposed
organic matter-these have no fangs.
Tagmatization can also take the form of three
separate sections:
a.) head
b.) thorax
c.) abdomen
Insects are defined as those animals with an
exoskeleton, three pairs of legs, and often breathe
through specialized spiracles and trachea system.
The legs of an insect uniramous - or single branched
(versus biramous or “two branched) leg-found in
crustaceans…see page 669 of text.) are always paired and by
definition, there are six legs. Though all insects have six legs, they do
not all have three body parts. If the head and the thorax are fused, that
section is called the “cephalothorax”.
Page 3 (Cont. #33 A/P Bio.)
The specialized cells that detect light in the insects and arachnids are of three
types:
a.) Compound eyes: (ommatidia)
1.) appositional eyes- where each compartment of the compound eyes has a
lens and receives an inverted image to a central core (rhabdom)
2.) superpositional eyes- where each compartment of the compound eyes has
a lens, BUT the central core (rhabdom) receives a single right-side-up
image .
b.) Simple eyes: (ocelli) - these eyes contain a single lens- and obtain an inverted
image on the back of the eye
The circulatory system of the arthropoda is an open circulatory system - flowing
around cells of certain organs making exchange of nutrients and wastes one of rapid
diffusion. The circulatory system DOES NOT MOVE gasses into and out of
individual cells.
The respiratory system of the insect is primarily through spiracles located
(usually) in the abdomen of the insect (see power point presentation). The spiracles
are openings in the abdomen (that can be opened and closed by the insect using tiny
muscles) attached to tubes called trachea (just like out trachea). The tubes branch and
become smaller and smaller (now called tracheoles) until each tubule ends attached to
a single cell in the insect (with a water based surfactant for diffusion of gasses).
The excretory system limits the loss of water by concentrating nitrogen into uric
acid or guanine. The by-product of protein breakdown leaves a nitrogen waste
product that must be eliminated by any animal. Nitrogen can be removed from an
organism in four forms:
1.) ammonia- highly polar, dissolves in water easily-highly toxic… formula NH3
The only way this can be released safely from an animal is with copious amounts of
water. This type of elimination is found only in animals that live in the water (for the
most part).
2.) urea- not quite as polar, dissolves in water, but to get rid of urea, an animal
MUST use up a fair amount of water- formula: 3HN-C-NH3
O
3.) Uric acid- not polar at all, fairly insoluble in water- whitish/chalky material
formula:
5.) Guanine-not at all soluble in waterwhitish/chalky
material- formula:
Page 4 (Cont. #33 A/P Bio.)
To get rid of waste-some terrestrial insects developed Malpighian Tubules. See picture
below:
Page 5 (Cont. #33 A/P Biology)
Malpighian tubules are actually specialized projections between the Mid-gut and Hindgut. The tubules are “bathed” in the open blood circulatory system, extracting out salts
and waste, concentrating them as uric acid or guanine to be excreted through the anus.
_____ 1.) Tagmatization is:
a.) the fusion of body segments to form specialized body parts
b.) the segmentation of an insect’s body into a “head”, “thorax”, and “abdomen”
regions
c.) the de-evolution of a more complex organism to a more simple organism
d.) the fusion of one or more segments to form sexual organs
e.) none of the above are correct
_____ 2.) The more simple the animal the ….
a.) more complex the development must be
b.) the better the chance that it can regenerate most cells
c.) less likely it can regenerate most cells
d.) the higher the number of more specialized cells it must have
e.) the more likely it is to be a parasite
_____ 3.) In moving from the Annelids to the Arthropods, there seems to be a
development of a water limiting exterior shell (water-proof)- a strategy first found in:
a.) virus b.) plants c.) bacteria d.) protists e.) spores of fungi
_____ 4.) When animals isolate functions with specialized cells…
a.) they become harder to kill
b.) they decrease their need to be parasites
c.) they increase their need of organisms to ingest
d.) they are pressured to become autotrophs
e.) none of the above are correct
_____ 5.) All of the following could be benefits for having a water-proof exoskeleton
EXCEPT:
a.) help protect the organism from physical damage
b.) help the animal grow larger
c.) help the animal limit the loss of water
d.) help give the organism shape and anchors for muscles
e.) none of the above can be an exception
_____ 6.) Why is an exoskeleton limiting to range of motion?
a.) it is a hard shell impervious to many chemicals
b.) it first starts out as a soft shell that hardens over time
c.) it has a definite shape and therefore limited range of motion
d.) it is limited based on the number of muscles that can be anchored to the skeleton
e.) the exoskeleton can only have muscle attachments a special angles
Page 6 (Cont. #33 A/P Biology Arthropods and Echinoderms)
_____ 7.) What is one of the dangers of having an exoskeleton?
a.) it has limited range of motion
b.) it does not allow for exchange of gasses
c.) it does not allow for the intake of water
d.) molting leaves the animal more vulnerable to attack
e.) there are no dangers to having an exoskeleton
_____ 8.) Fusing of segments in an organism over time can form:
a.) three separate body sections: head, thorax, and abdomen
b.) two separate body sections: cephalothorax and abdomen
c.) specialized appendages such as legs
d.) specialized appendages such as wings
e.) all of the above are correct
_____ 9.) Centipedes and millipedes are:
a.) invertebrates
b.) insects
c.) crustaceans
d.) echinoderms
e.) all of the above are correct
_____ 10.) Ocelli are:
a.) simple eyes that contain a single lens
b.) superpositional eyes where each compartment has a single lens
c.) appositional eyes where each compartment has a single lens
d.) complex eyes that form a single image in the brain ganglia
e.) none of the above are correct
_____ 11.) What is the connection between the Malpighian tubules of the arthropod and
the “flame cells” of the Platyhelminthes (Planaria):
a.) they are both used for reproduction
b.) they are both used to help excrete waste
c.) they are both used to exchange gasses
d.) they are both used to defend the organism
e.) none of the above are correct
_____ 12.) What is the common theme between ammonia, urea, uric acid, and guanine?
a.) these are all food sources for all animals
b.) these are all building blocks for DNA
c.) these are all used to help animals excrete nitrogen wastes
d.) these are all used to help conserve water
e.) all of these are correct
Page 7 (Cont. #33 A/P Bio)
_____ 13.) In the Arthropods- the circulatory system DOES NOT:
a.) help move gasses into an out of individual cells
b.) help move nutrients into and out of cells
c.) help move sugars, amino acids, and fats into and out of cells
d.) none of the above are correct
_____ 14.) Nitrogen wastes are a result of:
a.) the breakdown of lipid material for energy
b.) the breakdown of protein for energy
c.) the breakdown of sugars for energy
d.) the breakdown of water for energy
e.) none of the above are correct
_____ 15.) What advantage is there by getting rid of nitrogen by urea over ammonia?
a.) you get rid of two nitrogen atoms in urea
b.) urea is soluble in water and less toxic than ammonia
c.) both (a.) and (b.) are correct
d.) none of the above are correct
16.) Speculate what the advantage of tagmatization is and why is there such variation in
the insect population.
17.) How do insects breathe or exchange gasses? Be specific!
Page 8 (Cont. #33 A/P Bio.)
18.) What kind of circulatory system does the insect have? Why is this efficient and why
might it be inefficient?
19.) Why is it more efficient to lose nitrogen by excreting guanine versus urea? Why do
you think humans do not excrete uric acid or guanine instead of urea?
Date: ________________
Lesson Plan for Handout #33 AP Biology
Objective: TLWD ability to define and contrast the differences between a mucous layer
of the annelids and the chitinous layer of the arthropods. Moreover, students will be able
to explain this divergent evolution based on environmental changes and determine the
pros and cons of this divergence in terms of successful strategies to : conserve water in
the insects and the changes that had to be made so insects do not have to have constant
contact with water, AND the diverse crustaceans that share many of the same traits- yet
generally require constant contact with water when given handout #33.
Content:: Transition between Annelids to: Arthropods -with contact with water
(crustaceans); and without constant contact with water (insects/arachnids).
Method: Power point, white board, discussion.
Homework: Handout #33
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