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28.3 Reproduction
Lesson Objectives
Compare asexual and sexual reproduction.
Contrast internal and external fertilization.
Describe the different patterns of embryo development in animals.
Explain how terrestrial vertebrates are adapted to reproduction on land.
Lesson Summary
Asexual and Sexual Reproduction Most animals reproduce sexually. Some animals are
also able to reproduce asexually.
▶ Asexual reproduction requires only one parent allowing for rapid reproduction.
▶ Sexual reproduction requires two parents. This type of reproduction maintains genetic
diversity in a population by creating individuals with new combinations of genes.
Internal and External Fertilization In sexual reproduction, eggs and sperm meet either
inside or outside the body of the egg-producing individual.
▶ During internal fertilization, eggs are fertilized inside the body of the egg-producing
individual.
▶ In external fertilization, eggs are fertilized outside the body.
Development and Growth Embryos develop either inside or outside the body of a
parent in various ways.
▶ Oviparous species are those in which embryos develop in eggs outside the parents’ bodies.
▶ In ovoviviparous species, embryos develop within the mother’s body, but they depend
entirely on the yolk sac of their eggs.
▶ Viviparous species’ embryos obtain nutrients from the mother’s body. Some mammals
nourish their embryos by means of a placenta—a specialized organ that enables exchange
of respiratory gases, nutrients, and wastes between the mother and her developing young.
▶ As invertebrates, nonvertebrate chordates, fishes, and amphibians develop, they undergo
metamorphosis, resulting in changes to their shape and form.
▶ Some insects undergo gradual or incomplete metamorphosis. Immature forms, or nymphs,
resemble adults, but they lack functional sexual organs and some adult structures.
▶ Other insects undergo complete metamorphosis. Larvae change into a pupa, the stage in
which an insect larva develops into an adult.
Reproductive Diversity in Chordates Chordates had to adapt to reproduction on land.
Most chordates need a wet or moist environment for their eggs.
▶ The eggs of most aquatic organisms must develop in water. Reptiles, birds, and a few
mammals have evolved amniotic eggs in which an embryo can develop outside its
mother’s body, and out of water, without drying out.
▶ Mammals have various reproductive adaptations. But all mammalian young are nourished
by milk produced by the mother’s mammary glands.
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Asexual and Sexual Reproduction
1. What does asexual reproduction allow animals to do?
It allows animals to increase their numbers rapidly.
2. What is an advantage of sexual reproduction?
It helps a species maintain genetic diversity.
3.
Shade the arrows showing haploid stage of the life cycle. Draw small
dots in the arrows showing diploid stages.
Meiosis
Female medusa
(shaded)
(dotted)
Sperm
Egg
Male medusa
Fertilization
Young medusa
develops.
Zygote
Young medusa
Polyp
(dotted)
Zygote grows
into a larva.
The larva
attaches to a
hard surface
and develops
into a polyp.
(dotted)
Budding
polyp
Internal and External Fertilization
4. What is the difference between external and internal fertilization?
In external fertilization, eggs are fertilized outside the body of the egg-producing
individual. In internal fertilization, eggs are fertilized inside the body of the eggproducing individual.
Development and Growth
Write the letter of the correct answer on the line at the left.
B
5. In which mode of reproduction do the embryos develop inside the mother’s body
using the egg yolk for nourishment?
A. oviparous
C. viviparous
B. ovoviviparous
D. herbivorous
C
6. Organisms that develop placentas are
A. oviparous.
C. viviparous.
B. ovoviviparous.
D. herbivorous.
7. Explain the difference between complete and incomplete metamorphosis.
In complete metamorphosis, the insect goes through immature stages that do not
look like the adult form. In incomplete metamorphosis, the immature form, the
nymph, looks similar to the adult form.
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Reproductive Diversity in Chordates
8.
Embryo
Amnion
Allantois
Shell
Chorion
Yolk sac
9. Complete the table about mammal reproduction.
Types of Mammalian Reproduction and Development
Group
How Are Young Born?
How Are Young Fed?
Monotremes
Young hatch from soft-shelled eggs laid outside
the mother’s body.
Young get milk from pores
on the mother’s abdomen.
Marsupials
Embryo is born at a very early stage of
development and attaches to a nipple
inside a pouch.
Young drink from a nipple
inside the mother’s pouch.
Placental
mammals
Embryos develop inside the mother. Wastes
and nutrients pass through the placenta.
Young are generally nursed by
the mother.
10. How might the shape of an amniotic egg complement its function?
SAMPLE ANSWER:
The slightly elongated, pointed shape may help the mother lay the egg
more easily. In addition, the shape keeps the egg from rolling far from a nest.
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28.4 Homeostasis
Lesson Objectives
Explain how homeostasis is maintained in animals.
Describe the importance of body temperature control in animals.
Lesson Summary
Interrelationship of Body Systems Homeostasis is the maintenance of a relatively stable
internal environment. All body systems work together to maintain homeostasis. Fighting
disease-causing agents is a large part of maintaining homeostasis. Most animals have an
immune system that attacks pathogens.
▶ Vertebrates and many invertebrates regulate many body processes using a system of
chemical controls.
▶ Endocrine glands, which produce and release hormones, regulate body activities by
releasing hormones into the blood.
Body Temperature Control Control of body temperature is important for maintaining
homeostasis, particularly in areas where temperature varies widely with time of day and with
season.
▶ An ectotherm is an animal whose regulation of body temperature depends mostly on its
relationship to sources of heat outside its body. Most reptiles, invertebrates, fishes, and
amphibians are ectothermic.
▶ An endotherm is an animal whose body temperature is regulated, at least in part, using
heat generated by its body. Birds and mammals are endothermic.
Interrelationship of Body Systems
1. Complete the graphic organizer about body systems working together.
Circulatory
System
Respiratory
System
The Main Organ
Systems
Contributing to
the Delivery of
Oxygen and
Nutrients to Cells.
Digestive
System
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2. What is homeostasis?
Homeostasis is the ability of an animal to maintain a stable internal environment.
3. Name the body system that helps protect mammals from disease and describe how it
accomplishes this task.
The immune system protects mammalian bodies from disease. It does this by distinguishing between “self” and “other.” Once the immune system discovers “others” in
the body, it attacks the invaders.
4. What are endocrine glands?
Endocrine glands are part of the body system that regulates many body processes
using chemical controls. Endocrine glands release chemicals called hormones that
affect other organs and tissues.
Body Temperature Control
5. List three features that animals need in order to control their body temperature.
Animals need a way to generate heat, a way to conserve heat, and a way to eliminate
excess heat.
6. How do ectotherms control their body temperature?
They rely on interactions with the environment.
7. Explain how the human body cools itself.
Humans sweat to help reduce their body temperature. As sweat evaporates, it
removes heat from the skin and the blood in capillaries just under the surface of the
skin. Thus, as warm blood flows through the cooled capillaries, it loses heat.
8. Name one advantage and one disadvantage of endothermy.
One advantage is that endotherms can move around easily during cool nights or in
cold weather. One disadvantage is that endotherms require a lot of fuel in the form of
food in order to generate body heat.
For Questions 9–15, complete each statement by writing the correct word or words.
9. Control of body temperature is important for maintaining homeostasis .
10. Cold muscles contract more
slowly
than warm muscles.
11. An animal that must absorb most of its heat from the environment is a(n)
ectotherm
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12. An animal that uses heat generated by its own body to maintain its body temperature is
a(n) endotherm .
13. Endotherms have a higher
14. Endothermy evolved
after
body fat
15. Mammals use
metabolic
and
rate than ectotherms.
ectothermy.
hair
as insulation in order to stay warm.
Match each organism with the method of controlling body heat. Methods may be used more
than once.
Organism
Body Heating Method
B
16. mammals
A. Ectothermy
A
17. fish
B. Endothermy
A
18. amphibian
A
19. invertebrate
B
20. birds
A
21. reptiles
For Questions 22–25, write True if the statement is true. If the statement is false, change the
underlined word or words to make the statement true.
True
22. The first land vertebrates were ectotherms.
True
23. Some scientists hypothesize that some dinosaurs were endotherms.
twice
24. Current evidence suggests that endothermy evolved at least four
times.
endotherms
25. Most animals living in polar regions are ectotherms.
26. Explain how an organism’s circulatory, digestive, or excretory system helps the organism
maintain homeostasis.
SAMPLE ANSWER:
The excretory system of an organism helps it maintain homeostasis by
regulating water balance and getting rid of toxic waste products. For example, the
kidneys excrete or retain excess liquid, but they filter waste products out of the bloodstream so that the waste products will not poison cells.
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Chapter Vocabulary Review
1. In the box below, draw a picture of the arrangement of a joint, including at least one
ligament and at least one tendon. Label your picture.
Students’ drawings should show the articulation point of two bones. This point
should be labeled as a joint. Connective tissues should be drawn connecting the two
bones. This tissue should be labeled as a ligament. Another connective tissue should
connect a bone to a muscle. This tissue should be labeled as a tendon.
For Questions 2–7, complete each statement by writing the correct word or words.
2. A single, specific reaction to a stimulus is a(n)
placenta
3. A structure called a(n)
tissues from the mother’s body.
response
.
forms when an embryo’s tissues join with the
4. One of the most important adaptations to life on land is the
protects the growing embryo and keeps it from drying out.
amniotic egg
, which
ovoviviparous
5. In
animals, the eggs develop inside the mother’s body, and the
embryo uses the yolk for nourishment.
6. A(n)
exoskeleton
7. A(n)
endoskeleton
is a tough external covering of the body.
is an internal skeleton.
For Questions 8–11, write True if the statement is true. If the statement is false, change the
underlined word or words to make the statement true.
True
8. A stimulus is any kind of signal that carries information and can be
detected.
viviparous
9. In oviparous animals, the embryos develop inside the mother’s body
and obtain their nourishment from their mother, not the egg.
pupa
10. In complete metamorphosis, the stage in which an insect changes
from larva to adult is called a(n) nymph.
True
11. A group of nerve cells that control the nervous system in many
invertebrates is called a(n) ganglion.
Write the letter of the correct answer on the line at the left.
C
12. Mammals are characterized by hair and
A. lungs.
C. mammary glands.
B. prehensile tails.
D. four-chambered hearts.
B
13. Animals that can generate their own body heat are known as
A. ectotherms.
C. chordates.
B. endotherms.
D. invertebrates.
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After the incredible birth of the bonnethead
shark at the Doorly Zoo, the zoo’s public
relations department was probably working
overtime. The birth of this shark provided a
perfect opportunity to promote the zoo.
SHE’S JUST LIKE
HER MOTHER
Learning
Promoting Zoo Births
Zoos work responsibly to foster the reproduction of animals. The birth of a zoo animal is
something to be celebrated and promoted, especially when it involves an endangered or
threatened animal. Zoo births are helpful to zoos in many ways. For example, they can bring
in additional visitors and encourage donations to the zoo.
A zoo’s public relations department can find many ways to promote the birth of an animal.
They may create and issue press releases, posters, pamphlets, commercials, and billboards. Their
efforts may lead local television and radio stations to cover the animal birth in news reports. The
following is an example of what a transcript of a live report by a local television station might
have been like after a Sumatran tiger gave birth to triplets at the San Francisco Zoo.
How could this be? Well, Leanne
had
decided to take a tiger-size lick of
the
camera that was monitoring her, fogg
ing
up part of the lens. The birthing box
was
not completely visible, either. It was
not
until the thirsty new mom left the box
to
get a drink that the zookeeper noticed
the
two other cubs. Zookeepers do not
want
to disturb the mother and her young
yet.
Leanne is doing a great job of taking
care
of her babies—even protecting them
from
the camera lens. Sumatran tigers are
an
endangered species, with only about
600
remaining in the wild. Zoo officials
hope
that these web-footed cubs will soon
be
swimming just as fast as other Sum
atran
tigers.
Live at 5 San Francisco News
REPORTING LIVE FROM THE
SAN FRANCISCO ZOO
March 14, 2008 - I’m reporting live from
the San Francisco Zoo. Zookeepers were
in for a couple of surprises today at the San
Francisco Zoo. The zoo has been buzzing with
excitement and activity since their 230-pound
Sumatran tiger, Leanne, gave birth to one
cub on March 6. But just this week, the zoo
revealed that Leanne actually had triplets! The
zoo’s chief veterinarian did not suspect that
there was more than one cub until 6 days ago.
Continued on next page ▶
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Science and Global
Awareness
1. What is the tone of this television report, and how is it intended to make you feel?
SAMPLE ANSWER:
The tone is one of excitement. It is probably intended to make the
viewer want to visit the zoo to see the tiger triplets.
2. Suppose you were giving this report. What information would you add to the report?
Explain your answer.
SAMPLE ANSWER:
I would give more information about the cubs, which is the main focus
of the story, and thus the reason people are watching the report. I would give details
about how big they were when they were born, when they will be moving about, and
how healthy they are.
3. What do you think is the purpose of this television report?
SAMPLE ANSWER:
I think the purpose is to get viewers excited. They left out just enough
information to keep viewers interested, which may serve to encourage viewers to visit
the zoo.
4. What are some words and phrases in the broadcast that appeal to listeners’ emotions and
make them want to visit the zoo?
Examples of words and phrases in this report that appeal to a listener’s emotions
include surprises, buzzing with excitement, and new mom. These words and
phrases are all emotionally charged.
5. What are two facts you learned about Sumatran tigers from this report?
SAMPLE ANSWER:
Sumatran tigers have webbed feet and can swim fast. There are only
about 600 left in the wild.
Promote Zoo News
The skills used in this activity include information and media literacy, creativity and
intellectual curiosity.
Find out about the latest news at a zoo close to your town or in your area by calling the
zoo and asking to speak with its public relations department, visiting the zoo, or looking at
the zoo’s Web site. Choose an event, such as the recent birth or acquisition of an animal,
that you can promote to encourage more people to visit the zoo. After researching the event,
create a poster to promote it. Your poster should include persuasive text, photographs or
illustrations, contact information, and how to visit the zoo.
Display copies of your poster around your school. You may also want to contact the zoo and
encourage them to use your poster.
Evaluate students’ posters based on the organization of the text and art, the appeal of
the art as an enticement to visit the zoo, the succinctness and completeness of the text,
and the information it contains.
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