Transcript Ch 28 Animal Systems II

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2.
3.
Infer Why might sexual reproduction, as opposed
to asexual reproduction, produce a population
better able to survive disease or environmental
changes
Predict Why would you expect most species that
employ external fertilization to reproduce in the
water
Compare and Contrast What is the difference
between a nymph and a pupa
CH 28 ANIMAL SYSTEMS II
28.3 Reproduction
Asexual Reproduction
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Many invertebrates and a few chordates
Requires only one parent
Can reproduce rapidly
Lack genetic diversity.
Types of Asexual Reproduction
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Divide in two
Budding
Parthenogenesis
 Females
lay eggs that develop without being fertilized
by a male.
Sexual Reproduction
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Involves meiosis, creates gametes
Male and female gamete join to create zygote
Genetic diversity
Requires two individuals of different sexes
Greater needs.
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Most animal species that reproduce sexually have
individuals that are either male or female
 Some
species are hermaphrodites
 Some species switch sexes.
Reproductive Cycles
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Some invertebrates have life cycles that alternate
between sexual and asexual reproduction.
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Blood flukes mature in the body of an infected
person
Reproduce sexually and release embryos that pass
out of the body in feces
Embryos develop into larvae and infect snails and
reproduce asexually
Larvae infect people.
Jellyfish
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Aurelia polyps produce medusas asexually by
budding.
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Medusas reproduce sexually by producing eggs and
sperm that are released into the water.
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After fertilization, the resulting zygote grows into a
free-swimming larva.
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Larva eventually attaches to a hard surface and
develops into a polyp continuing the cycle.
Internal Fertilization
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Eggs are fertilized inside the body of the eggproducing individual
Many aquatic and all terrestrial animals
Sperm may taken in from surrounding water, be
gathered by the female, or deposited in side the
female.
External Fertilization
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Eggs are fertilized outside the body of the eggproducing individual
Aquatic invertebrate and vertebrates.
Development and Growth
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After fertilization, the zygote divides through
mitosis and differentiates
Development occurs under different circumstances
in different species
Care and protection given to developing embryos
also varies widely.
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Animals may be oviparous, ovoviviparous, or
viviparous.
Oviparous
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Embryos develop in eggs
outside the parents’ bodies
Most invertebrates, many
fishes and amphibians, most
reptiles, all birds, and a few
mammals.
Ovoviviparous
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Embryos develop within the
mother’s body, but depend
entirely on the yolk sac of their
eggs
Young do not receive any
additional nutrients from the
mother
Guppies and some shark
species.
Viviparous
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Embryos obtain nutrients
from the mother’s body
during development
Most mammals and some
insects, sharks, bony fishes,
amphibians, and reptiles.
Viviparous
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Young are nourished by secretions produced in the
mother’s reproductive tract in insects, and in some
sharks and amphibians.
Viviparous
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Placenta
 Specialized
organ that enables exchange of respiratory
gases, nutrients, and wastes between the mother and
her developing young
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In placental mammals.
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Most newborn mammals and newly hatched birds
and reptiles look a lot like miniature adults.
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As invertebrates, nonvertebrate chordates, fishes,
and amphibians develop, they undergo
metamorphosis
Metamorphosis
 Developmental
process that leads to dramatic changes
in shape and form.
Aquatic Invertebrates
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Have a larval stage that looks nothing like an adult
Swim or drift in open water before undergoing
metamorphosis and assuming their adult form
May have multiple larval stages.
Terrestrial Invertebrates
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Some undergo gradual or
incomplete metamorphosis
Nymph
 Immature
forms that resemble
adults
 Lack functional sexual organs and
some adult structures
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Molt several times and gradually
acquire adult structures.
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Some undergo complete
metamorphosis
Larvae look nothing like their
parents, and they feed in
different ways
Pupa
 Stage
in which an insect larva
develops into an adult
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Controlled by amount of juvenile
hormone produced.
Care of Offspring
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Species that provide intensive or long-term
parental care give birth to fewer young than do
species that offer no parental care
Type and amount of care varies greatly.
The Amniotic Egg
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Provides a protected
environment for an embryo to
develop out of water
One of most important
vertebrate adaptations to life
on land
Reptiles, birds, and a few
mammals.
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Amnion
 Fluid-filled
sac that surrounds
and cushions the developing
embryo.
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Chorion
 Regulates
the transport of
oxygen from the surface of
the egg to the embryo and
the transport of carbon
dioxide in the opposite
direction.
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Yolk sac
 Contains
nutrient-rich food
supply for the embryo
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Allantois
 Stores
waste produced by the
embryo
 Later fuses with the chorion.
Mammal Adaptations
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The three groups of mammals:
 Monotremes
 Marsupials
 Placentals
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All nourish their young with mother’s milk.
Monotremes
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Lay soft-shelled, amniotic eggs that are incubated
outside her body
Young are nourished by milk produced by the
mother.
Marsupials
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Bear live young that usually complete their
development in an external pouch
Young spend months attached to a nipple drinking
milk and growing inside.
Placentals
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Nourished through a placenta before they are born
and by their mother’s milk after they are born
Born at a fairly advanced stage of development.