Infer Why might sexual reproduction, as opposed to asexual reproduction, produce a population better able to survive disease or environmental changes

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1. Infer Why might sexual reproduction, as opposed
   to asexual reproduction, produce a population
   better able to survive disease or environmental
   changes
2. Predict Why would you expect most species that
   employ external fertilization to reproduce in the
   water
3. Compare and Contrast What is the difference
   between a nymph and a pupa

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Ch 28 Animal Systems II

• 28.3 Reproduction

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Asexual Reproduction

• Many invertebrates and a few chordates
• Requires only one parent
• Can reproduce rapidly
• Lack genetic diversity.

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Types of Asexual Reproduction

• Divide in two
• Budding
• Parthenogenesis
• Females lay eggs that develop without being
  fertilized by a male.

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Sexual Reproduction

• 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.

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Reproductive Cycles

• 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.

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Jellyfish

• 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.

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Internal Fertilization

• Eggs are fertilized inside the body of the
  egg-producing 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.

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External Fertilization

• Eggs are fertilized outside the body of the
  egg-producing individual
• Aquatic invertebrate and vertebrates.

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Development and Growth

• 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.

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Oviparous

• Embryos develop in eggs outside the parents
  bodies
• Most invertebrates, many fishes and amphibians,
  most reptiles, all birds, and a few mammals.

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Ovoviviparous

• Embryos develop within the mothers 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.

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Viviparous

• Embryos obtain nutrients from the mothers body
  during development
• Most mammals and some insects, sharks, bony
  fishes, amphibians, and reptiles.

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Viviparous

• Young are nourished by secretions produced in the
  mothers reproductive tract in insects, and in
  some sharks and amphibians.

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Viviparous

• Placenta
• Specialized organ that enables exchange of
  respiratory gases, nutrients, and wastes between
  the mother and her developing young
• 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.

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Aquatic Invertebrates

• 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.

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Terrestrial Invertebrates

• Some undergo gradual or incomplete metamorphosis
• Nymph
• Immature forms that resemble adults
• Lack functional sexual organs and some adult
  structures
• 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
• Controlled by amount of juvenile hormone produced.

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Care of Offspring

• 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.

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The Amniotic Egg

• 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
• Allantois
• Stores waste produced by the embryo
• Later fuses with the chorion.

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Mammal Adaptations

• The three groups of mammals
• Monotremes
• Marsupials
• Placentals
• All nourish their young with mothers milk.

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Monotremes

• Lay soft-shelled, amniotic eggs that are
  incubated outside her body
• Young are nourished by milk produced by the
  mother.

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Marsupials

• Bear live young that usually complete their
  development in an external pouch
• Young spend months attached to a nipple drinking
  milk and growing inside.

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Placentals

• Nourished through a placenta before they are born
  and by their mothers milk after they are born
• Born at a fairly advanced stage of development.