Transcript Reproduction - The Bronx High School of Science

Why is reproduction an important life
function?
Why is reproduction an important life
function?
Reproduction is the only life process
that is optional for the organism, but
essential for the survival of the
species.
Unlike highly evolved organisms (e.g.
Humans- who may choose when and
where to reproduce)……..
Most organisms live to reproduce and
to fulfill their niche in their habitat
within an ecosystem.
Darwin’s “survival of the fittest” = the
fitness of the individual to pass on
their genetic information from one
generation to the other.
SUCCESSFUL REPRODUCTION
How does asexual reproduction differ
from sexual reproduction?
Asexual Reproduction
• Involves the process of
mitosis (2n)
• Before reproduction,
there is a single
organism.
• Following division,
there is a genetically
identical daughter
organism that
originated from the
parent.
Sexual Reproduction
• Involves the process of
meiosis (n)
• Begins with the fusion
of male and female
gametes to form a
zygote
• Zygote is genetically
different from the
parents
Why is sexual reproduction more
advantageous than asexual
reproduction in the scope of
evolutionary biology?
Why is sexual reproduction more
advantageous than asexual
reproduction in the scope of
evolutionary biology?
Sexual reproduction increases the
genetic diversity of the offspring.
Mutations may arise and can give one
generation an adaptive advantage in
the environment over the other
generation.
Differences in Reproduction in the
Animal Kingdom
Hydra
Phylum: Cnidaria- Reproduction
Asexual
•bud forms & falls off parent polyp
to become new polyp
Sexual
•Medusa (14) releases egg & sperm
into water
•fertilization in water to form zygote
• zygote develops into larva called
planula (1)
•planula develops into polyp
•polyp develops to new medusa
Budding in Hydra
Platyhelminthes
Phylum: Platyhelminthes
•reproductive system
•sexual- hermaphrodites
•both testes and ovaries, uterus in
mesoderm layer
•cross- or self-fertilization
•asexual
•binary fission
•fragmentation and regeneration
Phylum: Platyhelminthes
Class: Turbellaria
Reproduction
•asexual by binary fission
•sexual- hermaphrodites
•cross-fertilization
•some mate by “penis-fencing”
•sperm injected in body wall
•fertilization and early
development inside “mother”
•juveniles that resemble adult
released
With mating in the flatworms…….
there is a
“Thin line between Love and Hate”
Penis Fencing
Phylum: Platyhelminthes
Class: Cestoda
•long flat body made of many units
called proglottids
•proglottid = complete
reproductive unit with male and
female gonads
•youngest proglottid behind head
•older proglottids w/ eggs shed in
feces of definitive host
•reproductive output high
•many proglottids per tapeworm
•many eggs per proglottid
Mollusks
Mollusks are hermaphrodites.
Self-fertilization- only if no other mate
is available.
Cross-fertilization- is predominant
form of reproduction.
Heart. Most molluscs have an open circulatory
system. The dorsally located heart pumps
circulatory fluid called hemolymph through arteries
into sinuses (body spaces). The organs of the
mollusc are thus continually bathed in hemolymph.
Nephridium. Excretory organs
called nephridia remove metabolic
wastes from the hemolymph.
The long digestive tract is
coiled in the visceral mass.
Visceral mass
Coelom
Intestine
Gonads
Mantle
Stomach
Mantle
cavity
Shell
Radula
Anus
The nervous
system consists
of a nerve ring
around the
esophagus, from
which nerve
cords extend.
Figure 33.16
Gill
Foot
Nerve
cords
Esophagus
Mouth
Mouth
Radula. The mouth
region in many
mollusc species
contains a rasp-like
feeding organ
called a radula. This
belt of backwardcurved teeth slides
back and forth,
scraping and
scooping like a
backhoe.
Earthworm
Insects
Grasshopper Mating
• Many insects
– Undergo metamorphosis during their development
• In incomplete metamorphosis, the young, called
nymphs
– Resemble adults but are smaller and go through a
series of molts until they reach full size
• Insects with complete metamorphosis
– Have larval stages specialized for eating and growing
that are known by such names as maggot, grub, or
caterpillar
• The larval stage
– Looks entirely different from the adult stage
• Metamorphosis from the larval stage to the
adult stage
– Occurs during a pupal stage
(a) Larva (caterpillar)
(b) Pupa
(c) Pupa
(d) Emerging adult
(e) Adult
Transition from Water to Land
As organisms transitioned from water
to land, the needs for fertilization and
development had to change.
Fluid was needed for flagellated sperm
to find the egg to ensure fertilization.
Water was needed to prevent the eggs
from drying out on land.
External Fertilization
vs.
Internal Fertilization
External Development
vs.
Internal Development
Fish and Amphibians
External Fertilization
External Development
Frog Anatomy and Reproduction
Red-eyed Tree Frogs in Amplexus
External Development of Frog
Reptiles and Birds
Internal Fertilization
External Development
Internal Fertilization
Mammals
Internal Fertilization
Internal Development
Before we talk about internal
development……
let’s tackle internal fertilization and the
Human Reproductive System.
How do the structures of the Human
Reproductive System enable the
process of Sexual Reproduction*?
*Sexual Reproduction entails internal
fertilization and internal development
Male Reproductive Structures
It is important for the Scrotum to
maintain cooler temperatures than
body temperature. Why?
Viable sperm are temperaturedependent. Enzymes are sensitive to
temperature and pH, including
enzymes found in sperm.
Female Reproductive Structures
Now that we understand the
structures that enable fertilization,
let’s consider the Big Moment!
Copulation or Coitus
Fertilization
Embryonic development
Embryonic Germ Layers
Diploblastic- 2 layers
-ectoderm and endoderm
-no mesoderm
-ex. Cnidarians, Porifera (sponges)
Triploblastic- 3 layers
-ectoderm, mesoderm and endoderm
-all animals with bilateral symmetry
Embryonic Germ Layers
ectoderm
-outer layer
-forms animal’s outer covering, in
some phyla central nervous system
endoderm
-inner layer
-forms lining of digestive tract, in
vertebrates forms liver, lungs
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Mesoderm
mesoderm
-between ectoderm/endoderm in
triploblast
-forms muscles between digestive
tract and animal’s outer covering
Embryonic Cleavage:
Determinate (Protostomes) vs. Indeterminate (Deuterostome)
In humans, the first few divisions are indeterminate. If cells in the
embryo separate within the first divisions, the result is identical twins.
External Development vs. Internal
Development
Let’s say this isn’t the right time for
reproduction……..
Female Menstrual Cycle
Birth Control