Chapter 13 Flashcards
Animals may reproduce
only asexually, only asexually, or alternate between the two
How is asexual reproduction an advantage when environmental conditions are stable?
asexual reproduction results in offspring that are genetically identical to the parents
Some eggs can develop by
parthenogenesis: a process in which the egg develops without being fertilized and the adults that result are haploid
Parthenogenesis is a characteristic of honeybees
haploid individuals are male drones and diploid individuals are female workers
Some sessile animals are
hermaphrodites and can mate with any animal of their species
When hermaphrodite animals reproduce
both animals act as male and female and both donate and receive sperm
Sexual reproduction offers
increased variation among offspring and the possibility of greater reproductive success in a changing environment
During sexual reproduction,
a small flagellated haploid sperm (n) fertilizes a larger, nonmotile haploid egg (n) to form a diploid (2n) zygote
the zygote then undergoes cleavage, gastrulation, and organogenesis
How do fish and amphibians reproduce sexually?
carry out external fertilization, where the female sheds thousands of eggs to be fertilized by sperm directly in the environment
Fish and amphibian reproduction:
The likelihood that sperm and egg will actually fuse is
low, and the rate of predation of those that actually form a zygote is high
to compensate, millions of eggs and sperm are released at one time
Birds, reptiles, and mammals carry out
internal fertilization; usually they reproduce fewer zygotes and provide more parental care
Haploid is the currently the term used exclusively to mean
the n number of chromosomes
Animal: fish Fertilization: Development: Number of eggs: Parental care:
external
external
many
none
Animal: amphibian Fertilization: Development: Number of eggs: Parental care:
external
external
many
none
Animal: reptiles Fertilization: Development: Number of eggs: Parental care:
internal
external (inside the egg)
few
some
Animal: birds Fertilization: Development: Number of eggs: Parental care:
internal
external (inside the egg)
few
much
Animal: mammals Fertilization: Development: Number of eggs: Parental care:
internal
internal
few
much
The 4 advantages of asexual reproduction
- enables animals living in isolation to reproduce without a mate
- creates numerous offspring quickly
- there is no expenditure of energy maintaining elaborate reproductive systems or hormonal cycles
- because offspring are clones of the parent, asexual reproduction is advantageous when the environment is stable and favorable
Types of asexual reproduction
fission
budding
fragmentation
parthenogenesis
Fission
the separation of an organism into 2 new cells (amoeba, bacteria)
Budding
involves the splitting off of new individuals from existing ones (hydra)
Fragmentation
and regeneration occur when a single parent breaks into parts that regenerate into new individuals. (sponges, planaria, sea star)
Parthenogenesis
involves the development of an egg without fertilization
-resulting adult is haploid (honeybees and some lizards)
Sexual reproduction has 1 major advantage over asexual reproduction
variation
Human Male Reproductive System
testes vas deferens prostate gland scrotum urethra
Testes
(testis, singular)- male gonads; the site of sperm formation
Vas deferens
the duct that carries sperm during ejaculation from the epididymis to the penis
Prostate gland
the large gland that secretes semen directly into the urethra