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
Scrotum
the sac outside the abdominal cavity that holds the testes; the cooler temperature that enables sperm to survive
Urethra
the tube that carries semen (the nutritive fluid that carries sperm) and urine
The Human Female Reproductive System
ovary oviduct or fallopian tube uterus vagina cervix endometrium
Ovary
where meiosis occurs and where the secondary oocyte forms prior to birth
Oviduct or Fallopian tube
where fertilization occurs; after ovulation, the egg moves through the oviduct to the uterus
Uterus
where the blastula stage of the embryo will implant and develop during the 9 month gestation, should fertilization occur
Vagina
the birth canal; during labor and delivery, the baby passes through the cervix and into the vagina
Cervix
the mouth of the uterus
Endometrium
lining of the uterus
The menstrual cycle consists of a
series of changes in the ovary and uterus that is controlled by the interaction of hormones
Human females release a
at internals that average about every 28 days from puberty until menopause
The release of an egg (really a secondary oocyte)
is one of four stages of the cycle
Follicular phase
several tiny cavities called follicles in the ovaries grow and secrete increasing amounts of estrogen in response to follicle-stimulating hormone (FSH) from the anterior pituitary
Ovulation
the secondary oocyte ruptures out of the ovaries in response to a rapid increase in luteinizing hormone (LH) from the anterior pituitary
When does ovulation occur?
on or about the 14th day after menstruation
Luteal phase
after ovulation, the corpus luteum (the cavity of the follicle left behind) forms and secretes estrogen and progesterone that thicken then endometrium (lining) of the uterus
Menstruation
if implantation of any embryo doesn’t occur, the buildup of the lining of the uterus breaks down and is shed
-tissue and some blood are discharged from the vagina
Hormonal control of the menstrual cycle
the hypothalamus in the brain releases GnRH, which stimulates the anterior pituitary to release FSH and LH, which, in turn, stimulate the ovary to release estrogen and progesterone
-the 2 hormones prepare the uterus for implantation of an embryo
Spermatogenesis
the process of sperm production, is a continuous process that begins at puberty and can continue into old age
When does spermatogenesis begin?
begins as the luteinizing hormone (LH) induces the testes to produce testosterone
-together FSH and testosterone stimulate sperm production in the testes
Each spermatogonium cell (2n) divides by
mitosis to produce 2 primary spermatocytes (2n) which can undergo meiosis I to produce produce 2 secondary spermatocytes (n)
Each secondary spermatocyte then undergoes
meiosis II, which yield four spermatids (n)
-these spermatids differentiate and move to the epididymis where they becomes motile
Each spermatogonium cell undergoes meiosis to produces
four active, equal size sperm
Oogenesis
the production of ova, begins prior to birth
-a female baby is born with all the primary oocytes she will ever have
Within the embryo, an oogonium cell (2n) undergoes
mitosis to produce 2 primary oocytes (2n)
-these remain inactive within follicles in the ovaries until puberty, when they become reactivated by hormones
Once follicles become reactivated by hormones,
meiosis I occurs, producing secondary oocytes (n) that are released monthly at ovulation
-meiosis II doesn’t occur until a sperm penetrates the secondary oocyte during fertilization, this could be 40 years after meiosis I
During meiosis I and II, the cytoplasm divides unequally. Almost all the cytoplasm remains
in the egg, leaving 2 tiny polar bodies that have very little cytoplasm and which will disintegrate
1 primary oogonium cell produces only
one active egg cell
Embryonic development
- a small, flagellated, haploid sperm (n) fertilizes a larger, nonmotile, haploid egg (n) to form a diploid (2n) zygote
- the zygote then undergoes cleavage, a succession of mitotic divisions that results in the formation of a hollow ball called a blastula
Embryonic development consists of 3 stages
cleavage
gastrulation
organogenesis
Cleavage
the rapid mitotic cell division of the zygote that begins immediately after fertilization
-the cells are dividing so quickly that individual cells have no time to grow in size
What do embryologists consider the end of the cleavage to be characterized by?
the production of a fluid-filled ball of cells called a bastula
-the individual cells of the bastula are called blastomeres, and the fluid-filled center is a blastocoel
Gastrulation
the continuation of the process that beganduring cleavage
-involves differentiation; the rearrangement of the blastula to produce a 3-layered embryo called a gastrula
The gastrula consists of 3 differentiated layers called
the embryonic germ layers
ectoderm, endoderm, and mesoderm
they will develop in all the parts of the adult animal
What will each germ layer become?
ectoderm- skin and nervous system
endoderm- forms the viscera, including the lungs, liver, and digestive organs
mesoderm- muscle, blood, and bones
Some primitive animals (sponges and cnidarians) develop a noncellular layer,
the mesoglea, instead of the mesoderm
Organogenesis
the process by which cells continue to differentiate, producing organs from the 3 embryonic germ layers
Once all the organ systems have been developed, the embryo
increases and size and becomes a fetus
Pattern of embryo development
zygote > cleavage > blastula > gastrulation > gastrula > organogenesis > fetus
The 4 membranes that arise outside the bird embryo
known as the extraembryonic membranes
chorion, yolk sac, amnion, and allatois
Chorion
lies under the shell and allows for diffusion of respiratory gases between the outside environment and the inside of the shell
Yolk Sac
enclose the yolk, the food for the growing embryo
Amnion
encloses the embryo in protective amniotic fluid
Allantois
- analogous to the placenta in mammals
- it’s the channel for respiratory gases to and from the embryo
- also the place where the nitrogenous waste uric acid accumulates until the chick hatches
