biology chapter 4

Question 1

embryology

Answer 1

is the study of the development of a unicellular zygote into a complete multicellular organism

Question 2

fertilization

Answer 2

an egg can be fertilized within 12-24 hours following ovulation. Occurs in the lateral, widest portion of the oviduct when sperm traveling from the vagina encounter an egg.

Question 3

cleavage

Answer 3

early embryonic development characterized by a series of rapid mitotic divisions

Question 4

indeterminate cleavage

Answer 4

is one that results in cells that maintain the ability to develop into a complete organism

Question 5

identical twins

Answer 5

are a result of indeterminate cleavage

Question 6

determinate cleavage

Answer 6

results in cells whose future differentiation pathways are determined at an eary developmental stage

Question 7

morula

Answer 7

solid ball of embryonic cells

Question 8

blastulation

Answer 8

begins when the morula develops a fluid-filled cavity called the blastocoel, which by the fourth day becomes a hollow sphere of cells called the blastula

Question 9

gastrula

Answer 9

once implanted in the uterus, cell migrations transform the single cell layer of the blastula into a three-layered structure called this

Question 10

ectoderm

Answer 10

integument (including the epidermis, hair, nails, and epithelium of the nose, mouth, and anal canal), the lens of the eye, the retina, and the nervous system

Question 11

endoderm

Answer 11

epithelial linings of the digestive and respiratory tracts (including the lungs), and parts of the liver, pancreas, thyroid, and bladder lining

Question 12

mesoderm

Answer 12

muscoloskeletal system, circulatory system, excretory system, gonads, connective tissue through the body, and portions of digestive and respiratory organs

Question 13

neurulation

Answer 13

by the end of gastrulation, regions of the germ layers begin to develop into a rudimentary nervous system

Question 14

notochord

Answer 14

a rod of mesodermal cells develops along the longitudinal axis just under the dorsal layer of ectoderm

Question 15

neural tube

Answer 15

which gives rise to the brain and spinal cord (central nervous system)

Question 16

neural crest

Answer 16

cells at the tip of each neural fold

Question 17

peripheral nervous system

Answer 17

including the sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells

Question 18

chorion

Answer 18

the chorion lines the inside of the shell. It is a moist membrane that permits gas exchange

Question 19

allantois

Answer 19

this sac-like structure is involved in respiration and excretion and contains numerous blood vessels to transport O2, CO2, water, salt, and nitrogenous wastes. Fish eggs do not have an allantois or an amnion

Question 20

amnion

Answer 20

this membrane encloses the amniotic fluid. Amniotic fluid provides an aqueous environment which protects the developing embryo from shock

Question 21

yolk sac

Answer 21

the yolk sac encloses the yolk. Blood vessels in the yolk sac transfer food to the developing embryo

Question 22

first trimester

Answer 22

during the first weeks, the major organs begin to develop. The heart begins to beat at approximately 22 days, and soon afterward, the eyes, gonads, limbs, and liver start to form. By 5 weeks the embryo is 10 mm in length; by 6 weeks the embryo has grown to 15 mm. the cartilaginous skeleton begins to turn into bone by the seventh week. by the end of 8 weeks, most of the organs have formed, the brain is fairly developed, and the embryo is referred to as a fetus. at the end of the third month, the fetus is about 9 cm long

Question 23

second trimester

Answer 23

during the second trimester, the fetus does a tremendous amount of growing. It begins to move around in the amniotic fluid, its face appears human, and its toes and fingers elongate. By the end of the sixth month, the fetus is 30-36 cm long

Question 24

third trimester

Answer 24

the seventh and eighth months are characterized by continued rapid growth and further brain development. During the ninth month, antibodies are transported by highly selective active transport from the mother to the fetus for protection against foreign matter. the growth rate slows and the fetus becomes less active, as it has less room to move about

Question 25

labor

Answer 25

a series of strong uterine contractions that can be divided into three distinct stages

Question 26

first stage

Answer 26

the cervix thins out and dilates, and the amniotic sac ruptures, releasing its fluids. During this time contractions are relatively mild

Question 27

second stage

Answer 27

characterized by rapid contractions, resulting in the birth of the baby, followed by the cutting of the umbilical cord

Question 28

final stage

Answer 28

the uterus contracts, expelling the placenta and the umbilical cord