Developmental Biology

Question 1

Fertilization

Answer 1

in mammals, an egg can be fertilized within 24 hrs after ovulation

Question 2

Cleavage

Answer 2

• a series of rapid mitotic division
• results in progressively smaller cells w/ an increasing ratio of nuclei to cytoplasm
• increases the surface-area-to-volume ratio - improving gas to nutrient exchange
• first complete cleavage of a zygote occurs approx 32 hours after fertilization
• the second cleavage occurs 60 hrs and the third cleavage approx 72 hrs = 8 celled embryo reaches th uterus

Question 3

Morula

Answer 3

a solid ball of embryonic cells

Question 4

Blastulation

Answer 4

• begins when the morula develops a fluid-filled cavity called the blastocell - after the 4th day becomes the blostula
• the blastula is the stage of the embryo that implants in the uterus

Question 5

Gastrulation

Answer 5

• after week 2, the embryo is fully implanted in the uterus

- blastula becomes a 3-layered structure called gastula

Question 6

Ectoderm

Answer 6

integumentary system, lens of the eye, the retina, and the nervous system

Question 7

Endoderm

Answer 7

epithelial linings of the digestive and respiratory tracts

Question 8

Mesoderm

Answer 8

musculoskeletal system, circulatory system, excretory system, gonads, connective tissue, and the portions of digestive and respiratory organs

Question 9

Neurulation

Answer 9

• at the end of gastrulation, regions of the germ layers begin to develop into a rudimentary nervous system - starts before week 3
• the notochord develops into a closed tube, which gives rise to the brain and spinal cord (CNS)
• the cells at the tip of each neural fold give rise to many components of the PNS - sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells

Question 10

Organogenesis

Answer 10

body organs begin to form

Question 11

Growth

Answer 11

organs increase in size

Question 12

Gametogenesis

Answer 12

Eggs develop in women and sperm develop in men

Question 13

Placental Development

Answer 13

• the placenta and umbilical cord supply oxygen and nutrients to the fetus and removes carbon dioxide to metabolic wastes
• the umbilical cord are outgrowth of the amnion, chorion, allontois, and yolk sac
• the amnion contains the amniotic fluid that acts as a shock absorber of external pressure
• placenta formation begins with the chorion, a membrane that surrounds the amnion that assists with the transfer of nutrients from the mother to the fetus
• the allontois become the umbilical vessels which will connect the fetus to the developing placenta

Question 14

Gestation

Answer 14

approx 9 months and subdivided into 3 trimesters

Question 15

First Trimester

Answer 15

major organs begin to develop and heart beats ~ 22 days

Question 16

Second Trimester

Answer 16

the fetus begins to move around the amniotic fluid

Question 17

Third Trimester

Answer 17

further brain development, fetus becomes less active and has less room to move around

Question 18

Birth and Maturation

Answer 18

• labor can be divided into 3 distinct stages
• first stage: the cervix thins and dilates and the amniotic sac ruptures, releasing its fluids
• second stage: rapid contractions resulting in the birth of the baby
• final stage: uterus contacts expelling the placenta and the umbilical cord

Question 19

Congenital Disorders

Answer 19

-birth defects can be caused by chemical and biological agents (teratogens)

Question 20

Epicotyl

Answer 20

percurser of the upper stem and leaves

Question 21

Cotylodons

Answer 21

Seed leaves

Question 22

Hypocotyl

Answer 22

the lower stem and room

Question 23

Endosperm

Answer 23

Feeds the embryo

Question 24

Seed Coat

Answer 24

develops from the outer covering of the ovule; the embryo and its seed coat together, comprise the seed