Developmental Biology

Question 1

where does fertilization of the gg occur?

Answer 1

in the latera, widest portion of the oviduct

Question 2

cleavage–no growth in protoplasm occurs; cell volume stays constant, rapid mitotic divisions result in multiple cells decreasing in size–increases SA-volume ratio, improving gas and nutrient exchange

Answer 2

ya

Question 3

♣ first complete cleavage of a zygote occurs aprrox 32 hours after fertilization
♣ second cleaves occurs after 60 hours
♣ third after 72
• by this point, the 8 cell embryo reaches the uterus

Answer 3

ya

Question 4

what is a morula?

Answer 4

a solid ball of embryonic cells that occurs after continuing division

Question 5

what is blastulation?

Answer 5

begins when morula develops a fluid-filled cavity called the blastocoel

• -by the forth day, the blastocoel is hollow and the hollow sphere of cells is termed the blastula
• -the blastula is the stage where the developing embryo implants in the uterus

Question 6

• Gastrulation
o Embryo is fully implanted in the uterus after a week or two
o Cell migrations transform the single cell layer of the blastula into a three-layered structure called the gastrula
♣ These three primary germ layers give rise to specific structures:
• Ectoderm
o Integumentary system
♣ Includes epidermis, hair, nails, and epithelium of the nose, mouth, and anal canal)
♣ Lens of the eye, the retina
♣ Nervous system
• Endoderm
o Epithelial linings of the digestive and respiratory tract (including the lungs) and parts of the liver, pancreas, thyroid, and bladder lining
• Mesoderm
o Musculoskeletal system
o Circulatory system
o Excreteory system
o Goands
o Connective tissue throughout the body
o Portions of digestive system
Respiratory organs

Answer 6

ya–draw out

Question 7

• Neurulation
o By the end of gastrulation, regions of the germ layers begin to develop into a rudimentary NS
♣ Process known as neurulation
♣ Starts before week 3
o Notochord
♣ Rod of mesodermal cells develops along the longitudinal axis of the embryo just under the dorsal layer of the ectoderm
♣ Has an inductive effect on the overlaying ectoderm
• Causes it to bend inwards
o Forms a groove along the dorsal surface of the embryo
• Dorsal ectoderm folds on either side of the groove
o Neural folds grow upward and final fuse
♣ Forms a closed tube
♣ This is the neural tube
• Gives rise to the brain and spinal cord (CNS)
• Onc ethe neural tube is formed, it detaches from the ectoderm
♣ Cells at the tip of the neural fold are called neural crest cells
• Migrate laterally and give rise to many components of the peripheral NS
o Including the sensory ganglia
o Autonomic ganglia
o Adrenal medulla
o Schwann cells
♣ Sometimes neural tube does not close properly
• Results in a condition called spina bifida
• Incident of SB can be dramatically decreased if the mother takes folic acid

Answer 7

ya–draw this out

Question 8

what are the major developmental stages?

Answer 8

organogenesis, growth, gametogenesis

Question 9

what is organogenesis?

Answer 9

organs develop; cells interact, proliferate, differentiate, migrate, etc

Question 10

what is growth?

Answer 10

organs grow in size–continues into adulthood

Question 11

what is gametogenesis?

Answer 11

eggs and sperm develop in females and males–permits repro

Question 12

what are the placenta and umbilical cord grown from?

Answer 12

amnion, chorion, allantois, yolk sac

Question 13

what is the amnion?

Answer 13

o Thin, tough membrane
o Contains a watery fluid called amniotic fluid
♣ Acts as a shock absorb of external pressure during gestation and localized pressure from uterine contractions during labour

Question 14

what is the chorion?

Answer 14

o Placenta formation begins with the chorion
o A membrane that surrounds the amnion
o Assists with transfer of nutrients from the mother to the fetus

Question 15

what is the allantois?

Answer 15

o The third membrane
o Develops as an outpocketing of the gut
o Blood vessels of the allantoic wall englarge and become the umbilical vessels
♣ Connect the fetus to the developing placenta

Question 16

what is the yolk sac?

Answer 16

o Site of early development of blood vessels

o Becomes associated with umbilical vessels

Question 17

what happens during the first trimester?

Answer 17

♣ Major organs begin to develop
♣ Heart begins to beat at approximately 22 days
♣ Soon after, the eyes, gonads, limbs, and liver start to form
♣ By 5 weeks, the embryo is 10mm in length
♣ By 6, the embryo has grown to 15mm
♣ Cartilaginous skeleton begins to turn itno bond by the 7th week
♣ By the end of 8, most 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 ~9cm long

Question 18

what happens during the second trimester?

Answer 18

♣ Fetus does a lot of growing
♣ Begins to move around in the amniotic fluid
♣ Face appears human
♣ Toes and fingers elongate
♣ By the end of the sixth month, the fetus is 30-36cm long

Question 19

what happens during the third trimester?

Answer 19

♣ The 7th and 8th month are characterized by continued rapid growth and further brain development
♣ During the ninth month, Abs are transported by highly selective active transport from the mother to the fetus
Growth rate slows and the fetus becomes less active as it has less room to move about

Question 20

describe the divisions of labour

Answer 20

1st stage: ♣ cervix thins and dilates
♣ amniotic sac ruptures
♣ contractions at this stage are relatively mild
2nd stage: ♣ characterized by rapid contractions
♣ results in the birth of the baby
• umbilical cord is cut
3rd stage: ♣ uterine contracts and expels placenta and umbilical cord

Question 21

when do congenital disorders occur?

Answer 21

Errors can occur in fetal development due to deleterious genes or problems with the gestational environment

Question 22

what is vertical transmission?

Answer 22

♣ When a mother passes on an infection directly to the fetus

♣ Can occur either during development or during birth

Question 23

other enviro factors leading to birth defects?

Answer 23

♣ Radiation
♣ Restraint
♣ Trauma
♣ Poor nutrition

Question 24

what is experimental embryology?

Answer 24

o This field of study aims to investigate the effects of radiation, restraint, trauma, and poor nutrition and other factors on development
o Uses techniques of molecular biology
♣ Such as visualizing antigens using immunohistochemistry
o Uses genetic techniques
Such as manipulating specific genes and performing reseath on the behaviour of stem cells

Question 25

seed formation in plant

Answer 25

♣	Zygote divides mitotically
•	Forms mass of cells called embryo
♣	Embryo consists of the following parts
•	Epicotyl
•	Cotyledons	
•	Hypocotyl
•	Endosperm

Question 26

how is fruit formed in plants?

Answer 26

Fruit is formed from the ovary walls, the base of the flower, and other consolidated flower pistil components

Question 27

fruit serves as a means of seed dispersal oEnables the seed to be carried farther by air, water, or by animals
♣ Animals=ingestion and subsequent elimination
o Seed is released from the ovary and will germinate under proper conditions of temperature, moisture, and oxygen

Answer 27

ya

Question 28

what is the epicotyl?

Answer 28

o Precursor of the upper stem and leaves

Question 29

what are cotyledons?

Answer 29

Seed leaves
♣ Dicots have two seed leaves
♣ Monocots only have one

Question 30

what is the hypocotyl?

Answer 30

lower stem and root

Question 31

what is the purpose of the endosperm in plants?

Answer 31

feeds the embryo
In dicots, the cotyledon absorbs the endosperm
• Seed coat
o Develops from the outer covering of the ovule
♣ Embryo and its seed coat together comprise the seed

Question 32

what are meristem cells?

Answer 32

 Growth in higher plants is restricted to the embryonic (undifferentiated) cells
• Called meristem cells
o These tissues undergo active cell reproduction
o Gradually, the cells elongate and differentiate into cell types characteristic of species

Question 33

what is the apical meristem?

Answer 33

Found in the tips of root and stems

• Growth in lengh occurs only here

Question 34

what is the lateral meristem?

Answer 34

Aka cambium
• Located b/w the xylem and the phloem
• This tissue permits growth in diameter an can differentiate into new xylem and phloem cells
• Not an active tissue in monocots (grasses) or herbaceous dicots (alfalfa)
o Is predominant in woody dicots, such as oaks