Development 3

Question 1

What is gastrulation?

Answer 1

embryonic cells differentiate into 3 layers

Question 2

What is ectoderm?

Answer 2

outerlayer of cells

will become skin and nervous system (brain and spinal cord for CNS)

Question 3

What is mesoderm?

Answer 3

middle layer of cells

will become skeleton, muscles, and reproductive structures

Question 4

What is endoderm?

Answer 4

inner layer of cells

will become digestive and respiratory lining and endocrine glands

Question 5

IB: How do neural tubes develop?

Answer 5

Neural tube of embryonic chordates is formed
by infolding of ectoderm followed by elongation
of the tube

Neural tube: hollow structure in which the brain and spinal cord forms

Dorsal nerve: developed by early on neurulation (first month of gestation (development of womb)

Area on dorsal surface becomes neural plate (basis for nervous system)

Question 6

IB: How does neural development work?

Answer 6

Neurons are initially produced by differentiation in neural tube

Immature neurons migrate to a final location

An axon grows from each immature neuron in response to chemical stimuli

A developing neuron forms multiple synapses

Synapses that are not used do not persist

Neural pruning involves the loss of unused neurons

The plasticity of the nervous system allows it to change with experience.

Question 7

What happens during the 1st trimester?

Answer 7

0-12 weeks from fertilization

zygote begins cell division as it moves down oviduct

becomes blastocyst and implants in uterus

development of body organs (heart beats by week 4, testosterone secretes by week 7 if Y chromosome present which develops testes)

sucking reflex

by week 8 all major structures evident

embyro is now a fetus

embyro is most sensitive due to rapid growth

sensitive to radiation and drugs (teratogens), maternal lifestyle, viral infection, radiation

Question 8

What happens during the 2nd trimester?

Answer 8

weeks 13 -24

fetus grows rapidly to 30cm

quite active, hair begins to develop, cartilage turns to bone

Question 9

What happens during the 3rd trimester?

Answer 9

weeks 25-38

rapid growth to 51cm
fetal activity decreases (less room to move)

fully mature (ready for birth)

Question 10

IB: Sex determination in males

Answer 10

SRY gene in Y chromosome causes the embryonic gonads to develop testes and secrete testosterone

Gene carries DNA-binding protein called TDF (testis determining factor), which stimulates the expression of other genes that causes testis development