Development
Steps of Development
Differentiation of cells into different types.
Growth: increase in overall size once food reaches
embryo.
Formation of shape
induction: one set of cells influences
development of others
programmed cell death
cell movement
Embryonic Cell
Layers
ectoderm: will form nervous system and epidermis.
endoderm: gives rise to gut, digestive glands,
internal structures.
mesoderm: gives rise to muscles, skeleton, reproductive
organs.
coelom (body cavity) develops in the mesoderm.
Neurulation
Neurulation (3rd week in humans): development of
the nervous system and head. two folds rise and join to form neural
tube.
neural tube develops into brain and spinal cord.
Extraembryonic
Membranes
chorion: outermost membrane that functions in gas
exchange.
amnion: delicate membrane that contains the amniotic
fluid.
allantois: storage area to collect metabolic waste.
yolk sac: surrounds the yolk.
Organogenesis
in Humans
Third week: nervous, digestive, and circulatory
systems begin to form. heart begins to pulsate.
Fourth- fifth weeks: limb buds appear.
Fourth- twelfth weeks: heart, eyes, and brain develop.
Third month: movement begins. the most obvious
progress is growth.
Metamorphosis
in Insects
Complete metamorphosis (moth)
egg
larva: worm-like appearance.
pupa: inside cocoon; tissues are reorganized.
adult
Incomplete metamorphosis (grasshopper)
egg
nymph: series of stages that look progressively
more like the adult.
adult
Twinning
Identical twins: 1 egg, 1 sperm. same DNA.
Fraternal twins: 2 eggs fertilized by different
sperm. different DNA.
Development
in Flowering Plants
Seed Structures
hypocotyl: stalk-like part of embryo attached below
the cotyledon.
plumule: embryo shoot with undeveloped leaves.
epicotyl: attached at the upper end of the hypocotyl.
radicle: at the lower end of the hypocotyl.
meristem; region of cell division in the radicle
and epicotyl.
Seed Germination
radicle emerges from seed.
hypocotyl lengthens, forming the stem and upper
root.
epicotyl emerges, forming leaves and part of stem.
cotyledons shrink.