Section 38.1 (in part) and Section 47.1Biology – Campbell • Reece

PLANT AND ANIMAL DEVELOPMENT

Seed Dormancy•Dormancy is a condition of extremely low metabolic rate and suspension of growth and development•Breaking dormancy:•Some germinate as soon as they are in a suitable environmental•Others wait for specific environmental cues to increase the chances that germination will occur at a time and place most advantageous to the seedling

Examples of Environmental Cues•Substantial rainfall•Fire that removes competing vegetation•Where winters are harsh, seeds may require extended exposure to cold•Sufficient light•Seed coats weakened by chemicals as they pass through an animal’s digestive tract

Seed Germination•Germination depends on imbibition, the uptake of water by the dry seed•Causes the seed to expand and rupture its coat•Triggers metabolic changes that enable the embryo to resume growth

Seed Development•The first organ to emerge is the radicle (embryonic root)•The shoot tip then breaks through the soil surface•The epicotyl spreads its first foliage leaves•The foliage leaves begin photosynthesis

Seed Development

Animal Development•Fertilization is followed by 3 successive stages that begin to build the body•Cleavage – creates a multicellular embryo from the zygote•Gastrulation – produces a three-layered embryo called the gastrula•Organogenesis – generates rudimentary organs from which adult structures grow

Cleavage•A succession of rapid cell divisions that follow fertilization•The cells undergo the S and M phases of cell division, but often skip the G1 and G2 •The embryo does not get larger•Morula – solid ball of cells•Blastocoel – fluid-filled cavity•Blastula – hollow ball

Cleavage

Cleavage

Gastrulation•A dramatic rearrangement of the cells of the blastula•Some of the cells of the blastula move to an interior location, forming 3 cell layers•Gastrula – three-layered embryo•3 layers – endoderm, ectoderm, mesoderm

Gastrulation•Archenteron – deep, narrow pouch that forms from invagination•Blastopore – the opening at the end of the archenteron (will become the mouth or anus depending on the type of animal)

3 Embryonic Germ Layers

Organogenesis•The first organs to develop in chordates are the neural tube and notochord •Neural tube – will become the brain and spinal cord•Notochord – helps form the vertebrae; persist as the vertebral discs in adults

•As organogenesis progresses, morphogenesis and cellular differentiation continue to refine the organs

Organogenesis

Organ Systems