Plant and animal development

1. Plant and animal development Section 38.1 (in part) and Section 47.1 Biology – Campbell • Reece

2. 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

3. 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

4. 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

5. 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

6. Seed Development

7. 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

8. 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

9. Cleavage

10. Cleavage

11. 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

12. 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)

13. 3 Embryonic Germ Layers

14. 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

15. Organogenesis

16. Organ Systems