Principles of Development

Biodiversity Concepts

• Biodiversity and Ecosystems

  • Types of biodiversity include:

  • Genetic diversity

  • Species diversity

  • Ecosystem diversity

• Threats to Biodiversity

  • Habitat loss

  • Invasive species

  • Overexploitation

  • Pollution

  • Climate change

Learning Outcomes

Students will be able to:

• Distinguish between direct and indirect development.

• Explain and describe four processes of embryonic development.

• Compare protostomes with deuterostomes and explain three developmental differences.

• Describe functions of four extraembryonic membranes in amniotes.

Topics Covered

1. Direct and Indirect Development

2. Early Embryogenesis

3. Cleavage

4. Childbirth Difficulties

Developmental Stages in Embryogenesis

• Embryogenesis Process Overview

  • 1 Month to 9 Months Development Sizes:

  • 1 Month: Size of a currant

  • 2 Months: Size of a cherry

  • 3 Months: Size of a plum

  • 4 Months: Size of a pear

  • 5 Months: Size of an apple

  • 6 Months: Size of a grapefruit

  • 7 Months: Size of a pineapple

  • 8 Months: Size of a honeydew melon

  • 9 Months: Size of a watermelon

Steps in Animal Development

1. Cleavage:

   • From zygote to morula (not hollow); no size increase.

2. Blastulation:

   • From morula to blastula; embryo starts to grow.

3. Gastrulation:

   • Transitions from a single-layered blastula to a three-layered gastrula through invagination.

4. Neurulation:

   • Formation of neural tube from the neural plate.

Key Points

• Cleavage increases the number of cells without volumetric growth.

• Morula (solid), blastula (hollow).

Differences Between Protostomes and Deuterostomes

• Cleavage Patterns:

  • Protostomes: Spiral cleavage

  • Deuterostomes: Radial cleavage

• Coelom Formation:

  • Protostomes: Forms between body wall and gut

  • Deuterostomes: Forms as an outgrowth of the gut

• Blastopore Fate:

  • Protostomes: Becomes mouth

  • Deuterostomes: Becomes anus

Notable Examples

• Protostomes: Segmented worms, insects, spiders, arthropods, mollusks.

• Deuterostomes: Echinoderms and chordates.

Embryo Development Steps Recap

1. Zygote Formation: Begins with fertilization.

2. Cleavage: Formation of morula without growth.

3. Morula Formation: Cell differentiation into trophoblast and embryoblast.

4. Blastocyst Formation: Formation of blastocoel and growth.

5. Gastrulation: Emergence of three germ layers: ectoderm, mesoderm, endoderm.

6. Neurulation: Neural plate forms a neural tube influenced by the notochord.

Human Embryonic Development Insights

• Cleavage happens before implantation in humans.

  • Stages: Fertilization, Morula, Blastula, Implantation.

Modified Amniotic Egg in Humans

• Extraembryonic Membranes:

  • Allantois

  • Chorion

  • Amniotic cavity (with amniotic fluid)

  • Yolk sac (nutrient source)

Key Considerations

• Embryonic development includes determination, differentiation, growth, and morphogenesis.

• Sequence of stages: Cleavage, Blastulation, Gastrulation, Neurulation.

• Transition from morula to hollow mono-layer blastula, then to gastrula.