Back to: ZOOLOGY 400 Level
Welcome to class!
Hello, superstar learner! I’m truly happy to see your curiosity and passion for learning shining bright today. You’re doing incredibly well, and today’s class is going to be extra exciting. We’ll be learning about how life continues after fertilisation — it’s all about Early Embryogenesis in Animals. This is where the zygote — that single cell formed after fertilisation — starts becoming a whole animal. Amazing, right?
Early Embryogenesis In Animals
Embryogenesis is the process by which a fertilised egg (zygote) transforms into a multicellular embryo. It’s like watching a house being built, starting from just one brick. In animals, this early development follows specific stages that help the embryo grow, organise, and prepare for later development.
Cleavage
The first step after fertilisation is cleavage — a rapid series of cell divisions without the embryo growing in size. The zygote divides into smaller cells called blastomeres. These divisions happen quickly, and the embryo looks like a cluster of cells.
These divisions form a solid ball of cells called a morula.
The morula then develops into a hollow ball of cells called the blastula (in mammals, it’s called a blastocyst).
Gastrulation
Next comes gastrulation, a very important stage. The blastula reorganises into three layers of cells, each of which will develop into different parts of the body:
Ectoderm – forms skin, brain, and nervous system
Mesoderm – forms muscles, bones, blood, and the heart
Endoderm – forms the lining of the gut, liver, and lungs
This layered structure is called a gastrula.
Neurulation
In animals with backbones (vertebrates), the next step is neurulation — the development of the nervous system. The ectoderm thickens to form the neural plate, which folds into a neural tube — the foundation of the spinal cord and brain.
Example: Imagine you’re building a house. The cleavage stage is like laying multiple blocks to make the foundation. Gastrulation is deciding what each room will be — bedroom, kitchen, living room. Neurulation is like wiring the house for electricity — setting up the nervous system!
Summary
- Early embryogenesis begins with the zygote undergoing cleavage into many small cells.
- The morula becomes a hollow blastula (or blastocyst).
- Gastrulation forms three germ layers: ectoderm, mesoderm, and endoderm.
- Each germ layer develops into specific tissues and organs.
- Neurulation forms the neural tube, which becomes the brain and spinal cord.
Evaluation
- What is cleavage in embryogenesis?
- Name the three germ layers and what they form.
- What is the role of the blastula?
- Describe the process of neurulation.
- Why is gastrulation a critical step in development?
You just took a deep look into how life begins to take shape — and you did it like a champ! Your understanding is growing, and you’re becoming more powerful with every lesson. Keep going strong, because Afrilearn is right here cheering you on. Your future in science is brighter than ever!