1. Explain how the amount of yolk in an egg affects cleavage and early developme

Question

1. Explain how the amount of yolk in an egg affects cleavage and early development.

2. Explain the general effects of an endocrine disruptor. Why is much of what we know about endocrine disruption from model organisms?

3. Imagine a hummingbird species has detected the odor of nectar. Explain how the signal is received and then transmitted from one neuron to the next. In your explanation diagram the6 stages of an action potential and indicate what initiates the action potential.

4. Hormones play a significant role in the digestion and processing of nutrients. Explain where each of the following comes from and how each functions in nutritional processes: secretin, insulin, glucagon.

5. Compare and contrast the following mechanisms for hormone transport: endocrine signaling, paracrine signaling, autocrine signaling, synaptic signaling, neuroendocrine signaling, and pheromone signaling

Explanation / Answer

1) Ovum after fertilisation enters series of mitotic divisions. This series of cell division is called as cleavage or segmentation. Yolk is stored in egg as deutoplasm. Depending upon the amount of yolk, cleavage can be total (holoblastic) or partial (meroblastic cleavage). In eggs with relatively little yolk, cleavage furrows can cut through the cytoplasm relatively easily and cleavages are therefore holoblastic. When high concentrations of yolk is present inside the egg, cleavage furrows cannot penetrate the yolk and cytoplasmic cleavage is limited to relatively yolk free areas, yielding a meroblastic type of cleavage.

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