4. H ow does the quantity of yolk found in the unfertilized egg influence the ma

Question

4. H ow does the quantity of yolk found in the unfertilized egg influence the maturity of the individual at the end of embryonie development? 5. Wh y do birds and mammals have extraembryonic membranes but not the starfish or frog? 6. Which membrane functions most similarly in both birds and humans? 7. Are all four membranes present in both animals? 8. Which membrane(s) are most important I providing nutrients for the chick? humans? For 9. Which membrane(s) are most important in gas exchange for the chick? For humans? 10. Do you think that the amount of parental care which will be given after hatching or birth influences embryonic developmental patterns? Explain.

Explanation / Answer

4. Yolk contains fats and proteins and is the nutritive substance in egg. The amount of yolk in tends to affect the cleavage pattern of the embryos. It can obstruct the cleavage. When development of embryos take place from egg with less amount of yolk then such embryos become planktotrophic larvae. When development of embryos take place from egg with more amount of yolk then they become lecithotrophic lar­vae.

5. In birds and mammals embryo is present in the amnion, an extraembryonic membrane. This amnion is believed to be an adaptation to terrestrial life because it contains the embryo in fluid which prevents the embryo from drying out. Starfish and frogs do not need amnion and hence the extraembryonic membranes are not present in them.

6. Amnion functions most similarly in birds and humans because it contains embryo in the amniotic fluid.

7. Yes, all the four membranes are present in both animals (mammals).

8. In chicks yolk sac is important for providing the necessary nutrients. In humans yolk sac till embryo grows and then placenta is important for providing nutrients.

9. For gas exchange in chicks chorioallantois is important. For humans it is allantois.

10. Yes, the amount of parental care given does influence embryonic developmental patterns because this care proves to be beneficial in facilitating offspring performance traits which in turn tend to affect offspring fitness.

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