Question

Why is the relative size of the yolk sac in a mammal egg much smaller than that found in an amniotic egg?

The yolk sac is relatively smaller in the mammal because its function in an amniotic egg (source of nutrients) has been taken over by the placenta.

Amniotic eggs require larger yolk sacs to support longer maturation times compared to mammal eggs that develop more quickly.

The embryos of animals with amniotic eggs like reptiles are larger than the embryos of placental mammals, so they need more nutrients.

Because amniotic eggs develop outside the body, they require larger yolk sacs to support embryos exposed to variable environmental temperatures. Mammal eggs develop at a more constant, favorable temperature inside the body.

Answer 1

The correct option is the first option :

The yolk sac is relatively smaller in the mammal because its function in an amniotic egg (source of nutrients) has been taken over by the placenta.

other options are incorrect because:

option 2:

it is incorrect because maturation of mammals may be even longer than amiontes, such as human egg takes more time to mature than the egg of bird, like hen.

Option 3:

Embryo always starts from a single cell, fertilized egg . It is not necessary that reptiles have larger embryo than mammals.

Option 4:

Both require energy to to support the developing embryo . In amniotic eggs it is supplied by yolk sac where as in mammals it is supplied through Palacenta as stated in OPTION 1.