Ablastula is
a. a digestive organ
b. the innermost germ layer
c. a layer of embryological tissue
d. a hollow ball of cells in an embryo

d. a hollow ball of cells in an embryo

Explanation:

Blastula is a stage during early embryo development which arrives between morula stage and gastrula stage. This stage is characterized by a hollow ball of cells which surround a cavity known as blastocoele. This layer of cells which surround the blastocoele is known as blastoderm and it is formed by the repeated cleavages of zygote (fertilized egg). This cavity inside blastoderm i.e.  blastocoel is filled with fluid. Soon after the blastula develops fully, it turns into a gastrula and the process is called as gastrulation.

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.