Answer;
Primitive streak.
At the onset of the embryonic period, the primitive streak appears. It will eventually become the neural tube.
Explanation;
The primitive streak is a transient structure which forms on day 15 of human development.
It marks the start of gastrulation; the process in which the inner cell mass in converted into the trilaminar embryonic disc.
It originates from the anterior epiblast.
Answer : Abiotic factors refer to non-living physical and chemical elements in the ecosystem. ... Biotic factors are living or once-living organisms in the ecosystem. These are obtained from the biosphere and are capable of reproduction. Examples of biotic factors are animals, birds, plants, fungi, and other similar organisms.
