The slide of stages in starfish development illustrates stages from unfertilized egg to gastrula—typical of echinoderms and chordates that have very little yolk in the egg. Three embryonic cell layers—ectoderm, endoderm, and mesoderm—are established. All adult tissues are derived from these layers.
<span>B) they are survivors of the ecological disturbance
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The mass number, also known as an atomic mass number or nucleon number, refers to the total number of neutrons and protons (in a combination known as nucleons) in an atomic nucleus. It determines the atomic mass of atoms. However, while calculating the mass number, the small contribution of mass from electrons is ignored.
Mass number is equal to Number of protons + Number of neutrons
Mass number = 11 + 7 = 18.
Hence, the correct answer is 18.
Answer:
Soil is composed of small pieces of a variety of materials, so it is a heterogeneous mixture.
Explanation: