Answer: A. Brain - Organ level
B. Neurons - Cellular level
C. Neurotransmitters - Chemical level
D. Neurons and neuroglial cells - Tissue level
E.Brain combined with the spinal cord and spinal nerves - Organ System level
Explanation: There are five levels of organisation of life; cell, tissue, organ, system and organism.
The smallest unit is cell. Neurons are nerve cells.
Aggregation of cells forms a tissue. Neurons and neuroglial cells aggregate to form nervous tissues and are hence at tissue level.
Aggregation of tissues forms an organ. Brain is an example of organ. It is formed from aggregation of nervous tissues.
Tissues aggregate to form organs while aggregation of organs constitute a system. The nervous system consist of brain combined with spinal cord and spinal nerves.
The nervous system release chemicals called neurotransmitters.
<span>Activation energy refers to the amount of energy required by certain chemicals for them to have a reaction.
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(A) a change in a developmental gene or in its regulation that altered that spatial organization
Two factors contributed to the success of the pteridophytes: the extreme miniaturization of the gametophytic generation and an important development of the sporophytic generation (development of the tree forms).
Pteridophytes are a group of plants that peaked in the Carboniferous (-300 million years). It is the first great terrestrial plant civilization. These plants would have appeared in the Devonian -400 million years ago, perhaps from certain primitive terrestrial plants which, unlike bryophytes, would have favored the diploid generation on the haploid generation.
Particularly well adapted to terrestrial life, they have created, thanks to the development of tree forms, immense forests whose fossilization is at the origin of coal deposits.
Pteridophytes are at the origin of an evolutionary lineage based on the extreme miniaturization of gametophytic generation and an important development of sporophytic generation, leading to all tracheophytes including current flowering plants. Pteridophytes are well adapted to terrestrial life, however fertilization still requires the presence of water since male gametes are swimmers.
