<span>
are always unicellular
may have evolved from prokaryotes
</span><span>are more primitive than prokaryotes
</span>
Answer:
temporal reproductive isolation
Explanation:
The correct answer would be temporal reproductive isolation.
<u>Reproductive isolation</u> generally refers to series of biological mechanisms or processes that prevent members of different species from mating/fertilization or prevent the product of their mating to be invalid.
Some reproductive isolation processes prevent members of different species from mating or prevent fertilization as a result of mating. These processes are known as pre-zygotic reproductive isolation mechanisms.
Some other processes ensure that the product of fertilization (when it occurs) is invalid. These are known as post-zygotic isolation mechanisms.
<em>A good example of the pre-zygotic reproductive isolation process is </em><em>when closely related by different species bloom at different times</em><em>. This will prevent mating or cross-pollination to happen between the different species. This is known as temporal reproductive isolation.</em>
Answer:
Neurons have stable, relatively unchanging internal environments.
Explanation:
Neurons or nerve cells is the structural and functional unit of the nervous system. Neurons consists of the dendrites, axon, cell body and different cell organelles.
The neurons have mitochondria that meets the high ATP requirement and and consume more oxygen. The network of rough endoplasmic reticulum and ribosomes produce large number of proteins in neuron. The internal environment is never stable and gets changed as the nerve impulse transmission occur through the neuron. The membrane potential of the neuron gets changed and changes its internal environment.
Thus, the correct answer is option (B).
Answer:
I, II, III
Explanation:
A threshold stimulus is a stimulus that is capable to produce a response in excitable tissues such as neurons and muscle fibers. At threshold potential, the outward movement of K+ and inward movement of Na+ become equal to each other. When the potential exceeds the threshold potential, more and more Na+ enter the cell to depolarize it and to allow the opening of Na+ channels. Therefore, to fire an action potential, the threshold must be exceeded.
Conduction of action potential is all or none phenomenon which means that either it occurs or it does not occur. As an impulse is passed by each successive part of an exon, it enters the refractory period during which there is no conduction of nerve impulse. It ensures the one-way conduction of impulse from the cell body to the axon terminal only.
Chromatin is the lose form of genetic material & the "normal state" of DNA, RNA, and protein in the nucleus and in the cells.
Chromosomes are a condensed form of chromatin. Chromatin becomes chromosomes in the Prophase of Mitosis and Prophase 1 and Prophase 2 of Meiosis. It loosens again in the Telophase in Mitosis and Telophase 1 and Telophase 2 in Meiosis.
Sister Chromatids are made when chromosomes replicate during the cell cycle. The replication leads to the formation of the chromatids. The chromatids are joined by a single centromere. They separate during Anaphase 2 of meiosis.
I hope that this helps! Sorry if it doesn't I tried my best to explain!
