Earth revolves once around the sun in 365 days during a non-leap year
There are 365 days in a year
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Answer:
Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period. Index fossils are useful because they tell the relative ages of the rock layers in which they occur.
Answer:
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Explanation:
To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners.
Prokaryotic organisms are single-celled organisms that lack a cell nucleus, and their DNA therefore floats freely in the cell cytoplasm. To synthesize a protein, the processes of transcription and translation occur almost simultaneously. When the resulting protein is no longer needed, transcription stops. As a result, the primary method to control what type of protein and how much of each protein is expressed in a prokaryotic cell is the regulation of DNA transcription. All of the subsequent steps occur automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
Eukaryotic cells, in contrast, have intracellular organelles that add to their complexity. In eukaryotic cells, the DNA is contained inside the cell’s nucleus and there it is transcribed into RNA. The newly synthesized RNA is then transported out of the nucleus into the cytoplasm, where ribosomes translate the RNA into protein. The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus in the cytoplasm. The regulation of gene expression can occur at all stages of the process (Figure 1). Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetic level), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level), when the RNA is translated into protein (translational level), or after the protein has been made (post-translational level).
The correct order of the following events on the mass flow of materials in the phloem is:
- Leaf cells produce sugar by photosynthesis.
- Solutes are actively transported into sieve tubes.
- Water diffuses into the sieve tubes.
- Sugar moves down the stem.
Correct answer: letter C.
This is because the mass flow of materials in the phloem must pass through all these processes in a consecutive and orderly manner, from the cell to the stem, in order to allow nutrients and other vital materials to reach from the plant roots to the leaves and fruits.
<h3>How is this transport of nutrients and other vital materials achieved?</h3>
This is accomplished by the transport of solutes through the phloem's network of channels, which contain fluids, mineral salts, vitamins and other nutrients essential to plant health. Mass flow also helps distribute oxygen and carbon dioxide to all parts of the plant. These materials are necessary for plant respiration and growth.
Learn more about the phloem:
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