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Masja [62]
3 years ago
5

Veins have a much lower blood pressure than arteries. What prevents backflow of blood in veins?

Biology
1 answer:
pentagon [3]3 years ago
4 0
Having traveled through the arteries and capillaries, the blood have already lost considerable amount of pressure when it is to travel through the veins. The veins are composed of one-way valves as when the veins are squeezed, it pushes the blood to the valves. 
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ATP powers the cellular processes of the elodea

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What occurs to the cell during mitosis?
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During mitosis the cell splits and becomes two
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Record the stages of meiosis in eukaryotic cells realizing that there are two cell divisions involved, each having their particu
Leya [2.2K]
1.1
Meiosis I
The first meiotic division: diploid → haploid
    Prophase I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes join and occurs crossing over.
    Metaphase-I: the homologous chromosomes align in the middle of the cell. Spindle fibers from the centrosomes connect to the chromosomes.
    Anaphase -I: Spindle fibers contract and split the homologous chromosomes, moving them to opposite poles of the cell.
    Telophase -I: Chromosomes decondense; cell divides to form two haploid cells.

1.2 Meiosis II
The second division: separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I)

     Prophase II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
    Metaphase-II:  the chromosomes align in the middle of the cell. Spindle fibers from the centrosomes connect to the chromosomes (at the centromere)
    Anaphase-II: Spindle fibers contract and split the sister chromatids, and moves them to opposite poles of the cell.
    Telophase-II: Chromosomes decondense,cells divides again to form another 2 haploid daughter cells. Final: 4 new cells.


2. The differences:
Mitosis:
- has 1 division per cycle
- one cell produces 2 new cells
- the genetic information in the mother-cell and the daughter-cells are the same. ( the number of chromosomes is also the same)
- it occurs in somatic cells
Meiosis:
- two divisions per cycle
- one cell when divides produces 4 new cells
- the new cells have different genetic information. mixes the genetic material from the parent cells
- the number of chromosomes of the daughter cells is half of the mother's.

3. Prokaryotic organisms don't divide through mitosis, they use a different process called binary fission. Only eukaryotic organisms, or those whose cells have a defined nuclei, undergo mitosis. Bacteria, for example, are prokaryotic organisms that use binary fission.

4.
 It can't occur. Cross over is the exchange of DNA between homologous chromosomes.  That will result in recombinant chromosomes during sexual reproduction. It can't occur on different chromosomes because they don't code for the same genes.

5. There are a lot of different theories about that, but it's mostly believed that meiosis must evolve before sexual reproduction. That's because The cell replicates their information first and then divides. Plus the cell does that even though it didn't recombine DNA with another organism (sexual reproduction).

3 0
3 years ago
Both coal and diamonds are forms of elemental carbon. Coal is brittle while diamonds are considered to be the hardest Of all sub
Art [367]

arbon, as with many elements, can arrange its atoms into several different geometries, or "allotropes." In pure diamond, every carbon atom is covalently bonded to exactly 4 other carbon atoms in a very specific and energetically favorable geometry. The diamond cannot be broken or scratched unless many covalent bonds are broken, which is difficult to do. In another common allotrope, graphite, every carbon atom is covalently bonded to only 3 other carbon atoms, and the atoms are arranged in sheets that are not covalently bonded to each other. The sheets can be broken apart easily, ultimately meaning that graphite can be easily scratched. Coal is composed of particles of different allotropes of carbon, and some "amorphous carbon," which has no defined geometry in its atomic structure. Without a continuous network of covalent bonds, coal is easily scratched (i.e. it is not hard).



8 0
3 years ago
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