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Alenkinab [10]
3 years ago
8

7. When did whale ancestors begin living full time in the water?

Biology
1 answer:
antoniya [11.8K]3 years ago
8 0
Around 40 million years ago

The earliest whales that we think were fully aquatic, that is, they never left the water, are found around 40 million years ago, during the middle Eocene. That means that the transition from terrestrial animals to fully aquatic animals took about 12 million years.
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Why do we need to breath air instead of water????
Georgia [21]
Mainly because our lungs are made to intake air, and if we where to inhale water we would drown. oxygen can only be obtained from the air because our lungs would be able to expell the excess stuff from air easier than in water. hope i helped.
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3 years ago
Sequence the steps, 1–4, in the order required to create a permanent slide of human cheek cells. [1 mark] Specimen dehydrated Sp
gogolik [260]

Answer:

The correct order is dehydration, embed in wax, cut into sections, staining

Explanation:

There are certain proceedings needed to obtain stained sections of vegetable or animal tissues for their microscope observations.

These steps are:

  • Obtention of the material: The tissue is cut to an adequate size.
  • Fixation: When tissues are extracted from the organism, they suffer autolysis and putrefaction, so they need to be fixated in order to keep their cells in the best state possible. Fixation involves preserving the original morphological and molecular characteristics of the tissue. Fixation avoids autolysis, putrefaction, distortion, and retraction of cells and the tissue that could affect its volume or morphology.  
  • Dehydration. Once fixated, the fixator must be eliminated and the tissue is dehydrated by using a gradual series of solutions with alcohol in ascendant concentrations. Dehydration must be gradual to avoid tissue deformation.
  • Inclusion. To obtain thin cuts that can be observed under the optic microscope, the tissues must be included in a consistent, firm substance, that might be either hydrophilic or hydrophobic. A hydrophobic medium is paraffin wax, that provides hardness and plasticity.  
  • Cut. The tissue included in wax must be cut in slides or sections thin enough to allow the diffusion and penetration of light. A microtome is used to perform these cuts. When using paraffine for tissue inclusion, the cuts are about  5 to 20 micrometers of thickness.
  • Stain. Once the cuts are performed, paraffin wax must be eliminated. This can be done by using an organic solvent. Then the tissue must be stained. Hematoxylin and Eosin are the most common dyes. Animal tissues in general do not have any natural color, so they need to be stained to be observed.  
7 0
3 years ago
Which best describes red blood cells?
sesenic [268]
Answer: C. They transport oxygen throughout the body.
It is the primary function of red blood cells.

Hope it helped!
4 0
3 years ago
Read 2 more answers
Which statement about an individual that is homozygous for an allele is not true?
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Statement D. Is not true.
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How old is a bone that has 12.5% of the original amount of radioactive carbon-14 remaining
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The bone would be 17,100 years old.
6 0
3 years ago
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