With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells. Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. The cell theory was eventually formulated in 1839.

The three tenets to the cell theory are:
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in organisms.
3. Cells arise from pre-existing cells.

Which of these contributed to formation of the cell theory? Choose ALL that apply.

A. Robert Hooke observed cork cells under the microscope coining the term "cell."

B. Matthias Schleiden suggested that every structural part of a plant was made up of cells or the result of cells.
C. Theodor Schwann stated that along with plants, animals are composed of cells or the product of cells in their structures.
D. Leeuwenhoek observed motile organisms which included protozoans and other unicellular organisms, like bacteria, calling them “animalcules,” .
E. Spontaneous generation was a widely held belief that stated that some vital force contained in or given to organic matter can create living organisms from inanimate objects.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

hi! do you know the answer for this flvs question?

what do anaerobic organisms have in common with photosynthetic organisms?

they both appeared on earth at about the same time.

they both can only exist as single-celled organisms.

they both need an energy source in order to survive.

they both produce carbon dioxide as a waste product.

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