At the beginning of the 19th century, it was thought that the substances that made up living things were special and could not be synthesized by ordinary chemical methods. However we now know that molecules found in living things are built on a skeleton of this element O nitrogen. O sulfur. O oxygen. O carbon. O phosphate.
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Living cells are composed primarily of 4 atoms. All molecular structures are systematically built from these elements, although there are many others that participate in the function of these structures. They are: nitrogen, carbon, oxygen, and phosphorus. oxygen, carbon, phosphorus, and hydrogen. hydrogen, carbon, nitrogen, and oxygen. carbon, nitrogen, hydrogen, and water. water, carbon, nitrogen, and phosphorus.
Marlyn J.
About 25 of the 92 natural elements are known to be essential to life. Which four of these 25 elements make up approximately 96% of living matter? a. carbon, sodium, hydrogen, nitrogen b. carbon, oxygen, phosphorus, hydrogen c. oxygen, hydrogen, calcium, nitrogen d. carbon, hydrogen, nitrogen, oxygen e. carbon, oxygen, nitrogen, calcium 2. In what way are elements in the same column of the periodic table the same? a. They have the same number of protons. b. They have the same number of neutrons. c. They have the same number of electrons. d. They have the same number of electrons in their valence shell. e. They have the same number of electron shells. 3. Nitrogen (N) is much more electronegative than hydrogen (H). Which of the following statements is correct about the atoms in ammonia (NH3)? a. Each hydrogen atom has a partial positive charge; the nitrogen atoms has a partial negative charge b. The nitrogen atom has a strong positive charge; each hydrogen atom has a strong positive charge. c. Each hydrogen atom has a slight negative charge; each nitrogen atom has a strong positive charge. d. The nitrogen atom has a slight positive charge; each hydrogen atom has a slight negative charge. e. There are covalent bonds between hydrogen atoms and polar bonds between each hydrogen and nitrogen atom. 4. What is the maximum number of hydrogen atoms that can be covalently bonded in a molecule containing two carbon atoms (carbon has 4 valence electrons)? a. 2 b. 3 c. 4 d. 6 e. 8 5. Refer to the first three rows of the periodic table. If life arose on a planet where carbon is absent, which element might fill the role of carbon? a. Boron b. Silicon c. Nitrogen d. Aluminum e. Phosphorus
Sri K.
A short primer on bonding... Most living things are mainly composed of different combinations of the same five elements. These elements are carbon, oxygen, hydrogen, nitrogen and phosphorus (mainly found in nucleic acids – which was not a focus for this test). Carbohydrates and fats are comprised of carbon, hydrogen and oxygen. Proteins are composed of a chain of amino acids. Amino acids are made of a central carbon bonded to 4 different groups: a carboxyl group (–COOH), an amine group (–NH2), a hydrogen atom (–H), and a side group that varies depending on the type of amino acid. Twenty common amino acids can combine in various ways to make different protein molecules. The sequence of amino acids in each protein is unique to that protein, so each protein has its own unique 3-D shape. A. Why do these particular elements bond together to form organic molecules? B. What is unique to carbon that makes it the most important element in organic molecules? C. As you have learned, it is the number of valence electrons that allow certain elements to bond with one another. What is the significance of the valence electrons to an element? D. If carbon has 4 valence electrons, then it can form 4 bond(s). E. If hydrogen has 1 valence electrons, then it can form 1 bond(s). F. If oxygen has 6 valence electrons, then it can form 2 bond(s). G. If nitrogen has 5 valence electrons, then it can form 3 bond(s).
Dominador T.
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