Question

1.Diagram hydrogen bond formation between adjacent water molecules. What leads to this ability to form hydrogen bonds between water molecules? Discuss at least four special properties of water due to its ability to form hydrogen bonds and give biological examples of each. Besides water, list two other kinds of substances that readily form hydrogen bonds in living systems.

2. Discuss four basic types of chemical bonds, and give one example of each type. Be sure to show how the bonds form and any properties/characteristics of the atoms helping to form those specific kinds of bonds. Also, relative to atomic structure, what makes it possible for two different atoms to bond, and what makes it impossible for two different atoms to bond?

3. Sketch and label all important structures (that we discussed) in a generalized plant cell and in a generalized animal cell. Be sure to include the function of each structure. Highlight the structure(s) only in plant cells and the structure(s) only in animal cells.

4. Discuss the endosymbiotic hypothesis and the invagination hypothesis with respect to eukaryotic cell development. What membrane-bound bodies is each responsible for forming? Regarding the endosymbiotic hypothesis, what is the evidence that supports this?

Answer 1

# Hydrogen bond formation between adjacent water molecules

Water is called a polar molecule because electrons are not shared equally between hydrogen and oxygen atoms. For this reason, the hydrogen becomes positively charged and water becomes negatively charged. The opposite charges of hydrogen and oxygen atoms help to create hydrogen bonds between water molecules.

# Ability to form hydrogen bonds between water molecules:

Hydrogen bonds are a special type of dipole. Dipole attraction between H and any other atom, it may be F, O, C and N but it is not a covalent bond.

A hydrogen bond is formed when the attraction between H bonded covalently with a high electronegative atom and with another electronegative atom.

Now in case of water, this Hydrogen bond occurs because:

H covalently bonded with electronegative atom O and form a weak bonding with another electronegative O atom of the neighbor water molecule.

In the water molecule due to Oxygen's high electronegative power it attracts electrons more than less electronegative H. As a result, O atom becomes positively charged partially and H atoms become negatively charged partially. So an O-H....O weak bond formed like the figure. The water molecule has a single pair of electrons on the highly electronegative O atom.

# 4 unique properties of water :

1. Adhesion: It is a special property of water. The bonding of water with other surfaces is known as adhesion.

Eg: the adhesive nature of water is helpful for blood circulation, or water transport system. The absorption of water by root is also a result of adhesion.

2. Surface tension: for surface tension tiny drop of water is form. It is a result of cohesion.

Eg: It helps water molecules to goes upward through the xylem.

3. Cohesion: the property of water attached together is known as cohesion.

Eg: the upward movement of water is caused by the cohesion nature of water.

4. Boiling point: water has a fixed boiling point that is 100° C which is relatively high than others. This is because of the hydrogen bonds. For the higher boiling point, water exists on earth as a liquid form that is needed for all living organisms.

Eg: the thermoregulation in the cell is maintained by water.

​​​​​​Two other kinds of substances that readily form hydrogen bonds in living systems are DNA and Antibodies.

DNA: Adenine, Guanine, Cytosine, Thymine are the 4 bases found in the structure of double-helix DNA. Adenine and Thymine (A-T), Guanine, and Cytosine (G-C) connect by a hydrogen bond. The double helix strand of DNA strands connected by the hydrogen bond between the complementary nucleotides.

Antibodies: Antibodies are made up of protein. The protein present in the living organism is in the folded structure. The folded three-dimensional structure of a protein is determined by a hydrogen bond.