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Biology - Unit 9 Revision Guide

Terms in this set (28)

- A covalent bond holds together two atoms that share one or more pairs of electrons
- Electrons in a covalent bond may be equally or unequally shared between the atoms
Outline Covalent bond
- An atom gives up 1 or more of its electrons to another atom.
- The resulting oppositely charged ions attract one another, forming an ionic bond
Outline Ionic bond
- Hydrogen bonds form when partial opposite charges in different polar molecules attract each other
- Individual hydrogen bonds are rather weak, but collectively they are quite strong
Outline Hydrogen bond
Nonpolar covalent bonds are a type of chemical bond
Nonpolar-->where two atoms share a pair of electrons with each other.
Polar covalent bonding is a type of chemical bond
Polar --> where a pair of electrons is unequally shared between two atoms.
Compare and contrast polar and nonpolar covalent bonds
H2O
Write the molecular formula for water
Water is described as being polar because it has a slight charge difference across the different poles of the molecule
- The oxygen atom is slightly negative (δ-) while the hydrogen atoms are slightly positive (δ+)
Describe the cause and effect of the polar nature of water
The charge difference across the molecule (dipole) allows water to form weak associations with other polar molecules
- The slightly negative poles (δ-) will attract the slightly positive poles (δ+) of other molecules, and vice versa
Describe how water is able to form hydrogen bonds
Partially positive hydrogen atoms of one water molecule are attracted to the partially negative oxygen atom of another water molecule
Outline the bonding that occurs within and between water molecules
- Thermal properties - Water can absorb much heat before changing state (requires breaking of hydrogen bonds)
- Cohesive / Adhesive properties - Water will 'stick' to other water molecules (cohesion) and charged substances (adhesion)
- Solvent properties - Water dissolves polar and ionic substances (forms competing polar associations to draw materials apart)
Outline the properties of water (cohesive, adhesive, thermal and solvent)
Description:
- It takes a large amount of energy to raise the temperature of water by 1 degree
- Due to the high amount of hydrogen bonds between the water molecules
Benefit:
- This is a benefit because the temperature of large bodies of water remains relatively constant, protecting life from possibly lethal temperature fluctuations
- At the cellular level water absorbs the heat produced by cell processes, regulating the temperature of cell
- This is also how our body temperature is kept relatively constant
Explain why the thermal properties of water are useful to living organisms - High Specific Heat ('heat capacity')
Description:
- Measure of how much energy is needed to be added to vaporize water
- High amount of energy needed because hydrogen bonds need to be broken in order for water molecules to fly off as gas.
Benefit:
- As water evaporates, the surface left behind becomes cooler (=Evaporative cooling)
- It allows organisms to cool with sweating so a consistent body temperature is maintained.
Explain why the thermal properties of water are useful to living organisms - High Heat of Vaporization
Cohesion is the property of like molecules (of the same substance) to stick to each other due to mutual attraction. Adhesion is the property of different molecules or surfaces to cling to each other.
Contrast adhesion with cohesion
The high surface tension of water makes it sufficiently dense for certain smaller organisms.
Outline an example of the cohesive property of water being of benefit to life
The capillary action is necessary to allow water to be transported up plant stems via transpiration stream.
Outline an example of the adhesive property of water being of benefit to life
It is such a good solvent because its polarity allows it to dissolve both ionic bonds and other polar molecules by bonding with other substances and dissolving the bonds in the solute.
Explain why water is such a good solvent
Polar solutes such as ionic compounds and polar molecular compounds.
List the types of molecules that water will dissolve
It is capable of dissolving substances and enabling key chemical reactions in the animal, plant, and microbial cells.
Explain why solvency is important to life
Water and methane are relatively similar in size and have comparable valence structures (both have tetrahedral orbital formations).
- Water absorbs more heat before changing state
- Water has significantly higher melting and boiling point
- Water has a higher specific heat capacity
- Water has a higher heat of vaporization
- Water as a higher heat of fusion
Compare and contrast that chemical and physical properties of methane and water.
Water and methane have different thermal properties because water is polar and can form intermolecular hydrogen bonds while methane is non-polar and can only form weak dispersion forces between its molecules.
Explain why water and methane have different thermal properties based on their molecular structures.
Evaporation of water as sweat is a mechanism employed by humans to cold down. The change from water to vapor requires energy input which comes from the surface of the skin when it is hot. As a result, when the swear evaporates the skin is cooled because water has s high heat capacity, it absorbs the thermal energy from the surface of the skin before it evaporates. Thus, water functions as a highly effective coolant, making it the principal component of sweat.
Explain sweating as a mechanism to cool the body.
Hydrophilic → Polar and ionic molecules
Hydrophobic → Non-polar and non-ionic molecules
State which types of molecules are hydrophilic and hydrophobic
Hydrophilic → dissolve in water
Hydrophobic → do not dissolve in water
Outline how to identify molecules as hydrophilic or hydrophobic
Glucose (hydrophilic) → Glucose dissolves into blood plasma (which is mostly water) and can be transported in the plasma to the cells of the body.
Outline how glucose is transported in the blood
Sodium (hydrophilic) → The ions will be able to fully soluble in water and travel in the blood plasma through the body.
Outline how sodium is transported in the blood
Amino acids (variable) → Amino acids dissolve and are able to be transported in the blood plasma. However, in proteins, amino acids with hydrophobic R groups will clump together in the middle of the protein, away from water.
Outline how are amino acids transported in the blood
Cholesterol (hydrophobic) → To travel through the blood, cholesterol is transported inside little molecular "sacs" made of amphipathic molecules.
Outline how cholesterol is transported in the blood
Fats (hydrophobic) → To travel through the blood, fats and oils are transported inside little molecular "sacs" made of amphipathic molecules.
Outline how fats are transported in the blood
Oxygen (hydrophobic) → Since oxygen doesn't easily dissolve in blood plasma, it must be transported to the cells of the body through the blood by a transport protein (hemoglobin).
Outline how oxygen is transported in the blood
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