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Biology Core Concepts
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1
Question
Why is water (\$H_2O\$) essential for life at the cellular level?
Page 23
Answer
Because it is the medium in which chemicals dissolve and chemical reactions occur inside cells and body fluids, enabling metabolic processes.
2
Question
What is one leading hypothesis for the origin of Earth's water?
Page 23
Answer
Extraterrestrial delivery: water was brought to Earth by colliding asteroids after the planet cooled.
3
Question
What is the Goldilocks zone and why is it important for liquid water?
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Answer
The Goldilocks zone is the habitable zone around a star where temperatures allow liquid water to exist — not too hot and not too cold — making it important for life as we know it.
4
Question
What makes the water molecule polar?
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Answer
Unequal sharing of electrons in the covalent O–H bonds causes the oxygen to carry a partial negative charge and the hydrogens partial positive charges, creating a polar molecule.
5
Question
Define a covalent bond in the context of water.
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Answer
A covalent bond is when two atoms share electrons; in water this is the sharing of electrons between oxygen and hydrogen atoms.
6
Question
What is a hydrogen bond and how does it form between water molecules?
Page 23
Answer
A hydrogen bond is a relatively weak intermolecular attraction where the slightly positive hydrogen of one water molecule is attracted to the slightly negative oxygen of another water molecule.
7
Question
Why are hydrogen bonds important in biological molecules?
Page 23
Answer
They mediate intermolecular attractions that stabilize structures and processes such as water uptake in plants, DNA double helix formation, and protein folding.
8
Question
What is cohesion with respect to water, and why does it matter?
Page 23
Answer
Cohesion is the attraction between water molecules via hydrogen bonds; it allows formation of continuous water columns (e.g., xylem in plants) and contributes to properties like surface tension.
9
Question
What is surface tension and what molecular property of water causes it?
Page 23
Answer
Surface tension is the tendency of a liquid surface to resist external force and behave like an elastic membrane; it is caused by cohesive hydrogen bonding between surface water molecules.
10
Question
What is adhesion in the context of water and capillary action?
Page 23
Answer
Adhesion is the attraction between water molecules and charged or polar surfaces; when combined with cohesion it enables capillary action, allowing water to climb narrow spaces like plant walls.
11
Question
How does water act as a solvent for ionic compounds like salt?
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Answer
Polar water molecules surround and stabilize individual ions (e.g., chloride and sodium) through electrostatic attractions and hydrogen bonding, causing the ionic lattice to dissociate and dissolve.
12
Question
List common types of solutes in biological fluids mentioned in the notes.
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Answer
Sugars (e.g., glucose, sucrose), salts, amino acids, and urea.
13
Question
Why is water described as an 'excellent solvent' for polar and charged particles?
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Answer
Because its polar nature allows water molecules to form hydrogen bonds and electrostatic interactions with charged or polar solutes, stabilizing them in solution.
14
Question
Define buoyancy and state the condition for an object to float in water.
Page 25
Answer
Buoyancy is the upward force a fluid exerts on an object; an object floats if its density is less than the density of water and sinks if its density is greater.
15
Question
What is viscosity and what does higher viscosity imply about a fluid's flow?
Page 25
Answer
Viscosity measures a fluid's resistance to flow; higher viscosity means the fluid flows more slowly (e.g., honey vs water).
16
Question
Why does water have a higher viscosity than air?
Page 25
Answer
Because hydrogen bonds between water molecules increase friction among molecules, slowing flow compared to non-bonded gas molecules in air.
17
Question
What does thermal conductivity measure?
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Answer
Thermal conductivity measures the rate at which heat passes through a material.
18
Question
Why is fat a good thermal insulator in living bodies?
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Answer
Because fat has low thermal conductivity, so it slows heat transfer and helps retain body heat.
19
Question
What is specific heat capacity and why is water's high value biologically important?
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Answer
Specific heat capacity is the energy required to raise a material's temperature by 1 °C; water's high value means it can absorb/release large amounts of heat with little temperature change, stabilizing environments and aiding cooling (e.g., sweating).
20
Question
How do hydrogen bonds influence water's specific heat capacity?
Page 25
Answer
Hydrogen bonds require energy to break; because many bonds must be broken to raise water temperature, a lot of energy is absorbed, giving water a high specific heat capacity.
21
Question
Give an example of water acting as a stable habitat compared to terrestrial environments.
Page 25
Answer
Aquatic animals experience more stable temperature conditions because water absorbs/releases heat with little temperature change due to its high specific heat capacity.
22
Question
What are the three parts of a nucleotide?
Page 26
Answer
A phosphate group, a five-carbon sugar (deoxyribose in DNA), and a nitrogenous base.
23
Question
Which sugar is present in DNA nucleotides and how many carbons does it have?
Page 26
Answer
Deoxyribose is present in DNA nucleotides and it has five carbons (a pentose).
24
Question
Where is the genetic information located in a nucleotide?
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Answer
In the nitrogenous base; sequences of bases encode genetic information.
25
Question
What bases comprise DNA and what single-letter codes represent them?
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Answer
Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
26
Question
How are nucleotides joined to form the backbone of DNA and RNA?
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Answer
Nucleotides are joined via covalent phosphodiester bonds between the sugar of one nucleotide and the phosphate of the next, forming a sugar-phosphate backbone.
27
Question
To which end (3' or 5') are new nucleotides added during nucleic acid synthesis?
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Answer
New nucleotides are always added to the 3' end of a growing nucleotide chain.
28
Question
What is a codon?
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Answer
A codon is a triplet of nucleotide bases that specifies one amino acid in the genetic code.
29
Question
How many bases form the smallest unit that encodes a single amino acid?
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Answer
Three bases (one codon) encode a single amino acid.
30
Question
What defines complementary base pairing in DNA?
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Answer
Adenine pairs with Thymine via two hydrogen bonds, and Guanine pairs with Cytosine via three hydrogen bonds.