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Summary IB Biology HL Unit 2 Notes
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The notes hereby are created as a summary of IB Biology HL Unit 2. The information is mainly gathered from IB Books as well as supplementary materials.
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IB BIOLOGY UNIT 2: MOLECULAR BIOLOGYORGANIC COMPOUNDS
● An organic compound is one that contains carbon and is found in living things.
● Exceptions to organic compounds include carbonates such as CO32- and oxides of carbon such as
CO2.
● Carbon forms the basis of organic life due to its ability to form large and complex molecules via
covalent bonding. Carbon atoms can form four covalent bonds, with bonds between carbon atoms
being particularly stable. This property allows carbon to form a wide variety of organic compounds that
are chemically stable.
● There are four principle organic compound groups that contribute to a living organism: carbohydrates,
lipids, nucleic acids, and proteins. These four groups interact with each other in a wide variety of
ways in order to carry out the metabolic processes of each cell.
● Complex macromolecules may commonly be comprise of smaller, recurring subunits called
monomers, that come together to form the larger polymers.
FALSIFYING VITALISM
● Vitalism was the belief that living organisms and non-living things differed fundamentally because living
organisms contained a non-physical element. This led to the belief that organic compounds, which
were thought to be found only in living organisms, possessed a vital force lacking from inorganic
molecules.
● Vitalism has since been disproven with the discovery that organic molecules can be artificially
synthesized.
● In 1828, Frederick Woehler mixed two inorganic compounds — cyanic acid and ammonium — and
found that the crystalline substance produced was urea, an organic compound previously believed only
to be produced by the living organisms. This artificial synthesis of urea demonstrated that organic
molecules are not fundamentally different to inorganic molecules.
METABOLISM
● Metabolism describes the totality of chemical processes that occur within a living organism to
maintain life. It can, in other words, be defined as the web of all enzyme-catalyzed reactions that
occur within a living organism.
● Metabolic reactions serve two key functions:
● Providing a source of energy for cellular processes such as growth and reproduction;
● Enabling the synthesis and assimilation of new materials for use within the cell.
● Metabolism is the sum of Anabolism and Catabolism.
● Anabolic reactions describe the set of metabolic reactions that build up complex molecules from
simpler ones.
● The synthesis of organic molecules via anabalism typically occurs via condensation and reduction
reactions.
● Condensation reactions occur when monomers are covalently joined and water is produced as
a by-product.
,● Anabolic reactions use energy to construct new bonds and hence, are said to be endergonic /
endothermic.
● Examples of anabolic reactions are as follows:
● condensation of two monosaccharides into a disaccharide and water;
● condensation of glycerol and fatty acids into a triglyceride and water;
● condensation of many amino acids into a protein and water.
● Catabolic reactions describe the set of metabolic reactions that break complex molecules down into
simpler molecules.
● The breakdown of organic molecules via catabolism typically occurs via hydrolysis and oxidation
reactions.
● Hydrolysis reactions require the consumption of water to break the bonds within the polymers.
● Catabolic reactions release energy while breaking bonds and hence, are said to be exergonic /
exothermic.
● Examples of catabolic reactions are as follows:
● hydrolysis of a polysaccharide into many monosaccharides;
● hydrolysis of a triglyceride into glycerol and fatty acids;
● hydrolysis of a polypeptide into amino acids.
TRACE ELEMENTS
● The most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen,
phosphorus, and nitrogen.
● Trace elements, on the other hand, are chemical elements that are still required by living organisms,
but are not found as abundant as the above elements:
● Calcium which is involved in muscle contraction and synaptic transmission;
● Iron which is found in haemoglobin and needed for oxygen transport;
● Sodium which is involved in the generation of nerve impulses;
● Sulphur which is found in some amino acids, allowing disulfide bridges to form.
WATER STRUCTURE
● Water (H2O) is made up of two hydrogen atoms covalently bonded to an
oxygen atom.
● This covalent bonding, however, involves the unequal sharing of electrons
between the atoms as the oxygen, due to its higher electronegativity, attracts
the electrons more strongly than hydrogens. Since the electrons will be
closer to the oxygen atoms, there will be a slight charge difference
between the atoms making up the water molecule (oxygen will be slightly
negative, and hydrogens will be slightly positive), making the molecule
polar.
● Some of water's physical properties are as follows:
● It is nearly colorless, odorless, and tasteless.
● It has a boiling of 100℃ and a freezing point of 0℃.
HYDROGEN BONDING IN WATER
, ● The polar nature of the water molecules allows them to form weak
associations with other polar or ionic molecules as the slightly negative pole
on water will attract the slightly positive poles of other molecules, and vice
versa.
● When a hydrogen atom with a slightly positive charge as a result of its bond
with either one of fluorine, oxygen, or nitrogen attracts another molecule, it
forms a hydrogen bond.
● Hydrogen bonds are relatively stronger than other short-lived polar
associations due to the high electronegativity of F, O and N.
● Water can form hydrogen bonds with other water molecules between the hydrogen and oxygen
atoms of two different water molecules.
● This intermolecular bonding between water molecules gives water its distinct thermal, adhesive,
cohesive, and solvent properties.
THERMAL PROPERTIES OF WATER
● Water has the capacity to absorb significant amounts of heat before changing temperature (high
specific heat capacity). This is due to the high energy needed to break the hydrogen bonds before a
change in state can occur.
● Consequently, water is an excellent medium for living organisms as it is relatively slow to change its
temperature and thus, supports the maintenance of constant internal and external temperature
conditions. This way, water acts as a temperature stabilizer, absorbing as much heat as possible
without changing its temperature.
● The evaporation of water as sweat is a fundamental mechanism employed by humans as a means of
cooling down.
● The change of water from liquid to vapour requires a high input of energy due to the high heat of
vaporization of water. This energy is provided by the body from the surface of the skin when it is hot,
and therefore, when sweat evaporates, the skin is cools down.
● Because water has a high specific heat capacity, it absorbs a lot of thermal energy before it
evaporates. Thus, water functions as a highly effective coolant, making it the principal component of
sweat.
● Water is a good medium for metabolic reactions as it has the capacity to absorb the heat released
as a by-product of exothermic reactions.
● Stroma where light-independent reactions take place, matrix of the mitochondria with the Krebs cycle
and the ETC, as well as the cytoplasm and nucleoplasm where reactions such as transcription and
translation take place are important aqueous mediums for metabolic reactions.
COHESIVE & ADHESIVE PROPERTIES OF WATER
● Cohesion is the ability of "like" molecules to stick together.
● Water is strongly cohesive as it can form hydrogen bonds with other water molecules due to the
attraction between the oppositely charged poles of each water molecule.
● This strong cohesiveness formed as a result of the hydrogen bonding between water molecules allow
the liquid to resists resistable levels of external force, explaining its high surface tension. This even
makes water sufficiently dense for certain small organisms to move along its surface.
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