1. IB BIOLOGY
Topics 3.1 & 3.2

2. C H O N
carbon hydrogen oxygen nitrogen
Organic molecules contain both carbon and hydrogen

3. Element Prokaryotes Plants Animals
Sulfur (S) Proteins Proteins proteins
Calcium (Ca) Flagella movement Forms cell plate Shells, bones and
during cytokinesis teeth
Phosphorus (P) Nucleic acids and Nucleic acids and ATP Nucleic acids and
ATP ATP
Iron (Fe) Cytochrome- used Cytochrome- used in Haemoglobin;
in respiration mitochondrial Cytochrome- used
respiration in mitochondrial
respiration
Sodium (Na) Main ion in cytoplasm Transmission of
nerve impulses

4.  Polar molecule (has + and – ends)
O is slightly –; H is slightly +
Oxygen attracts electrons more strongly

5.  Hydrogen bonding- + and – ends of
H2O attract each other (not a real bond, only
an attraction force)
 High specific heat- Polarity allows it to
dissolve other polar molecules like sugars
and amino acids, a ‘universal solvent’
 Causes cohesion

6.  Transparent: allows plants/algae to
survive under water, other organisms
to see in water.
 Ice floats, protecting the water
below from freezing, allowing
organisms to survive
 Cohesion allows for some organisms
to ‘walk’ on water

7.  Water has a high specific heat, heat of fusion /
heat of vaporization which allows it to store a lot of
heat.
Value to organisms:
 can absorb larger amounts of energy and still remain liquid. Ex:
large body of water have a constant temperature
 coolant effect = water absorbs large amounts of heat and cools the
body (sweat)

8.  water requires high input of water to break the H
bonds to go from liquid to gas (high specific heat)
 Evaporation off the surface of organism allows it to
lose heat.
 Value to organism:
 Desert plants increase transpiration when in danger of over-
heating
 Mammals sweat for thermo-regulation

9.  Good for allowing metabolic reactions
 Water is a good solvent due to polarity
 Liquid between the temperatures in most
regions of the Earth
 Value to organism:
 Watery habitat dissolves substances that can be
absorbed by organisms
 Watery cytoplasm dissolves substances
 Easy for metabolic reactions to take place between
dissolved substances.

10.  High specific heat
 Heat transport- blood can transfer heat from hot regions of
the body to cooler areas for thermoregulation.
 Water is dense
 Allows it to support large particles like blood cells, fat and
transport by flowing
 Polarity
 allows substances to be dissolved and therefore transported
to all parts of organism.
 Cohesion
 As water evaporates off of leaves, other water molecules are
pulled from below in the xylem of plants

11.  Most abundant
 Short term energy storage
 General molecular formula (CH2O)n
 Basic unit: monosaccharides (fructose, glucose, galactose)
 Two monosaccharides: disaccharides (maltose, lactose, sucrose)
 Anything larger than this: polysaccharides (starch, glycogen, cellulose)

12.  Glucose: one of main products of photosynthesis, starts cellular
respiration - cell uses it as a source of energy
 Galactose: sugar in milk
 Fructose: sugar found in honey, fruits, vegetables
 Ribose/Deoxyribose: RNA/DNA structure

13.  Sucrose — common table sugar
(glucose + fructose)
 Lactose — major sugar in milk
(glucose + galactose)
 Maltose — product of starch digestion
(glucose + glucose)

14.  Starches: plant storage (excess glucose)
 Glycogen: animals storage (excess
glucose).
-The liver and skeletal muscle are major
deposits of glycogen. Starch grains in potato cells
 Cellulose: plant structure (cell wall).
Probably the single most abundant organic
molecule in the biosphere. (fibers – paper,
cotton)
Cellulose fibers

15. Condensation: 2 molecules are joined together + 1 water molecule produced
Hydrolysis: water helps break molecule into smaller units (monomers)

16.  Glycerol + fatty acid chains
 Large number of C - H bonds = non-polar molecules.
 Insoluble in water
phospholipid
 Functions:
- Long term energy storage
- Thermal insulation (Arctic animals)
- Major component of the cell membrane
The fatty "tail" is non-polar (Hydrophobic)
The phosphate "head" is a polar (Hydrophilic)

17.  Saturated: full of hydrogens – solid
at room temperature
 Unsaturated: one or more double
bonds connecting carbons – liquid at
room temperature

18.  Cis – Trans
- Oil for frying causes some of the
cis bonds to convert to trans bonds.
Fatty acids with trans bonds are
carcinogenic.
 Cholesterol = fat-like substance;
 controls how fluid the cell membrane
will be
 necessary to produce vitamin D and
steroids (testosterone, estrogen,
progesterone, cortisone…)

19.  Animals use fats for
energy storage
 Fat stores lots of calories
in a small space - 9Kca/g -
against carbs (4Kcal/g)

20.  Made of amino acids
 Contain nitrogen
 Many functions:
- Structural (muscles, collagen, keratin)
- Enzymes (metabolism)
- Carriers (hemoglobin, albumin)
- Antibodies
- Hormones (ex. insulin)
- Membrane pumps (ATP pumps), receptors, neurotransmitters
- Movement (actin, myosin)

21.  peptide bond = joins two amino acids