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is held together by Hydrogen bonds

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Because it is a liquid at room
temperature, water can-

Provide habitats for living things in
river lakes and seas

Form a major component of the tissues
in living organisms

Provide a reaction medium for chemical

Provide an effective transport medium
e.g in blood and vascular tissue


density of water provides an ideal habitat for living things especially during
the winter where due to its anomalous expansion, ice floats thus insulating the
water body from the extreme conditions and protecting aquatic life.


is a good solvent for many biological substances in living things even ionic
solutes such as sodium chloride and covalent solutes such as glucose.

Molecules and ions can move around and
react together in water

Molecules and ions can be transported
around living things



plays an important part in reactions such as photosynthesis and hydrolysis
reactions such as digestion of starch, proteins and lipids.






Cells host a huge range of chemical reactions. Enzymes
catalyse many of these. Enzyme activity is sensitive to temperature and
reactions only occur in a narrow range of temperatures. Water helps to buffer
temperature changes because of its relatively high specific heat
capacity (the heat required to raise 1 kg of water by 1 oC).
It also has relatively large enthalpy of vaporisation (heat
energy required to convert a liquid to a gas) and enthalpy of fusion (heat
energy required to convert a solid to a liquid). This is reflected in the
unusually high boiling and melting points of water:




A group of
molecules containing C, H, and O

contain carbon hydrogen and Oxygen. Carbohydrates are hydrated carbon, which
means that for every carbon there are two hydrogen atoms and one oxygen atom.


a)      Act as a source of
energy (this is because carbohydrates are purely sugars e.g. Glucose)

b)      Act as a store of
Energy (these storage forms are efficient because they are hydrophobic and thus will not affect the water potential of the
cells e.g. Starch and Glycogen)

c)      Also act as
structural units (e.g. cellulose in plants and chitin in insects)

d)      Some carbohydrates
are also part of other molecules such as nucleic acids and glycolipids

e)      Heparin is a
polysaccharide (carbohydrate) which acts as anticoagulant and prevents
intravascular clotting.

f)       Many antigens are
glycoprotein (which contains oligosaccharide) in nature and give immunological
properties to the blood.

g)      Many Hormones like
FSH (Follicular Stimulating Hormone that takes part in ovulation in females)
and LH (Leutinizing Hormone) are glycoprotein and help in reproductive

h)      Hyaluronic acid found in
between joints acts as synovial fluid and provides frictionless movement.



There are three
types of Carbohydrates:-

Monosaccharaides- These are the simplest carbohydrates most suited to be a source energy
sugars) in living things, this is because of the large number of carbon
–hydrogen bonds. They are sweet sugars that are soluble in water and insoluble
in non-polar solvents. Monosaccharides have
a sweet taste. Examples of monosaccharides include
glucose (dextrose), fructose (laevulose) and galactose. They exist in straight
chains or in a rings or cyclic forms.

Disaccharides- any of a group of sugars
with a common formula, C12H22O11, as sucrose, maltose,
and lactose, which on hydrolysis yield two monosaccharides. Sweet and soluble sugars
most commonly maltose, sucrose sand lactose. They are formed by joining two
monosaccrides. When they join a through a condensation reaction, (A condensation reaction is an organic reaction in which two
smaller molecules combine to form a larger molecule and a much simpler
molecule. The simpler molecule produced is often water, which is why the phrase
“condensation reaction” is used, while sometimes being referred to as
a dehydration. Condensation reactions are important for the creation of many
important biological molecules, such as carbohydrates and proteins) ,a glycosidic
bond is formed.



Polysaccharides- Polymers of monosaccharide Made of hundreds or thousands of
monosaccharide monomers bonded together. Polysaccharides are long chains of monosaccharides linked by
glycosidic bonds.



Proteins are made
up of amino acids that contain elements like carbon, hydrogen, oxygen and

Amino acids are
linked together by peptide bonds, when linked by such bonds, they are referred
to residues.

Primary Structure

This is the
sequence of amino acids joined by a peptide bond until a Polypeptide chain is
formed. Number and order of the amino acids in the chain is very important
because one change in the sequence and the function of the protein is altered.
This order also determines the shape of the secondary, tertiary and quaternary

Secondary Structure

This is
three-dimensional form of the Protein. One-way the polypeptide chain fold is an
Alpha helix structure with 36 amino acids per 10 turns of the helix. The Helix
is held together by hydrogen bonds between the –NH group of one amino acid and
the –co group of another four parts of it in the chain. Another way the chains
can fold is in a Zigzag structure such that as the chain folds over itself to
produce ?-pleated sheet. Hydrogen bonds between the -NH group and the –CO group
of another down the strand hold the sheet together.

Tertiary Structure

When these Pleats
and coils fold themselves along the areas of straight chains of amino acids
this forms the tertiary structure. it held together by hydrogen , ionic,
hydrophobic/hydrophilic. It can also fold into fibrous or globular Proteins.

Quaternary Structure

Refers to the
Number and arrangement of multiple folded Protein Subunits in a Multi-subunit
complex. It include organizations from simple dimes to large homologies and
complexes with defines or variable numbers of Subunits.





acid is found in the nuclei of all eukaryotic cells within the cytoplasm of
prokaryotic cells and some viruses


a)      DNA is a polymer as
it is made up of many repeating monomer units called nucleotides.

b)      The molecule of DNA
consists of two polynucleotide strands running in opposite directions, so they
are described as anti-parallel.

c)      Each nucleotide
consists of a phosphate group, a five-carbon sugar called deoxyribose and one
of four nitrogenous bases. Adenine, Guanine, Thymine or Cytosine.

d)      Covalent bond
between the sugar residue and the phosphate group in a nucleotide is also
called a phosphodiester bond.

e)      DNA molecules are
long which allow them to carry out their function of carrying encoded genetic


DNA polymers direct the production of other polymers
called proteins

protein is one or more polymers of monomers called amino acids. Proteins are
the workhorse molecules in your cells. They act as enzymes, structural support,
hormones, and a whole host of other functional molecules. All traits derive
from the interactions of proteins with each other and the surrounding



RNA is structurally
different from DNA in a number of ways;-

a)      The sugar molecule
in each nucleotide in ribose.

b)      The nitrogenous bas
Uracil which is a pyrimidine replaces the pyrimidine base Thymine.

c)      The polynucleotide
chain is usually single stranded.

d)      There are three
forms of RNA- mRNA, tRNA and ribose RNA


These are a group
of substances that are soluble in alcohol rather than water. They include
triglyceride phospholipids, glycolipids and cholesterol






Triglycerides are
made up of glycerol and fatty acids






Glycerol has three
carbon atoms. It is an alcohol, which means it has free –OH groups









Fatty acids

Fatty acids have a
carboxyl group (-COOH) on one end, attached to a hydrocarbon tail made of only
carbon and hydrogen atoms.

IF a fatty acid is
saturated it means there are no C=C bonds in a molecule. If a Fatty acid is
Unsaturated, there is a double bond between two of the carbons atoms instead
which means that fewer hydrogen atoms can be bonded to the molecule


Saturated fat

A saturated fat is a type
of fat in which the fatty acid chains have all or
predominantly single bonds. A fat is made of two kinds of smaller
molecules: glycerol and fatty acids. Fats are made of long
chains of carbon (C) atoms. Some carbon atoms are linked by single bonds
(-C-C-) and others are linked by double bonds (-C=C-). Double
bonds can react with hydrogen to form single bonds. They are
called saturated, because the second bond is broken up and each half of
the bond is attached to (saturated with) a hydrogen atom.





Unsaturated fat

An unsaturated fat is
a fat or fatty acid in which there is at least
one double bond within the fatty acid chain. A fatty acid chain
is monounsaturated if it contains one double bond
and polyunsaturated if it contains more than one double bond.

Where double bonds are
formed, hydrogen atoms are subtracted from the carbon chain.
Thus, a saturated fat has no double bonds, has the maximum number of
hydrogens bonded to the carbons, and therefore is “saturated” with
hydrogen atoms



Functions of Triglycerides

Triglycerides can be broken down in
respiration and thus act as energy source.

Because triglycerides are insoluble in
water they can be stored without affecting the water potential, they are used
as energy stores.

Adipose tissue is a storage location
for lipids in whales acing as a heat insulator from the cold-water

Because aft is less dense than water it
is used by aquatic animals to help them stay afloat.

They also form a significant part of
the phospholipid bilayer of animal cells.



carcinogen is any substance that promotes carcinogenesis or the formation of
cancer. Most of these substances have the ability to disrupt the cell division
process or damage the genome responsible for cell division. Some of these
substances emit gamma rays or Alpha particles that can cause cancer an example
is radionuclides. Other substances that do not emit radiation but cause cancer
like Cigarettes contain chemical compounds like polycyclic aromatic
hydrocarbons (PAH, such as benzoapyrene), Benzene, and Nitrosamine.

into carcinogens causing mutations in the DNA of living organisms’ shows that
any substances with the ability interrupt the cell cycle of an organism by
changing the DNA sequence of said organism is technically a carcinogen. For
example a free radical, that is, a molecule that has either one too many
electrons or not enough and will actively react to become stable, If it was to
come into contact with DNA it will Either add an e- or take one away, this
would force the Dna molecule to change its order and actively disrupt processes
like the cell cycle either leading to complete shutdown of the process or

the correct order of DNA is the pillar that metabolic processes like the cell
cycle leading to cell division , any and all changes to the order of the
molecule i.e. mutation that may lead to the cell signals that stop or limit
cell division to become inactive . Thus, incontrollable division will start


tars and coke oven emissions
sawdust (certain species)
products (progesterone, safrole)


On the
other hand, Scientists can disrupt the cycle for continuous cell division for
purposes lie a skin transplant, research into stem cells or the growth of full




growth regulators are signal molecules produced within the plant at extremely
low concentrations. Hormones regulate cellular processes in targeted cells
locally and, moved to other locations, in other functional parts of the plant.
Hormones also determine the formation of flowers, stems, leaves, the shedding
of leaves, and the development and ripening of fruit.

of plant regulators are, Ethane, gibberellins and auxin.

Ethane-This plant hormone is synthesized in
the plant for stages like germination, ripening of fruits, abscission of
leaves, and senescence of flowers. Synthesis of Ethane is through the Yang

of Ethane as a plant growth hormone

Causes leaf and flower senescence

Causes senescence of mature xylem cells
in preparation for plant use

Induces leaf abscission

Induces seed germination

Induces root hair growth — increasing
the efficiency of water and mineral absorption

Induces the growth of adventitious
roots during flooding

Causes fruit ripening

Induces a climacteric rise in
respiration in some fruit, which causes a release of additional ethylene.

Affects gravitropism

Inhibits stem growth and Causes stem
and cell broadening and lateral branch growth outside of seedling stage

Inhibits shoot growth and stomatal
closing except in some water plants or habitually flooded ones such as some
rice varieties, where the opposite occurs

Induces flowering in pineapples


Gibberellins-These plant hormones regulate growth and developmental Processes
like stem elongation, germination, dormancy, flowering, enzyme induction, and
leaf and fruit senescence.


are plant regulators with morphological characteristics i.e. Characteristics
like shape of height of a structure. Auxins are cardinal to plant body

participates in phototropism (growth in response to the direction of light), geotropism (growth in response
to the direction of gravity), hydrotropism (Growth or movement response
of a cell or organism water) and other developmental changes. The uneven
distribution of auxin such as unidirectional light or gravity force, results in
uneven plant tissue growth. Generally, auxin governs the form and shape of
plant body, direction and strength of growth of all organs, and their mutual




Synthetic auxins-These
are auxins that have been artificially made to control the growth of plants for
economic profit. Some auxins are also used as herbicides.


4-Dichlorophenoxyacetic acid (2, 4-D)
acetic acid (?-NAA)
6-dichlorobenzoic acid
5, 6-trichloropicolinic acid (tordon or picloram)
acid (2,4,5-T)


since Synthetic Auxins have been used for herbicides many types of weeds have
developed a resistance to the product not to mention that the auxin is harmful
to some greenhouse plants.

auxins do not have any method of deciding what plant response to give to what
plant thus if an auxin to increase plant growth is applied to the weed ,
it  will have the effect of increase
growth which would increase competition for nutrients with other desired  plants being grown significantly.

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