Core Concepts (Biological Compounds) Flashcards
Name the four key inorganic ions
in living organisms
● Magnesium ions (Mg2+)
● Iron ions (Fe2+)
● Calcium ions (Ca2+)
● Phosphate ions (PO43-)
What is the role of Mg2+ in plants?
Mg2+ is used to produce chlorophyll.
What is the role of Fe2+ in animals?
Fe2+ is found in haemoglobin and is
involved in the transport of oxygen.
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What is the role of PO43- in living
organisms?
PO43- is used to produce ` ADP and ATP`.
What is the role of Ca2+ in living
organisms?
Ca2+ is used to strengthen tissues such
as bones and teeth in animals and cell walls in plants.
Why is water a polar molecule?
O is more electronegative than H. O attracts
the electron density in the covalent bond
more strongly, forming δ- O and δ+ H.
Describe hydrogen bonding between
water molecules
Weak intermolecular forces of attraction
form between a lone pair on a δ- O and a
δ+ H on an adjacent molecule.
What is a metabolite?
A molecule formed or used in metabolic
reactions.
Describe the role of water as a
metabolite.
Water is a reactant in photosynthesis
and hydrolysis reactions. Water is a
product in aerobic respiration and
condensation reactions.
Why is water’s high specific heat
capacity important for organisms?
Water acts as a temperature buffer, enabling
endotherms to resist fluctuations in core
temperature and to maintain optimum enzyme
activity.
Why is water’s high latent heat of
vaporisation important for organisms?
When water evaporates, it has a cooling effect.
This is important in homeostasis; organisms can
lose heat through sweating or panting.
Why is water an important solvent for
organisms?
Water is a polar universal solvent. It enables
chemical reactions to take place within cells,
the transport of materials in the plasma and
the removal of metabolic waste.
Why does water have a high surface
tension?
Due to the ordered arrangement and
cohesion of molecules at the surface of
water.
Why is the high surface tension of water
important for organisms?
● Enables the transport of water and nutrients
through plants stems and small blood
vessels in the body
● Allows small insects to ‘walk’ on water
What is a monosaccharide? (3)
● Simple sugar
● General formula (CH2O)n
● Soluble in water
Give some examples of
monosaccharides.
● Glyceraldehyde
● Ribose
● Deoxyribose
● α- and β- glucose
● Fructose
● Galactose
What is the name of the bond formed
when two monosaccharides react?
Glycosidic bond
What is a disaccharide? (3)
● Molecule formed by the condensation of two
monosaccharides, forming a glycosidic bond
● Formula C12H22O11
● Soluble in water
Give some examples of disaccharides and their
monosaccharide constituents.
● Sucrose (Glucose-Fructose)
● Maltose (α-Glucose-α-Glucose)
● Lactose (Glucose-Galactose)
What is a polysaccharide?
A polymer of monosaccharides, formed
by many condensation reactions.
Give some examples of polysaccharides.
● Starch
● Glycogen
● Cellulose
● Chitin
What is the function of starch?
Energy storage in plants
Describe the structure of starch.
● Polymer of α-glucose monomers
● Two forms: amylose and amylopectin
● Amylose: α-1,4-glycosidic bonds, unbranched
● Amylopectin: α-1,4- and α-1,6-glycosidic bonds,
branched
What is the function of glycogen?
Energy storage in animals.
How does the structure of glycogen
relate to its function?
It is highly branched enabling the rapid
hydrolysis of glucose molecules.
Describe the structure and function of
cellulose.
● Linear polysaccharide that is the main component of the cell wall
in plants
● Consists of many β-glucose molecules joined by β-1,4-glycosidic
bonds
● Alternate glucose molecules rotated 180° allowing hydrogen bonds
between parallel chains, forming myofibrils
Describe the structure and function of
chitin.
● Linear polysaccharide found in the exoskeletons of insects and
crustaceans as well as fungal cell walls
● Consists of many β-glucose molecules (with amino acid side chains)
joined by β-1,4-glycosidic bonds
● Alternate glucose molecules rotated 180° allowing hydrogen bonds
between parallel chains, forming myofibrils
Explain how a triglyceride is formed
One molecule of glycerol forms ester bonds
with three fatty acids via condensation
reactions.
Relate the structure of triglycerides to
their functions.
● High energy-to-mass ratio - energy storage, high calorific value
from oxidation
● Insoluble hydrocarbon chain - no effect on water potential of cells,
used for waterproofing
● Slow conductor of heat - thermal insulation, e.g. adipose tissue
● Less dense than water - buoyancy of aquatic animals
What is a phospholipid?
A type of lipid formed by the condensation of
one molecule of glycerol, two molecules of fatty
acid and a phosphate group.
Relate the structure of phospholipids to
their functions.
Glycerol backbone attached to two hydrophobic fatty acid
tails and one hydrophilic polar phosphate head:
● Forms phospholipid bilayer in water - component of cell
membranes
● Tails splay outwards - waterproofing, e.g. skin
What is the difference between saturated
and unsaturated fats?
● Saturated fats have no C=C bonds, and are solid at room
temperature due to strong intermolecular forces
● Unsaturated fats have one or more C=C bonds, and are liquid
at room temperature due to weak intermolecular forces
Differentiate between monounsaturated
and polyunsaturated fatty acids.
● Monounsaturated fatty acids contain one
C=C bond
● Polyunsaturated fatty acids contain more than
one C=C bond
What is meant by a low density
lipoprotein (LDL)?
● Combination of triglycerides from saturated fats
and protein
● Blocks receptor sites, reducing cholesterol
absorption
● Known as ‘bad’ lipoproteins
How do LDLs contribute to the risk of
cardiovascular disease?
The high blood cholesterol level caused
by LDLs leads to formation of
atherosclerosis plaques.
Describe the general structure of an
amino acid.
● Amine group (-NH2)
● Variable side chain (R)
● Carboxyl group (-COOH)
● H atom
How are polypeptides formed?
Many amino acid monomers join together
in condensation reactions, forming
peptide bonds (-CONH-).
What is the primary structure of a
protein?
The individual sequence of amino acids
in a protein.
Describe the secondary structure of a
protein.
The local interactions of the amino acids in
the polypeptide chain resulting in α-helixes or
β-pleated sheets. Hydrogen bonds hold the
arrangements in place.
Describe the tertiary structure of a
protein.
The folding of a protein to make a three-dimensional
structure. Held in place by various interactions and bonds:
● Disulfide bonds
● Ionic bonds
● Hydrogen bonds
● Hydrophobic interactions
Describe the quaternary structure of a
protein.
● Interactions of more than one polypeptide chain
● May involve addition of prosthetic groups, e.g.
metal ions or phosphate groups
Describe how the structure of fibrous
proteins relates to their function.
● Long polypeptide chains, folded in parallel
● Little tertiary/quaternary structure aside from cross-linkages for strength
● This makes them insoluble and good for structural roles
Describe how the structure of globular proteins relates to their function.
● Spherical, compact, highly folded with complex
tertiary/quaternary structures
● Hydrophilic R groups face outwards and hydrophobic
R groups face inwards therefore water-soluble
● Metabolic roles, e.g. enzymes
What is the difference between a
reducing and non-reducing sugar?
● A reducing sugar has a free aldehyde or ketone functional
group so can act as a reducing agent
● A non-reducing sugar does not have a free aldehyde or
ketone functional group so it cannot act as a reducing
agent
Describe the Benedict’s test for reducing
sugars.
- Add an equal volume of the sample being tested and
Benedict’s reagent - Heat the mixture in an electric water bath at 100°C for 5
minutes - Observe the colour of the precipitate formed
Describe the positive result for reducing
sugars.
Colour change from green to yellow to
orange to brown to a brick red depending
on the quantity of reducing sugar present.
Describe the Benedict’s test for
non-reducing sugars.
- Negative test for reducing sugar
- Hydrolyse non-reducing sugars with an equal volume of dilute HCl
- Heat in a boiling water bath for 5 minutes
- Add NaHCO3
to neutralise the acid - Re-test resulting solution with Benedict’s reagent
- Observe the colour of the precipitate formed
Describe the positive result for
non-reducing sugars.
Colour change from green to yellow to
orange to brown to brick red depending on
the quantity of non-reducing sugar present.
Name the food test used to identify
proteins.
Biuret test
Describe the biuret test.
- Add an equal volume of the sample to be tested
and NaOH - Add a few drops of dilute copper (II) sulfate solution
- Mix gently and record any observations
Describe the positive result of a
biuret test.
Colour change from pale blue to purple.
Describe the iodine-potassium iodide
test for starch.
● Add iodine-KI solution
● Colour change from orange to
blue-black in the presence of starch
Describe the emulsion test for fats
and oils.
● Add ethanol to the sample and shake
● Allow the mixture to settle
● Add an equal volume of water
● Record any observations
Describe the positive result of an
emulsion test.
White, cloudy emulsion forms.
Describe the emulsion test for fats
and oils.
● Add ethanol to the sample and shake
● Allow the mixture to settle
● Add an equal volume of water
● Record any observations
Describe the structure of centrioles.
● Cylindrical structure
● Organised into microtubules in a 9+0 pattern
● Found in pairs in centrosomes
Describe the structure of a chloroplast.
● Disk shaped surrounded by double membrane
● Thylakoids - flattened discs stacked to form grana
● Grana - contain photosystems with chlorophyll
● Intergranal lamellae - tubes attach thylakoids in adjacent
grana
● Stroma - fluid-filled matrix
What is the function of a chloroplast?
Site of photosynthesis
Describe the structure of the permanent
vacuole in plants
● Surrounded by a single membrane, tonoplast
● Contains cell sap (mineral ions, water,
enzymes, soluble pigments)
Describe the function of the permanent
vacuole in plants.
● Controls turgor pressure
● Water storage
● Isolates harmful waste products
● Maintains pH
Define plasmodesmata
Microscopic channels between plant cell
walls that facilitate communication and
symplastic transport.
Define prokaryotic cell
A type of cell that does not contain any
membrane-bound organelles or a true
nucleus.
Describe the structure and function of
the flagella in prokaryotic cells.
● Long, whip-like protrusion made of flagellin
● Rotates to propel the organism
● Sensory organ
Describe the structure and function of
the flagella in prokaryotic cells.
● Long, whip-like protrusion made of flagellin
● Rotates to propel the organism
● Sensory organ
How is genetic information stored in
prokaryotes?
Describe the positive result of an
emulsion test.
White, cloudy emulsion forms.
Micronutrients definition
Inorganic nutrients needed in minute (trace) amounts e.g. copper and zinc
Inorganic definition
Compounds that do not contain carbon bonded to hydrogen e.g. water, carbon dioxide, nitrogen gas
Macronutrients definition
Inorganic ions needed in small amounts e.g. magnesium, iron, phosphate and calcium
Organic definition
Compounds that are based on carbon and contain carbon bonded to hydrogen e.g. carbohydrates, proteins and lipids
