Year 12 Biology Revision- STANDARD ANSWERS
Extra info or key points for extra marks
Biological Molecules
What are the four classes of biological molecules?
• Carbohydrates
• Lipids
• Proteins
• Nucleic acid
What does nucleic acid do?
• Carries the genetic code for the production of proteins
What are monomers?
• The smaller units from which larger molecules are made
What are examples of monomers?
• Glucose, fructose, galactose, amino acids, nucleotides
What are polymers?
• Molecules made from a large number of monomers joined together
What are examples of polymers?
• Starch, cellulose, glycogen
Why aren't lipids polymers?
• They are formed from different molecules; glycerol and fatty acids
What are all living things made up of?
• Nitrogen, oxygen, carbon, hydrogen
Monomer Polymer
Carbohydrates Monosaccharides Polysaccharides
Proteins Amino acid polypeptide
Nucleic acid nucleotides DNA/ RNA
What is metabolism?
• All the chemical reactions that take place in the body summed up
What is a condensation reaction?
• The joining of two molecules together with the formation of a chemical bond and
releases a small molecule (water)
• Key points: release water, a new molecule is made, the larger molecule is made from
the smaller molecules bonding together
What is a hydrolysis reaction?
• The breaking of a chemical bond between two molecules using water.
• Key points: Requires water, breaks down covalent bonds called glycosidic bonds, two
smaller molecules are formed by splitting a larger molecule
Carbohydrates
What are carbohydrates?
• Sugars, starches and fibres that take up 10% of living cells and contain carbon,
oxygen and hydrogen mostly in the formation of Cn(H2O)n where n can be 3-7
What are monosaccharides?
• Simple sugars and monomers from which larger carbohydrates are made
What are the properties of monosaccharides?
• Sweet
• Very soluble in water
What are the different types of simple sugars?
• Glyceraldehyde- C3H6O3 (called a TRIOSE because it has 3 carbon)
, • Ribose- C5H10O5, deoxyribose- C5H10O4 (called PENTOSES because they have 5
carbons)
• Glucose- C6H12O6, fructose- C6H12O6, galactose- C6H12O6 (called HEXOSES
because they have six carbons)
What does glucose look like in terms of its structure?
• Straight chain structure of a ring form
• Ring contains 5 carbons, known as a pyranose ring
What is an isomer?
• Each of two or more compounds with the same formula but a different arrangement
of atoms in the molecule and different properties.
What are the isomers of glucose and what are the differences?
• Alpha and beta glucose
• Alpha glucose has the –OH on the lower side and –H on the upper side on the first
carbon whereas Beta glucose has the –H on the lower side and the –OH on the upper
side on the first carbon.
• Way to remember: Beta spells OHH (OH first and H second). Also, Alpha –OH on
carbon 1 lines up with the –OH on carbon 4
What does fructose look like (MEMORISE)
• A structural isomer to glucose
• A furanose ring as it only has four carbons in its ring and one oxygen
What are disaccharides?
• The condensation of two monosaccharides, forming glycosidic bonds and releasing
water
What are polysaccharides?
• The condensation of many glucose units, forming glycosidic bonds and releasing
water
• Polymers
Example Type of carbohydrate Function/ Uses
Glucose Monosaccharide • Energy source in
animals
• Used to make ATP
Fructose Monosaccharide • Component of flower
nectar
• Fruits and honey
, Galactose Monosaccharide • Milk/ Breast milk
Lactose (glucose + Disaccharide • Sugar found in milk
galactose)
Sucrose (glucose + Disaccharide • Transport form of
fructose) carbohydrate in
phloem
Maltose (glucose + Disaccharide • Hard candies
glucose) • Sweetener
Cellulose (β glucose Polysaccharide • Component of plant
condensed) cell walls
• Structural support
Glycogen (α glucose Polysaccharide • Energy source in
condensed) animals
• Used to make ATP
What does sucrose look like (MEMORISE)
• 1-5 α glycosidic bond
What are reducing sugars?
• Sugars that when reacting with other molecules, give out electrons known as
reduction
• All monosaccharides (glucose, fructose and galactose) and some disaccharides do this
What does maltose (disaccharide) look like?
• 2 α glucose molecules joined together in a condensation reaction and releasing 1
water
• 1,4 α glycosidic bond
What does lactose (disaccharide) look like?
• An β glucose and galactose molecule joined together in a condensation reaction and
releasing 1 water
• 1, 4 β glycosidic bond
, What are the principal polysaccharides for storage?
• Glycogen and starch
Why are polysaccharides suitable for storage?
• They are large, insoluble molecules.
• They are not sweet
• Chains may be branched, unbranched or folded
What is starch and what are the two polysaccharides it made out of?
• A storage compound in plants in the form of small granules or grains
• Amylose and amylopectin
What is the structure of amylose? (DESCRIBE)
• Straight unbranched chains of 200-1500 α glucose molecules
• Takes a helix shape
• 1-4 α glycosidic bond
• Basically maltose but with extra α glucose as it is a polysaccharide and not a
disaccharide
What makes the structure of amylose specific to its function?
• Compact due to coiling; it has more glucose and therefore more chemical energy
• Traps iodine molecules in its coil, causing colour change
• Large, insoluble molecule; this means it doesn’t affect the water potential. If it did
cells will become hypertonic. So, water will move from a high-water potential to a low
water potential into cells via osmosis and burst cells. This also means it can’t diffuse
out of cells
What is the structure of amylopectin? (DESCRIBE)
• Branched molecule at 1-6 α glycosidic bond containing 2000- 200,000 α glucose
molecules
• Forms 1-4 α glycosidic bond and 1-6 α glycosidic bond
• The molecule branches every 3 α glucose molecules
• very similar structure to glycogen
What makes the structure of amylopectin specific to its function?
Extra info or key points for extra marks
Biological Molecules
What are the four classes of biological molecules?
• Carbohydrates
• Lipids
• Proteins
• Nucleic acid
What does nucleic acid do?
• Carries the genetic code for the production of proteins
What are monomers?
• The smaller units from which larger molecules are made
What are examples of monomers?
• Glucose, fructose, galactose, amino acids, nucleotides
What are polymers?
• Molecules made from a large number of monomers joined together
What are examples of polymers?
• Starch, cellulose, glycogen
Why aren't lipids polymers?
• They are formed from different molecules; glycerol and fatty acids
What are all living things made up of?
• Nitrogen, oxygen, carbon, hydrogen
Monomer Polymer
Carbohydrates Monosaccharides Polysaccharides
Proteins Amino acid polypeptide
Nucleic acid nucleotides DNA/ RNA
What is metabolism?
• All the chemical reactions that take place in the body summed up
What is a condensation reaction?
• The joining of two molecules together with the formation of a chemical bond and
releases a small molecule (water)
• Key points: release water, a new molecule is made, the larger molecule is made from
the smaller molecules bonding together
What is a hydrolysis reaction?
• The breaking of a chemical bond between two molecules using water.
• Key points: Requires water, breaks down covalent bonds called glycosidic bonds, two
smaller molecules are formed by splitting a larger molecule
Carbohydrates
What are carbohydrates?
• Sugars, starches and fibres that take up 10% of living cells and contain carbon,
oxygen and hydrogen mostly in the formation of Cn(H2O)n where n can be 3-7
What are monosaccharides?
• Simple sugars and monomers from which larger carbohydrates are made
What are the properties of monosaccharides?
• Sweet
• Very soluble in water
What are the different types of simple sugars?
• Glyceraldehyde- C3H6O3 (called a TRIOSE because it has 3 carbon)
, • Ribose- C5H10O5, deoxyribose- C5H10O4 (called PENTOSES because they have 5
carbons)
• Glucose- C6H12O6, fructose- C6H12O6, galactose- C6H12O6 (called HEXOSES
because they have six carbons)
What does glucose look like in terms of its structure?
• Straight chain structure of a ring form
• Ring contains 5 carbons, known as a pyranose ring
What is an isomer?
• Each of two or more compounds with the same formula but a different arrangement
of atoms in the molecule and different properties.
What are the isomers of glucose and what are the differences?
• Alpha and beta glucose
• Alpha glucose has the –OH on the lower side and –H on the upper side on the first
carbon whereas Beta glucose has the –H on the lower side and the –OH on the upper
side on the first carbon.
• Way to remember: Beta spells OHH (OH first and H second). Also, Alpha –OH on
carbon 1 lines up with the –OH on carbon 4
What does fructose look like (MEMORISE)
• A structural isomer to glucose
• A furanose ring as it only has four carbons in its ring and one oxygen
What are disaccharides?
• The condensation of two monosaccharides, forming glycosidic bonds and releasing
water
What are polysaccharides?
• The condensation of many glucose units, forming glycosidic bonds and releasing
water
• Polymers
Example Type of carbohydrate Function/ Uses
Glucose Monosaccharide • Energy source in
animals
• Used to make ATP
Fructose Monosaccharide • Component of flower
nectar
• Fruits and honey
, Galactose Monosaccharide • Milk/ Breast milk
Lactose (glucose + Disaccharide • Sugar found in milk
galactose)
Sucrose (glucose + Disaccharide • Transport form of
fructose) carbohydrate in
phloem
Maltose (glucose + Disaccharide • Hard candies
glucose) • Sweetener
Cellulose (β glucose Polysaccharide • Component of plant
condensed) cell walls
• Structural support
Glycogen (α glucose Polysaccharide • Energy source in
condensed) animals
• Used to make ATP
What does sucrose look like (MEMORISE)
• 1-5 α glycosidic bond
What are reducing sugars?
• Sugars that when reacting with other molecules, give out electrons known as
reduction
• All monosaccharides (glucose, fructose and galactose) and some disaccharides do this
What does maltose (disaccharide) look like?
• 2 α glucose molecules joined together in a condensation reaction and releasing 1
water
• 1,4 α glycosidic bond
What does lactose (disaccharide) look like?
• An β glucose and galactose molecule joined together in a condensation reaction and
releasing 1 water
• 1, 4 β glycosidic bond
, What are the principal polysaccharides for storage?
• Glycogen and starch
Why are polysaccharides suitable for storage?
• They are large, insoluble molecules.
• They are not sweet
• Chains may be branched, unbranched or folded
What is starch and what are the two polysaccharides it made out of?
• A storage compound in plants in the form of small granules or grains
• Amylose and amylopectin
What is the structure of amylose? (DESCRIBE)
• Straight unbranched chains of 200-1500 α glucose molecules
• Takes a helix shape
• 1-4 α glycosidic bond
• Basically maltose but with extra α glucose as it is a polysaccharide and not a
disaccharide
What makes the structure of amylose specific to its function?
• Compact due to coiling; it has more glucose and therefore more chemical energy
• Traps iodine molecules in its coil, causing colour change
• Large, insoluble molecule; this means it doesn’t affect the water potential. If it did
cells will become hypertonic. So, water will move from a high-water potential to a low
water potential into cells via osmosis and burst cells. This also means it can’t diffuse
out of cells
What is the structure of amylopectin? (DESCRIBE)
• Branched molecule at 1-6 α glycosidic bond containing 2000- 200,000 α glucose
molecules
• Forms 1-4 α glycosidic bond and 1-6 α glycosidic bond
• The molecule branches every 3 α glucose molecules
• very similar structure to glycogen
What makes the structure of amylopectin specific to its function?
