AQA A-level biology paper 1

define monomer

Monomers are smaller units from which larger molecules are made

Define Polymer

Polymers are molecules made from a large number of monomers joined together

What are the three monomers needed to know?

• Monosaccharides (e.g glucose)

• Amino acids

• nucleotides

What are the polymers needed to know?

• Starch

• Cellulose

• Glycogen

• Protein

• DNA/RNA

What are the two key types of chemical reactions?

• Condensation

• Hydrolysis

What is a condensation reaction?

• Joins two molecules together

• forms a chemical bond

• involves the elimination of a water molecule.

What is a hydrolysis reaction?

• Breaks a chemical bond

• between two molecules

• involves the use of a water molecule

What is a carbohydrate?

Contains only Carbon, Hydrogen and oxygen

what are the three types of carbohyrates?

• Monosaccharides

• Disaccharides

• Polysaccharides

What are the three monosaccharides?

• Glucose

• Fructose

• Galactose

What are the three types of Disaccharides?

• Sucrose

• Maltose

• Lactose

What are the three types of Polysaccharides?

• Starch

• Cellulose

• Glycogen

What bond forms between two Monosaccharides?

A condensation reaction forms a Glycosidic bond

How do you make each disaccharide?

• Glucose + glucose → Maltose + water

• Glucose + Galactose → Lactose + water

• Glucose + Fructose → Sucrose + water

What are the functions of each polysaccharide and where are they found?

• Starch - plants - store of glucose

• Cellulose - plants - structural strength

• Glycogen - Animals - store of glucose

what are the bonds between monomers in Starch?

1-4 glycosidic bonds in amylose, 1-4 and 1-6 in amylopectin

what are the bonds between monomers in Cellulose

1-4 glycosidic bonds

what are the bonds between monomers in Glycogen

1-4 and 1-6 glycosidic bonds

What is the structure of Starch

Made of 2 polymers - amylose (an unbranched helix) and amylopectin (a branched helix)

What is the structure of cellulose?

Polymer forms long, straight chains.

Chains held in parallel by many hydrogen bonds forming fibrils

Every other B Glucose is inverted 180

What is the structure of Glycogen?

A highly branched molecule

How does the structure of Starch impact its function

• helix is compact to fit a lot of glucose in a small space

• Branched structure increases surface area for rapid hydrolysis into glucose

• insoluble so won’t affect the water potential

How does the structure of cellulose impact its structure?

• Many hydrogen bonds provide collective strength

• Insoluble - won’t affect water potential

How does the structure of Glycogen impact its function

• Branched structure increases surface area for rapid hydrolysis back to glucose

• insoluble - won’t affect the water potential

What is the test for starch and what is the positive result?

• Iodine solution

• Orange → Blue black

What is the test for reducing sugars and what is the positive result? (All monosaccharides and disaccharides apart from Sucrose)

• Add Benedict’s and heat.

• Solution turns from blue to green, yellow, orange or brick red (the more red the higher the concentration of reducing sugar).

What is the test for non-reducing sugars and what is the positive result (only sucrose)

• Following a negative Benedict’s test - reagent remains blue

• Add acid and boil

• cool the solution and then add an alkali to neutralise it.

• Add Benedict’ reagent again and heat

• Blue to orange or brick red

• CLUE: WOULD BE MORE MARKS

What are triglycerides?

Triglycerides are formed by the condensation reaction of one molecule of glycerol and three molecules of fatty acids.

What is a phospholipid?

A phospholipid is one of the fatty acids of a triglyceride is swapped for a phosphate - 2 x fatty acids, one glycerol and one phosphate group.

What bond forms between a glycerol and a fatty acid?

A condensation reaction forms a ester bond

What is the difference between an unsaturated or a saturated fatty acid?

Saturated - Means only containing one type of bond - straight chain

Unsaturated - means more than one type of bond i.e a C=C - so will be angled/not straight

How does the structure of a triglyceride result in its properties?

• Energy store - Due to a large ratio of energy-storing carbon-hydrogen bonds compared to the number of carbon atoms a lot of energy is stored in the molecule.

• Due to the high ratio of hydrogen-oxygen atoms they act as a metabolic water source. Triglycerides can release water if they are oxidised - this is essential of animals in the desert such as camels.

• Triglycerides do not affect water potentials and osmosis - this is because they are large and hydrophobic, making them insoluble in water.

• Lipids have a relatively low mass - therefore a lot can be stored without increasing the mass and preventing movement.

How does the structure of a phospholipid result in its properties?

• Made of a Glycerol molecule, two fatty acids chains and a phosphate group (attached to glycerol).

• Two condensation reactions form two ester bonds.

• Hydrophilic head of the phospholipid interacts with water as it is charged.

• The fatty acid chain is not charged and it is known as the hydrophobic tail and it repels water, but will interact with fats.