A molecule with a slightly positive end and a slightly negative end because of unequal sharing of electrons.

Name the three common disaccharides and their monosaccharides.

Maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose).

What is a glycosidic bond?

The covalent C–O–C bond formed between two monosaccharides in a condensation reaction.

What is a condensation reaction?

A reaction that joins two molecules together and releases a molecule of water.

A reaction in which a molecule of water is added to break a bond, such as a glycosidic or ester bond.

Name the two components of starch.

Amylose (unbranched, helical) and amylopectin (branched).

Why is glycogen more suitable than starch for animals' energy store?

It is more highly branched with more ends, so glucose can be hydrolysed and released more quickly.

Give three features that make polysaccharides good energy stores.

Insoluble (no osmotic effect), compact, and made of many glucose units; branching allows rapid hydrolysis.

What is a triglyceride made from?

One glycerol molecule and three fatty acids, joined by three ester bonds.

How many water molecules are released when a triglyceride forms?

Three, one for each ester bond formed.

How do saturated and unsaturated fatty acids differ?

Saturated have no C=C double bonds; unsaturated have one or more, which kink the tail.

Why are saturated fats usually solid at room temperature?

Their straight tails pack closely together, so there are stronger intermolecular forces between molecules.

Water, carbohydrates and lipidsEdexcel A-Level Biology A: Flashcards

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Why is water a good solvent for ions?

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Why is water a good solvent for ions?: Water molecules are dipoles, so the δ− oxygen is attracted to positive ions and the δ+ hydrogens to negative ions, surrounding and separating them.
What is a dipole?: A molecule with a slightly positive end and a slightly negative end because of unequal sharing of electrons.
Name the three common disaccharides and their monosaccharides.: Maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose).
What is a glycosidic bond?: The covalent C–O–C bond formed between two monosaccharides in a condensation reaction.
What is a condensation reaction?: A reaction that joins two molecules together and releases a molecule of water.
What is hydrolysis?: A reaction in which a molecule of water is added to break a bond, such as a glycosidic or ester bond.
Name the two components of starch.: Amylose (unbranched, helical) and amylopectin (branched).
Why is glycogen more suitable than starch for animals' energy store?: It is more highly branched with more ends, so glucose can be hydrolysed and released more quickly.
Give three features that make polysaccharides good energy stores.: Insoluble (no osmotic effect), compact, and made of many glucose units; branching allows rapid hydrolysis.
What is a triglyceride made from?: One glycerol molecule and three fatty acids, joined by three ester bonds.
How many water molecules are released when a triglyceride forms?: Three, one for each ester bond formed.
How do saturated and unsaturated fatty acids differ?: Saturated have no C=C double bonds; unsaturated have one or more, which kink the tail.
Why are saturated fats usually solid at room temperature?: Their straight tails pack closely together, so there are stronger intermolecular forces between molecules.

Exam questions on Water, carbohydrates and lipids

Blood plasma in a mammal is mostly water. It carries dissolved glucose, amino acids and mineral ions around the body between the gut, the liver and the tissues.
Explain why an ionic compound such as sodium chloride dissolves in water.2 marks
Glycogen is stored in the liver and muscle cells of mammals. Starch is stored in the tubers of potato plants. Both are made by joining sugar molecules together.
Describe how maltose is broken down into glucose.2 marks
A marathon runner stores glycogen in her muscles and liver and relies on it during the race. A potato plant stores starch in its tubers over winter. Both stores are made from the same monomer.
Explain how the structure of glycogen makes it suitable as an energy store in the runner's muscles.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).