Carbohydrates & Lipids 2.3

This is a topic about the molecules which are rich in energy. Three types of carbohydrates, monosaccharides, disaccharides and polysaccharides as well as lipids such as tryglycerides which make up many oils in the human body.  It includes the analysis of molecule shapes and their function or solubility, and also consideration of applications such as GMO potatoes for glue manufacure, and the heart disease risks of trans-fats.

Key words

Learn and test your biological vocabulary for 2.3 Carbohydrates and Lipids using these flashards.

Clean sweep - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

Read the slides and look up any words or details you find difficult to understand.

Video tutorial

A short video tutorial is planned here.

Revision summary list for 2.3 Carbohydrates & Lipids

  • Condensation reactions link Monosaccharide monomers together to
    form disaccharides (Sucrose, lactose and maltose) and polysaccharides.(cellulose starch and glycogen)
  • Fatty acids can be saturated, monounsaturated or polyunsaturated.
    and cis or trans isomers if they are unsaturated. (molecule names not required)
  • Three fatty acids and one glycerol molecules can form a Triglycerides by condensation reactions.
  • How the structure of cellulose and starch (amylose & amylopectin) in plants and glycogen in humans relates to function.
  • For long-term energy storage in humans
    lipids are better than carbohydrates.
  • Potatoes have been genetically modified to reduce the level of amylose to
    produce a more effective adhesive.
  • Evaluate the conflicting evidence for health risks of trans fats and saturated fatty acids and evaluate the methods used
  • Abiliy to use molecular visualization software like jmol to compare cellulose, starch and glycogen.
  • Ability to work out a BMI using a nomogram or by calculation

Revision mind map

This diagram summaries the main sections of topic 2.3.
Test if you can draw something like these concept maps from memory. 
Even better, design your own

Review questions

This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding.


Which of the following are all carboydrate monomers?

The simple sugars which act as momomers in larger carbohydrate molecues are, glusose, fructose, and galactose.

They are often joined together, e.g. glucose and glucose form maltose.

Long chains of glucose molecules form polysaccharides.


The image below shows a molecule commonly found in the human digestive system

What type of molecule is this?

Each of the momomer units is a glucose molecule, so this is a disaccharide, in fact maltose.


What are the functions of the molecules, Cellulose, and Starch in plants?

Plant cells walls are built of cellulose mainly.

There is starch in the cell but this is found in the chloroplast, or in the cytoplasm. It is used to store energy.


What is the difference in structure between amylose and amylopectin?

Amylose is an unbranched polysaccharide, and Amylopectin is a branched polysaccharide.

Both are found in starch.


The molecules below are both of the same type, fatty acids.

Which of the descriptions below is the best description of these two molecules.

The rerms cis- and trans- apply to unsaturated fatty acids but from these diagrams we cannot tell.

Saturated fatty acids have no double bonds in the carbon chain (except the =0 in the carboxylic acid)

Both of these are unsaturated fatty acids.


Which of the following molecules are monosaccharides?

  1. Lactose
  2. Galactose
  3. Sucrose
  4. Fructose
  5. Glucose

Monosacharides are Galactose, Fructose and Glucose.

The three disaccharides named in the syllabus are Maltose, Sucrose and Lactose.


The diagram below shows a graph of the results of a long study into the incidence of heart disease (CHD).

When satrurated fat replaced 5% of the energy in a diet the % incidence of CHD increased by 20%

Which of the following conclusions could be made about Trans-fat?

An ability to evaluate evidence about the health impact of trans-fats is expected.
In this case the evidence strongly suggests that trans-fat increases the risk of CHD more than other fat types.


What type of reaction is it that makes a macromolecule from smaller monomer units?

Condensation reactions are those where two -OH groups join forming a covalent bond and releasing a water molecule.

These reactions often join molecules together, e.g. glucose and glucose form maltose.

Long chains of glucose molecules form polysaccharides.

Total Score:

Revision fun activity

Everyone needs something a bit light hearted from time to time when revising. That's the aim of this last activity.
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Cabohydrates & Lipids - Matching cards memory games

The idea is that this game is fun to do but it still counts as revision.