2. Learning Objectives
• Why is water so important to living things.
• What are carbohydrates, fats and proteins
made of, and their properties.
• The role of carbohydrates, fats and proteins in
living organisms.
• How to test for the presence of biological
materials.
• The structure of DNA
3. What are you made of?
• We are made of many different chemicals.
• Mostly, we are made of water. Almost 80%.
• We also contain:
– Carbohydrates
– Proteins
– Fats
• These are the substances our cells are made
of and they are vital for life.
4. Water
• Inside every living organism, chemical
reactions are going on all the time.
• This is called metabolism.
• Metabolic reactions only take place if the
chemicals which are reacting are dissolved in
water.
• Water is a very important solvent.
• If cells dry out, the reactions stop, and the
organism dies.
5. Water
• Water is also needed for other reasons:
• Plasma is the liquid part of blood.
– It contains water.
– Substances like glucose are dissolved in the plasma so they can
be transported around the body.
• Digestion:
– Water is needed to dissolve enzymes and nutrients in the
alimentary canal (digestive system) so that digestion can take
place.
• Excretion:
– Helps to remove waste products.
– The kidneys remove urea from the body, which is dissolved in
water, forming urine.
7. Sugars (Monosaccharides)
• The simplest kinds of carbohydrates are called
simple sugars or monosaccharides.
• Glucose is a simple sugar that is made of 6
carbon atoms joined in a ring, with the
hydrogen and oxygen atoms around it.
C6H12O6
8. Sugars
• Although the contain many atoms, simple
sugars are very small.
• They are soluble in water.
• They taste sweet.
9. Sugars (Disaccharides)
• If 2 simple sugar molecules join together, a
larger molecule called a complex sugar or
dissaccharide is made.
• Examples:
– Sucrose (the sugar we use in hot drinks)
– Maltose (malt sugar)
• They are also soluble in water and taste sweet.
10. Sugars (Polysaccharides)
• If many simple sugars join together, a very
large molecules is made.
• This is called a polysaccharide.
• Examples:
– In plants: cellulose and starch
– In animals: glycogen
• Most polysaccharides are insoluble and do
not taste sweet.
11. Function of carbohydrates
• Carbohydrates are needed for energy.
• The energy is released by respiration.
• Usually, the carbohydrate used is glucose.
• Animals transport glucose around the body in the
blood system.
• Plants also use glucose for respiration but they
don’t transport glucose around their bodies.
• Instead, they transport sucrose and then change
the sucrose to glucose when they need it.
12. Functions of carbohydrates
• Plants store carbohydrates as starch.
– They can store them in large quantities in their
seeds and we use these as food.
• Animals store carbohydrates as glycogen.
– Only small amounts can be stored.
– They are stored in the cells in the liver and
muscles.
• Cellulose is a strong polysaccharide used in
the cell wall.
13. Testing for carbohydrates
• We can test for the presence of sugars by
adding Benedict’s solution to a food and
heating it.
• If the mixture contains a reducing sugar
(simple sugar) then it will turn red.
• If there is no sugar the mixture will remain
blue.
• See page 42 for a diagram of the experiment.
14. Testing for carbohydrates
• We can test for starch using iodine solution:
– You add a couple of drops to a sample of food.
– If there is starch present, the iodine will turn
blue/black.
– If there is no starch present, the iodine will stay
orange brown.
15. Fats
• Fats are also known as lipids.
• They also contain only carbon, hydrogen and
oxygen.
• They are made of 4 smaller molecules:
– Glycerol
– 3 fatty acids.
• They are insoluble in water.
• At room temperature they are liquids called
oils.
17. Functions of fats
• Similar to carbohydrates:
– They can be used to release energy.
– They release twice as much energy as
carbohydrates.
• Most cells use carbohydrates first when they
need energy.
• The extra energy in fat makes them useful for
storing energy.
18. • Animals:
– The cells that store fats are called adipose tissue.
– Adipose tissue is also useful for keeping heat
inside the body.
• Plants:
– Store oils in their seeds for germination (plant
grow from a seed)
19. Testing for fats and oils
• To test for fats we use the ethanol emulsion test:
– Cut up food and mix it with ethanol.
– Pour the ethanol into water.
– If there is fat present, the mixture breaks up in the
water to make an emulsion.
– It looks white and cloudy, like milk.
– If there is no fat present, the mixture stays
transparent.
– Page 45 shows a picture of a positive test result.
20. Proteins
• Proteins contain carbon, hydrogen and
oxygen.
• They also contain nitrogen and small amounts
of sulphur.
21.
22. Amino acids
• There are about 20 different kinds of amino
acid.
• Any of them can be joined together to make a
protein molecule.
23.
24. Functions of proteins
• Some proteins are soluble in water:
– Haemoglobin (the red pigment in blood)
• Some proteins are insoluble:
– Keratin (hair and fingernails are made of this)
• Most proteins are used for making new cells.
• Cell membranes and cytoplasm contain lots of
proteins.
25. Functions of proteins.
• Proteins are also needed to make antibodies.
– These help to kill bacteria and viruses in the body.
• Enzymes are also proteins.
• The shape is determined by the order of
amino acids. This will decide the specific
function of the protein.
26. Testing for proteins
• The test for protein is called the Biuret test.
– Mix the food with water.
– Add dilute copper sulphate solution.
– Then add dilute potassium hydroxide solution.
– If the mixture turns purple, protein is present.
– If the mixture stays blue, no protein is present.
27. Coursebook questions
• Page 44 – questions on carbohydrates & water
• Page 45 – questions on fats
• Page 46 – questions on proteins
