Cells

YOU ARE LEARNING:

Identifying Molecules

We can use specific tests to identify biomolecules.

To find out if a solution contains a specific biological molecule, we can do certain tests

There are three beakers here with three different solutions

One contains proteins, another contains reducing sugars and the other contains both proteins and reducing sugars.

If you add biuret reagent to all three solutions, two of them will turn purple! So if biuret reagent makes a solution turn purple, it means that that solution contains _________________.

Here you added iodine solution to all three beakers. The solution in one of them turned blue-black. So iodine solution turns a solution blue-black if the solution contains ____________.

Benedict's reagent is blue, but when it comes into contact with ____________ and is heated, it turns the solution orange/red.

If you add sudan III solution to a solution that contains _______________, the solution will split in two and one part will go red.

Have a look at this table

So there are tests for 4 biological molecules

Proteins, starch, reducing sugars and lipids (fats).

If you add Biuret reagent to a solution containing proteins, the solution will turn ____________.

If you add ___________________ to a solution containing reducing sugars, the solution will go from blue to orange/red when heated.

If you add Sudan III solution to a solution containing lipids, the solution will split in two and turn one layer ____________.

If you add iodine solution to a solution containing starch, the solution will turn ____________.

If you add ___________________ to a solution containing lipids, the solution will turn milky white.

___________ is the only type of molecules that has 2 tests.

When you test to see if a solution contains a specific biological molecule, you add a specific reagent and look for a specific ____________.

A bit of practice

___________________ makes solutions containing lipids split in two and turns and one layer red.

___________________ makes solutions containing proteins turn purple.

___________________ makes solutions containing starch turn blue-black.

When you add ethanol ** and ** water to a solution containing lipids*, the solution will turn* blue-black*.*

When you add Benedict's reagent to a solution containing reducing sugars*, the solution will turn* orange/red*.*

Summary!

You can do different tests to find out if a solution contains a specific molecule

You can look for starch, reducing sugars, proteins and lipids (fats).

Notice there are two tests for lipids.

The reagents are specific to the molecules

You add a specific reagent to look for a specific molecule, by looking to see if the solution turns a specific colour.