CIE IGCSE Biology Unit 4: Biological Molecules

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10 Terms

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carbohydrates

- Carbon, Hydrogen, Oxygen

- glucose, glycogen, cellulose, starch

<p>- Carbon, Hydrogen, Oxygen</p><p>- glucose, glycogen, cellulose, starch</p>
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fats

- Carbon, Hydrogen, Oxygen

- fatty acids, glycerol

<p>- Carbon, Hydrogen, Oxygen</p><p>- fatty acids, glycerol</p>
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proteins

- Carbon, Hydrogen, Oxygen, Nitrogen

- amino acids

<p>- Carbon, Hydrogen, Oxygen, Nitrogen</p><p>- amino acids</p>
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Amino acids

different sequences of amino acids

give different shapes to protein molecules

e.g. active site of enzymes and the binding site of

antibodies

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Iodine Test for Starch

Steps:

1. Obtain sample with expected trace of starch

2. Dissolve in solvent eg: ethanol or water

3. Add iodine solution to test for starch

Results: Starch causes iodine solution to turn blue-black

<p>Steps:</p><p>1. Obtain sample with expected trace of starch</p><p>2. Dissolve in solvent eg: ethanol or water</p><p>3. Add iodine solution to test for starch</p><p>Results: Starch causes iodine solution to turn blue-black</p>
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Benedicts's Test for Reducing Sugar

Steps:

1. Place substance into test tube

2. Place test tube into water bath and heat

3. Add in same volume with substance of Benedict's solution into test tube

Results:Presence of reducing sugar causes Benedict's solution to turn from blue to red

- Test for sucrose: as it is not a reducing sugar it gives a negative result, sucrose needs to be broken down into monosacchirides

<p>Steps:</p><p>1. Place substance into test tube</p><p>2. Place test tube into water bath and heat</p><p>3. Add in same volume with substance of Benedict's solution into test tube</p><p>Results:Presence of reducing sugar causes Benedict's solution to turn from blue to red</p><p>- Test for sucrose: as it is not a reducing sugar it gives a negative result, sucrose needs to be broken down into monosacchirides</p>
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Biuret Test for Proteins

Steps:

1. Fill test tube with extracted to be tested

2. Add biuret solution into test tube

3. Gently shake test tube for faster reaction

Results: Positive results causes biuret solution to turn from blue to purple

<p>Steps:</p><p>1. Fill test tube with extracted to be tested</p><p>2. Add biuret solution into test tube</p><p>3. Gently shake test tube for faster reaction</p><p>Results: Positive results causes biuret solution to turn from blue to purple</p>
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Ethanol emulsion test for fats

Steps:

1. Cut up sample to be tested

2. Add ethanol into test tube with sample

3. Put rubber stopper and shake contents

4. Add distilled water and shake contents again

Results: Positive results shows a suspension of white substance that is the presence of fats

<p>Steps:</p><p>1. Cut up sample to be tested</p><p>2. Add ethanol into test tube with sample</p><p>3. Put rubber stopper and shake contents</p><p>4. Add distilled water and shake contents again</p><p>Results: Positive results shows a suspension of white substance that is the presence of fats</p>
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DCPIP test for vitamin C

Steps:

1.Add solution into test tube

2.Drop DCPIP solution drop by drop and shake

3.Record number of drops required for DCPIP to turn colourless until solution doesn't dissolve

Results: presence of vitamin c causes DCPIP solution to turn colourless

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Structure of DNA

- two strands coiled together to form a

double helix

- each strand contains chemicals called

bases

- cross-links between the strands are formed by pairs of bases

- the bases always pair up in the same way:

A with T, and C with G

<p>- two strands coiled together to form a</p><p>double helix</p><p>- each strand contains chemicals called</p><p>bases</p><p>- cross-links between the strands are formed by pairs of bases</p><p>- the bases always pair up in the same way:</p><p>A with T, and C with G</p>