Biological Molecules
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Questions and Answers

Which of the following is a type of carbohydrate?

  • Insulin
  • Cholesterol
  • Glucose (correct)
  • Triglyceride

Proteins are a category of biological molecules that do not contain carbon.

False (B)

What is the basic unit of triglycerides?

Glycerol

When two glucose molecules join together, they form _____

<p>maltose</p> Signup and view all the answers

Match the following types of biological molecules with their characteristics:

<p>Carbohydrates = Long chains of simple sugars Lipids = Made up of triglycerides Proteins = Polymers made from amino acids Nucleic Acids = DNA and RNA structures</p> Signup and view all the answers

Which of the following statements about lipids is true?

<p>They can be solid or liquid at room temperature. (A)</p> Signup and view all the answers

Starch, glycogen, and cellulose are polysaccharides made from glucose.

<p>True (A)</p> Signup and view all the answers

Lipids are divided into fats and _____ based on their state at room temperature.

<p>oils</p> Signup and view all the answers

What is the main component that makes up proteins?

<p>Amino acids (D)</p> Signup and view all the answers

There are only 5 different amino acids that are used to form proteins.

<p>False (B)</p> Signup and view all the answers

What color change indicates a positive test for glucose when using Benedict's solution?

<p>orange or brick red</p> Signup and view all the answers

Amino acids join together to form __________.

<p>proteins</p> Signup and view all the answers

Match the following terms with their correct descriptions:

<p>Amino acids = Building blocks of proteins Benedict's solution = Test for reducing sugars Proteins = Chains of amino acids Food tests = Methods to identify nutrients</p> Signup and view all the answers

What happens if even a small change occurs in the order of amino acids?

<p>A different protein is formed (D)</p> Signup and view all the answers

Benedict's test requires the sample solution to be heated to 80-90 °C.

<p>False (B)</p> Signup and view all the answers

What is the general structure of an amino acid?

<p>A central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and an R group.</p> Signup and view all the answers

What color change indicates a positive test for starch using iodine?

<p>Orange-brown to Blue-black (A)</p> Signup and view all the answers

What is the outgoing color of the DCPIP solution when a positive test for vitamin C occurs?

<p>Blue (A)</p> Signup and view all the answers

The Biuret test for protein shows a color change from blue to violet.

<p>True (A)</p> Signup and view all the answers

DNA is a molecule that contains the instructions for growth and development in some organisms only.

<p>False (B)</p> Signup and view all the answers

What solution is used to test for the presence of lipids in a food sample?

<p>ethanol</p> Signup and view all the answers

What are the individual units of DNA called?

<p>nucleotides</p> Signup and view all the answers

A positive test for protein will show a color change from blue to ______.

<p>violet</p> Signup and view all the answers

The structure of DNA is commonly described as a ______ helix.

<p>double</p> Signup and view all the answers

Match the food test with its corresponding positive result:

<p>Iodine Test = Blue-black color Biuret Test = Violet color Ethanol Test = Cloudy emulsion</p> Signup and view all the answers

What is the first step in the iodine test for starch?

<p>Add drops of iodine solution (C)</p> Signup and view all the answers

Match the following food tests with their respective substances being tested:

<p>DCPIP = Vitamin C Ethanol = Lipids Benedict's solution = Reducing sugars Iodine solution = Starch</p> Signup and view all the answers

To test for proteins, you should mix the food sample with water and look for a pink color change.

<p>False (B)</p> Signup and view all the answers

How many strands does a DNA molecule consist of?

<p>Two (C)</p> Signup and view all the answers

The ethanol test is used to identify the presence of proteins in food samples.

<p>False (B)</p> Signup and view all the answers

What happens when a positive test for lipids is obtained?

<p>a cloudy emulsion forms</p> Signup and view all the answers

What should you include when describing food tests in exam answers?

<p>Starting color and color change for a positive result</p> Signup and view all the answers

Which of the following statements about nucleotides is true?

<p>Nucleotides differ in the base attached. (D)</p> Signup and view all the answers

Adenine pairs with Cytosine in DNA.

<p>False (B)</p> Signup and view all the answers

What holds the two strands of DNA in a double helix together?

<p>Hydrogen bonds</p> Signup and view all the answers

The components that form the backbone of a DNA strand are phosphate and __________.

<p>deoxyribose sugar</p> Signup and view all the answers

Match the DNA base with its complementary pair:

<p>Adenine = Thymine Cytosine = Guanine Thymine = Adenine Guanine = Cytosine</p> Signup and view all the answers

What role do the base pairs in DNA primarily serve?

<p>They hold the code for the formation of proteins. (C)</p> Signup and view all the answers

Nucleotides are composed of a phosphate group, a sugar, and an amino acid.

<p>False (B)</p> Signup and view all the answers

What structure do the phosphate and sugar components of nucleotides resemble?

<p>The sides of a ladder</p> Signup and view all the answers

Flashcards

Organic Molecules

Molecules that contain carbon. Carbohydrates, proteins, and lipids are examples.

Carbohydrates

Made of long chains of simple sugars. Examples include glucose, maltose, starch, glycogen, and cellulose.

Monosaccharide

A simple sugar, like glucose, that cannot be broken down further.

Disaccharide

Two monosaccharides joined together. Maltose is an example, formed from two glucose molecules.

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Polysaccharide

Many monosaccharides joined together. Examples include starch, glycogen, and cellulose.

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Triglyceride

The basic unit of most fats (lipids) in the body. Made of one glycerol molecule and three fatty acid chains.

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Fatty Acids

Long chains of carbon atoms that make up part of a triglyceride. They vary in size and structure.

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Fats vs Oils

Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature).

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What is a protein?

A long chain of amino acids joined together.

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How many different amino acids are there?

There are about 20 different amino acids.

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Amino acid structure

All amino acids share a common basic structure, but the 'R' group is different for each one.

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Protein variety

Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins.

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Protein change

Even a small difference in the order of amino acids results in a different protein being formed.

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Food test for glucose

Benedict's solution is used to test for glucose (a reducing sugar). A positive test shows a color change from blue to orange or brick red.

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How to perform the glucose test?

Add Benedict's solution to the sample solution in a test tube, heat in a water bath at 60-70°C for 5 minutes, observe the color change.

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Iodine test

A test used to detect the presence of starch in a sample. A positive test will show a color change from orange-brown to blue-black.

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What is the color change in a positive iodine test?

The color change from orange-brown to blue-black indicates the presence of starch in the sample.

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Biuret test

A test used to detect the presence of protein in a sample. A positive test will show a color change from blue to violet/purple.

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What is the color change in a positive Biuret test?

In a positive Biuret test, the solution changes color from blue to violet/purple, indicating the presence of protein.

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Ethanol test

A test used to detect the presence of lipids (fats and oils) in a sample. A positive test will show a cloudy emulsion forming.

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Why does an emulsion form in a positive ethanol test?

The ethanol dissolves the lipids, and when mixed with water, the lipids separate out, creating a cloudy emulsion.

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How do you perform the ethanol test?

First, mix the food sample with ethanol and shake well. Then, add an equal volume of cold water to the ethanol mixture.

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What does a cloudy emulsion indicate in the ethanol test?

A cloudy emulsion in the ethanol test indicates the presence of lipids (fats and oils) in the sample.

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Nucleotide

A building block of DNA, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base.

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DNA Bases

The four nitrogenous bases found in DNA: Adenine (A), Cytosine (C), Thymine (T), and Guanine (G).

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Base Pairing Rules

Adenine always pairs with Thymine (A-T), and Cytosine always pairs with Guanine (C-G).

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DNA Backbone

The sugar-phosphate structure of DNA, forming the two sides of the DNA double helix.

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DNA Double Helix

The twisted ladder-like structure of DNA, formed by two strands of nucleotides held together by base pairs.

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What holds DNA strands together?

Hydrogen bonds form between the nitrogenous bases of the two DNA strands, holding the helix together.

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DNA Code

The sequence of bases in DNA carries the genetic information needed to build proteins.

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Importance of Base Pairing

The specific base pairing rules in DNA ensure accurate replication of genetic information.

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DCPIP Test

A biochemical test used to detect the presence of vitamin C (ascorbic acid) in a sample. It involves the addition of DCPIP (dichlorophenolindophenol) solution, which is blue, to the sample. A positive result is indicated by the disappearance of the blue color, as vitamin C reduces DCPIP.

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DNA Structure

The molecular structure of deoxyribonucleic acid (DNA), which is a double helix consisting of two strands of nucleotides wound around each other. Each nucleotide contains a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).

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What is the starting colour of DCPIP solution?

The starting color of the DCPIP (dichlorophenolindophenol) solution is blue.

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What colour change indicates a positive DCPIP test?

A positive DCPIP test is indicated by the disappearance of the blue color, turning the solution clear or colorless due to the reduction of DCPIP by vitamin C.

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What does the ethanol test observe?

The ethanol test observes the formation of an emulsion, which appears cloudy or milky, indicating the presence of lipids. The ethanol interacts with the lipids, disrupting their structure and forming tiny droplets that scatter light, making the mixture cloudy.

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What are the basic units of DNA?

The basic units of DNA are called nucleotides. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).

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Study Notes

Biological Molecules

  • Biological molecules are the building blocks of life, and most of these fall into three categories: Carbohydrates, proteins, and lipids.
  • These categories all contain carbon, which makes them organic molecules.

Chemicals & Life

  • Most molecules in living organisms are categorized as carbohydrates, proteins, and lipids.
  • These molecules all contain carbon.

Chemical Elements Table

  • Carbohydrates: Contain carbon, oxygen, and hydrogen.
  • Proteins: Contain carbon, oxygen, hydrogen, and nitrogen; some may also contain sulfur.
  • Lipids: Contain carbon, oxygen, and hydrogen.

Large Molecules are Made from Smaller Molecules

  • Carbohydrates: Long chains of simple sugars (monosaccharides).
  • Glucose is a simple sugar (monosaccharide).
  • Two glucose molecules combine to form maltose (disaccharide).
  • Multiple glucose molecules combine to form starch, glycogen, or cellulose (polysaccharides).

Fats

  • Most fats in the body are triglycerides.
  • Triglycerides consist of one glycerol molecule bonded to three fatty acid chains.
  • Fatty acids vary in size and structure
  • Lipids are categorized into fats (solid at room temp) and oils (liquid at room temp).

Proteins

  • Proteins are long chains of amino acids.
  • There are approximately 20 different amino acids.
  • Amino acids have similar basic structures, but differ in their 'R' group.
  • Amino acids combine to form proteins.
  • The order of amino acids determines the protein's structure and function.

Food Tests

Food Test for Glucose (Reducing Sugar)

  • Materials: Benedict's solution, test tube, water bath, food sample
  • Procedure: Add Benedict's solution to the food sample in a test tube and heat in a water bath (60-70°C). Observe color changes, positive result shows color change from blue to orange/brick red.

Food Test for Starch

  • Materials: Iodine solution, test tube, food sample
  • Procedure: Add iodine solution to the food sample, observe color changes. Positive result shows orange-brown changing to blue/black.

Food Test for Protein

  • Materials: Biuret solution, test tube, food sample
  • Procedure: Add Biuret solution to the food sample in a test tube, observe color changes. Positive result shows a colour change from blue to violet/purple.

Food Test for Lipids

  • Materials: Ethanol, water, test tube, food sample.
  • Procedure: Mix the food sample with ethanol and shake. Add an equal volume of water. Observe changes in the solution. A positive test shows a cloudy emulsion forming

Food Test for Vitamin C

  • Materials: DCPIP solution, test tube, food sample, distilled water
  • Procedure: Add DCPIP solution to a test tube with a food sample solution. A positive test shows the blue dye turning colorless.

DNA Structure

  • DNA (deoxyribonucleic acid) contains the instructions for growth and development in all organisms.
  • DNA is a double helix, consisting of two strands wound around each other.
  • DNA is made up of nucleotides.
  • Nucleotides each consist of a phosphate, deoxyribose sugar, and a base.
  • The four bases are adenine (A), cytosine (C), guanine (G), and thymine (T).
  • Adenine always pairs with thymine, and cytosine with guanine.
  • These connected bases form the "rungs" of the DNA ladder.
  • The phosphate and sugar form the "sides" of the ladder.
  • The sequence of bases in DNA determines the order of amino acids in proteins.
  • Chromosomes are long strands of DNA wrapped around proteins.
  • The nucleus of a cell contains chromosomes.

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Cambridge CIE IGCSE Biology PDF

Description

Test your knowledge on biological molecules including carbohydrates, lipids, and proteins. This quiz covers their structures, functions, and properties, such as glucose tests and the formation of macromolecules. Dive in to strengthen your understanding of essential biomolecules!

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