Biological Molecules

Question 1

What are the three types of sugars called?

Answer 1

Monosaccharides
Disaccharides
Polysaccharides

Question 2

Give three examples of monosaccharides

Answer 2

Glucose
Fructose
Ribose

Question 3

Give three examples of disaccharides

Answer 3

Sucrose
Maltose
Lactose

Question 4

Give three examples of polysaccharides

Answer 4

Starch
Cellulose
Glycogen

Question 5

Draw the glucose molecular formation

Answer 5

(Find drawing in book)

Question 6

Why is glucose arranged in a ring structure?

Answer 6

Because it’s more stable.

Question 7

What are the two types of glucose molecules?

Answer 7

Alpha glucose
Beta glucose

Question 8

How are disaccharides formed?

Answer 8

Formed by a condensation reaction of 2 monosaccharides. The bond between them is called a 1, 4 glycosidic bond.

Question 9

What is a condensation reaction?

Answer 9

Where a water molecule is removed.

Question 10

How are disaccharides broken down?

Answer 10

Broken down from the hydrolysis reaction at the 1, 4 glycosidic bond to form 2 monosaccharides.

Question 11

What is a hydrolysis reaction?

Answer 11

When a water molecule is added.

Question 12

How is the disaccharide maltose formed?

Answer 12

By 2 monosaccharides (glucose) where a hydrogen molecule from one monosaccharide on its Carbon 1 and a hydrogen and oxygen molecule from another monosaccharide on its Carbon 4 is removed and both monosaccharides are joined together to create the glycosidic bond.
(Use book for diagram.)
Both molecules which are removed create H2O.

Question 13

How does an alpha glucose differ from a beta glucose?

Answer 13

An alpha glucose has its OH molecule situated downwards in its molecular formation while the beta glucose has the OH molecule pointing upwards in its molecular formation.

Question 14

What is starch?

Answer 14

Starch is a mixture of two polysaccharides of the alpha glucoses Amylose and Amylopectin.

Question 15

What is the role of starch?

Answer 15

Plants store excess glucose as starch.
When a plant needs more glucose for energy, it breaks down starch to release the glucose.

Question 16

What is the structure and function of Amylose?

Answer 16

Structure = A long, unbranched chain of alpha glucose.
Angles of the Glycosidic bond (GB) give it a coiled structure.

Function = Makes the starch compact and therefore really good for storage as it can fit more into a small space.

Question 17

What is the structure and function of Amylopectin?

Answer 17

Structure = A long, branched chain of alpha glucose.

Function = Its side branches allow the enzymes that break down the molecule to get at the GB’s easily, therefore glucose can be released quickly.

Question 18

What is the structure and function of Glycogen?

Answer 18

Structure = Similar to Amylopectin but has many more side branches coming of its long chain. It is a compact molecule therefore good for storage.

Function = Animals store excess glucose as glycogen. It’s plenty side branches allow the stored glucose to be released quickly which is important for energy release in animals.

Question 19

What is the structure and function of Cellulose?

Answer 19

Structure = Made up of long, unbranched chains of beta-glucose.
When beta-glucose molecules bond, they form straight cellulose chains.

Function = Cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils.
Strong fibres means that the cellulose provides structural support for cells.

Question 20

What are lipids?

Answer 20

Made from a variety of different components but they all contain hydrocarbons.
There are two types of lipids.

Question 21

What are the two types of lipids?

Answer 21

Triglycerides
Phospholipids

Question 22

What is the structure of a triglyceride?

Answer 22

One molecule of glycerol with three fatty acids attached to it.
The fatty acid molecules have long ‘tails’ made of hydrocarbons.
The tails are ‘hydrophobic’ (they repel water molecules). These tails make lipids insoluble in water.

Question 23

What is the structure of fatty acids?

Answer 23

Two kinds of fatty acids — saturated and unsaturated.
All fatty acids consist of the same basic structure, but the hydrocarbon tails vary.
Draw the structure of one.

Question 24

What are the properties of saturated fatty acids?

Answer 24

No double bonds between their carbon atoms.
The fatty acid is ‘saturated’ with hydrogen.
Have high melting points
At room temperature they are solids.

Question 25

Draw the diagram for fatty acids.

Answer 25

Draw on book or blank page on ipad notes.

Question 26

What are the properties of unsaturated fatty acids?

Answer 26

They have double bonds between carbon atoms, which cause the chains to link.
Found in cold-blooded animals and plants.
At room temperature it is liquid.

Question 27

Draw the diagram for the unsaturated fatty acid.

Answer 27

Draw on a blank piece of paper or on iPad notes.

Question 28

How is a triglyceride formed?

Answer 28

Triglycerides are formed by condensation reactions.
An ester bond forms between the two molecules, releasing a molecule of water.
This process happens twice more to form a triglyceride.

Question 29

Draw how a triglyceride is formed.

Answer 29

Draw on a black sheet of paper or draw on iPad notes.

Question 30

What are the properties of triglycerides?

Answer 30

Insoluble in water, therefore don’t affect the water potential and doesn’t cause water to enter cells by osmosis.
Used for storage, insulation and protection in fatty issue.
Yield more energy per unit mass than other compound, therefore good for energy storage.
Triglycerides containing saturated fatty acids have a higher melting point.
Triglycerides containing unsaturated fatty acids have a lower melting point.

Question 31

What are phospholipids?

Answer 31

Lipids found in cell membranes.
Similar to triglycerides except one fatty acid molecule is replaced by a phosphate group.
The phosphate group is hydrophilic, while the fatty acid tails are hydrophobic.

Question 32

What is the function of a phospholipid?

Answer 32

Make up the bilayer of cell membranes, where the cell membranes control what enters and leaves a cell.

Question 33

What is the structure of a phospholipid?

Answer 33

Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side.
The centre of the bilayer is hydrophobic so water-soluble substances are unable to pass through — the membrane acts as a barrier to those substances.

Question 34

Draw a phospholipid bilayer.

Answer 34

Draw on blank piece of paper or on iPad notes.

Question 35

What is the procedure for the emulsion test on lipids?

Answer 35

Shake the test substance with ethanol for about a minute, then pour the solution into water.
Any lipid will show up as a milky emulsion
The more lipid there is, the more noticeable the milky colour will be.

Question 36

What are the two types of sugars?

Answer 36

Reducing sugars
Non-reducing sugars.

Question 37

What do reducing sugars contain and how are you able to test for a reducing sugar?

Answer 37

Contain all monosaccharides and some disaccharides.
To test for reducing sugars— add Benedict’s reagent to a sample and heat it in a water bath thats been brought to a boil temperature.
If the test’s positive, it will form a coloured precipitate (brick-red precipitate).
If the test is negative, the solution will stay blue and that shows there is no reducing sugar present.
The higher the conc. of reducing sugar, the further the colour change goes.

Question 38

How do you test for non-reducing sugars?

Answer 38

If the result of the reducing sugars is negative, there could still be a non-reducing sugar present.
To test for non-reducing sugars, like sucrose, you have to break them down into monosaccharides.
To do this, you take a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in a water bath that has been brought to a boiling temperature.
Then you neutralise it by adding sodium hydrogencarbonate.
Then just carry out the Benedict’s tests the same thing done for the reducing sugar.
The sample will stay blue if there is no non-reducing sugar present but will turn into a brick-red precipitate if there is a non-reducing sugar present.

Question 39

Is an amino acid a polymer or a monomer?

Answer 39

Monomer.

Question 40

Is a polypeptide a polymer or a monomer?

Answer 40

Polymer.

Question 41

What is the general structure of an amino acid?

Answer 41

There are 4 groups; the amino group, the r group, the carboxyl group and the amine group.
The amino group is made of 2 hydrogens and one nitrogen.
The r group can be any type of amino acids.
The carboxyl group is made from one carbon, one OH, and one oxygen with a double bond connecting both carbon and oxygen.
The amine group is one hydrogen.

Question 42

How are dipeptides and poly peptides formed?

Answer 42

• Amino acids are linked together by condensation reactions to form dipeptides and polypeptides.
• A molecule of water is released during the reaction.
• The bonds formed between the amino acids are called peptide bonds.
• The reverse reaction (hydrolysis) occurs when dipeptides and polypeptides are broken down.

Question 43

Name the sub structures in the full protein structure. (4)

Answer 43

•Primary structure.
• Secondary structure.
• Tertiary structure.
• Quaternary structure.

Question 44

Name the four sub structures in the protein structure.

Answer 44

• Primary
• Secondary
• Tertiary
• Quaternary

Question 45

Explain the primary structure in the protein structure.

Answer 45

This is the sequence of amino acids in the polypeptide chain.

Question 46

Explain the secondary structure in the protein structure.

Answer 46

• This is where hydrogen bonds form between the amino acids in the chain.
• This makes it automatically coil into an alpha helix or fold into a beta pleated sheet.

Question 47

Explain the tertiary structure in the protein structure

Answer 47

• The coiled or folded chain of amino acids are coiled further or folded further.
• This is because more bonds are formed between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds.
• Disulfide bridges are also formed whenever two molecules of the amino acid, cysteine, come close together.
• The tertiary structure forms the proteins final 3D structure.

Question 48

Explain the quaternary structure in the protein structure.

Answer 48

• Some proteins are made of several different polypeptide chains held together by bonds.
• This fourth structure is the way these polypeptide chains are assembled together.
• For proteins made from more than one polypeptide chain (e.g. insulin and haemoglobin), the quaternary structure is their final 3D shape.

Question 49

What is the structure of an enzyme and how does it relate to its function?

Answer 49

• Spherical in shape due to the tight holding of the polypeptide.
• Soluble and often have roles in metabolism - some enzymes break down large food molecules (digestive enzymes) and other enzymes help to synthesise large molecules.

Question 50

What is the structure of antibodies and how does it relate to its function?

Answer 50

• Made up of two light (short) polypeptide chains and two heavy (long) polypeptide chains bonded together.
• Have variable regions, where the amino acid sequences vary greatly.
• Involved in the immune response and are found in the blood.

Question 51

What is the structure of transport proteins and how does it relate to its function?

Answer 51

• Channel proteins are a type of transport proteins.
• Channel proteins contain hydrophobic and hydrophilic amino acids, which cause the protein to fold up and form a channel.
• These proteins are then able to transport molecules and ions across membranes.

Question 52

What is the structure of structural proteins and how does it relate to its function?

Answer 52

• They are physically strong.
• Consist of long polypeptide chains lying parallel to each other with cross-links between them.
• They include keratin (found in hair and nails) and collagen (found in connective tissue). Collagen has 3 polypeptide chains tightly coiled together, which makes it strong.
• This makes it a great supportive tissue in animals.

Question 53

How do you conduct the biuret test for proteins?

Answer 53

1. The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
2. Then you add some copper (II) sulfate solution.

• If protein is present, the solution turns purple.
• If there’s no protein, the solution will stay blue.

When using dilute sodium hydroxide, there is a safety hazard. Therefore, safety goggles need to be worn as it’s an irritant.

Question 54

How are enzymes able to speed up the rate of chemical reactions?

Answer 54

• They act as biological catalysts.
• They catalyse metabolic reactions— both at a cellular level and for the organism as a whole.
• Enzyme action can be intracellular (within cells) or extracellular (outside cells).

Question 55

What is the structure of an enzyme?

Answer 55

Enzymes have an active site, which has a specific shape.
The active site is the part of the enzyme where the substrate molecules bind to.
Enzymes are highly specific due to their tertiary structure.

Question 56

How is an enzyme able to lower the activation energy?

Answer 56

When a substrate fits into the enzymes active site it forms an enzyme-substrate complex which lowers the activation energy. There are two reasons why;
• If two substrate molecules need to be joined, being attached to the enzyme holds them close together. This reduces any repulsion between the molecules so they can bond more easily.
• If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.

Question 57

Explain the ‘induced fit’ model of an enzyme.

Answer 57

• The model helps to explain why enzymes are so specific and only bond to one particular substrate.
• The substrate doesn’t only have to be the right shape to fit the active site, but it also has to make the active site change shape in the right way.
• The substrate binds into the active site and it changes its shape slightly and is now complementary to each other.
• It is now able to produce its products.

Question 58

What are the properties of an enzyme and how is it able to combine with the complementary substrate?

Answer 58

• Enzyme properties are related to their tertiary structure.
• Enzymes are very specific— they only catalyse one reaction. This is because only one complementary substrate will fit into the active site.
• The active site’s shape is determined by the enzyme’s tertiary structure.
• Each enzyme has a different tertiary structure and therefore a different shaped active site.

• If the active site and substrate have a complementary shape, they form an enzyme-substrate complex, speeding up the reaction.
• If the active site and substrate do not have a complementary shape, the substrate can’t fit into the the active site so the reaction can’t be catalysed.

Question 59

How is it possible to change the tertiary structure of an enzyme?

Answer 59

• Because the primary structure of a protein is determined by a gene. A mutation in the gene is able to change the tertiary structure of the enzyme produced.
• Also it can be altered by changes in pH or temperature.

Question 60

What are the factors which can affect enzyme activity?

Answer 60

• Temperature.
• pH.
• Substrate concentration.
• Enzyme concentration.
• Concentration of competitive inhibitors.
• Concentration of non-competitive inhibitors.

Question 61

Explain temperature as a factor that affects enzyme activity.

Answer 61

• The rate of an enzyme-controlled reaction increases when the temperatures increased.
• More heat means more kinetic energy, so molecules move faster.
• This makes the substrate molecules more likely to collide with the enzymes’ active sites.
• The energy of these collisions also increases, which means each collision is more likely to result in a reaction.

• But if the temperature gets too high, the reaction stops. The rise in temp. makes the enzyme’s molecules vibrate more.
• If the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape.
• The active site changes shape and the enzyme and substrate no longer fit together.
• At this point, the enzyme is denatured and no longer functions as a catalyst.

Question 62

Explain pH as a factor that affects enzyme activity.

Answer 62

• All enzymes have an optimum pH value. Most human enzymes work best at pH 7 which is neutral, but there are exceptions.
• Above and below the optimum pH, the H+ and the OH- ions found in acids and alkalis can disrupt the ionic and hydrogen bonds that holds the enzyme’s tertiary structure in place.
• The enzyme becomes denatured, and the active site changes shape.

Question 63

Explain substrate concentration as a factor that affects enzyme activity.

Answer 63

• The higher the substrate concentration, the faster the reaction— more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be occupied.
• Though, this is only true up until a ‘saturation’ point, where all the active sites are occupied.
• Beyond the saturation point, all the active sites are still occupied but there are spare substrate molecules; adding more won’t make a difference.
• Therefore an increase in substrate concentration has no further affect on the rate of reaction.

Question 64

Explain enzyme concentration as a factor that affects enzyme activity.

Answer 64

• The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with on and form an enzyme-substrate complex.
• Therefore increasing the concentration of the enzyme increases the rate of reaction.
• But, if the amount of substrate is limited, there comes a point when there’s more than enough enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect.

Question 65

Explain competitive inhibitors as a factor that affects enzyme activity.

Answer 65

• Competitive inhibitor molecules have a similar shape to that of a substrate molecules.
• They compete with the substrate molecules to bind to the active site. As they have bonded to the active site before the substrate, no reaction is able to take place and the substrate molecule is left out.

How much the enzyme is inhibited it’s based on the relative concentrations of the inhibitor and substrate;
• If there is a high conc. of the inhibitor, it’ll take up nearly all the active sites and hardly any of the substrate will get to the enzyme.
• If there is a high conc. of substrate, then the substrate’s chances of getting to the active site before the inhibitor increases.

• Increasing the conc. of the substrate will increase the rate of reaction.

Question 66

Explain non-competitive inhibitors as a factor that affects enzyme activity.

Answer 66

• Non-competitive inhibitor molecules bind to the enzyme away from its active site.
• This causes the active site to change shape so the substrate molecules can no longer bind to it.
• Non-competitive inhibitor molecules don’t compete with the substrate molecules to bind to the active site because they are a different shape. This reduces the rate of reaction.
• Increasing the conc. of substrate won’t make any difference— enzyme activity will still be inhibited unlike with competitive inhibitor molecules.

Question 67

What is DNA and RNA?

Answer 67

• DNA and RNA are both types of nucleic acids.
• They’re found in all living cells and they both carry information.
• They’re polymers of nucleotides.

Question 68

What is the function of DNA?

Answer 68

It is used to store your genetic information— all the instructions needed to grow and develop from a fertilised egg into a fully grown adult.

Question 69

What is the function of RNA?

Answer 69

• Its’ function is to transfer genetic information from DNA to the ribsosomes, where the ribosomes read the RNA to make polypeptides in a process called translation.
• Ribosomes are made from RNA and proteins.

Question 70

What is a nucleotide?

Answer 70

A type of biological molecule which is made from three different components: a Pentose sugar (a sugar with 5 carbon atoms), a nitrogen-containing organic base (organic meaning it contains carbon), and a phosphate group.
These are the monomers that make up DNA and RNA.

Question 71

What is the structure of a polynucleotide?

Answer 71

• This is where many nucleotides join together to form polynucleotide strands.
• The nucleotides join up via a condensation reaction between the phosphate group of one nucleotide and the sugar of another. This is connected by an ester bond and once connected a phosphodiester bond is made which consists of the phosphate group and the two ester bonds.
• The chain of phosphates and sugars is known as the sugar-phosphate backbone.

Question 72

What is the structure of DNA?

Answer 72

• DNA has a double helix structure— a DNA molecule is formed from two separate strands which wind around each other to form a spiral.
• The strands are polynucleotides.
• DNA molecules are really long and coiled up very tightly, so a lot of genetic information is able to fit into a small space in the cell nucleus.

Question 73

What is the DNA nucleotide structure?

Answer 73

• A DNA nucleotide is made from a phosphate group, the pentose sugar deoxyribose and a nitrogen-containing organic base.
• Each DNA nucleotide had the same sugar and phosphate, whereas the base can vary.
• There are four possible bases— adenine (A), thymine (T), cytosine (C) and guanine (G).
• The bases pair up with a particular partner and as they do the two polynucleotide strands in DNA become antiparallel— they run in opposite directions and are able to twist to form the DNA double helix.

Question 74

What is complementary base pairing in the DNA nucleotide structure?

Answer 74

• This is where two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base can only join with one particular partner.
• Adenine always pairs with thymine and cytosine always pairs with guanine.
• Because of this pairing, it means that there are always equal amounts of adenine and thymine in a DNA molecule and equal amounts of cytosine and guanine.
• Two hydrogen bonds form between A and T, and three hydrogen bonds form between C and G.

Question 75

What is the structure of RNA?

Answer 75

RNA is made of nucleotides that contain a sugar, a phosphate group and one of four different bases.

Question 76

What are the four main ways in which the structure of RNA differs from the structure of DNA?

Answer 76

• The sugar in RNA nucleotides is a ribose sugar not a deoxyribose. It is still a pentose sugar though.
• Uracil (U), replaces thymine as a base and therefore always pairs with adenine in RNA.
• The nucleotides form a single polynucleotide strand not a double one.
• RNA strands are much shorter than most DNA polynucleotides.

Question 77

Why did many scientists doubt that DNA was able to carry the genetic code?

Answer 77

• Because it has a relatively simple chemical composition. It was argued that protein was the carrier as it was more chemically varied.

Question 78

What is semi-conservative replication of DNA?

Answer 78

• This is where DNA copies itself before cell division so that each new cell has a full amount of DNA.
• This method is called semi-conservative replication because half of the strands in each new DNA molecule are from the original DNA molecule.
• This means that there’s genetic continuity between generations of cells.

Question 79

What is the process of semi-conservative replication of DNA?

Answer 79

1. The enzyme DNA helicase breaks the hydrogen bonds between the bases of the two polynucleotide DNA strands. This makes the helix unwind to form two single strands.
2. Each original single strand acts as a template for a new strand, where free floating nucleotides are now able to pair with their complementary base as the original bases are exposed— A with T and C with G.
3. The DNA polymerase joins the nucleotides of the new strands together via a condensation reaction. Hydrogen bonds form between the bases on the original and new strands.
   Each new DNA molecule contains one strand from their original DNA molecule and one new strand.

Question 80

What is the action of DNA polymerase during DNA replication?

Answer 80

• Each end of a DNA strand is slightly different in structure. One end is called the 3’ (three prime) end and one end is called the 5’ (five prime) end.
• During DNA replication, the active site of DNA polymerase is only complementary to the 3’ end of the newly forming DNA strand— so the enzyme can only add nucleotides to the new strand at the 3’ end.
• This means that the new strand is made in a 5’ to 3’ direction as the DNA polymerase moves down the template strand in a 3’ to 5’ direction.
• The new strand is made in a 5’ to 3’ direction rather than an obvious 3’ to 5’ as the strands in the double helix are antiparallel— they run in opposite directions.

Question 81

What is the evidence that validated the semi-conservative replication theory created by Watson and Crick?

Answer 81

The Meselson and Stahl’s experiment validated the semi-conservative replication theory.
They both showed that DNA is replicated using the semi-conservative method. Their experiment used two isotopes of nitrogen— heavy nitrogen (15N) and light nitrogen (14N).

Question 82

Explain the Meselson and Stahl’s experiment.

Answer 82

1. Two samples of bacteria were grown for many generations— one in a nutrient broth containing light nitrogen, and one in a broth with heavy nitrogen. As the bacteria reproduced, they took up nitrogen from the broth to help make nucleotides for new DNA. So the nitrogen gradually became part of the bacteria’s DNA.
2. A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge. The DNA from the heavy nitrogen bacteria settled lower down the centrifuge tube than the DNA from the light nitrogen bacteria— because its heavier.
3. Then the bacteria grown in the heavy nitrogen broth were taken out and put in a broth containing only light nitrogen. The bacteria were left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge.
   • If replication was conservative, the original heavy DNA, which would still be together, would settle at the bottom and the new light DNA would settle at the top.
   • If replication was semi-conservative, the new bacterial DNA molecules would contain one strand of the old DNA containing heavy nitrogen and one strand of new DNA containing light nitrogen. So the DNA would settle out between where the light nitrogen DNA settled out and where the heavy nitrogen DNA settled out.
4. As it turned out, the DNA settled in the middle, showing that the DNA molecules contained a mixture of heavy and light nitrogen. The bacterial DNA has replicated semi-conservatively in the light nitrogen.
   • Once they had confirmed that DNA replication in bacteria was semi-conservative, other scientists carried out experiments to show that it was the universal method for DNA replication in all living things.

Question 83

Why is energy important? (ATP based)

Answer 83

Plants and animals need energy for biological processes to occur;
Plants need energy for things like active transport, DNA replication, cell division and protein synthesis.
Animals need energy for things like active transport, DNA replication, cell division and protein synthesis.

Question 84

What is ATP?

Answer 84

• ATP stands for adenosine triphosphate.
• ATP is made from the nucleotide base adenine, combined with a ribose sugar and three phosphate groups.
• It is known as a nucleotide derivative because it’s a modified form of a nucleotide.
• Once made, ATP diffuses to the part of the cell that needs energy. The energy in ATP is stored in high energy bonds between the phosphate groups.

Question 85

What occurs when energy is needed for a biological process? (ATP based)

Answer 85

• When energy is needed by a cell, ATP is broken down into ADP (adenosine diphosphate) and Pi (inorganic phosphate).
• This is a hydrolysis reaction— a phosphate bond is broken and energy is released.
• The reaction is catalysed by the enzyme ATP hydrolase.

Question 86

What happens to the products of ATP when it goes through its hydrolysis reaction?

Answer 86

ATP hydrolysis can be coupled to other energy-requiring reactions in the cell— this means the energy released can be used directly to make the coupled reaction happen, rather than being lost as heat.
The released inorganic phosphate can also be put to use— it can be added to another compound (known as phosphorylation), which often makes the compound more reactive.

Question 87

How is ATP made?

Answer 87

• By a condensation reaction between ADP and Pi. This happens during both respiration and photosynthesis, and is catalysed by the enzyme ATP synthase.

Question 88

What is the structure of water? (Include its polarity)

Answer 88

• A molecule of water is one atom of oxygen (O) joined to two atoms of hydrogen by shared electrons.
• Water is a polar molecule— it has a partial negative charge on one side and a partial positive charge on the other side.
• In the structure of a water molecule, because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge. The unshared negative electrons on the oxygen atom give it a slight negative charge.

Question 89

What is hydrogen bonding in the structure of water?

Answer 89

• Hydrogen bonds are weak bonds between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule.
• Hydrogen bonds form between water molecules because the slightly negatively charged oxygen atoms of water attract the slightly positively charged hydrogen atoms of other water molecules.
• This hydrogen bonding gives water some of its useful properties.

Question 90

What are the 5 properties of water?

Answer 90

• A metabolite
• Important solvent
• High latent heat of vaporisation
• High specific heat capacity
• Strong cohesion

Question 91

Explain water as ‘a metabolite’ within its properties.

Answer 91

• This is where water is involved in many metabolic reactions— a condensation or hydrolysis reaction.
• A hydrolysis reaction requires a molecule of water to break a bond.
• A condensation reaction releases a molecule of water as a new bond is formed.

Question 92

Explain water as an ‘important solvent’ within its properties.

Answer 92

• A solvent is a liquid that other substances can dissolve.
• The positive and negative changes of water attract other molecules causing them to separate from each other— dissolve.
• This means living organisms can take up useful substances dissolved in water and these dissolved substances can be transported around the organism’s body.

Question 93

Explain water having a ‘high latent heat of vaporisation’ within its properties.

Answer 93

• Latent heat is the heat energy that’s needed to change a substance from one state to another.
• Water vaporises when the hydrogen bonds holding water molecules together are broken. This allows the water molecules on the surface of the water to escape into the air as a gas.
• It takes up a lot of energy (heat) to break the hydrogen bonds between water molecules, so a lot of energy is used up when water evaporates. This results in water having a high latent heat of vaporisation— lots of heat is required to change it from a liquid to a gas.
• This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water. When water evaporates it carries away heat energy from a surface, which cools the surface and helps to lower the temperature, (when humans sweat to cool down).

Question 94

Explain water having a ‘high specific heat capacity’ within its properties.

Answer 94

• Hydrogen bonds give water a high specific heat capacity— the energy needed to raise the temp. of 1 gram of a substance by 1ºC.
• When water is heated, a lot of energy is used to break the hydrogen bonds between the water molecules. This means there is less energy available to actually increase the temp. of the water and therefore results in needing a lot of energy to eventually heat up water.
• This is useful for living organisms because it means that water doesn’t experience rapid temp. changes. This makes water a good habitat as the temp. under water is likely to be more stable than on land.

Question 95

Explain water having ‘strong cohesion’ within its properties.

Answer 95

• Cohesion is the attraction between molecules of the same type.
• Water molecules are very cohesive (they tend to stick together) because they are polar.
• Strong cohesion helps water to flow, making it great for transporting substances.
• Strong cohesion also means that water has a high surface tension when it comes into contact with air. This is the reason why sweat forms droplets, which evaporate for the he skin to cool down.

Question 96

What are inorganic ions?

Answer 96

• An inorganic ion is one which doesn’t contain carbon.
• There are inorganic ions in the cytoplasm of cells and in the body fluids of organisms.
• An ion’s role determines whether it is found in high or low conc.

Question 97

What is the role of ions in haemoglobin?

Answer 97

• Haemoglobin is a large protein that carries oxygen around the body, in the red blood cells.
• It’s made up of four different polypeptide chains, each with an iron ion (Fe2+) in the centre. This binds to the oxygen in haemoglobin.
• When oxygen is bound the Fe2+ ion temporarily becomes an Fe3+ ion, until oxygen is released.

Question 98

What is the role of hydrogen ions?

Answer 98

pH is calculated based on the conc. of hydrogen ions (H+) in the environment, therefore more H+ present, the lower the pH. Enzyme-controlled reactions are all affected by pH.

Question 99

What is the role of sodium ions?

Answer 99

• Glucose and amino acids need help to be able to cross cell membranes. A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions (Na+). This is known as co-transport.

Question 100

What is the role of phosphate ions?

Answer 100

• When a phosphate ion (PO4 3-) is attached to another molecule, its known as a phosphate group.
• DNA, RNA and ATP all contain phosphate groups.
• It’s the bonds between phosphate groups that store energy in ATP.
• The phosphate groups in DNA and RNA allow nucleotides to join up to form the polynucleotides.