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OCR A-level Biology > Biological molecules 1 (Water and Carbohydrates) > Flashcards

Biological molecules 1 (Water and Carbohydrates) Flashcards

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1
Q

What percentage of water makes up a living cell?

A

80%

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2
Q

Roles of water

A
  1. biological solvent
  2. regulates temperature
  3. transport medium
  4. site of chemical reactions
  5. used in hydrolysis
  6. acts as a cooling mechanism (sweat evaporating)
  7. provides habitats
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3
Q

Properties of water

A
  1. polar molecule
  2. individual bonds provide stability
  3. high specific heat capacity
  4. hydrogen bonding
  5. ice is less dense than liquid water
  6. water is a good solvent (polar molecule)
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4
Q

Water is a polar molecule, what properties does this provide?

A
  1. makes it cohesive

2. a good solvent

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5
Q

Define Cohesive

A

the attraction between molecules of the same type of type meaning they sick together, this allows water to be a great transport mechanism

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6
Q

How does polarity allow water to be a good solvent?

A

The slightly positive end will be attracted to the negative ion and the slightly negative end will be attracted to the positive ion, allowing ions to dissolve as they become surrounded

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7
Q

Polar

A

A partial positive charge on one side and a partially negative charge on the other

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8
Q

Charge of oxygen molecule in water

A

slightly negative

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9
Q

Charge of hydrogen molecule in water

A

slightly positive

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10
Q

Define hydrogen bonding

A

primarily electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom

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11
Q

What properties does hydrogen bonding account for in water?

A
  1. High specific heat capacity

2. High latent heat of evaporation

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12
Q

Specific heat capacity

A

The energy needed to raise the temperature of 1g of substance by 1℃

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13
Q

Specific heat capacity of water

A

H bonds between molecules absorb at lot of energy therefore water takes a lot of energy to heat it up.

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14
Q

High latent heat of evaporation

A

It takes a lot of heat energy to break the H bonds in water, this is useful for organisms as it allows water to be a good cooling mechanism (e.g sweating)

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15
Q

Water is less dense when it freezes, describe the structure

A

Molecules are held further apart in ice because each molecule forms 4 H bonds to other molecules making a lattice structure. Less dense than L water allowing it to float

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16
Q

Elements in carbohydrates

A

Carbon, hydrogen and oxygen

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17
Q

In what three sugars do carbohydrates exist in?

A

Modnosaccarides, disaccaride and polysaccharides

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18
Q

How many carbon atoms in a polysaccharide?

A

8 or more

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19
Q

Glucose

A

An abundant monosaccharide, containing six carbon atoms (hexose sugar) and is highly soluble

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20
Q

Two structural isomers of glucose

A

Alpha and beta

21
Q

Alpha glucose

A

Hydrogen above the OH on C1

22
Q

Beta glucose

A

Hydrogen below the OH on C1

23
Q

Condensation reaction

A

A reaction between two monosaccharides to from a disaccharide, a hydrogen atom on one monosaccharide bonds to an OH group releasing a molecule of water

24
Q

Opposite of condensation reaction

A

Hydrolisis

25
Q

What bond is formed in alpha glucose following a condensation reaction?

A

1-4 glycosidic bond

26
Q

How does b-glucose join during a condensation reaction?

A

Every other one gets turn upside down in order to join chains

27
Q

Pentose sugars

A

Pentose monosaccharides contain 5 carbon atoms and are long enough to form a ring (e.g maltose, sucrose and lactose)

28
Q

Maltose

A

Formed from two glucose alpha 1-4 glycosidic bonds

29
Q

Sucrose

A

Formed from glucose + fructose and forms alpha 1-2 glycosidic bonds

30
Q

Lactose

A

Formed from galactose and glucose joined by a 1-4 glycosidic bond

31
Q

Define polysaccharide

A

Polymers containing many monosaccharides linked via glycosidic bonds and are formed via condensation reactions

32
Q

Examples of polysaccharides

A

Starch, cellulose and glycogen

33
Q

Glycosidic bond

A

A type of covalent bond that joins and carbohydrate to another molecule

34
Q

Starch

A
  1. Used for medium term storage in plants (NEVER ANIMALS)
  2. can be broken down to a-glucose
  3. found in seeds and tubers
  4. insoluble
  5. compact
35
Q

Molecular structure of starch

A

Made of both amylose and amylopectin

36
Q

Amylose

A

Made of condensations between alpha glucose, the are linked 1-4 , NO branches

37
Q

Amylopectin

A

Long chains of a-glucose, straight chains linked 1-4 and branches linked 1-6

38
Q

Glycogen

A
  1. Medium term storage for animals
  2. similar to starch, shorter chains and more branches
  3. more readily hydrolysed
  4. contains chains and branches
  5. insoluble
  6. does not diffuse out of cells (too big)
  7. a-glucose
39
Q

Why does glycogen have short chains and many branches?

A

Easier for enzymes to access ‘free ends’ on the branches

40
Q

Cellulose

A
  1. NOT storage provides structural purposes only
  2. made of b-glucose
  3. to form a straight chain each monomer rotates 180
  4. straight unbraced chains
  5. the H bonds alone are very weak but together create a stronger structure
  6. difficult to hydrolyse
41
Q

What does Benedict’s test for?

A

Reducing sugars

42
Q

Benedict’s test method

A
  1. Place sample in boiling tube
  2. add equal volume of Benedict’s reagent
  3. heat mixture gently in water bath for 5 minutes
43
Q

Benedict’s test result

A

Positive = Brick red precipitate, Negative = Blue copper ions remain

44
Q

Reducing sugar

A

any sugar that is capable of acting as a reducing agent all monosaccharides (glucose) and some disaccharides (maltose and lactose)

45
Q

Non-reducing sugar

A

For example sucrose

46
Q

Reagent test stops for non-reducing sugar

A
  1. add HCl (to hydrolyse the bond and break down to monosaccharides of sucrose) and heat in a water bath
  2. neutralise the solution with sodium hydrogen carbonate
  3. then carry out Benedict’s procedure and record observations
47
Q

Test strips for glucose

A

The test strips are coated in a reagent. They are dipped into a test solution and compared to a colour chart

48
Q

Iodine to test for stach

A

Add iodine dissolved in potassium iodide solution, if starch is present it will change form browny-orange to blue-black

OCR A-level Biology (2 decks)

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