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AS Level Biology Unit 1 > 1.1 chemical elements are joined together to form biological compounds > Flashcards

1.1 chemical elements are joined together to form biological compounds Flashcards

1
Q

Name the four key inorganic ions
in living organisms.

A

● Magnesium ions (Mg2+)
● Iron ions (Fe2+)
● Calcium ions (Ca2+)
● Phosphate ions (PO4 3-)

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2
Q

What is the role of Mg2+ in plants?

A

Mg2+ is used to produce chlorophyll

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3
Q

What is the role of Fe2+ in animals?

A

Fe2+ is found in haemoglobin and is
involved in the transport of oxygen.

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4
Q

What is the role of PO4 3- in living
organisms?

A

PO4 3- is used to produce ADP and ATP.

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5
Q

What is the role of Ca2+ in living
organisms?

A

Ca2+ is used to strengthen tissues such
as bones and teeth in animals and cell
walls in plants.

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6
Q

Why is water a polar molecule?

A

O is more electronegative than H. O attracts
the electron density in the covalent bond
more strongly, forming δ- O and δ+ H.

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7
Q

Describe hydrogen bonding between
water molecules

A

Weak intermolecular forces of attraction
form between a lone pair on a δ- O and a
δ+ H on an adjacent molecule.

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8
Q

What is a metabolite

A

A molecule formed or used in metabolic
reactions.

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9
Q

Describe the role of water as a
metabolite

A

Water is a reactant in photosynthesis
and hydrolysis reactions. Water is a
product in aerobic respiration and
condensation reactions.

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10
Q

Why is water’s high specific heat capacity important for organisms?

A

Water acts as a temperature buffer, enabling
endotherms to resist fluctuations in core
temperature and to maintain optimum enzyme activity.

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11
Q

Why is water’s high latent heat of vaporisation important for organisms?

A

When water evaporates, it has a cooling effect.
This is important in homeostasis

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12
Q

Why is water an important solvent for organisms?

A

Water is a polar universal solvent. It enables
chemical reactions to take place within cells,
the transport of materials in the plasma and
the removal of metabolic waste.

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13
Q

Why does water have a high surface tension?

A

Due to the ordered arrangement and
cohesion of molecules at the surface of
water.

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14
Q

Why is the high surface tension of water
important for organisms?

A

● Enables the transport of water and nutrients through plants stems and small blood vessels in the body
● Allows small insects to ‘walk’ on water

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15
Q

What is a monosaccharide?

A

single sugar

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16
Q

Give some examples of monosaccharides.

A

● Glyceraldehyde
● Ribose
● Deoxyribose
● α- and β- glucose
● Fructose
● Galactose

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17
Q

What is the name of the bond formed
when two monosaccharides react?

A

glycosidic

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18
Q

What is a disaccharide?

A

Molecule formed by the condensation of two
monosaccharides, forming a glycosidic bond

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19
Q

Give some examples of disaccharides and their monosaccharide constituents.

A

Sucrose (Glucose-Fructose)
Maltose (α-Glucose-α-Glucose)
Lactose (Glucose-Galactose)

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20
Q

What is a polysaccharide?

A

A polymer of monosaccharides, formed
by many condensation reactions

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21
Q

Give some examples of polysaccharides.

A

● Starch
● Glycogen
● Cellulose
● Chitin

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22
Q

What is the function of starch?

A

energy storage in plants

23
Q

Describe the structure of starch

A

● Polymer of α-glucose monomers
● Two forms: amylose and amylopectin
● Amylose: α-1,4-glycosidic bonds, unbranched
● Amylopectin: α-1,4- and α-1,6-glycosidic bonds, branched

24
Q

What is the function of glycogen?

A

Energy storage in animals.

25
Q

How does the structure of glycogen relate to its function?

A

It is highly branched enabling the rapid
hydrolysis of glucose molecules

26
Q

Describe the structure and function of cellulose.

A

● Linear polysaccharide that is the main component of the cell wall in plants
● Consists of many β-glucose molecules joined by β-1,4-glycosidic bonds
● Alternate glucose molecules rotated 180° allowing hydrogen bonds between parallel chains, forming myofibrils

27
Q

Describe the structure and function of chitin.

A

● Linear polysaccharide found in the exoskeletons of insects and
crustaceans as well as fungal cell walls
● Consists of many β-glucose molecules (with amino acid side chains)
joined by β-1,4-glycosidic bonds
● Alternate glucose molecules rotated 180° allowing hydrogen bonds
between parallel chains, forming myofibrils

28
Q

Explain how a triglyceride is formed.

A

One molecule of glycerol forms ester bonds
with three fatty acids via condensation
reactions.

29
Q

Relate the structure of triglycerides to their functions.

A

● High energy-to-mass ratio - energy storage, high calorific value from oxidation
● Insoluble hydrocarbon chain - no effect on water potential of cells, used for waterproofing
● Slow conductor of heat - thermal insulation, e.g. adipose tissue
● Less dense than water - buoyancy of aquatic animals

30
Q

What is a phospholipid?

A

A type of lipid formed by the condensation of
one molecule of glycerol, two molecules of fatty acid and a phosphate group

31
Q

Relate the structure of phospholipids to their
functions.

A

Glycerol backbone attached to two hydrophobic fatty acid tails and one hydrophilic polar phosphate head:
● Forms phospholipid bilayer in water - component of cell membranes
● Tails splay outwards - waterproofing, e.g. skin

32
Q

What is the difference between saturated and unsaturated fats

A

● Saturated fats have no C=C bonds, and are solid at room temperature due to strong intermolecular forces
● Unsaturated fats have one or more C=C bonds, and are liquid at room temperature due to weak intermolecular forces

33
Q

Differentiate between monounsaturated and
polyunsaturated fatty acids

A

● Monounsaturated fatty acids contain one
C=C bond
● Polyunsaturated fatty acids contain more than one C=C bond

34
Q

What is meant by a low density lipoprotein (LDL)?

A

● Combination of triglycerides from saturated fats and protein
● Blocks receptor sites, reducing cholesterol
absorption
● Known as ‘bad’ lipoproteins

35
Q

How do LDLs contribute to the risk of
cardiovascular disease?

A

The high blood cholesterol level caused
by LDLs leads to formation of
atherosclerosis plaques

36
Q

Describe the general structure of an
amino acid.

A

● Amine group (-NH2)
● Variable side chain (R)
● Carboxyl group (-COOH)
● H atom

37
Q

How are polypeptides formed?

A

Many amino acid monomers join together
in condensation reactions, forming
peptide bonds (-CONH-).

38
Q

What is the primary structure of a protein?

A

The individual sequence of amino acids
in a protein

39
Q

Describe the secondary structure of a protein.

A

The local interactions of the amino acids in
the polypeptide chain resulting in α-helices or
β-pleated sheets. Hydrogen bonds hold the
arrangements in place.

40
Q

Describe the tertiary structure of a protein.

A

The folding of a protein to make a three-dimensional structure. Held in place by various interactions and bonds:
● Disulfide bonds
● Ionic bonds
● Hydrogen bonds
● Hydrophobic interactions

41
Q

Describe the quaternary structure of a protein.

A

● Interactions of more than one polypeptide chain
● May involve addition of prosthetic groups, e.g. metal ions or phosphate groups

42
Q

Describe the quaternary structure of a protein.

A

● Interactions of more than one polypeptide chain
● May involve addition of prosthetic groups, e.g. metal ions or phosphate groups

43
Q

Describe how the structure of fibrous proteins relates to their function.

A

● Long polypeptide chains, folded in parallel
● Little tertiary/quaternary structure aside from cross-linkages for strength
● This makes them insoluble and good for structural roles

44
Q

Describe how the structure of globular proteins relates to their function.

A

● Spherical, compact, highly folded with complex tertiary/quaternary structures
● Hydrophilic R groups face outwards and hydrophobic R groups face inwards ∴ water-soluble
● Metabolic roles, e.g. enzymes

45
Q

What is the difference between a reducing and non-reducing sugar?

A

● A reducing sugar has a free aldehyde or ketone functional group so can act as a reducing agent
● A non-reducing sugar does not have a free aldehyde or ketone functional group so it cannot act as a reducing agent

46
Q

Describe the Benedict’s test for reducing sugars.

A
  1. Add an equal volume of the sample being tested and Benedict’s reagent
  2. Heat the mixture in an electric water bath at 100°C for 5 minutes
  3. Observe the colour of the precipitate formed
47
Q

Describe the positive result for reducing sugars.

A

Colour change from green to yellow to
orange to brown to brick red depending on
the quantity of reducing sugar present

48
Q

Describe the Benedict’s test for non-reducing
sugars

A
  1. Negative test for reducing sugar
  2. Hydrolyse non-reducing sugars with an equal volume of dilute HCl
  3. Heat in a boiling water bath for 5 minutes
  4. Add NaHCO3 to neutralise the acid
  5. Re-test resulting solution with Benedict’s reagent
  6. Observe the colour of the precipitate formed
49
Q

Describe the positive result for non-reducing sugars

A

Colour change from green to yellow to
orange to brown to brick red depending on
the quantity of non-reducing sugar present.

50
Q

Name the food test used to identify proteins.

A

biuret test

51
Q

Describe the Biuret test.

A
  1. Add an equal volume of the sample to be tested and NaOH
  2. Add a few drops of dilute copper (II) sulfate solution
  3. Mix gently and record any observations
52
Q

Describe the positive result of a
biuret test.

A

Colour change from pale blue to purple

53
Q

Describe the iodine-potassium iodide
test for starch

A

● Add iodine-KI solution
● Colour change from orange to
blue-black in the presence of starch

54
Q

Describe the emulsion test for fats and oils.

A

● Add ethanol to the sample and shake
● Allow the mixture to settle
● Add an equal volume of water
● Record any observations

AS Level Biology Unit 1 (10 decks)

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