C3: Biological molecules

Question 1

why do we need water

Answer 1

– is a solvent in which chemical reactions take place – is essential for photosynthesis
– keeps cells turgid or firm
– helps in the transport of mineral salts in plants
– regulates body temperature
– helps to transport dissolved substances around the body

Question 2

what are carbohydrates

Answer 2

organic molecules made up of elements: carbon, hydrogen, oxygen

• The ratio of hydrogen atoms to oxygen atoms in carbohydrates is 2:1.
  eg, glucose = C6H12O6
• The general formula for carbohydrates is CnH2mOm.

Question 3

name some single sugars/monosaccharides

Answer 3

glucose, fructose, galactose

Question 4

name some double sugars/disaccharides

Answer 4

maltose, sucrose, lactose

Question 5

what are single sugars

Answer 5

• Basic unit of carbohydrate
• Small enough to pass through cell membranes
• Common single sugars: glucose, fructose
  glucose - found in plants and animals
  fructose - common in plants but rare in animals

Question 6

what are double sugars

Answer 6

• Formed when two single sugars are joined together
• Common double sugars:
  – maltose (malt sugar)
  – sucrose (cane sugar)

Question 7

2 glucose sugars = ?

Answer 7

maltose

Question 8

how can you split maltose into 2 single sugar glucose molecules

Answer 8

mix the maltose with an enzyme

• as double sugars can be split into 2 single sugar molecules in the presence of an enzyme

Question 9

name some reducing sugars

Answer 9

every single and double sugar except for sucrose is accepted

Question 10

how can we test for reducing sugars

Answer 10

benedicts test

Question 11

what are complex carbohydrates

Answer 11

• Consist of many molecules of single sugar joined together
• Examples of complex carbohydrates made of many glucose
  molecules:
  – starch
  – cellulose
  – glycogen

Question 12

the structure, role and occurrence of:
starch
cellulose
glycogen

Answer 12

starch:
store of glucose
* structure: several thousand glucose molecules joined together.
* role: storage form of carbohydrates in plants.
* occurrence: storage organs of plants, e.g. potato tubers/tapioca.

cellulose:
* structure: Many glucose molecules joined together but bonded differently from starch.
* role: Cellulose cell walls protects plant cells. Serves as dietary fibes to prevent constipation.
* occurrence: Cell walls of plants.

glycogen:
store of glucose
* structure: Branched molecule of many glucose molecules.
* role: Storage form of carbohydrates in animals.
* occurrence: Stored in liver and muscles of mammals.

Question 13

what makes glycogen and starch suitable stores

Answer 13

• insoluble in water
• large molecules that cannot diffuse through cell membranes
• easily hydrolysed to glucose when needed
• made of molecules that have compact shapes, so they occupy lesser space

Question 14

how do we test for starch

Answer 14

by carrying out iodine test

Question 15

what are carbohydrates for/ functions

Answer 15

• to provide energy for cell activities
• to form supporting structures (e.g. cell wall)
• for conversion into other organic compounds (e.g. amino acids and fats)
• to form nucleic acids (e.g. DNA)
• to synthesise lubricants
• to synthesise nectar in flowers

Question 16

what are fats

Answer 16

• Fats are organic molecules made up of the elements:
  – carbon
  – hydrogen
  – oxygen
• Fats contain much less oxygen in proportion to hydrogen.
• The proportions of the elements in fats are not fixed (no general formula).

lean fat = no fat

Question 17

fat molecules are made up of…

Answer 17

glycerol and 3 fatty acid chains

Question 18

fat are broken down into…

Answer 18

fatty acids and glycerol

Question 19

what are the functions of fats

Answer 19

• Are a source and store of energy
• Act as an insulating material to prevent excessive heat loss
• Are a solvent for fat soluble vitamins and some hormones ( turn ppl orange)
• Form the main part of cell membranes
• Help reduce water loss from skin surface

Question 20

how can we test for fats

Answer 20

carrying out an ethanol elmusion test

Question 21

what are proteins

Answer 21

• Proteins are organic molecules made up of the elements:
  – carbon
  – hydrogen
  – oxygen
  – nitrogen
• Each protein molecule is made up of smaller basic units called amino acids.

Question 22

amino acids are the…

Answer 22

the building blocks of proteins

Question 23

amino acids are made up of…

Answer 23

– an amino group
– an acid group
– a side chain

Question 24

how are protein structure formed

Answer 24

• Amino acids are the building blocks of proteins.
• Peptide bonds link up amino acids to form a polypeptide.
• Two or more polypeptide chains fold to form a 3-D molecule, called protein.

Question 25

what are the functions of proteins

Answer 25

Proteins are needed for the synthesis of:
* new protoplasm (nucleus, cytoplasm, cell surface membrane) for growth and repair of worn-out cells
* enzymes and some hormones
* antibodies ( fight virus + bacteria)

Question 26

how can we test for proteins

Answer 26

carrying out a biuret test