biological molecules

Question 1

what elements make up carbohydrates?

Answer 1

carbon, hydrogen, oxygen

Question 2

what are single sugars

Answer 2

basic unit of a carbohydrate that can pass through the cell surface membrane and be absorbed into cells

Question 3

common examples of single sugars

Answer 3

glucose and fructose

Question 4

what are double sugars and some examples?

Answer 4

two single sugars joined tgt, egs are maltose (glucose+glucose) and sucrose (glucose+fructose)

Question 5

functions of carbohydrates

Answer 5

1. act as a substrate for aerobic respiration to release energy for cellular activities
2. form nucleic acid (eg. DNA)
3. synthesis nectar in some plants
4. synthesis lubricants (eg. mucus)
5. to be converted to other organic products (eg. Amino acids)
6. provide supporting structures (eg. cellulose cell wall)

Question 5

how to test for reducing sugars ?

Answer 5

Benedicts test

1. add in 2 cm^3 of the food sample to 2cm^3 of Benedicts solution into a test tube
2. shake the mixture thoroughly and put the test tube in a boiling water bath for 2-3 minutes
3. observe the colour change

Question 6

benedict’s test colour changes?

Answer 6

1. solution remains blue —> no reducing sugars
2. Benedicts solution forms a green precipitate—> trace amounts of reducing sugars
3. benedict’s solution forms a yellow or orange precipitate —> moderate amount of reducing sugars
4. Benedicts solution forms a brick red precipitate—> high amounts of reducing sugars

Question 6

how to test for starch

Answer 6

iodine test

• positive result: iodine solution turns from brown to blue-black
• negative result: iodine solution remains brown

Question 7

why are glycogen and starch suitable stores of carbohydrates in mammals and plants

Answer 7

1. they are insoluble in water, so they wont change the water potential of the cells
2. they are too large to pass through the cell surface membrane, so they wont get lost outside of the cell
3. they can easily be broken down into glucose molecules when needed
4. they are compact and take up less space than individual glucose molecules

Question 8

what elements are present in fats?

Answer 8

carbon, hydrogen and oxygen

Question 9

functions of fats

Answer 9

1. source for long-term storage and energy
2. insulating material that prevents excessive heat loss (eg. blubber —> doesn’t really apply to humans)
3. act as a solvent for fat-soluble minerals or hormones
4. essential part of cells, specifically the cell surface membrane
5. prevents excessive water loss through the skin. eg, the skin glands secrete an oily-substance to prevent water loss through evaporation

Question 10

test for fats

Answer 10

ethanol emulsion test

1. add 2 cm^3 of ethanol to 2cm^3 of a liquid food sample. mix the solution well
2. add 2cm^3 of water and mix the solution thoroughly
3. positive test: a white emulsion is formed

for solid food samples: crush the food sample into smaller pieces and decant the ethanol before adding in the water

Question 11

what elements make up proteins?

Answer 11

carbon, nitrogen, hydrogen, oxygen

Question 12

functions of proteins

Answer 12

1. synthesis of new cytoplasm for growth and repair of worn-out body cells
2. synthesis of enzymes and some hormones
3. formation of antibodies to combat diseases