Biological molecules - carbohydrates

Question 1

how are carbohydrates joined together?

Answer 1

with a glycosidic bond formed in a condensation reaction

Question 2

What are common monosaccharides?

Answer 2

glucose, galactose, fructose

Question 3

How many carbon atoms does glucose have?

Answer 3

six

Question 4

What is the difference between alpha and beta glucose?

Answer 4

same molecular structure but different displayed structures, OH above in beta and below in alpha

Question 5

what is the general formula for monosaccharides?

Answer 5

(CH2O)n

Question 6

What are the three examples of disaccharides?

Answer 6

maltose = α glucose + α glucose
sucrose = α glucose + fructose
lactose = α glucose + galactose

Question 7

What are three examples of polysaccharides?

Answer 7

glycogen, starch and cellulose

Question 8

How is glycogen adapted for use in animals?

Answer 8

-main energy storage
-it has a large number of side branches so energy can be released quickly as enzymes can act simultaneously on these branches
-also relatively large but compact
-insoluble so cannot diffuse out of cells

Question 9

how is starch adapted for use in plants?

Answer 9

-stores energy
-insoluble so cannot affect water potential
-compact so lots of energy can be stored in a small space
-when hydrolysed the released α glucose can be transported easily

Question 10

What is the role of cellulose in the cell wall?

Answer 10

-stopping the cell wall from bursting under osmotic pressure because it exerts inward pressure that stops the influx of water

Question 11

What are microfibrils in cellulose?

Answer 11

strong threads which are made of long cellulose chains running parallel to one another that are joined together by hydrogen bonds forming strong cross linkages

Question 12

What does Benedict’s solution test for?

Answer 12

the presence of reducing sugars

Question 13

what precipitate is produced in Benedict’s test?

Answer 13

red copper oxide is formed as the sugar donates an electron to the reagent (copper sulfate)

Question 14

How do you test for a non-reducing sugar?

Answer 14

-carry out normal benedict’s test, stays blue
- add dilute HCL and place in water bath, this hydrolyses into monosaccharides
-add sodium hydrogencarbonate to neutralise as benedict’s will not work in acidic conditions, use pH paper
-add benedict’s reagent again and heath should turn brick-red if reducing sugar is present