Starch and cellulose

Question 1

Describe the function of starch

Answer 1

1) Cells get energy from glucose. Plants store excess glucose as starch, so when a plant needs more glucose for energy it breaks down starch to release the glucose
2)

Question 2

Describe the structure of starch

Answer 2

1)Starch is made if two polysaccharides of alpha-glucose - amylose and amylopectin

2)
-Amylose - a long unbranched chain of alpha glucose with 1,4 glycosidic bonds. The angles of the glyocidc bonds give it a coiled structure. This makes it compact so its really good for storage - can fit more in to a small space.
-Amylopectin - a long, unbranched chain of alpha glucose, with 1,4 and 1,6 glycocidic bonds. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bond easily. This means that the glucose can be realised quickly

3)Starch is insoluble in water, so it doesn’t cause water to enter cells by osmosis. This makes it good for storage

Question 3

Describe the structure of cellulose

Answer 3

1) Cellulose is made of long, unbranched chains of Beta-glucose, joined by 1-4 glycosidic bonds
2) The glyocidic bonds are straight, so the cellulose chains are straight
3) Between 50 and 80 cellulose chains are linked together by a large number of hydrogen bonds to form strong threads called microfibrils. The strong threads mean cellos provides structural support for cells

Question 4

Explain the arrangement of cellos microfibrils in the cell wall

Answer 4

-The cell wall contains cellulose microfibrils in a net-like arrangement
-The strength of the microfibrils and their arrangement in the cell wall gives plant fibres strength

Question 5

Explain what is secondary thickening of cells walls

Answer 5

1) When some structural plant cells(like sclerenchyma and xylem) have finished growing. They produce a secondary cell wall between the normal cell wall and usually has more of a woody substance called lignin
2)The secondary cell wall is thicker than the normal cell wall and usually has more of a woody substance called lignin
3) The growth of a secondary cell wall is called secondary thickening
4) Secondary thickening makes plant fibres even stronger

Question 6

Difference between starch and cellulose

Answer 6

Starch:
-Has Alpha glucose
-Branched chain
-No hydrogen bond between the chains

Cellulose:
-Has Beta glucose
-Straight chain
-Hydrogen bonds between the chains

Question 7

Describe the structure of a cellulose cell wall

Answer 7

-It is a polymer chain made from beta glucose
-Cellulose molecules are held together by hydrogen bonds
-Has an arrangement of microfibrils in a net like pattern

Question 8

Describe the structure of a cellulose microfibril.

Answer 8

-Cellulose contain beta-glucose
-The glucose molecules are joined by condensation reactions
-There are only 1,4 glycosidic bonds between monomers
-It has an unbranched straight chain
-The microfibril is in a net-like arrangement
-Cellulose chains held together by hydrogen bonds

Question 9

Explain why starch must be broken down before it can be used by the cells of the gro plant.

Answer 9

-So that is can be broken down into glucose
-Which is soluble and used in respiration

Question 10

Describe the arrangement of glucose monomers in a cellulose molecule.

Answer 10

-Monomers are connected by 1,4 glycosidic bond
-Alternative monomers are converted

Question 11

Suggest how lignin adds strength to xylem tissue

Answer 11

-Lignin holds the microfibrils together
-Lignin keep the microfibrils parallel