1 The Cell Wall

Question 1

label plant cell

Answer 1

see book

Question 2

cell wall (3)

Answer 2

• gives plants strength and support
• made of insoluble cellulose
• usually freely permeable to everything that dissolves in water, does not act as a barrier

Question 3

suberin

Answer 3

a waterproof chemical that impregnates cellulose cell walls in cork tissues and makes them impermeable (reduces permeability of cell wall)

Question 4

lignin

Answer 4

a chemical that impregnates cellulose cell walls in wood and makes them impermeable (reduces permeability of cell wall)

Question 5

middle lamella (3)

Answer 5

• first layer
• is made when a plant cell divides into two new cells
• mostly made of pectin

Question 6

pectin (4)

Answer 6

• a polysaccharide that acts like glue and holds the cell walls of adjacent plant cells together
• has lots of negatively charged carboxyl groups that combine with positive calcium ions to make calcium pectate
• then calcium pectate binds to the cellulose on either side
• the cellulose microfibrils and the matrix build up on both sides of the middle lamella

Question 7

primary cell walls (2)

Answer 7

• the first very flexible plant cell walls to form, with all the cellulose microfibrils orientated in similar direction
• gives mostly shape, and some strength

Question 8

secondary cell wall (3)

Answer 8

• secondary thickening
• the cellulose microfibrils have built up at different angles to each other, making the cell wall more rigid and almost impossible to break
• function= gives strength

Question 9

Hemicelluloses (3)

Answer 9

• poysaccharides containing many different sugar monomers
• holds together the layers so they don’t slide against eachother
• makes even harder

Question 10

plant fibres

Answer 10

long cells with cellulose cell walls that have been heavily lignified so they are rigid and very strong

Question 11

cellulose (4)

Answer 11

• similar to starch and glycogen
• consists of long chains of b-glucose joined by 1.4 glycosidic bonds, where one of the monomer units has to be turned around so the bonding can take place
• cellulose is very strong because many hydrogen bonds are made
• cellulose molecules do not coil or spiral, they remain strong straight chains

Question 12

cross-linking (glucose) (2)

Answer 12

• because the hydroxyl groups stick out on both sides of the molecule (b-glucose), hydrogen bonds can be made between the partially positively charged hydrogen atoms of the hydroxyl groups and the partially negatively charged oxygen atoms in other areas of the glucose molecules
• holds neighboring chains firmly together

Question 13

draw b-glucose

Answer 13

see book

Question 14

compare and contrast cellulose with starch molecules (4)

Answer 14

• cellulose molecules do not coil or spiral and remain long, straight chains
• while starch molecules form compact globular molecules that are useful for storage
• cellulose made of b-glucose with only 1.4 glycosidic bonds
• while starch made up of a- glucose monomers with 1.4 and 1.6 glycosidic bonds

Question 15

formation of cellulose fibrils (2)

Answer 15

• in the cell wall groups of 10 000- 100 000 cellulose molecules form microfibrils
• these are deposited in layers which are held together by a matrix of hemicelluloses and other short-chain carbohydrates

Question 16

turgid (2)

Answer 16

• how cell is most of the time

- firm, swollen

Question 17

flaccid (2)

Answer 17

• when water is in short supply

- floppy, soft

Question 18

plasmodesmata (5)

Answer 18

• cytoplasm bridges between plant cells that allow communication between the cells
• produced as the cell divides (the two cells do not separate completely, threads of cytoplasm remain between them)
• these threads pass through gaps in the newly formed cell walls and signalling substances can pass from one cell to another through the cytoplasm
• cell walls are thinner in the region of the plasmodesmata
• secondary thickening (when hemicelluloses and lignin are deposited) does not take place in the areas around the plasmodesmata, leaving pits

Question 19

symplast (2)

Answer 19

• the interconnected cytoplasm of the cells

- all of the material (cytoplasm, vacuole, etc.) contained within the surface membrane of a plant cell

Question 20

pits (3)

Answer 20

• left because secondary thickening does not take place around plasmodesmata
• pits allow water to move between the xylem vessels
• important for maintaing a flow of water at even pressure through the plant

Question 21

name the monomer that makes up cellulose

Answer 21

beta-glucose

Question 22

how are the monomers in cellulose held together?

Answer 22

by glycosidic bonds in an unbranched chain

Question 23

where can calcium pectate be found?

Answer 23

middle lamella

Question 24

which properties can lignin give to cell walls in plants?

Answer 24

strength and waterproofing

Question 25

name a plant tissue that has lignin in its cell walls

Answer 25

xylem