Polysaccharides and plant organelle

Question 1

Why are polysaccharides insoluble?

Answer 1

They are a large molecule and unable to split water molecules therefore exert no osmotic force

Question 2

What are the properties of starch?

Answer 2

Made of alpha glucose
Plant cell- acts energy store
20% amylose (1,4 bonds)
80% amylopectin- more branched therefore more compact and can be broken down more quickly (1,4 and 1,6 bonds)

Question 3

What are the properties of glycogen?

Answer 3

In animal cells and fungi
Found in the liver and skeletal muscle
Lots of mitochondria ->glycogen ->glucose (respiration)
similar to amylopectin – short chains (1,6 bonds)
Can be broken down quicker

Question 4

What are the properties of Cellulose?

Answer 4

Made of beta glucose
180° to neighbour
1,4 bonds 
Cellulose ->microfibrils ->fibres
Microfibril make up matrix (crisscrossed) 
Layers held by weak hydrogen bonds
Plant cell wall made up of 50% Celulose

Question 5

What is the plant cell wall made up of and what are its properties?

Answer 5

50% Celulose
Fully permeable = prevents bursting
Does not stretch = provides support

Question 6

What is a palisades cell?

Answer 6

Long thin and cylindrical that are tightly packed
Forms a continuous layer to absorb sunlight
Lots of chloroplasts that move to the side where the sunlight is entering
Large vacuole = pushes chloroplasts to the edge of the cell

Question 7

What is the cell wall?

Answer 7

Made mostly of Cellulose(also lignin = impermeable)
Give strength and rigidity
Allows water through plasmodesmata

Question 8

What is plasmodesmata?

Answer 8

Channels which connects cytoplasm of adjacent cells

Question 9

What is a vacuole?

Answer 9

contains cell sap = sugar, amino acids, minerals
Helps keep so rigid and turgid

Membrane bound sacs=tonoplast

Question 10

What is the xylem?

Answer 10

Transports water

Cells die and they are broken down, lignin thickens and forms a continuous tube

Question 11

What are chloroplasts?

Answer 11

Grana-stacks of 100 thylakoids (membrane disks)
Linked by intergranal lamellae
Double membrane
Contains a fluid matrix called stroma=starch grain, ribosome and circular DNA (2nd stage Photosynthesis)

Question 12

What’s the difference between alpha glucose and beta glucose?

Answer 12

Same molecular formula but different structural formula

Beta glucose is joined at 180°= Pleat/fibre

Question 13

Gas exchange of insects

Answer 13

Needs of the reducing water loss and exchanging gases conflict
Waterproof coverings
Small SA:V

Oxygen diffuses into the trachea along the diffusion gradient (spiracles open and closed via valves)
Lower towards the end of the tracheoles due to respiration
Movement of muscles speed up gas exchange

Question 14

How does transpiration work?

Answer 14

Water evaporates from leaves via transpiration
Water molecules form hydrogen bonds hence stick together
Water forms a continuous stream of xylem = cohesion
Passive process requires no energy required

Question 15

What is cohesion tension

Answer 15

Transpiration pull puts xylem under pressure
Negative pressure
Greater in day (stem narrower)
Weaker at night (stem wider) 
Passive process (no energy required)

Question 16

Why does water movement occur through symplastic pathway

Answer 16

-Mesophyll cells lose water to air spaces
-these cells now have a lower water potential of the water enters via osmosis from neighbouring cells
-Water is lost from the cells (lower WP)
-Process continues
WP- pulls water up xylem (across lead mesophyll)

Question 17

What is the Symplastic pathway

Answer 17

Water crosses cell-surface membrane via osmosis into cytoplasm through the plasmodesmata

Problematic as it crosses cell membrane

Question 18

What is the apoplastic pathway

Answer 18

Most water passes along the cell walls and intercellular Spaces
Path of least resistance

Question 19

What is the vacular pathway

Answer 19

Water enters root hair vacuole via osmosis
Move from vacuole to vacuole
Most problematic because a high number of membranes crossed

Question 20

What is the role of the casparin (waxy) strip

Answer 20

Controls water/mineral movement
Stop viruses
Contains a ring of suberin (waterproof material) that forces movement through the cell membrane

Question 21

Why are stomata located on the underside of a leaf

Answer 21

Water vapour accumulates
Water potential gradient reduced
Reduces osmosis

Question 22

How does water enter the xylem from the endodermis in the root

Answer 22

The casparian strip blocks the Apoplastic pathway
Active transport of ions into the xylem by the endodermis
Lower WP in xylem so water moves in via osmosis
(Down the WP gradient)

Question 23

How does water transported to the leaves

Answer 23

Transpiration from leaves (evaporation of water)
Creates cohesion tension (negative pressure)
Water molecules bind to xylem
creates a continuous column of water