Polysaccharides and plant organelle Flashcards
Why are polysaccharides insoluble?
They are a large molecule and unable to split water molecules therefore exert no osmotic force
What are the properties of starch?
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)
What are the properties of glycogen?
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
What are the properties of Cellulose?
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
What is the plant cell wall made up of and what are its properties?
50% Celulose
Fully permeable = prevents bursting
Does not stretch = provides support
What is a palisades cell?
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
What is the cell wall?
Made mostly of Cellulose(also lignin = impermeable)
Give strength and rigidity
Allows water through plasmodesmata
What is plasmodesmata?
Channels which connects cytoplasm of adjacent cells
What is a vacuole?
contains cell sap = sugar, amino acids, minerals
Helps keep so rigid and turgid
Membrane bound sacs=tonoplast
What is the xylem?
Transports water
Cells die and they are broken down, lignin thickens and forms a continuous tube
What are chloroplasts?
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)
What’s the difference between alpha glucose and beta glucose?
Same molecular formula but different structural formula
Beta glucose is joined at 180°= Pleat/fibre
Gas exchange of insects
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
How does transpiration work?
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
What is cohesion tension
Transpiration pull puts xylem under pressure Negative pressure Greater in day (stem narrower) Weaker at night (stem wider) Passive process (no energy required)
Why does water movement occur through symplastic pathway
-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)
What is the Symplastic pathway
Water crosses cell-surface membrane via osmosis into cytoplasm through the plasmodesmata
Problematic as it crosses cell membrane
What is the apoplastic pathway
Most water passes along the cell walls and intercellular Spaces
Path of least resistance
What is the vacular pathway
Water enters root hair vacuole via osmosis
Move from vacuole to vacuole
Most problematic because a high number of membranes crossed
What is the role of the casparin (waxy) strip
Controls water/mineral movement
Stop viruses
Contains a ring of suberin (waterproof material) that forces movement through the cell membrane
Why are stomata located on the underside of a leaf
Water vapour accumulates
Water potential gradient reduced
Reduces osmosis
How does water enter the xylem from the endodermis in the root
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)
How does water transported to the leaves
Transpiration from leaves (evaporation of water)
Creates cohesion tension (negative pressure)
Water molecules bind to xylem
creates a continuous column of water
