plants Flashcards
Photosynthesis def
Process where light energy is absorbed by chlorophyll and converted into chemical energy
Chemical energy is use to synthesise glucose from water and carbon dioxide
Water and carbon dioxide are the raw materials for photosynthesis
Oxygen is released in the process
Enzymes are required for the process
Photosynthesis formula
Water + carbon dioxide – (chlorophyll and light energy)→ glucose + oxygen
6H20 + 6CO2 -> C6H12O6 + 6O2
uses of glucose (6)
1, Used immediately for cellular respiration to release energy for cellular activities or for formation of cellulose cell wall
2, At day, ROP is highest so glucose is formed faster than it can be used
Excess glucose is converted into starch
3, At night, P does not occur so starch is converted back into glucose by enzymes
4, Combines with nitrates and mineral salts to form aa
- aa converted into protein for new protoplasm of leaf
- aa transported to other parts of the plant for synthesis of new protoplasm, storage as proteins
5, Converted to sucrose
Transported to storage organs e.g. seeds
Maybe converted into starch
starch maybe converted back to glucose
6, Converted into fats
Storage
Cellular respiration
synthesis of new protoplasm
Intake of CO2 by plants:
During photosynthesis, CO2 is rapidly used up
Concentration of CO2 in intercellular air spaces of leaf is lower than that of the atmosphere
Concentration gradient forms
CO2 molecules diffuse from atmosphere into the intercellular air spaces down the concentration gradient via stomata
CO2 dissolves in the thin film of moisture on surface of mesophyll cells
Dissolved CO2 diffuses into the mesophyll cells
Intake of water by plants:
Xylem transports water molecules and dissolved mineral salt ions from roots to leaf
Once out of veins, water molecules move from cell to cell through the mesophyll of leaf
Transpiration def
loss of water through aerial parts of plant, mostly the stomata of leaf
how water enters then leaves the leaf
Water molecules are transported to leaf via xylem by transpiration pull
Water molecules move into deeper inner cells via osmosis
Water molecules move into the mesophyll cells via osmosis
Water molecules move out of mesophyll cells to form a thin layer of moisture on surface of mesophyll cells
WP of mesophyll cells are lower than that of neighbouring cells
More water molcules are removed from the xylem vessels
Water evaporates from thin film of moisture and moves into intercellular airspaces
Wate vapour accumulates in large air spaces near stomata
Water vapour diffuses through the stomata into atmosphere through transpiration
phloem func and adaptation
translocation is the trasnport of manufactured food such as aa and sucrose by phloem from leaves to other parts of the plant for growth,repair or stirage
Minute pores are present in the sieve plate, allowing for rapid translocation of manufactured food such as sucrose and aa from leaves to ogther parts of plant via sieve tubes
Companion cells contains numerous mitochondria that carry out increased rate of respiration to release more energy for loading sugars from mesophyll cells into the sieve tubes by AT
xylem func and adaptation
Transport of water and dissolved mineral salt ions from roots to stem and leaves
Provides mechanical support for plants
Cell walls of xylem is strengthened with lignin by providing mechnical support to prevent the collapse of vessel
Long, continuous hollow lumenwith no cross wall and protoplasm, reduce resistance to transport of water and mineral salts from roots to stem and leaves at a faster rate
adaptation of RHC
Long and narrow to increase surface area to volume ratio of RHC so that rate of absorption of water molecules and dissolved mineral ions is faster
Contains many mitochondria so that aerobic respiration in mitochondria releases energy for the AT of ions into cell
CSM prevents thecell sap from leaking out. The cell sap contains sugars, amino acids and salts. It has a lower WP than soil solution. Water molecules enter the RHC via osmosis
how water enters roots then xylem
WP of cell sap of RHC is lower than WP of soil solution
Water molecules enter the RHC via osmosis through a PPM
WP of cell sap next inner cells is lower than that of RHC
Water molecules enter inner cells from RHC via osmosis across a PPM
Cell to cell osmosis continues until water molecules reached and enters xylem vessel
guard cells in the day
In day, chloorplasts in guard cells absorb light energy and undergo photosynthesis to produce glucose
WP of cell sap of guard cells is lower than WP of cell sap of neighboruing cells
Water molecules enter the guard cells via osmosis through PPM
Guard cells swell and increase in size
Uneven thickening of walls of guard cells causes the thinner wall opposite the stomata to expand more than thicker wall around the stomata
Wall curves and pulls the stomata open
guards cells at night
No light energy absorbed by chloroplasts of guard cells so no photosynthesis occurs and no glucose is produced
WP of cell sap of guard cells is hugher than that of neighboruing cells’ cell sap
Water molecules enter neighbouring cells via osmosis across a PPM
The guard cell becomes flaccid and decreases in size
Stoma closes
factors affecting ROP
- conc of c02
- light intensity
- temp
Thin and broad lamina -
lets CO2 diffuse rapidly into inner cells + to let maximum light energy to be absorbed by cloroplasts in leaf + let all light energy reach mesophyll cells
Waxy cuticle layer on upper and lower epidermis -
reduce water loss (max retention of water for photosynthesis) because it is impermeable to water + transparent to let light reach all mesophyll cells