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
Stomata in epidermal layers
opens in sunlight to allow diffusion of gases in and out of leaf
Chloroplasts in mesophyll and guard cells -
chlorophyll absorbs light energy and converts it into chemical energy to be used in the formation of sugar
More chloroplasts in upper palisade mesophyll
- more light energy can be absorbed near leaf surface
- the palisade layers are tightly packed tgt to further increase nunber of photosynthetic cells available
Interconnecting air spaces in spongy mesophyll
- allow rapid diffusion of CO2 and O2 into and out of mesophyll cells
Presence of petiole -
holds leaf in position that allows leaf to absorb max light energy
Spongy mesophyll (3)
numerous large intercellular air spaces so that cells are spaced far apart and gases can diffuse into and out of mesophyll cells at a faster rate easily
Cells covered in thin film of moisture for gases to dissolve in so that the dissolved gases can diffuse into mesophyll cells at a faster rate easily
Contains chlororplasts for photosynthesis
go see drawing of xylema nd phloem in tb 174
yay
pith, cambium, cortex, epidermis
see tb 176
removal of phloem
prevnst the translocation of sugars
accumulates around the ring
lower water potential of that area
water molecules enter that area via osmosis across PPM
swelling
translocation studies: why do we anaesthetise the aphid
to allow us to cut off the proboscis during feeding and to ensure that it remians in the phloem sieve tube
ight dependent and independent stages of photosynthesis
Light-dependent stage: light energy is absorbed by chlorophyll and is converted into chemical energy. Water molecules are split into hydrogen and oxygen atoms. Oxygen produced is released as a by product
Light-independent stage: enzymes use the hydrogen atoms and chemical energy from the previous stage to convert carbon dioxide into glucose
Root pressure:
- cells around XV continuously pump ions into XV via AT
- WP of XV is lower than cell sap of surrounding cells
- water molecules enter the XVvia osmosis through PPM membrane
- flow upwards
- root pressure
capillary action
- the narrower the tube, thehigher level of moevment of water molecules
- adhesion to cell wall of xylem
- water moelcukes have cohesion between each other because of hydrogen bonding
Potometer
Measures rate of absorption of water by plant\
Purpose of air bubble: to determine rat of mvt of air bubble that indicates volume of water taken up by shoot
As shoot transpires, water is absorbed.
Rate of movement of water column = rate of absorption
Rate of absorption = rate of transpiration
precautions when using potometer
Cut shoot undertwater
Keep leaves dry
Set up apparatus comepletly underwater
Keep all joints air tight to prevent entry of air into potometer tube that will hindwr the movement of air bubble + ensure wate does not evaporate from joints
Importance of transpiration:
- Bring about transpiration pull to pull water and mineral salts from roots to all parts of the plant
- Transpiration cools the plant as evaporation of water helps to remove latent heat
- When stomata are open during transpiration, gaseous exchange occurs
- Turgidity is maintained as water that is lost in the aerial portions of the plant is replaced. Turgid cells keep the leaves spread out widely to absorb sunlight for photosynthesis
Wilting advantages:
When leaf folds up, surface area exposed to sunlight reduced.
Guard cells become flaccid and stomata closes, preventing excessive water loss
Reduces rate of transpiration
wilting disadvantages
Stomata close, decreasing intake of CO2 and rate of photosynthesis decreases.
Leaves droop and hence decrease absorption of sunlight, hence rate of photosynthesis decreases.
Water becomes a limiting factor and hence, rate of photosynthesis decreases.
Light intensity and ROT
Presence of light: sotmata opens, increased rate of transpiration
Absence of light: stomata closes, decreased rate fo transpiration
Humidity of air and ROT
High humidity in air
Contains alot of water vapour
concentration fo water vapour in atm increases
Less steep concentration gradient of water vapour btwn ICAS and atm
ROD of water vapour from ICAS to atm decreases
rate of transpiration decreases
High air movement and ROT
Water vapour is swept away from leaves as it diffuses out of the stomata
lower concentration of water vapour in atm
more steep concentration gradient of water vapour btwn ICAS and atm
ROD of water vapour from ICAS to atm increases
ROT increases
Temperature and ROT
High temp
Rate of evaporation increases
Rate of transpiration increases
Adaptive features of plants to reduce water loss
(5)
1.Sunken stomata
Traps water vapour outside stomata
Reduces steepness of concentration gradient between ICAS and atm
Reduces ROD pf water vapour out of leaf
2. Presence of hairs
Traps moistyure
Increases humidity
Reduc eair mvt
Reduce water vapour concentration gradient between ICAS and atm
Reduc eROD of water vapour out of leaf
3. Thick waxy cuticle
Prevent excessive loss of water vapour from plants
4. Leaf is rolled
Provide a humid environment
Reduce steepness of concnetraion graidnetof water vapour between ICAS and atm
Reduce ROD of water vapoyr out of leaf
5. No stomata on outer layer
Reduces evaporation
Reduce ROD of water vapour out of ICAS into atm
Reduce ROT
Reduce water loss
ICAS purpose
chamber containing air to increase leaf buiyancy to allow it to float on the surface of water
