chp 7: Nutrition in Plants [pure bio OLVL]

define photosynthesis

process whereby light energy is absorbed by chlorophyll & transformed into chemical energy used in the synthesis of carbohydrates from water & carbon dioxide

process of photosynthesis

1) light energy absorbed by chlorophyll
2) energy is transformed into chemical energy
3) energy is used to synthesize carbohydrates (glucose) from water & carbon dioxide. O2 is released

word equation of photosynthesis

Carbon Dioxide + Water --Light and chlorophyll--> Glucose + Oxygen

evidence for photosynthesis

glucose is the food compound produced
can be identified by iodine test
starch formation occurs in roots (not photosynthesis)

how to prepare a leaf for starch test

1) place in boiling water (kill leaf/denatures enzymes)
2) place in boiling alcohol (removes pigment)
3) place in boiling water again (soften leaf)
4) place on white tile, test for starch

conditions essential for photosynthesis

sunlight
CO2
chlorophyll
water
temperature

Where does photosynthesis occur?

leaf mesophyll layer, upper palisade

how do plants take in water

absorbed from soil by roots & carried in xylem

how do plants take in CO2

absorbed from air through stomata in leaf

how do plants take in light energy

chlorophyll in chloroplasts absorbs light energy -> chemical energy

what happens to glucose in plants

1) used immediately for cellular respiration or to form cellulose cell walls
2) excess glucose converted into starch in leaves/as sucrose to storage organs
3) reacts w nitrates & other mineral salts to form amino acids & proteins
4) forms fats for storage, usage in cell respiration & synthesis of new protoplasm

importance of photosynthesis

1) makes chemical energy available to animals & other organisms
2) removes CO2 & provides O2
3) energy is stored in fossil fuels through photosynthesis

lamina

thin broad lamina: short diffusion distance for gases, enables light to reach all mesophyll cells, provide large surface area for max absorption

waxy cuticle on both upper & lower epidermis

reduces water loss through evaporation & is transparent

petiole

holds leaf in position to absorb maximum light energy

upper epidermis

made up of a single layer of closely packed cells
covered by waxy & transparent cuticle

mesophyll

lies in between upper & lower epidermis
main site of photosynthesis

palisade mesophyll

one/two layers of closely packed & long cylindrical cells

spongy mesophyll

irregular shape
numerous large air spaces
carry out photosynthesis
lesser chloroplast than palisade
covered with a thin film of moisture
contains transport tissues

stomata

contains many minute openings called stomata that opens in presence of light for photosynthesis

lower epidermis

beneath mesophyll
single layer of closely-packed cells
covered by waxy cuticle; reduces water loss

how does CO2 & H2O enter leaf

1) in daylight, CO2 is rapidly used up (photosynthesis), CO2 concentration in leaf becomes lower than atmospheric air -> diffusion gradient, CO2 from air diffuses through stomata into air spaces in the leaf
2) surface of mesophyll cells have a thin film of water so CO2 can dissolve in it
3) dissolved CO2 then diffuses into the cells