Chapter 6 Flashcards
Plant Nutrition (18 cards)
Describe photosynthesis
process by which plants synthesize carbohydrates from raw materials using energy from light
State the equation for photosynthesis
carbon dioxide + water → glucose + oxygen
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(in the presence of light and chlorophyll)
What is chlorophyll and its function
a green pigment that is found in chloroplasts which transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
What are the uses of the glucose produced in photosynthesis
glucose: respiration for energy
sucrose: transport from sources to sinks in phloem
starch: insoluble (no osmotic probs), as an energy store
cellulose: formation of cell walls
nectar: attract insects for pollination
Mineral ions needed by plants
Nitrates: to form amino acids for protein-synthesis
Magnesium: to form chlorophyll
Steps to test leaf for starch
boil in water: kill the leaf
boil in ethanol: chlorophyll dissolves decolorizing the leaf
rinse in water: soften the brittle leaf
spread on white tile: easy to see color change
add iodine solution: if starch present – brown→blue/black
Steps to de-starch plant
leave in dark for 48 hours → plant uses up all its starch store
Investigate the need for chlorophyll
de-starch plant with variegated leaves
expose leaf to light for a few hours
test for starch
only parts that had chlorophyll have starch
Investigate need for CO₂
de-starch two plants
keep in sealed containers, one with sodium bicarbonate (CO₂ absorber) the other without
test for starch
the plant with the CO₂ absorber will have no starch
Investigate need for light
de-starch plant
cover part of leaf with foil and expose to sunlight
test for starch
only uncovered part will contain starch
Investigate relationship with light intensity
use aquatic plant (Elodea) in funnel in beaker with an inverted test tube at funnel’s nose
use a lamp at a distance D and count bubbles
light intensity is inversely proportional to the square of D
closer the plant → higher light-intensity → increase rate
Investigating the effect of light and dark on gaseous exchange in an aquatic plant
three test tubes with hydrogen carbonate indicator:
1. in dark with pond weed
2. in light with pond weed
3. in light without pond weed
hydrogencarbonate indicator is normally pink, an increase in CO₂ yellow, decrease in CO₂ purple
1 will be yellow as the plant cannot photosynthesize but still respires releasing CO₂
2 will be purple as the plant photosynthesizes and absorbs CO₂
3 will remain pink as there is no change in CO₂, it is a control to show that the pond weed is the cause of color change
Describe the effect of temperature on the rate of photosynthesis
As temperature increases,, particles gain energy, more successful collisions + close to enzyme’s optimum temp
Describe the effect of CO₂ conc. on the rate of photosynthesis
As CO₂ concentration increases, the diffusion gradient becomes steeper, allowing faster diffusion into leaf cells
What is a limiting factor
something present in the environment in such short supply that it limits life processes. for example: CO₂ levels, temperature, light intensity…
What is the leaf structure
top: cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
air spaces
vascular bundle
stomata
guard cells
lower epidermis
Explain the function of each structure
waxy cuticle: waterproofs the leaf
upper epidermis: secretes waxy cuticle, transparent to let light thru, acts as a barrier to pathogens
palisade mesophyll: long columnar cells to absorb most light, packed with chloroplasts, main site of photosynthesis
spongy mesophyll: packed with air spaces, photosynthesis
air spaces: place of gas diffusion, O₂ and CO₂
vascular bundle: xylem carries water and mineral ions to leaf and phloem sucrose and amino acids from sources to sinks
stomata: site of gas exchange
guard cells: control whether stomata are open or not
lower epidermis: contains stomata, acts as a protective layer
Leaf adaptations for photosynthesis
broad: large surface area- more light absorption and more CO₂ diffusion
thin: short CO₂ diffusion distance → faster diffusion
large air spaces: easy diffusion in n out of cells
lots of chloroplast in palisade cells: sunlight reaches them first
branching network of veins (vascular bundle): good water supply
