Photosynthesis
The Reaction
6CO2 + 6H2O --> C6H12O6 + O2
Chlorophyll absorbs light energy for the reaction. The products then contain more energy than the reactants
Reverse of aerobic respiration
Leaf Structure
Palisade tissue
Spongy mesophyll
Upper epidermis
Lower epidermis
Waxy Cuticle
Reduces water loss by evaporation
Protects palisade cells
Contains palisade cells full of chloroplasts
Pockets of air to allow gas exchange
Structural
Acts as barrier to pathogens and UV light
protects palisade cells and waterproofs leaf
Transparent to allow light through
Provides structural integrity
Increased amount of chlorophyll for a higher rate of photosynthesis
Arranged vertically for sunlight to pass through as many chloroplasts as possible
Regular shape = densely packed
More surface area exposed for the diffusion by the larger air gaps
Contain chloroplasts to use light not absorbed by the palisade tissue
Guard cells
Stomata
Controls the opening and closing of stomata
Gas exchange
on underside of leaf to stay cooler, lowing rate of transpiration
Evidence for Photosynthesis
Practical: Testing leaves for starch
Method
Remove leaf from plant
Add iodine solution to test for starch
Place in boiling water for 30 seconds to kill it and remove waxy cuticle
Wash with cold water to soften
Boil in ethanol to remove chlorophyll
Practical: Investigating the effect of light on gas exchange by a leaf
Results
Leaf in dark
Leaf in dim light
Leaf in light
Control (no leaf)
Key
High concentrations of CO2 (more than 0.04%)
CO2 in normal air (0.04%)
Low concentrations of CO2 (less than 0.04%)
yellow
orange
purple
orange
orange
yellow
Purple
Rates of Photosynthesis and Limiting Factors
Experimental Evidence
Practical: Measuring the rate of photosynthesis using pondweed
The beaker in between the Elodea and the light provides insulation to maintain a constant temperature
The bubbles of gas produced may be collected and tested
Light intensity is altered by changing the distance between the lamp and the pondweed
A piece of the pondweed Elodea is placed under water, weighed down with a paperclip
We find that when light intensity increases, it will plateau
This is due to carbon dioxide being the limiting factor
Compensation Point
The point at which there is no net loss or gain of CO2, respiration and photosynthesis are equal
Mineral Ions
Plants need a multitude of ions to synthesise compounds.
Deficiencies
Phosphate
Potassium
Nitrate
Magnesium
Making amino acids, proteins, chlorophyll, DNA et al.
Making DNA, ATP et al. Part of cell membranes
Needed for enzymes of respiration and photosynthesis to work
Part of chlorophyll molecule
Limited Growth of plant, older leaves turn yellow
Poor root growth, younger leaves turn purple
Leaves turn yellow with dead spots
Leaves turn yellow
Carnivorous plants
These plants obtain some nutrients, not energy from consuming animals
Nitrogen Cycle