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