Photosynthesis: Chlorophyll Dry Lab Assignment

PHOTOSYNTHESIS: CHLOROPHYLL DRY LAB ASSIGNMENT

TEACHER NOTES

Ministry Expectations:

C2.3 conduct a laboratory investigation of the process of photosynthesis to identify the products of the process, interpret the qualitative observations, and display them in an appropriate format.

C3.2 explain the chemical changes and energy conversions associated with the process of photosynthesis

Background Information:

Action spectrum is a graph that illustrates the effectiveness with which different wavelengths of light promote photosynthesis.

Absorption spectrum is a graph illustrating the wavelengths of light absorbed by a pigment.

Light Energy

. 5 % of the sun’s energy is transferred to carbohydrates by a photosynthesizing leaf . A form of electromagnetic energy (AKA radiation) travels in rhythmic waves called photons (a quantum or discrete amount of light energy). . When a photon meets a molecule, one of three things can happen: 1. reflection (bounces back) 2. transmission (passes through) 3. absorption (takes in) . Photons are characterized by a wavelength that is inversely proportional to their energy content (i.e.) photons with short wavelengths have high energy

Photons with long wavelengths have low energy

. Light from the sun is a mixture of photons of different energies. When passed through a transparent prism in an instrument called a spectroscope, photons separate from one another according to their energies forming an electromagnetic spectrum. . The wavelength absorbed by a particular pigment depends on the energy level available in that molecule to which light-excited excited electrons can be boosted to.

Electrons and Light Energy

. When a pigment absorbs the energy of a particular wavelength(s), the energy of the photon is taken over by the molecule raising electron(s) from the ground state to an excited state (higher energy) . During light-dependant reactions, a Mg electron from chlorophyll a is excited. The excited electron may be accepted by some electron acceptor or returned to its ground state.

Pigments Chlorophyll and Accessory Pigments . Pigments are substances that absorb visible light . Different pigments absorb light of different wavelengths, and the wavelengths that are absorbed disappear Chlorophyll a . Only chlorophyll can directly participate in the light reactions of photosynthesis . Absorb photons with energies in the blue-violet (380nm-450nm) and red (600nm-700nm) regions of the spectrum . Reflect photons hat have energies in the green (500nm-600nm) range . Therefore plants are green Accessory Pigments . Can absorb light (photons) that chlorophyll a absorb poorly – can transfer the energy to chlorophyll a which then initiates the light reaction . This broadens the spectrum of colours that can drive photosynthesis Chlorophyll b . Since its structure differs slightly from chlorophyll a , chlorophyll b absorbs slightly different wavelengths of colour (400nm-500nm and 600nm-650nm) . Reflects a yellow green Carotenoids B-carotene . Absorbs light energy in the range of 450nm-500nm (blue violet) . Transmit photons in the yellow to red range (appears yellow-orange) Xanthophylls – pigments in chloroplast membranes that give rise to the yellow colour in autumn leaves

Anthocyanins – pigments in vacuoles that give rise to the red colour in autumn leaves.

Why do leaves in autumn turn various shades of yellow red and brown?

. In autumn (cooler temp.) plants stop producing chlorophyll molecules and disassemble those already in the leaves. This causes the yellow, red, and brown colours of autumn leaves.

Note: Each pigment has a characteristic Absorption Spectrum or pattern of wavelength that it absorbs Instruction for the lesson:

The dry lab should be done after the teacher has taught topics such as light in photosynthesis, what are chlorophyll and their importance, action and absorption spectrum, and an introduction to wavelengths and energy of light and their relationship to one another.

This dry lab can be done in multiple ways:

1. Independently in class—provided enough time, the students can work on this as an in class assignment to be submitted at the end of class.

2. Collaboratively in class—students can work on the assignment in class in groups and their results can be placed on chart paper to be placed around the class. Option: they can also present their answers to the class.

3. Take home assignment—students can be given the assignment to do at home.

Accommodations:

Accommodations should be made for ELL and Special Ed. students according to their needs. For example, an ELL student may be given more time to complete the independent in-class assignment or in a group setting, they can be placed with others who are fluent in the language.