S173 Plants and People - Notes from Study Period 4 - Part 1 of 2

Study period 4 looks at how plants are used to provide energy for use by us.

Introduction
We see that the main ways we use energy are for heat, light, power, and transport and to provide this we currently use coal, oil, gas, petrol, diesel, peat, and uranium.

We consider that the properties of a good fuel are that it should provide high energy for its level of cost. Ease of transport, extraction and processing all factor in the cost of fuel.

Biofuels are produced from biological material that has been living recently, for example wood, in contrast to coal, which is a fossil fuel created from wood that died millions of years previously. Some biofuel can be produced from waste, such as recycled plant oils. Others can be produced from crops grown for the purpose of becoming a biofuel.

Energy from plants and climate change
We are given a really interesting table that shows the following:

Energy store                         Energy (megajoules per kilogram)
Plant oil                                37
Coal                                      24
Carbohydrates (inc sugars)  17
Wood (dry)                           16

We then look at the carbon cycle and learn that all living things have structural components based on carbon. Carbon moves between reserves found in living things, such as plants and animals; decomposing organic matter, such as soil; rocks, including fossil fuels; the atmosphere; and the oceans.
Levels of CO2 are monitored in Hawaii at the Mauna Loa Observatory. Levels are estimated to have risen from 280 parts per million (p.p.m) in 1800 to 387 p.p.m in 2009.

The link between energy and biofuels
Energy cannot be created it can only be converted from one form to another. The energy in the sugar created by plant via photosynthesis comes from visible light (mainly the blue and red portions of the visible spectrum) - sunlight. The plant forms other compounds within its tissues using this sugar and it is these compounds that can be used as biofuels.

Reactions involved in photosynthesis

Stage 1: the absorption of light. This occurs within specialised thylakoid membranes in the chloroplasts. These membranes can pack closely in flattened stack called grana.
Light reactions: energy from sunlight creates ATP and NADP.2H.

Stage 2: Takes place in the stroma, a fluid that surrounds the thykaloid membranes. The chloroplast is bounded by two membranes that are situated close togethe, called the chloroplast membrane.

Dark reactions: ATP and NADP.2H are used to convert carbon dioxide to sugar.

For more information on photosynthesis, click here.http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookps.html#Light%20Reactions