Biology for aChanging World

FIRST EDITION

Intro to BiologyDr. Steve Schwendemann

CHAPTER 5Energy Flow and Photosynthesis

Copyright © 2012 by W. H. Freeman and Company

Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz

Chapter 5Mighty Microbes

Copyright © 2012 by W. H. Freeman and Company

U.S. Energy Consumption

• The United States is the largest consumer of fossil fuels.

Energy Basics

• Energy is the capacity to do work. Cellular work includes processes such as building complex molecules and moving substances in and out of the cell.

• Without a source of energy, all life on earth would stop.

Energy Basics

• Energy cannot be created, so organisms must obtain it from an outside source. Humans and other animals obtain the energy they need by eating food.

• Food contains chemical energy – potential energy stored in the bonds of biological molecules. Breaking these bonds releases that stored energy, making it available to power cell functions.

Energy Basics

• Algae are very efficient energy converters – the oil they produce is rich in chemical energy. All they need to make this oil is sunlight, carbon dioxide, water, nitrogen, and phosphorus.

Energy is conserved• Energy cannot

be created or destroyed. When energy is transferred from food or fuel to the organisms or products that use it, that energy changes form. This principle is known as the “conservation of energy.”

Energy is conserved

• A cereal bar contains potential energy (stored energy) in the chemical bonds that hold the molecules of that bar together.

Energy is conserved• When a

cyclist eats and digests the bar, digestion breaks those chemical bonds, and the stored potential energy is released.

Energy is conserved

• As the cyclist climbs a hill, his body converts this potential energy into the kinetic energy (the energy of motion or movement) of muscle contraction and heat (the kinetic energy generated by random movement of molecules or atoms).

Energy is conserved• At the top of the

hill, the cyclist relies on potential energy to get him downhill. His relatively higher position means that he has “positional” potential energy.

Energy is conserved

• As the cyclists coasts down the hill, the friction of the wheels on the ground converts his positional potential energy into the kinetic energy of moving wheels and heat.

Energy is conserved

• From the cereal bar to the spinning wheels, energy is converted from one form into another. With every conversion, some energy is lost as heat.

Energy transformation is not efficient

• The conversion of energy from one form to another isn’t 100% efficient. With each energy transformation, a bit of energy is lost to the environment as heat.

• This inefficiency is the reason we need to keep supplying energy to any system.

Capturing energy: Photosynthesis

• For almost all living things on earth, the ultimate source of energy is the sun.

• Autotrophs are organisms such as plants, algae, and certain bacteria that capture the energy of sunlight by photosynthesis.

• Heterotrophs are organisms that obtain energy by eating other organisms.

Capturing energy: Photosynthesis

• Photosynthesis is the process by which plants and other autotrophs use the energy of sunlight to make energy-rich molecules using carbon dioxide and water

Capturing energy: Photosynthesis

• The process of photosynthesis can be summarized in the following equation:

Sunlight + Water + Carbon dioxide Oxygen + Glucose

Capturing energy: Photosynthesis

• Plants and other photosynthesizers use the energy of sunlight to make the molecule glucose using carbon dioxide as a source of carbon. In the process, water molecules are split and oxygen is given off as a by-product.

Capturing energy: Photosynthesis

• Photosynthesis occurs in chloroplasts – organelles present in leaves and algae.

Capturing energy: Photosynthesis

• Photosynthesis has two parts: a “photo” part and a “synthesis” part.

• During the “photo” part, light energy is captured in chemical form.

• During the “synthesis” part, chemical energy is used to generate glucose molecules using the carbon atoms of carbon dioxide.

Sunlight

• Light energy is the energy of the electromagnetic spectrum of radiation.

• Light energy travels to the earth in particles called photons, or packets of light energy. Photons of different wavelengths contain different amounts of energy.

Carbon fixation• Photosynthesis

captures carbon dioxide gas from the air and incorporates those carbon atoms into sugar, a process called carbon fixation.

• By converting inorganic gaseous carbon into an organic form that can be eaten by animals or used by plants to grow and increase their biomass, carbon fixation is ultimately the way carbon enters the global energy chain.

Photosynthesis: A closer look• Chlorophyll is the

pigment present in the green parts of plants that absorbs photons of light energy during the light reactions of photosynthesis.

Photosynthesis: A closer look

• When red and blue photons of sunlight hit chlorophyll during the light (“photo”) reactions, the electrons in its atoms become excited. These excited electrons are used to generate an energy-carrying molecule known as adenosine triphosphate (ATP), which is used in the “synthesis” part of photosynthesis to make sugar.