The Flow Of Energy Part 3: Photosynthesis

The Flow of Energy part 3 Photosynthesis

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• The range of colours which make up white light and are visible to the human eye is called the Visible Spectrum. • Infrared and Ultraviolet would be at either end of the spectrum and are not visible to humans

Photosynthesis • Colour is a property of light that depends on wavelength. When light falls on an object, some of it is absorbed and some is reflected. The apparent color of an opaque object depends on the wavelength of the light that it reflects; e.g., a red object observed in daylight appears red because it reflects only the waves producing red light. The color of a transparent object is determined by the wavelength of the light transmitted by it. An opaque object that reflects all wavelengths appears white; one that absorbs all wavelengths appears black.

White Light • White light is a mixture of all wavelengths of visible light. Certain wavelengths of light are absorbed by the leaf while others are reflected. When the reflected light reaches your eye, the eye and brain interpret the mixture of reflected wavelengths as color.

White light is separated into the different colors (=wavelengths) of light by passing it through a prism. Wavelength is defined as the distance from peak to peak (or trough to trough). The energy of is inversely proportional to the wavelength: longer wavelengths have less energy than do shorter ones.

• The order of colors is determined by the wavelength of light. Visible light is one small part of the electromagnetic spectrum. The longer the wavelength of visible light, the more red the color. Likewise the shorter wavelengths are towards the violet side of the spectrum. Wavelengths longer than red are referred to as infrared, while those

Pigments • Pigments are substances that absorb light at particular wavelengths and generally reflect light at other wavelengths. Pigments are important for photosynthesis because in order to convert light energy to chemical energy, the organism must first absorb light energy with the pigments involved in photosynthesis. When light is absorbed its energy is taken up by some of the electrons in the outer most energy level of the pigment molecules.

Chlorophyll • The intense green colour of chlorophyll is due to its strong absorbencies in the red and blue regions of the spectrum, shown in Because of these absorbencies the light it reflects and transmits appears green.

Cartenoids • Carotenoids: This is a class of accessory pigments that occur in all photosynthetic organisms.. Carotenoids absorb light maximally between 460 nm and 550 nm and appear red, orange, or yellow

Photosynthesis •

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Plants absorb a common gas called carbon dioxide, pull water up through their roots and use light to make sugar. Plants use the sugar to grow. Plants give off oxygen as a by-product. The green parts of the plant makes the sugar and oxygen.  Carbon dioxide + water + sunlight = sugar + oxygen Watch video

The thylakoid is the structural unit of photosynthesis •

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. Both photosynthetic prokaryotes and eukaryotes have these flattened sacs/vesicles containing photosynthetic chemicals. Only eukaryotes have chloroplasts with a surrounding membrane. Thylakoids are stacked like pancakes in stacks known collectively as grana. The areas between grana are referred to as stroma. While the mitochondrion has two membrane systems, the chloroplast has three, forming three compartments.

Photosynthesis is a two stage process • . The first process is the Light Dependent Process (Light Reactions), requires the direct energy of light to make energy carrier molecules that are used in the second process. The Light Independent Process (or Dark Reactions) occurs when the products of the Light Reaction are used to form C-C covalent bonds of carbohydrates

The Light Reactions • Photosynthesis is divided into 2 main sets of reactions . • 1. Light Reactions (Occurs in Grana) • The purpose of the light reactions is to change light energy into chemical energy of ATP and NADPH (enzyme). • Light energy is absorbed and converted to chemical energy • Water is split into H+ ions, oxygen and electrons • H+ from the water are attached to carrier co-enzymes (NADP) for use in photosynthesis (see page 157)

The Calvin Cycle AKA The Dark Reactions • (Occurs in Stroma) • The purpose of the Calvin Cycle is to change CO2 into sugar by adding energy & the H+ from ATP & NADPH. • a) Can occur in light or dark. • b) 6 CO2 & lots of ATP & NADPH are needed to make one sugar molecule. • c) The sugar is then used for plant growth or stored for use in

Energy Relationships • Respiration is almost the exact opposite reaction to photosynthesis. These two reactions work together to maintain a biological balance on earth. (I think this diagram is easier to understand than the one on page 160).

Photosynthesis and Respiration. • • • • •

Photosynthesis produces food stores energy uses water uses carbon dioxide • releases oxygen • occurs in sunlight

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Respiration uses food releases energy produces water produces carbon dioxide • uses oxygen • occurs in the dark as well as light

Photosynthesis and Respiration. • •

Photosynthesis  light energy

• 6CO2+6H20= C6H1 2O6+6O2   • Here is the equation for photosynthesis.  when a plant is exposed to 6 molecules of carbon dioxide and 6 molecules of water and light energy is present, glucose and

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Cellular Respiration         

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C6H12O6+6O2=CO2+H2 O

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notice that this equation is about the opposite of the equation for photosynthesis.  This is because the products of the photosynthesis reactions are the reactants of the reactions that take place during cellular respiration.  Conversely, the products of cellular respiration are the reactants of the photosynthesis reactions.

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The end of chapter 

Further Study • Here is a link to a good slideshow tutorial • This is a good website explaining the chemistry of autumn colours