Textbook Chapter 8 Review Book Topic 2 Photosynthesis Textbook Chapter 8 Review Book Topic 2

Transformation of Energy Energy – the ability to do work All organisms need energy to live and to carry out all chemical processes within (metabolism) Recall: Autotrophs can make their own food (energy) Heterotrophs need to eat food to obtain energy

Metabolism Photosynthesis Cellular Respiration Light energy from the sun is converted to chemical energy for use by the cell Cellular Respiration Organic molecules are broken down to release energy for use by the cell

History 1770s In sealed container, a candle can only burn for a short amount of time Within this container Animals could not survive Candle could not be relit Plants could survive and allow a candle to burn in their presence

1770s continued… First evidence that plants interact with the air by using the CO2 produced from the burning candle to replace the O2 which is being used by the candle and animals

1880s Basic needs for plant growth: Carbon dioxide Water Light Did you know that most energy enters the Earth’s biosphere through photosynthesis? Over 150 billion tons of sugar is produced by plants yearly!

Photosynthesis The process of capturing and transforming the sun’s energy into chemical energy in the form of glucose Carried out by green plants (producers) Uses CO2, H2O and light energy to make glucose and O2 Most of the O2 in the atmosphere is the result of photosynthesis

Remember plants are autotrophs, which means they make their own food from simple inorganic compounds Two major types: Photoautotrophs Use light energy to make food (ex. Green plants, algae) Chemoautotrophs Uses inorganic chemicals for their food-making reactions to produce energy (Ex. mostly bacteria)

Light Energy Sunlight is a form of energy known as radiation Travels in waves Wavelength is the distance between the crest of two different wavelengths Sunlight is a mixture of all visible wavelengths

Sunlight is called “white light” Colors: White All wavelengths of light are reflected equally by an object Black All wavelengths of light are being absorbed equally by an object The color you see is the wavelength which is being reflected by an object Ex. Red – all wavelengths are being absorbed but red is being reflected by the object Sunlight is called “white light”

Spectrum – white light passes through a prism and each wavelength is bent in different amounts Causes the light to spread out showing the order of their wavelengths Shortest – violet Longest – red The shorter the wavelength of light, the more energy available

Pigment – substance that absorbs light Different wavelengths of light are absorbed by particular pigments

Photosynthetic Pigments Chlorophyll Most abundant and important photosynthetic pigment In plants there are two types: Chlorophyll a Chlorophyll b Absorb red and blue light Reflect green light (this is why plants are green!)

Other pigments absorb light in regions not associated with chlorophyll a, increasing the range of the spectrum Carotenes (orange) Xanthophylls (yellow)

The presence of chlorophyll a hides the carotenes and xanthophylls in leaves Are not seen until autumn when chlorophyll starts to break down and leaves begin to turn color

Chloroplasts In green plants, photosynthesis occurs within chloroplasts Contain: Photosynthetic membranes arranged in flattened sacs called thylakoids Stacks of thylakoids are called grana Regions between the grana are known as stroma

In order for photosynthesis to occur it requires photosynthetic pigments AND the proteins in the thylakoid membrane

Main Ideas Some organisms produce their own food, whereas others obtain energy from the food they ingest Cells store and release energy through two reactions: photosynthesis and cellular respiration Energy is used to drive all cellular activities (metabolism) Plants contain chloroplasts with light-absorbing pigments that convert light energy into chemical energy

Leaf Structure Leaves are specialized to capture light for photosynthesis Wide Flat Large surface area for absorption Arrangement around stem maximizes exposure to light Environment determines leaf structure

Simple Compound

Internal Structure Outermost layer is a clear waxy cuticle Epidermis Protects inner tissues Slows down water loss from leaf Epidermis Below cuticle One cell thick Little or no pigment to allow light to reach photosynthetic pigment in inner leaf tissues

Inner Structure Continued Epidermis continued… Contains stomates Small openings on the underside of the leaf Allow the exchange of carbon dioxide, oxygen and water vapor between the leaf and the environment

A pair of guard cells surround each stomate Epidermis continued… A pair of guard cells surround each stomate Regulate the opening and closing of stomates (caused by osmosis) Closed when little water available, low temperatures or little light available

Internal Structure Continued… Mesophyll is located between the upper and lower layers of the epidermis Photosynthesis occurs here in a leaf

Mesophyll continued… Two layers Palisade mesophyll One to two cells thick Tall, tightly packed Filled with chloroplasts Spongy mesophyll Irregular shaped cells Large air spaces in between cells (stomates located near this layer to allow for gas exchange) Fewer chloroplasts

External Structure Each leaf contains a network of veins: Xylem: transports water and minerals from the roots upward to the stem Phloem: transports food and dissolved materials in both directions along the length of the plant

External Structure Continued… Veins are located throughout the mesophyll layer Vein patterns are a characteristic of a species

Chemistry of Photosynthesis

Chemical Reactions Summary of converting light energy to chemical energy: (light) 6 CO2 + 12 H2O  C6H12O6 + 6 O2 + 6 H2O Occurs in chloroplasts in the presence of light, carbon dioxide and water Produces sugar, oxygen and water

Both reactions depend on each other Occurs in two phases: Light dependent reactions Light independent reactions Both reactions depend on each other Light dependent reactions produce ATP that the light-independent reactions use to make glucose

ATP: The Unit of Cellular Energy Energy exists in many forms: Light energy Mechanical energy Thermal (heat) energy Chemical energy ATP = Adenosine triphosphate Most abundant biological energy-carrying molecule in all organisms

ATP Structure Contains: Adenine base Ribose sugar Three phosphate groups

ATP  ADP + P (releases energy) ATP Function Releases energy when the bond between the 2nd and 3rd phosphate is broken, releasing a phosphate ATP  ADP + P (releases energy) ADP = adenosine diphosphate ADP + P  ATP (stores energy)

SEE GUIDED NOTE SHEET AND REACTION DIAGRAMS FOR LIGHT-DEPENDENT AND LIGHT-INDEPENDENT REACTIONS

Factors Affecting Photosynthesis Light Intensity ↑ intensity, ↑ rate of photosynthesis Temperature Specific optimum temperature depending on plant At extremes enzymes are damaged, ↓ rate of photosynthesis

Slows photosynthesis if in low supply Water availability Slows photosynthesis if in low supply If severe shortage, photosynthesis stops Mineral availability If in short supply affects the rate of photosynthesis