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Photosynthesis
• Why don’t bushes or other trees usually grow underneath large trees?
Lesson Objectives• Identify the kind of energy that powers life.• State why living things need energy.• Evaluate the importance of autotrophs for providing energy
to all life.• Describe how autotrophs and heterotrophs obtain energy.• Define chemosynthesis.• Compare and contrast glucose and ATP.• Outline how living things make and use food.• Outline the stages of photosynthesis.• Describe the chloroplast and its role in photosynthesis.• Identify the steps of the light reactions and the Calvin
cycle.
Terminology Review
• What is energy?
_________________________________
• What is the ultimate source of all energy?
_________________________________
The ability to do work.
Sunlight
Kinds of energy which power life• What forms can energy come in?
__________________________________
• Where is energy stored? __________________________________
• How is this energy released? __________________________________
Light, heat, chemical, nuclear, magnetic, and electrical
In chemical bonds
By breaking the chemical bonds
How Do Organisms Get Energy? Autotrophs vs. Heterotrophs
Living organisms obtain chemical energy in one of two ways.
They make it themselves OR They consume those who can make it themselves
CAN MAKE IT THEMSELVES Autotrophs—Photosynthesize
• Plants, algae, and some bacteria
• Producers, begin food chains which feed all life– Store chemical energy in carbohydrate food
molecules• Organic molecules made through photosynthesis
store chemical energy (food)
Photosynthesis
• Provides over 99 percent of the energy supply for life on earth– Uses solar energy to convert water and
carbon dioxide into oxygen and glucose
CONSUMERSHeterotrophs• Animals, fungi, and many protists and
bacteria
• Consumers, cannot make their own food– Obtain energy through food consumption
• Autrotrophs or other Heterotrophs
– Highly diverse organisms
Chemosynthesis
• Other autotrophs: mostly bacteria in dark or low-oxygen environments – produce food using the chemical energy
stored in inorganic molecules such as hydrogen sulfide, ammonia, or methane.
Tubeworms deep in the Gulf of Mexico get their energy from chemosynthetic bacteria living within their tissues. No digestive systems needed!
Food to Energy Molecules: Glucose and ATP
• Two of the most important energy-carrying molecules
• Glucose: simple carbohydrate; energy-rich product of photosynthesis; chemical formula C6H12O6
– “deliverable” form of energy; carried in blood through capillaries and taken up by trillions of cells
– nearly universal food for life.
• ATP: store smaller quantities of energy; product of first stage of photosynthesis and used during second stage to make glucose
– provides cells with energy for cellular processes
– “useable” form of energy for your cells
Why Organisms Need Both Glucose and ATP
• Glucose more chemical energy in a smaller ‘‘package” than a molecule of ATP– more stable than ATP; better for storing and transporting
energy– BUT too powerful for cells to use.
• ATP right amount of energy to power life processes within cells– like a rechargeable battery
• energy released when broken down into ADP and phosphate
• “worn-out battery” ADP recharged using new energy to attach a new phosphate; rebuilds ATP.
ATP and ADP
• ATP: adenosine triphosphate; principle chemical compound in which living things store energy.
Adenine: nitrogen-containing compoundRibose: a 5-carbon sugar3 phosphate groups
• ADP: adenine diphosphate; structural similar to ATP but with one important difference: ADP has only two phosphate groups. ADP is converted to ATP when available energy is used to add a phosphate group to it.
ADP
two phosphates
Adenine: nitrogen-containing compoundRibose: a 5-carbon sugar2 phosphate groups
Releasing Energy from ATP
• Energy stored in ATP is released when it is converted to ADP and a phosphate group.
O
Adding or subtracting a 3rd phosphate group allows the cell to store and release energy as it is needed
Using Biochemical Energy• How the cells use ATP:
– To conduct active transport; like the sodium-potassium pump
• It moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell
• A single ATP molecule provides the energy to move three sodium ions and two potassium ions in different directions
– Powers movement within the cell• Moves cell organelles along microtubules by motor proteins
that use energy from ATP to generate force
http://student.ccbcmd.edu/~gkaiser/biotutuorials/eustruct/sppump.html
Photosynthesis: The Most Important Chemical Reaction for Life on Earth
• Necessary conditions include: – enzymes - proteins to speed up chemical
reactions – chlorophyll - a pigment which absorbs light – chloroplasts – which contain chlorophyll,
accessory pigments, and enzymes in patterns which maximize photosynthesis
Stages of Photosynthesis• Two stages:
– light reactions uses water; changes light energy into chemical energy
• releases oxygen as a waste product.
– Calvin cycle uses chemical energy in ATP and NADPH to make glucose
Chloroplasts: Theaters for Photosynthesis
• Chloroplast contain:– neat stacks called grana (singular, granum).
• consist of sac-like membranes, known as thylakoid membranes
– Thylakoid membranes• contain photosystems
– groups of molecules that include chlorophyll
• light reactions occur in thylakoid membranes.
– stroma • space outside the thylakoid membranes
• reactions of the Calvin cycle occur here
Chloroplasts Function• Work with enzymes and two basic
molecules: pigments and electron carriers
• Electron carrier molecules are usually arranged in electron transport chains (ETCs).
Photosynthesis Stage I: The Light ReactionsChloroplasts Capture Sunlight’s Energy
Light-Dependent Reactions
• Require LIGHT• Use light energy to produce
– Oxygen gas– Convert ADP to energy carrying ATP– Convert NADP+ to energy carrying NADPH
Photosynthesis Stage II: The Calvin CycleMaking Food “From Thin Air”
• Three major steps:– Carbon fixation– Reduction– Regeneration
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
Why is Carbon Dioxide “Fixed”• Life on Earth is carbon-based
– needed in building blocks of biological molecules– ultimate source of carbon is carbon dioxide
• Animals and most other heterotrophs cannot take in CO2 directly
• Only autotrophs can build low energy inorganic CO2 into high-energy organic molecules like glucose
Three Pathways for Carbon Fixation—Calvin Cycle
1. C-3 pathwaya. Most common b. 6-C molecule splits into two 3-C molecules
2. C-4 pathway a. creates a 4-C molecule 3. CAM (Crassulacean Acid Metabolism) a. cacti and succulents b. Fix carbon dioxide at night
Dry air, hot temperatures, bright sunlight lead to below two pathways:
Factors Affecting Photosynthesis
• Shortages of water slow process down; can stop it– Plants that live in dry areas have a waxy coating on
their leaves that reduces water loss
• Temperature also can slow or stop it– Enzymes used by plants for photosynthesis function
best between 0°C and 35°C (32°F to 95°F)
• Intensity of light – More light = greater rate of photosynthesis until
maximum reached• Maximum rate varies from plant to plant
Let’s Review• Where does photosynthesis occur?
_________________• What are the saclike photosynthetic membranes
in the chloroplast called? _________________• The thylakoids are arranged in stacks called
__________.• What is found inside the grana?
______________________________________• What are photosystems?
______________________________________• What do photosystems do?
______________________________________
In the chloroplasts
thylakoids
grana
Clusters of chlorophyll and other pigments
Proteins found in the grana
They capture the energy of sunlight
• How many stages does photosynthesis have? ______
• What are they? ____________________________________________________________________
• Where do the light-dependent reactions take place? __________________________________
• Where do the light-independent reactions take place? __________________________________
2
Light reactions
Light-independent reactions (Calvin cycle)
Thylakoid membrane
Stroma; region outside of the thylakoid membrane