Energy = the ability to do work
– Life on earth depends on a flow of energy
– Cells need energy constantly to continue functioning.

• Energy comes in many forms
– Examples:
• Light
• Heat
• Energy stored in chemical compounds (like glucose)

Most cellular processes require the input of energy.
Like what?

Examples:
– Synthesis of new molecules
• proteins, enzymes, DNA etc.
– Breakdown of molecules
• chemical digestion
– Build new structures
• membranes, organelles, etc.
– Maintain Homeostasis
• eliminate wastes, maintain body temp., active transport, cell movement etc.

• Where do cells get this energy?
– From food we eat
– We measure the energy content of food in calories.
– Certain reactions break down these molecules to release energy.

• Energy released from a Gummy Bear
• http://www.youtube.com/watch?v=uj9D3m c7tVg&feature=related&safe=active

– Can’t use energy directly from food
– Need to store it and release it gradually.
– Store it in molecules of ATP.

ATP (Adenosine Triphosphate)
– Source of cellular energy
– Stores energy as food is broken down so that it can be released slowly to cell when needed rather than all at once.
– A type of energy “currency”, that can be “paid out” as the cell needs it.

Structure of ATP (Adenosine triphosphate)
– 1 adenine (type of nitrogenous base)
– 1 ribose sugar (5 carbon ring)
– 3 phosphate groups

How is ATP Formed?
– Energy is stored in high energy phosphate bonds

– Cells bond a third phosphate group to ADP
– ADP
• (adenosine “di”phosphate)

– To release this energy again, the cell breaks off the 3 rd phosphate group and energy is released.
– Can happen over and over again.
– Like recharging a battery!

• How does ADP and ATP differ?
• How is this related to energy?

Storing Energy
Add a phosphate to ADP
ADP + phosphate + energy → ATP

Releasing Energy
Remove a phosphate from ATP
ATP → ADP + phosphate + energy
Note:
The enzyme that catalyzes this reaction is called ATPase.

• Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose.

ATP/ADP Cycle

How do organisms obtain food to make ATP?

• They eat it…
– Heterotrophs: obtain food from consuming other living things.
• Ex:
– Animals: herbivores, carnivores and omnivores
– Fungi
– Some protists
– Some bacteria

• They make it themselves…
– Autotrophs: use light energy from the sun to make their own food through photosynthesis.
• Ex:
– Plants
– Algae
– Some bacteria

• Process by which light energy is converted into the chemical energy of organic compounds (glucose).

• Occurs in the chloroplasts of plant cells
(as wells as some single celled organisms, that can carry out photosynthesis.)

• Stroma : protein containing fluid
• Grana : stacked membranes containing enzymes and chlorophyll.

Chlorophyll :
– green pigment necessary for photosynthesis.
– Absorbs red and blue wavelengths of light and reflects green light. (that’s why most plants look green)

• Note:
– Other photosynthetic pigments exist besides chlorophyll, but it is the main one used by autotrophs
• Ex: Carotenoids (orange/red colored pigment)

• Plants Take In :
– Carbon Dioxide Gas
– Water
– Sunlight (energy)
• Plants Produce :
– Glucose (form of stored energy)
– Oxygen Gas

• How Does the Chloroplast Work?
– Light Dependant Reactions (Photochemical)
– Light Independent Reactions (Carbon Fixation)

Light Dependant Reactions (Photochemical)
– Happen in the thylakoid membranes of grana
– Directly involve chlorophyll and sunlight
– Produces oxygen
– Converts ADP to ATP
– Converts NADP + to NADPH

• Chlorophyll absorbs sunlight
– Creates high energy electrons
– Electrons enter the electron transport chain
– Eventually produce some ATP

• Photolysis
– Water gets split inside grana
• Breaks into:
– One oxygen atom
– Two H + ions
– 2 electrons

• The Oxygen produced by splitting water gets released into the air
– Source of nearly all the oxygen in Earth’s atomosphere!
Thank you plants!!!
You make our lives possible.

• The H+ ions and electrons
– Join up with NADP + an
“electron carrier”
– It becomes NADPH

Making ATP
• H + ions build up and cross the thylakoid membrane causing ATP to form as ATP synthase (an enzyme) turns ADP into ATP

Light Independent Reactions (Calvin Cycle )
– Does not require light
– Happens in stroma
– Carbon Fixation :
• Carbon gets “Fixed” from a simple 1 carbon molecule
(CO
2
) to a complex 6 carbon one that holds stored energy (glucose/C
6
H
12
O
6
)

• Carbon Dioxide Molecules : (CO
2
)
– enters from atmosphere (through stomata)
– Combine to make PGAL a 3-carbon molecule
– 2 PGAL combine to produce a 6-carbon glucose
– Energy for these reactions to take place is provided by ATP and NADPH (from light reactions)

• Video Overview of Photosynthesis (5min)
• http://www.youtube.com/watch?v=mYbMP wmwx88&safe=active

• Factors Affecting Photosynthesis
– Temperature
– Light Intensity
– Water and Carbon Dioxide Availability
Tutor Vista: http://www.youtube.com/watch?v=vmmWiJ3g9Cg&safe= active

• Temperature:
– Enzymes are needed for photosynthesis
– Function best between 0°C and 35°C.
– Too hot or too cold and photosynthesis stops

• Intensity of Light :
– More intensity = more photosynthesis
– Remember blue and red wavelengths are most useful for photosynthesis

• Availability of Water and CO
2
:
– One of the raw materials for photosynthesis
– Split during photolysis reaction
– Water loss can kill plants
– They have evolved strategies
• Waxy coatings on leaves

• Stomata :
– small openings in plant leaves that normally admit carbon dioxide
– Water can also escape through opening
• Guard Cells :
– Can open or close stomata to help prevent excess water loss from plant

Stomata and Guard
Cells Video: http://www.youtube.com
/watch?v=cFX4JrsPaUs
&safe=active