Chapter 8: Energy and

Photosynthesis

Energy and Photosynthesis

• Energy is necessary for all life

–Plants and green organisms:

• Trap light energy in the form of sunlight and store it for later use

–All other organisms:

• Eat green plants to obtain energy

Adenosine Triphosphate (ATP)

• Energy molecule• Composed of:

– Adenosine molecule– Ribose sugar– 3 phosphate groups

• ATP becomes available for a cell to use when the bonds between the phosphate groups are broken– Releases energy when a phosphate group is removed– Bond breaks between the 2nd and 3rd phosphate

groups• Results in adenosine diphosphate (ADP)

• ATP is a small molecule– Stored energy (ex: a battery)

• Cells use energy to maintain homeostasis

Photosynthesis• Photo-: means light

• Synthesis: to put together

• Process that uses the sun’s energy to make simple sugars

• 2 phases

– Light-dependent reactions

– Light-independent reactions

History• Van Helmont (1600’s)

– Planted seedling in pot of soil, watering it regularly

– Concluded plant mass comes from the water

• Priestley (1700’s)– Candle with glass jar cover flame died– Mint sprig and candle with glass jar cover

flame burned– Conclusion: plants release oxygen

• Ingenhous– Supported Priestley will occur only when

mint plant is exposed to light

Photosynthesis Requirements

• Light (sun)• Carbon Dioxide (from the air)

– Taken in to plants through little openings in the leaves called stomata

• Water (from the ground)– Taken in through the roots of plants

• Chlorophyll and enzymes in the plant• Rate of photosynthesis depends on:

– The availability of sunlight, CO2, and H2O– The intensity (brightness) of light– Temperature (20-35º C is optimal)

• White light mixture of different wavelengths of light– Visible spectrum ROYGBIV

• Pigments: molecules that absorb specific wavelengths of sunlight– Ex: Chlorophyll (in chloroplasts): a and b

• Absorbs well in blue and red light• Absorbs most wavelengths except green (reflects

green light)• Makes plants appear green

– Other plant pigments:• Xanthophyll: yellow pigment• Carotene: orange pigment

• Equation: 6CO2 + 6H2O + light C6H12O6 + 6O2

Carbon Dioxide + Water Sugar + Oxygen gas• Chloroplast: cell organelle where

photosynthesis occurs– Light-dependent reactions take place in the

thylakoid membrane (contains pigments)

• Picture of a chloroplast:– Grana: stack of thylakoids– Stroma: outside of the thylakoids– Photosystem: clusters of pigment and protein

that absorb light energy (found in thylakoids)

Review:

1. Match the scientist with the appropriate experiment or conclusion:

Priestley van Helmont Ingenhousz_____ Plants need sunlight to produce oxygen

_____ Plants gain most of their mass by taking in water

_____ Using a candle and a jar, he observed that plants produce a substance that kept the candle burning

_____ He measured the mass of the soil in which a plant grew

_____ He observed plants exposed to light

Light-Dependent Reactions

• 1st phase• Requires light• Converts light energy into

chemical energy• ATP produced fuels light-

independent reactions• NADP+: electron carrier

– Holds 2 high-energy electrons and H+

– Converts NADP+ to NADPH

• Light reactions use trapped light energy to convert ADP to ATP and NADPH

– Occurs in the grana of chloroplasts

– Splits water (photolysis)• H: needed to make glucose• O: released as a waste product into the

atmosphere

Light

Light reactions

Dark reactions

ATP

H+

C6H12O6 (glucose)

(in grana) (in stroma)H2O as waste

O2 as waste

H2O in CO2 in

Light-Independent Reactions

• Does not require light

• Called dark reactions or the Calvin cycle

• Process of actually making glucose (uses CO2 to make simple sugars/starches)

– Uses energy from ATP and NADPH

• Can occur in the light or the dark

• Requires enzymes

• Occurs in the stroma of chloroplasts

• Any glucose not used immediately can be stored as starch or sugars

• Chemosynthesis

– Process of making food from inorganic compounds

– Does not use sunlight

• Uses Sulfur in deep sea vents

• Methanogens use Carbon Dioxide and Hydrogen

Autotrophs• Use photosynthesis

or chemosynthesis

– Make their own food

Bell Ringer:

1. The light-dependent reactions take place within the __________ membranes.

2. The light-independent reactions are also known as the ________.

3. In the light-dependent reactions, the gas ____ is produced.

4. High-energy sugars are produced during the _______ reactions.

5. The light-independent reactions take place in the ________.