Photosynthesis & Cellular Respiration

Chapters 8 and 9

Remember...

Autotrophs:•can generate their own food•are the base of many food chains•include plants, bacteria, etc.

8-1 Energy and Life

• Autotrophs are any organism that can make their own energy.

• Photoautotrophs undergo photosynthesis which changes light energy to chemical energy. – Ex. Plants and cyanobacteria

• Chemoautotrophs undergo chemosynthesis which changes inorganic chemicals such as hydrogen sulfate into chemical energy. – Ex. Nitrobacteria

Chemical Energy ATP• We use Adenosine Triphosphate

Contains adenosine, ribose, and 3 phosphate groups

• When ATP loses a phosphate, it becomes ADP (only has 2 phosphates) and energy is released

• What does ATP do?– Movement in the cell (organelles)– Moves ions across membranes

(sodium and potassium for many reactions)

Energy

• Most cells only contain small amounts of ATP, they can’t store large amounts

• Get new ATP from carbohydrates

Where do the carbohydratesget the stored energy?

8-2 Photosynthesis overviewEarly discoveries:

Jan Van Helmont (1580-1644)...Where does a plant get its mass as it grows?

From the soil?

Weighed the soil... Weighed the tree... Weighed the water...After 5 years, the tree had gained 150 lbs.The weight of the soil was nearly the same as when he started.

Van Helmont assumed the weight came from the water.

Joseph Priestley (1733-1804)...Best known for his study of the chemistry of gases

Plant releases a substance that keeps the candle burning...

What was released by the plant?

Jan Ingenhousz (1730-1799)

Light is essential to plant respiration.Aquatic plants produce oxygen bubbles in the light,but not in the dark.

Process of Science!

Properties of Light• White light from the sun is composed of a range of wavelengths.• Only 1-3% of light energy is harvested by plants = not very

efficient• James Clerk Maxwell- 1st person to recognize electromagnetic

spectrum

The Photosynthesis Equation

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy sugars

Plants use the sugars to produce complex carbohydratesSuch as starches. Plants obtain CO2 from the air or water.

Absorption of Light byChlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

Section 8-2

page 207

Figure 8-5 Chlorophyll Light Absorption

In addition towater and CO2,photosynthesisrequires light and chlorophyll, a molecule in chloroplasts.

Lights and Pigments

Chlorophyll is the plantsprinciple pigment

Light Used in Photosynthesis

During photosynthesis, the chlorophyll pigments can absorb only Some wavelengths of light...

The grana of the chloroplasts absorb mainly blue-violet and red-orange

Chlorophyll – main pigment absorbing light for photosynthesis Two types:

1. Chlorophyll a2. Chlorophyll b

Chlorophyll does not absorb light well in the green region of the spectrum.

Why are leaves sometimesred or yellow?

Photosynthesis takes place in the chloroplasts

8-3 The Reactions of Photosynthesis

Thylakoids are foundin the chloroplasts.

Thylakoids contain the pigment chlorophyll that captures light energy.

Text page 208

Photosynthesis occurs in two stagesThe light-dependent reactions require light to work

= Light ReactionThe light-independent reactions do not require light

= Dark Reaction

Light CO2

SugarsO2

Chloroplast

See TextPage 209

Light reactions are dependent on light and occurs only during the day

Light reactions involve:a. splitting water to release oxygen,b. energy production (ATP), andc. reduction of NADP+ to NADPH

The high energy NADPH is used to help build molecules the cell needs...LIKE GLUCOSE!

Energy comes from electrons “falling” to a more stable energy level.... Kinetic energy

Light-Dependent Reactions (con’t)

Produce oxygen gas Convert ADP and NADP+ into energy carriers ATP and NADPH

1. Photosynthesis begins when pigments in photosystem II absorb light2. Energy from the light excites electrons3. Electron transport and H+ ions from water-splitting result in a positive

charge inside the thylakoid, and negative charge outside 4. This difference provides the energy to make ATP (like a

battery!)

See Figure 8-10 (page 211)

Light Independent Reactions Stroma of the Chloroplast

• Also known as the Calvin Cycle

• They occur whether or not light is present.

• The The Calvin cycle uses ATP and energized ions from NADPH from the light-dependent reactions to produce high-energy sugars.

• Uses 6 carbon dioxide molecules to make a single 6-carbon sugar

Text page 212-213

Photosynthesis review...

Factors affecting photosynthesis...• shortages of water (reactant)• temperature• light intensity

Photorespiration

• Dark Reaction can’t tell difference between oxygen and carbon dioxide. If it uses Oxygen = waste

• It is only 30% efficient

Factors that Affect Rates- light

• At low light intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions.• As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate.• At high light intensity, photosynthetic rate levels out, not due to light intensity but due to other limiting factors, including competition between oxygen and carbon dioxide for the active site on RUBP carboxylase.

Factors that Affect Rates- carbon dioxide

• At high concentrations, the rate of photosynthesis begins to level out due to factors not related to carbon dioxide concentration.• One reason might be that some of the enzymes of photosynthesis are working at their maximum rate.• In general, carbon dioxide is found in low concentration in the atmosphere, and so atmospheric carbon dioxide levels may be a major limiting factor on photosynthesis when at low levels.

Factors that Affect Rates- temperature

• As temperature increases above freezing, the rate of photosynthesis increases. This occurs because molecules are moving more quickly and there is a greater chance of a collision resulting in a chemical reaction.• At some point, a temperature is reached that is an optimum temperature. The photosynthetic reaction rate is at its quickest rate at this point.• Above that temperature, the enzymes begin to denature, slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not occur at all.

Cellular Respiration and Glycolysis

• Energy arrives from the sun and is captured by green photosynthetic plants, and stored in the chemical bonds of glucose.

• Non photosynthetic organisms must obtain their energy ‐by the breakdown of these energy rich storage molecules in order to release the energy for their use.

• Photosynthesis stores this energy in glucose; glycolysis and cellular respiration release it.

• These are the processes by which cells can "burn" or breakdown glucose into CO2 and H2O and transfer most of the energy to the phosphate bonds of ATP.

Cellular Respiration PREVIEW

• Glucose > ATP• Anaerobic- w/o O2

• Aerobic- w O2

• C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP

PHOTOSYNTHESIS BACKWARDS!