Photosynthesis and Cellular RespirationSection 2 Energy in Living Systems CH 6 pg 112-118.

Photosynthesis and Cellular Respiration Section 2

Energy in Living Systems

CH 6 pg 112-118


Organisms classified on how they obtain energy

• Autotrophs– Make their own food from organic molecules– Most convert light energy into chemical energy

• Carbon Dioxide (CO2) and water (H2O) to organic compound

• Oxygen (O2) released

• Heterotrophs– Cannot make their own food inorganic compounds– Eat autotrophs or other heterotrophs


Photosynthesis


Harvesting Light Energy

• Photosynthetic organisms have chloroplasts– Chloroplasts are the organelles that convert

light energy into chemical energy.• Contains flat, disc-like sacs called thylakoids.

• this is the first stage of photosynthesis.


Thylakoids


• Sunlight composed of ROY G BIV, different colors. (Lgth = Amt of Engy)

• Color observed when light strikes an object, waves are reflected, transmitted, or absorbed

• Colors react depending on the pigment present

Light Absorption in Chloroplast


Harvesting Light Energy, continued

• Chlorophyll (a and b) – Absorbs blue and red light and reflects green

and yellow light• Carotenoids

– help plants absorb additional light energy– absorb blue and green light, reflect red,

orange and yellow(fall colors)


Two Electron Transport Chains• First reaction in photosynthesis is the light reaction takes

place in the chlorophyll– Light hits a thylakoid– Energy is absorbed by the pigment molecules and are

directed to a special chlorophyll molecule that acts as a reaction center

– Electrons are excited and move to other molecules and the electron transport chain.

• One ETC makes ATP and Second makes NADPH


Producing ATP

Step 1:• An enzyme splits water

molecules , e- is released.

• H+ ions stay within the thylakoid

• e- is charged by pigment• Oxygen gas is released

into the atmosphere

1st Electron Transport Chain


Step 2: • Carrier Proteins (ATP

Synthase) in the membrane pump H+ ions into the thylakoid,


Step 3: • Energy diffusion of H+

ions through ATP synthase is used to make ATP


2nd Electron Transport Chain

Step 4: Producing NADPH• Renergizing, Light excites

electrons that are passed on to the second chain.


Step 5: Making NADPH• Excited electrons

combine with H+ ions and NADP+ to form NADPH.

• NADPH is used to store energy in organic molecules. (used later in dark reaction)


Electron Transport Chains of Photosynthesis

Click to animate the image.


Producing Sugar

• The first two stages of photosynthesis depend directly on light to make ATP and NADPH.

• In the final stage of photosynthesis, ATP and NADPH are used to produce energy-storing sugar molecules from the carbon in carbon dioxide.

• The use of carbon dioxide to make organic compounds is called carbon dioxide fixation, or carbon fixation. (Light Independent, Dark Reaction, or Calvin Cycle)



Calvin Cycle

• Carbon Fixation, an enzyme adds CO2 to a five carbon molecule (RuBP)

• Takes place outside of the Thylakoid in the stroma, solution surrounding the thylakoids


Calvin Cycle• CO2 diffuses into the stroma

• The enzyme (RuBP) adds CO2 to a five carbon molecule

• This occurs 3 times to make six carbon molecule

• 6 carbon molecule splits into 2 – 3 carbon molecules (3 – PGA)


G3P

GPAG3P

RuPB

G3P


• Each of 3 – PGA is converted into G3P– G3P is a molecule with additional phosphate and H+

that were donated by ATP and NADPH– ADP and NADP are then recycled to the ETC

• One G3P molecule leaves the Calvin Cycle to be used to make carbohydrates

• The remaining G3P molecules are recycled back to the enzyme RuBP and reenters the Calvin Cycle


G3P

GPAG3P

RuPB

G3P



Factors that Affect Photosynthesis

• Light intensity• Carbon dioxide concentration• Temperature


Relationship

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Photosynthesis and Cellular RespirationSection 2 Energy in Living Systems CH 6 pg 112-118.

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