Photosynthesis Biology

What you will learn… 1. How do plants get food? 2. Photosynthesis overview 3. Leaf structure 4. Chloroplast structure 5. Pigments 6. Two Stages 6a. Light Reactions 6b. Dark Reactions 7. Relationship Between the 2 Stages 8. Factors Affecting the Photosynthetic Rate 9. Alternate Pathways

1.How do plants get food? Plants are autotrophs (meaning “self-feeders” in Greek) Often referred to as the producers of the biosphere because they produce its food supply

2.Photosynthesis Overview Photo, from the Greek word for light, refers to the first stage. Synthesis, meaning “putting together” refers to the sugar construction in the second stage

2.Photosynthesis: Overview The main purpose of photosynthesis is to make organic molecules (carbohydrates). Overall equation: 6 CO2 + 6 H20  C6H12O6 + 6 O2 Occurs in the leaves of plants in the chloroplasts. Oxygen is also produced in this process.

3.Leaf Structure Most photosynthesis occurs in the leaf. Gas exchange of CO2 and O2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. Stomata are able to open and close because water is also evaporated through them into the atmosphere from the plant.

3.Leaf Structure

4.Chloroplast Structure Similar to mitochondria, chloroplast has an outer membrane and an inner membrane, with an intermembrane space between them. Inner membrane is filled with a thick fluid called stroma *Stroma is where sugars are made from carbon dioxide and water

4.Chloroplast Structure Within stroma is a system of interconnected membranous sacs called thylakoids contains thylakoid space Built into thylakoid membranes are the chlorophyll molecules that capture light energy concentrated in stacks called grana.

5. Pigments Pigment is any molecule that is able to absorb light . Only light that is absorbed by pigments is useful for photosynthesis. Chlorophyll a is the most important photosynthetic pigment. Other pigments called antenna or accessory pigments are also present in the leaf. Chlorophyll b Carotenoids (orange / red) Xanthophylls (yellow / brown)

6.Two Stages of Photosynthesis 1. Light Reactions 2. Dark Reactins (Calvin Cycle)

6a.Light Reactions overview Occurs in thylakoid membranes light energy splits water into H2 and O2 H2 is used to store energy in ATP and NADPH O2 gas is a waste product.

6b.Dark Reactions overview Dark reactions, or Calvin Cycle * Occurs in the stroma Does not require light directly CO2 is turned into glucose through carbon fixation Process is powered by ATP and NADPH from light reactions

7. Summary of Photosynthesis

8. Abiotic Factors Affecting Photosynthetic Rate Photosynthetic rate is depended on environmental factors: Amount of light available Level of carbon dioxide temperature

8. Abiotic Factors Affecting Photosynthetic Rate Light intensity Up to a certain intensity, photosynthesis increases as more light is available to the chlorophyll. When all the chlorophyll molecules are activated (saturated) by the light, more light has no further effect.

8. Abiotic Factors Affecting Photosynthetic Rate Temperature: Increased temperature increases photosynthetic rate until an optimal temperature is reached. Above the optimal temperature, enzymes cannot function properly and photosynthesis will decrease.

8. Abiotic Factors Affecting Photosynthetic Rate Carbon Dioxide Levels: Increased carbon dioxide levels increases photosynthesis, unless limited by another factor, then levels off.

9. Alternate Pathways These pathways adapt to perform photosynthesis in dry and hot environment They are more efficient than the traditional C3 pathway which use CO2 directly from the air Plants with alternative pathways have a slightly different Calvin cycle. In C4 plants the location of the Calvin cycle is different In CAM plants the timing is different

9. Alternate Pathways C4 Pathway: CO2 fixation and the Calvin cycle take place in two separate location. Examples of C4 plants: corn, sugar cane

9. Alternate Pathway CAM Occurs in succulent plants (cacti) Carbon fixation (trapping CO2) takes place at night when the stomata are open Calvin cycle takes place during the day, when stomata are closed This way plants do not lose much water during hot and dry days.

9. Alternate Pathway