BIOCHAPTER 8 PHOTOSYNTHESIS (Modified from PowerPoint by Mrs. Fisch) SECTION 1 ENERGY AND LIFE

Autotrophs (auto = self; troph = nutrition)- use energy from sunlight or from chemical bonds in inorganic substances to make food. (Ex.: plants, algae and some bacteria) Heterotrophs (hetero = other) – obtain energy from food instead of directly from sunlight. (Ex.: animals, fungi, some bacteria)

Energy – the ability to do work. STORING ENERGY Energy – the ability to do work. ATP (adenosine triphosphate) – compound that cells use to store and release energy

Adenosine diphosphate (ADP) – has two phosphate groups instead of three. contains some energy, but not as much as ATP like a rechargeable battery When a cell has energy available, it can store small amounts of it by adding phosphate groups to ADP, producing ATP.

USING BIOCHEMICAL ENERGY ATP provides energy for: movement synthesis of macromolecules transport across cell membranes many other chemical reactions www.wikilectures.eu

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

WAYS OF OBTAINING ENERGY Photosynthesis (autotrophs) Fermentation (heterotrophs) (molecules broken down without using oxygen) Cellular respiration (heterotrophs) (molecules broken down using oxygen; provides much more energy)

Which molecule is used for energy storage? Which molecule is it changed to when the energy is used? What is the difference between the two? What type of organisms carry out photosynthesis?

SECTION 2. PHOTOSYNTHESIS: AN OVERVIEW Photosynthesis - uses the energy of sunlight to convert water and carbon dioxide into sugars (containing chemical energy) and oxygen.

In most plants, the major site of photosynthesis is the leaves. Carbon dioxide is taken in through pores called stomata (plural; singular = stoma). bookshare4u.blogspot.com

The water needed for photosynthesis is taken up from the soil through the roots, and carried by tube-like vascular tissue to the leaves. crescentok.com

“When a tiny seedling grows into INVESTIGATING PHOTOSYNTHESIS Scientists wondered: “When a tiny seedling grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from?”

Van Helmont’s experiment (1643) Put soil in pot and measured mass Recorded seedling mass Put seed in soil, watered, waited five years until the seedling became a tree. He weighed the dry soil at the end and it was almost the same. Conclusion: the mass of the tree came from water

VON HELMONT WILLOW TREE EXPERIMENT 5 years 2.3 kg (5 lb.) plant 90.8 kg (200 lbs) soil 76.8 kg (169 lbs. 3 oz.)  soil 57 g less

Priestley’s experiment (1771) Put a lit candle in a sealed jar. The flame died out. Placed a mint plant in the jar with the candle. The flame lasted longer Concluded: plants released a substance needed for candle to burn (later identified as the element oxygen).

PRIESTLEY’S EXPERIMENTS www.kshitij-pmt.com

Ingenhousz’s Experiment (1779) Put aquatic plants in light: produced oxygen Put aquatic plants in dark: no oxygen Conclusion: light is needed to produce oxygen

INGENHOUSZ’S EXPERIMENT http://www.macroevolution.net/jan-ingenhousz.html

Light is a form of energy. ENERGY COLLECTION Light is a form of energy. Sunlight is a mixture of different wavelengths of electromagnetic energy. visible spectrum: wavelengths we can see

Plants look green because leaves reflect green light. ENERGY COLLECTION pigments: light-absorbing molecules that plants use to gather the sun’s energy chlorophyll: the major pigment of plants. Chlorophyll absorbs visible light very well. Plants look green because leaves reflect green light.

ENERGY COLLECTION

SECTION 3. THE REACTIONS OF PHOTOSYNTHESIS Photosynthesis takes place inside an organelle, the chloroplast. Leaf Chloroplast Plant cells

Thylakoids— saclike photosynthetic membranes within chloroplast. Single thylakoid Chloroplast

Granum (singular; plural = grana): stack of thylakoids Chloroplast

Photosystems - the light-collecting units of the chloroplast, containing clusters of chlorophyll and other pigments Photosystems Chloroplast

Stroma - fluid portion outside of the thylakoids Chloroplast

CHLOROPLAST Stroma Outer Membrane Thylakoid Granum Inner Membrane

ENERGY COLLECTION When chlorophyll absorbs light, a large fraction of the light energy is transferred to electrons. Because light is a form of energy, any compound that absorbs light absorbs energy. Chlorophyll absorbs visible light especially well.

LIGHT DEPENDENT REACTIONS The first set of reactions require light and water. They take place within the thylakoid membranes of the chloroplast. Split H2O, producing O2, H+, and electrons Use the electrons to convert NADP+ to NADPH Convert ADP plus phosphate to ATP

LIGHT DEPENDENT REACTIONS

NADP+ is a carrier molecule. It accepts two electrons and a hydrogen ion (H+) and is converted to NADPH: NADP+ + H+ + 2e- → NADPH NADPH carries high-energy electrons to chemical reactions elsewhere in the cell (when hydrogen must be added to compounds). It is a form of chemical energy.

What is needed for the light-dependent reactions to happen? What are the products of the light-dependent reactions? Where do the light-dependent reactions take place? What three things are converted during the light reaction?

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) Require CO2 Take place outside the thylakoids, in the stroma. Use ATP and NADPH made in the light-dependent reactions Product: organic molecules like glucose (C6H12O6), a sugar that contains chemical energy.

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) The actual product is a 3-carbon molecule, glyceraldehyde-3-phosphate, which can be converted to sugars or other products. oregonstate.edu

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) To form one molecule of glucose (C6H12O6) (as described in text, p. 212-213): Six CO2 molecules combine with six 5-carbon molecules to make six 6-carbon molecules. X 2

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) These split to give twelve 3-carbon molecules. X 2

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) Using one ATP and one NADPH, each of these is converted to a different 3-carbon molecule (glyceraldehyde 3-phosphate). X 2

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) Two of these are removed and used to make one glucose. X 2 glucose

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) The ten remaining 3-carbon molecules are combined and rearranged to give six 5-carbon molecules (using 6 more ATP). X 2

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) These enter the next cycle.

LIGHT-INDEPENDENT REACTIONS (CALVIN CYCLE) Overall: 6 CO2 + 18 ATP + 12 NADPH + 12H+ → C6H12O6 + 18 ADP + 18 phosphate + 12 NADP+ + 10 H2O

AN OVERVIEW OF PHOTOSYNTHESIS CO2 Chloroplast Light NADP+ ADP + P CALVIN CYCLE (in stroma) LIGHT REACTIONS (in thylakoid) ATP Electrons NADPH O2 Sugar

FACTORS AFFECTING PHOTOSYNTHESIS Temperature The reactions of photosynthesis are made possible by enzymes that function best between 32°F to 95°F (0˚C to 35˚C) Temperatures above or below this range may affect those enzymes, slowing down the rate of photosynthesis or stopping it entirely.

Light High light intensity increases the rate of photosynthesis. After the light intensity reaches a certain level, however, the plant reaches its maximum rate of photosynthesis, as is seen in the graph.

Water Shortage of water can slow or even stop photosynthesis. Plants that live in dry conditions often have waxy coatings on their leaves to reduce water loss. They may also have biochemical adaptations that make photosynthesis more efficient under dry conditions.

How does this hurt their ability to carry out photosynthesis? At high temperatures, leaves close their stomata to avoid losing water. How does this hurt their ability to carry out photosynthesis? michaeldomingos.hubpages.com

www.colorado.edu

What 3 factors affect the rate of photosynthesis? What is the optimal temperature range for photosynthesis? What do plants have on their leaves to prevent water loss?