Ch. 7 PhotosynthesisCh. 7 Photosynthesis

Using Light to Make FoodUsing Light to Make Food

7.1 -7.57.1 -7.5

• What is photosynthesis?

• Light energy (from sun) is used to make sugar & other food from CO2 & H2O

• Can too much sunlight harm a plant?

• Yes. It can overwhelm the plant.

How it all happens• Is there a chemical equation for photosynthesis?• Yes. Carbon dioxide (CO2) is reduced to glucose &

water (H2O) is oxidized to oxygen gas (O2)• Where does the O2 come from?• From water, H2O

• What is an “autotroph?”

• It means a “self-feeder”

• Are all plants autotrophs?

• Yes, they make their own carbohydrates from CO2 which is a great fuel & don’t eat other organisms to live.

Examples of autotrophs

• Even thought they are autotrophs, what do plants require to synthesize sugar?

• Light=energy, CO2 & H2O to make sugar, this is endergonic so it stores the energy from light (Ch.5)

• Oak tree, cactus, Kelp (a large alga photosynthetic protist), and photosynthetic bacteria

Producers

• Why are plants considered producers of the biosphere?

• They make the biosphere’s organic food supply from raw material (CO2)

• What is the biosphere?• The portion of Earth that is

living, all life & where it lives• Are plants the only producers?• No, some bacteria, archaea

and protists also make food from inorganic materials. All organism that use light energy to make food are photosynthetic autotrophs.

Where it all happens

• Where does photosynthesis take place?

• In eukaryotic organelles called Chloroplasts (photosynthetic bacteria have no organells)

• Why are plants green?• Chlorophyll, a pigment in the

chloroplasts. It absorb all colors but green,(which reflect back at you) the light energy and then chloroplasts convert that into food.

Parts of a leaf

• Where are chloroplasts concentrated?

• In the mesophyll cells, green tissue on the interior of leaf.

• How does gas enter & exit plants? (CO2 & O2)

• Stomata (stoma, singular), the tiny pores on the leaf.

Parts of a Chloroplast

• Stroma, is a thick fluid, found in the inner membrane. What happens there?

• Stroma is the location of the Calvin cycle (CO2 -> sugar)

• Thylakoids are suspended in the stroma. What do they do?

• Thylakoids are the Location of light reaction. They are stacked into grana and contain the chlorophyll, that capture light energy.

• Where does O2 gas come from?

• It comes from water (H2O) and not carbon dioxide (CO2)

• What is the ratio of water molecules needed for each molecule of O2 gas

• 2:1, 2 water (H2O) molecules for every molecule of O2,

• Why is photosynthesis called Redox?• Leo goes ger - lose an electron oxidation / gain

an electron reduction • Water is split apart yielding O2, oxidized, the loss

of electrons along with hydrogen ions (H+)• Carbon dioxide is reduced to sugar, gaining

electrons along with hydrogen ions (H+)

• What is the opposite of photosynthesis?• The energy releasing process of cellular

respiration.

Using energy in glucose by oxidizing sugar and reducing O2 to H2O.

Photosynthesis occurs in two stages linked by ATP & NADPH

• What happens in the light reaction?

• Light energy is absorbed by chlorophyll (in thylakoids) and covert it into chemical energy (ATP & NADPH) (O2 is waste product)

• What happens in the Calvin Cycle and why has it been called the dark reaction?

• Occurs in stroma of chloroplast, series of reactions that assemble sugar using CO2 & energy from light reaction.

• Called the dark reaction because it does not require light directly.

Does run during day cause of ATP & NADPH from light cycle.