Photosynthesis and Respiration

Objectives: I can …• Compare and contrast photosynthesis to respiration• Describe the structures (and their functions) within a

plant involved in photosynthesis and respiration.• Differentiate between the steps and products of aerobic

respiration and those of anaerobic respiration• Evaluate and write the equations for photosynthesis and

respiration

Vocabulary:

Autotroph * heterotroph * ATP * ADP * glucose * pigments *

Stomata * pallisade layer * spongy layer * chlorophyll *

photosynthesis * chloroplasts * xylem * stomata * stroma *

Calvin cycle * thylakoid membrane * light dependent and

light independent reactions * Respiration (aerobic &

anaerobic) * glycolysis * ADP & ATP *

fermentation (alcoholic and lactic acid) * Krebs cycle (citric

acid cycle) * electron transport chain

PhotosynthesisOnly autotrophs (“self-feeding” Ex: plants, algae, blue-

green bacteria) can photosynthesize (make sugar from sunlight, water, and carbon dioxide). Heterotrophs can not (“other feeders” Ex: animals, fungi, most bacteria)

For photosynthesis to occur, the energy from the sun must be captured by pigments (light absorbing compounds). The primary pigment for photosynthesis in plants is the green pigment, chlorophyll.

Chlorophyll is found in the chloroplasts of plant cells. ALL photosynthesis takes place in the chloroplasts.

First, carbon dioxide must enter the leaves through small openings called stomata. The carbon dioxide must join with water collected by the roots which is carried to the leaf in tube-like structures called the xylem. Then the sun’s energy can begin the process of photosynthesis.

Photosynthesis occurs in the chloroplasts within the leaves and stem of plants. Most chloroplasts are found in the pallisade layer of a leaf. Some are found in the spongy layer.

Chloroplasts contain:

1) Thylakoid membranes hold the pigments, such as chlorophyll, that will absorb the sun’s energy. These are arranged in stacks called grana. This is where the light dependent reactions of photosynthesis take place. The light dependent reactions use the sun’s energy to split water molecules, create oxygen and convert ADP to ATP and NAD+ to NADPH.

2) Stroma is the area surrounding the thylakoid membranes. Here is where light independent reactions (a.k.a the Calvin cycle) occurs. Here ATP and NADPH from the light rxns. is used to make high energy sugars for storage.

Sugars made during the Calvin cycle are transported out of the leaves by the phloem. Xylem and phloem make up the vascular system (veins) within leaves, stems and roots.

Simplified Photosynthesis Equation:

6 CO2 + 6 H2O + sunlight C6H12O6 (sugar) + 6 O2

(from air to leaves) (Calvin cycle) (exit leaves to air)

Real Photosynthesis Equation:

6 CO2 + 12 H2O + sunlight C6H12O6 (sugar) + 6O2 + 6H2O (split during lt.dep.rxns.)

Respiration

ALL living things undergo respiration. Respiration is the process by which fats, proteins, and sugars are broken down to form ATP (or cellular energy source).

Aerobic Respiration (when oxygen is present):1) Glycolysis2) Kreb’s Cycle3) Electron Transport Chain

Anaerobic Respiration:When there is NO oxygen, glycolysis leads to anaerobic

respiration, a.k.a. fermentation, which produces very little ATP.

Overall Respiration Equation:

C6H12O6 (sugar) + 6 O2 6 CO2 + 6 H2O + ATP

Glycolysis (“breaking glucose”)The 6 carbons in glucose are divided into two 3-carbon molecules of

pyruvic acid.This process requires 2 ATP molecules. But 4 ATP are produced in the

end for a net gain of 2 ATP.NAD+ is converted to NADH which will participate in the electron

transport chain.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Glycolysis is followed by anaerobic respiration (fermentation) if no oxygen is present. There are 2 types:

1) Alcoholic fermentation:Pyruvic acid + NADH alcohol + CO2 + NAD+

Yeasts are used to purposely make CO2 so bread will rise.Other yeasts are used to make alcoholic beverages.

2) Lactic acid fermentation:Pyruvic acid + NADH lactic acid + NAD+

Bacteria used to make yogurt, cheese, etc. and our muscles produce lactic acid. This is what makes our muscles sore when we overdo it.

Glycolysis is followed by aerobic respiration when oxygen is present. Here, pyruvic acid from glycolysis passes into the Kreb’s cycle, a.k.a. the citric acid cycle.

Steps to the Kreb’s cycle:

1) Pyruvic acid enters the mitochondria of the cell.

2) CO2 and citric acid (briefly) are produced

3) More CO2 is produced. High energy carriers, FADH2

and NADH, are produced. A small amount of ATP (2) is produced.

4) Electrons are passed from FADH2 and NADH to the electron transport chain.

The Electron Transport Chain

Across the mitochondrial membrane folds, H+ ions build up on one side, making it positively charged while the other side is negatively charged. Electrons from the high energy FADH2 and NADH molecules drive the process.

This process is similar to a relay race where the runner must pass the baton to the next runner on the team in order to continue the race. Although the race might be going well up to this point, if the last runner drops the baton, the race is lost and the team’s efforts are wasted.

Only in the electron transport chain, electrons are passed and oxygen acts as the last runner on the team. If there is no oxygen present, no ATP is made so the “trophy” (ATP) is not handed out. And fermentation begins instead.

If oxygen is present, ADP can be converted to ATP, our cells’ energy currency. About 32 ATP are made this way. Added to the 2 from glycolysis and the 2 from the Kreb’s cycle and we get 36 ATP. This is where 38% of sugar’s energy goes, the rest goes to make body heat.