Photosynthesis and Cellular Respiration Overview

Photosynthesis

Converts light energy to a usable form

Respiration

Releases stored energy (Facilitates growth, development and reproduction)

Metabolism

Sum of all interrelated biochemical processes in living organisms

Anabolism

Forming chemical bonds to build molecules

Photosynthesis reactions

Store energy by constructing carbohydrates by combining carbon dioxide and water

Catabolism

Breaking chemical bonds

Cellular respiration reactions

Release energy held in chemical bonds by breaking down carbohydrates, producing carbon dioxide and water

Photosynthesis-respiration cycle

Involves the transfer of energy via oxidation-reduction reactions

Oxidation

Loss of electron(s)

Reduction

Gain of electron(s)

Hydrogen

Atom is lost during oxidation and gained during reduction

Oxygen

Usually the final acceptor of electrons

Energy for most cellular activity

Involves adenosine triphosphate (ATP)

ATP using light as an energy source

Takes place in chloroplasts and other green parts of the organisms

Photosynthesis equation

6CO2+12H2O + light → C6H12O6+6O2+6H2O

Carbon dioxide reach chloroplasts

By diffusing through stomata into leaf interior

Radiant energy received on earth

About 40% is in form of visible light

Wavelengths used more extensively

Violet to blue and red-orange to red

Photorespiration

Accelerates when the ratio of carbon dioxide to oxygen inside leaves changes

Photooxidation

Occurs if light intensity is too high, resulting in destruction of chlorophyll

Stomata close

Reduces supply of carbon dioxide available for photosynthesis if water in short supply or light intensities too high

Photosynthetic pigments

Include carotenoids (yellow and orange), phycobilins (blue or red, in cyanobacteria and red algae), and several other types of chlorophyll

Photosynthetic unit

About 250-400 pigment molecules grouped in light-harvesting complex

Two phases of photosynthesis

Light-dependent reactions & Light-independent reactions

Light-dependent reactions

In thylakoid membranes of chloroplasts, water molecules split apart, releasing electrons and hydrogen ions; oxygen gas released

Electron transport system

Electrons pass along this system during light-dependent reactions

NADP

Is reduced, forming NADPH (used in light-independent reactions)

Light-independent reactions

In stroma of chloroplasts, utilize ATP and NADPH to form sugars.

Calvin cycle

Carbon dioxide combines with RuBP (ribulose bisphosphate), and the combined molecules are converted to sugars (glucose). Energy furnished from ATP and NADPH produced during light-dependent reactions.

Absorption spectrum

Each pigment has its own distinctive pattern of light absorption.

Photosystem I

Contains chlorophyll a, small amount of chlorophyll b, carotenoid pigment, and P700.

P700

Reaction-center molecule - Only one that actually can use light energy.

Antenna pigments

Remaining pigments that assist in capturing light energy.

Iron-sulfur proteins

Primary electron acceptors, first to receive electrons from P700.

Photosystem II

Contains chlorophyll a, B-carotene, small amounts of chlorophyll b, and reaction-center molecule: P680.

Pheophytin (Pheo)

Primary electron acceptor in Photosystem II.

Photolysis

Water-splitting process occurring in Photosystem II.

Electron transport system

Consists of cytochromes, other electron transfer molecules, and plastocyanin.

Chemiosmosis

Photons move across thylakoid membrane by chemiosmosis.

Phosphorylation

ATP is formed from ADP.

Photorespiration

Competes with carbon-fixing role of photosynthesis.

4-Carbon pathway

Produces 4-carbon compound instead of 3-carbon PGA during initial steps of light-independent reactions.

C4 plants

Tropical grasses and plants of arid regions with Kranz anatomy.

CAM photosynthesis

Similar to C4 photosynthesis in that 4-carbon compounds are produced during light-independent reactions.

Respiration

Release of energy from glucose molecules that are broken down to individual carbon dioxide molecules.

Anaerobic respiration

Carried on in absence of O2.

Glycolysis

First step in cellular respiration.

Citric acid (Krebs) cycle

Second step in cellular respiration.

Electron transport

Third step in cellular respiration.

Sugar cleavage

Fructose split into two 3-carbon fragments: GA3P (glyceraldehyde 3-phosphate).

Pyruvic acid formation

Hydrogen, energy, and water removed, leaving pyruvic acid.

Chemiosmosis and oxidative phosphorylation

Chemiosmosis couples transport of protons into matrix with oxidative phosphorylation: formation of ATP.

Secondary metabolism

Metabolic processes not required for normal growth and development.

Assimilation

Conversion of organic matter produced in photosynthesis to build protoplasm and cell walls.

Digestion

Conversion of starch and other insoluble carbohydrates to soluble forms.