Chapter 8: Photosynthesis

Photosynthesis

The process in which carbon and energy are converted into carbohydrates.

Visible light

60% of the visible light from the sun is unavailable for photosynthesis.

Photorespiration

20% of the energy is lost to photorespiration.

Autotrophs

Photosynthesis occurs in autotrophs.

Equation

The equation for photosynthesis is CO2 + H2O → C6H12O6 + O2.

Calvin cycle

The Calvin cycle is a light-independent reaction that uses CO2 to synthesize carbohydrates.

Chloroplasts

Chloroplasts are the organelles where photosynthesis takes place.

Chlorophyll

Chlorophyll is a major component of photosynthesis and gives leaves their green color.

Accessory pigments

Accessory pigments are yellow and orange carotenoids that absorb wavelengths that chlorophyll does not absorb.

Photoexcitation

Photoexcitation occurs when a photon strikes a chlorophyll molecule and the electron moves to a higher energy level.

Fluorescence

Fluorescence occurs when an excited electron returns to its ground state, releasing heat and light.

Antenna complexes

Antenna complexes absorb light energy and transfer it to the reaction center chlorophyll.

Photosystem II

Photosystem II takes electrons from an electron donor (H2O) and passes them to photosystem I.

Photosystem I

Photosystem I uses the electrons and energy to make NADPH.

Photosynthetic electron transport chain

The photosynthetic electron transport chain transfers electrons from photosystem II to NADPH, generating ATP.

Cyclic electron flow

Cyclic electron flow produces ATP and H+ but does not produce NADPH.

Challenge 1

Excessive light energy can lead to the production of reactive oxygen species (ROS), which can damage cells.

Challenge 2

Photorespiration occurs when Rubisco catalyzes O2 instead of CO2, resulting in the loss of CO2 and energy.

Evolution of photosynthesis

The first organisms to have photosynthesis only had one photosystem and used other oxidized compounds to gain electrons.

Endosymbiosis

Over time, cyanobacteria lost the ability to survive outside the host cell and evolved to be inserted inside the cytoplasm.

Conjugation

Conjugation is a process where DNA is transferred between cells through a pilus.

Transformation

Transformation occurs when a recipient cell takes up DNA released by a donor cell.

Transduction

Transduction is a process where DNA is transferred between cells by viruses.