photosynthesis genbio q2

photosynthesis

The process by which green plants and other organisms transform light energy into chemical energy.

Photosynthetic organisms (photoautotrophs)

use sunlight energy to drive the synthesis of organic molecules from carbon dioxide and water.

1643: Jan Baptista Van Helmont

conducted experiments which led him to conclude that trees consumed water, not soil

1744: Joseph Priestly

discovered a gas dubbed “dephlogisticated air” by focusing solar rays on mercuric oxide. This gas was later named “oxygen”

1778: Jan Ingen-Housz

discovered that plants emitted oxygen gas in light, thereby initializing the concept of photosynthesis

1888: Thoedor Wilhelm Engelmann

discovered the effect of varying wavelengths of light on photosynthesis, and used this information to create the action spectrum

1932: Robert Emerson and William Arnold

stated that photosynthesis occurs by hundreds of chloroplasts cooperating with each other.

1950: Melvin Calvin

traced the path of carbons in photosynthesis, thereby founding the Calvin Cycle.

electromagnetic waves

are disturbances of electric and magnetic fields. These waves self- propagate in a vacuum or in matter.

wavelength

is the distance between the crests of electromagnetic waves.

400 (violet) and 700 nanometers (red)

The wavelengths of light operating in photosynthesis occur in the visible spectrum between ___________.

more energy

Electromagnetic radiation with shorter wavelengths carry

pigment

Why are plants green? _______- a compound that absorbs light. different ______ absorb different wavelengths of white light.

chlorophyll

is a pigment that absorbs red & blue light (photons) so green is reflected or transmitted.

Chlorophyll a

involved in light reactions

Chlorophyll b

assists in capturing light energy “accessory pigment”

Chlorophylls a and b

absorb violet, blue, and red light best. Because green light is transmitted and reflected by chlorophyll, plant leaves appear green to us.

Carotenoids

accessory pigments. captures more light energy

mainly in the leaves, stogma - pores and mesophyll cells

where does photosynthesis take place?

mesophyll

The ground tissue of a leaf; specialized for photosynthesis.

stomata (stoma)

Pores in a plant’s cuticle through which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere.

chloroplast

Organelle where photosynthesis takes place.

thylakoid

A flattened membranous sac whose membrane contains the pigment chlorophyll for photosynthesis and ATP- synthesizing enzymes.

granum (grana)

A stack of membrane-bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis.

light-dependent reactions and light-independent reactions (calvin cycle)

2 phases of photosynthesis

light-dependent reactions

take place in the thylakoid membrane and require a continuous supply of light energy. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP-an energy storage molecule—and NADPH reduced (electron-bearing) electron carrier.

Light-Independent Reactions (Calvin Cycle)

takes place in the stroma and does not directly require light. Calvin cycle uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars - glyceraldehyde-3-phosphate, or G3P, molecules - which join up to form glucose.

linear electron flow (noncyclic pathway)

A route of electron flow that involves both photosystems (I and II) and produces ATP, NADPH, and O2. The net electron flow is from H2O to NADP+.

cyclic electron flow

A route of electron flow that employs only photosystem I, producing ATP but not NADPH or O2. Cyclic electron flow can occur in photosynthetic bacteria that have photosystem I but not photosystem II, and also some organisms that possess both photosystems, including prokaryotes.

light-harvesting complex

When a photon (particle of visible light) strikes a pigment molecule in a ________.

reaction center complex

the energy is passed from molecule to molecule until it reaches the ________.

primary electron acceptor

an excited electron from the special pair of chlorophyll a molecules is transferred to the ___________.

Photosystem II (P680) generates ATP

Some of the energy from the electrons is used to pump hydrogen ions into the thylakoids. The hydrogen ion concentration is therefore higher inside the thylakoids than in the stroma outside. Hydrogen ions move down this concentration gradient through ATP-synthases (ATP-synthesizing enzymes) in the thylakoid membranes, providing the energy to drive ATP synthesis (by chemiosmosis).

Photosystem I (P700) generates NADPH

Some of the energy, in the form of energetic electrons, is added to electron-carrier molecules of NADP+ to make the highly energetic carrier NADPH.

Splitting water maintains the flow of electrons through the photosystems.

Some of the energy is used to split water molecules, generating electrons, hydrogen ions, and oxygen.

Carbon fixation (CO2 uptake), Synthesis of G3P (CO2 reduction), and Regeneration of RuBP (the CO2 acceptor)

Calvin Cycle three major phases

Carbon fixation (CO2 uptake)

Carbon dioxide and water combine with ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PG or PGA). The enzyme that catalyzes this first step is RuBP carboxylase, or rubisco.

Synthesis of G3P (CO2 reduction)

3-PG is converted to glyceraldehyde-3-phosphate (G3P or PGAL), using energy from ATP and NADPH. The G3P spun off from the Calvin cycle becomes the starting material for synthesis of glucose, and other carbohydrates including sucrose, starch, and cellulose, as well as other organic molecules. These reactions occur primarily outside of the chloroplast.

Regeneration of RuBP (the CO2 acceptor)

Ten molecules of G3P are used to regenerate six molecules of RuBP again using ATP energy.

photorespiration

a wasteful pathway that occurs when the Calvin cycle enzyme rubisco acts on oxygen rather than carbon dioxide.