Photosynthesis and Cellular Respiration

Honors Biology

Photosynthesis and respiration form a

continuous cycle because the products of one process

are the reactants for the other.

Photosynthesis

• Reactants: CO2, H2O, light

• Products: Carbohydrate, O2

• Write the equation…

Where do the reactants come from? How do they get into

the plant?• Water from rain – through

roots – remember CAPILLARY ACTION

• CO2 into leaves through stomata – openings in the leaf

• Light is trapped by chlorophyll in leaf cells

Stomata allow CO2 to enter and O2 and H2O to exit.

Guard cells control the opening and closing of the stomata.

Cellular Respiration• Reactants: carbohydrates, O2

• Products: CO2, H2O, and ATP for cell processes

• Write the equation…

Energy is stored in organic molecules made by linking carbon atoms together. Excess carbohydrates produced by plants provide food for animals.

Before we start…

• An electron carrier is an energy carrier.

• NADPH• NADH

• FADH2

Photosynthesis is the process that transforms light energy to chemical bond energy.

It takes place in the Chloroplast.

• Thylakoid membrane: internal membranes that trap energy

• Grana: stack of membranes• Stroma: liquid portion

of chloroplast

Photosynthesis consists of two reactions: light reactions and Calvin Cycle.

LIGHT REACTIONS:

the “photo” in photosynthesis

Electrons in chlorophyll absorb

Energy: when enough is absorbed, electrons

leave and release Energy along electron

transport chains.

Chlorophyll FA new kind of chlorophyll that catches sunlight from just beyond the red end of the visible light spectrum has been discovered. The new pigment extends the known range of light that is usable by most photosynthetic organisms. Harnessing this pigment’s power could lead to biofuel-generating algae that are super-efficient, using a greater spread of sunlight than thought possible.

Chlorophyll picks up replacement electrons when water is split.

Hydrogen’s electrons are taken, leaving H+.

Oxygen is released.

Energy from one ETC is stored as ATP.

H+ are pumped into the thylakoid until the

pressure increases and forces the H+ out

through ATP synthetase channels

into the stroma.

Energy from the other ETC is stored as NADPH

Excited electrons combine with H+ and

NADP (an electron acceptor)

NADPH and ATP are used in the Calvin

Cycle.

REVIEW OF LIGHT REACTION

• Light is absorbed• Water is split• NADPH and ATP are produced• Oxygen is released

CALVIN CYCLE: the “synthesis” in photosynthesis

Carbon Dioxide Fixation:

•Carbon (in CO2) is added to a FIVE- Carbon organic compound (already in the cycle)

•Produces SIX-Carbon molecule (unstable)

IMMEDIATELY

•SIX-Carbon Unstable Molecule is split

•Produces 2 THREE-Carbon PGA molecules

•2 THREE-Carbon PGA

•Added to NADPH and ATP (from light reaction)

•Produces 2 THREE-Carbon PGAL sugar

The 2 THREE-Carbon PGAL may combine to form

glucose or another carbohydrate.

Most are used to regenerate the original FIVE-Carbon compound to restart the

cycle.

PGA

PGAL

C6H12O6

Original 5-C

compound

Review of Calvin Cycle

• CO2 used

• NADPH and ATP from light reaction used

• Glucose produced

CELLULAR RESPIRATION

Two Stages

•Breakdown of Glucose

•Production of ATP

STAGE 1

•GLYCOLYSIS: “to break up glucose”

•Anaerobic: does not require oxygen

•Occurs in the cytoplasm

STAGE 1 continued

• Requires 2 ATP• Glucose is broken down into 2

THREE-Carbon molecules of pyruvate

• Produces 2 NADH and 4 ATP• NET gain of 2 ATP

After glycolysis, the remainder of the process

is aerobic (requires oxygen).

STAGE 2

• Pyruvate enters mitochondria• Converted to a TWO Carbon

Acetyl group

• CO2 is released

• NADH is produced• Acetyl group combines with

coenzyme A to make Acetyl coA

STAGE 2 continued

• Acetyl coA enters the Krebs cycle (Citric Acid Cycle)

• Acetyl coA combines with a FOUR-Carbon molecule already in the cycle to make a SIX-Carbon molecule (citric acid)

• coA is released• CO2 is released from the SIX-Carbon

molecule, leaving a FIVE-Carbon molecule (NADH made)

• CO2 is released again from the FIVE-Carbon molecule, leaving a FOUR-Carbon molecule (NADH and ATP made)

STAGE 2 continued

• FOUR-Carbon compound is converted to a new FOUR-Carbon compound, making FADH2

• New FOUR-Carbon compound is converted to the compound that started the cycle

• NADH and FADH2 are used in the electron transport chain

The short version:

• It produces ATP , NADH, and FADH2, and releases CO2

STAGE 2 continued

• Electron Transport Chain– NADH and FADH2 (from Krebs

cycle) pass through the ETC in the inner membranes of mitochondria

– Large amounts of ATP produced as H+ are pumped through the membrane

– At the end of the ETC, H+ and electrons combine with O2 to form H2O

The short version:

• It requires oxygen, uses NADH and FADH2, and it produces ATP for cell processes

When oxygen is not available

• Fermentation occurs in animals: e- from glycolysis are added to organic molecules to form Lactic Acid. – Not very efficient…only 2 ATP

• Alcoholic fermentation occurs in fungi and plants: Bacteria and yeast can convert pyruvic acid into alcohol and carbon dioxide.