CELL ENERGY

PHOTOSYNTHESIS

&

RESPIRATION

PHOTOSYNTHESIS

l PLANTS CONVERT ENERGY FROM SUNLIGHT TO CHEMICAL ENERGY

–SUNLIGHT => CARBOHYDRATES

CO₂ + H₂0 ==> (CH₂O)_N + 0₂

6CO₂ + 6H₂0 ==> C₆H₁₂0₆+ 60₂

BALANCED

REQUIREMENTS FOR PHOTOSYNTHESIS

l SUNLIGHT:

– autotrophs - green plants that produce their own food

– heterotrophs - organisms that obtain food from others

l PIGMENT:

– colored substances that absorb light.

u Chlorophyll - green (primary pigment), absorbs red and blue light

l ADENOSINE TRIPHOSPHATE (ATP):

– ATP => ADP + P + ENERGY

– ADP => AMP + P + ENERGY

LIGHT REACTIONS

l LIGHT REACTIONS USE LIGHT TO CAPTURE ENERGY AND STORE ENERGY

l 4 BASIC PROCESSES:

– LIGHT ABSORPTION

– ELECTRON TRANSPORT

– OXYGEN PRODUCTION

– ATP FORMATION

LIGHT REACTIONS - LIGHT ABSORPTION

l Pigment molecules called photosystems capture energy from the sun

– PHOTOSYSTEM I & PHOTOSYSTEM II

l Pigments absorb sunlight in the color spectrum that chlorophyll can’t absorb

l absorption of light causes a flow of energy throughout the cell

l special pairs of chlorophyll molecules are able to convert light energy into a useful chemical form

LIGHT REACTIONS - ELECTRON TRANSPORT

l Energy captured by the chlorophyll pair is transferred by electron carriers along an electron transport chain

l NADP+ : special carrier converts electrons to NADPH; a more useful form of energy

LIGHT REACTIONS - OXYGEN PRODUCTION

l As electrons move energy away from the chlorophyll to the NADP+, new electrons are put back from H₂O

2H₂O ==> 4H⁺ + O₂

u4 ELECTRONS ARE RELEASED

LIGHT REACTIONS - ATP FORMATION

l The H+ ions left after water is split are released and build up concentration in the cell.

– Outside membrane becomes negatively charged

– Inside membrane becomes positively charged

l As the membrane balances out the charge ATP is formed

Summary of light reactions

l Light reactions:

– use water, ADP, NADP+

– produce oxygen, ATP, NADPH

STEPS OF RESPIRATION

l DARK REACTIONS

– Generally take place in the light

– use products of light reactions

– uses CO₂ to make complex organic molecules

– operates in a cycle (Calvin cycle)

STEPS OF DARK REACTIONS

l 5 Carbon sugar + CO₂ => 3 carbon rubisco (enzyme)

l 3 carbon converts to PGAL with the help of ATP and NADPH

GLYCOLYSIS

l THE BREAKDOWN OF GLUCOSE

– OPPOSITE REACTION AS PHOTOSYNTHESIS

C₆H₁₂O₆ + 60₂ ==> 6CO₂ + 6H₂0

*REACTION PRODUCES ENERGY

(3811 CALORIES PER GRAM OF C₆H₁₂O₆)

STEPS OF GLYCOLYSIS

l Glucose goes through several reactions and splits into two 3 carbon PGAL molecules

– uses 2 ATP molecules in the process

l 2 PGAL molecules breakdown into 2 pyruvic acid molecules (a 3 carbon molecule)

– makes 4 ADP and 2 NADH molecules

l * 4 ATP molecules are made from 4 ADP molecules

l * NET GAIN OF 2 ATP MOLECULES

RESPIRATION

l THE BREAKDOWN OF FOOD TO ENERGY WITH THE HELP OF OXYGEN

– AEROBIC PROCESS: requires oxygen

– occurs in both plants and animals

– takes place in the mitrochondria

u1st set of reactions - inner membrane

u2nd set of reactions - between the inner membrane

STEPS OF RESPIRATION

l KREBS CYCLE

u1st set of reactions of respiration

utakes the pyruvic acid from glycolysis

udoes not produce any end products

STEPS OF THE KREBS CYCLE

l Pyruvic acid in cytoplasm converts to CO₂ and acetic acid in the mitochondria

l acetic acid enters the Krebs cycle

– acetic acid + 4 C => citric acid (6C)

l 18 other reactions take place

– 2 places CO₂ is released

– 4 places electrons transfer

– 1 place GDP is converted to GTP to make ATP

ENERGY TOTALS

l GLYCOLYSIS

– 2 ATP USED

– 4 ATP MADE

– 2 ATP RESERVE

– 4 NADH (10 ATP)

– TOTAL 12 ATP

l RESPIRATION

– 6 NADH, 2 FADH₂ (22 ATP)

– 2 GTP (2 ATP)

– TOTAL 24 ATP

SUMMARY

l Photosynthesis = “deposits” energy

l Respiration = “ withdraws” energy

l they are opposite reactions

l photosynthesis is the opposite of the breakdown of glucose

l the products of photosynthesis are the reactants of glucose breakdown

ANAEROBIC PROCESSES

l LACTIC ACID FERMENTATION

– Energy made in the absence of oxygen

– Regenerates NAD+ to be used by glycolysis

l ALCOHOLIC FERMENTATION

– Pyruvic acid combines with NADH to produce alcohol + carbon dioxide and NAD+