PHOTOSYNTHESIS AND CELLULAR RESPIRATION

Chap 5

Section 1

ENERGY AND LIVING THINGS• Metabolism involves

either using energy to build molecules or breaking down molecules in which energy is stored

• PHOTOSYNTHESIS - the process by

which light energy is converted to chemical energy of carbohydrates

• - sugar and starches

• AUTOTROPHS – organisms that use energy from sunlight or from chemical bonds inorganic substances to make organic compounds (food)

• Some prokaryotes use chemosynthesis to produce organic compounds

• HETEROTROPHS – organisms that must get energy from food instead of directly from sunlight or inorganic substances

• CELLULAR RESPIRATION – a metabolic process similar to burning fuel, but it converts food energy to ATP

• ATP provides cells with the energy needed to carry out the activities of life

• Chemical energy stored in food is released gradually

• The product of one chemical reaction becomes a reactant in the next reaction

• Some of the energy is released as heat, but the remaining energy is stored as ATP – portable form of energy

• Adenosine triphosphate

Flow of Energy• Energy flows

from sunlight or inorganic substances to autotrophs, such as grasses, and then to heterotrophs, such as rabbits and foxes

Energy Storage in Organisms• Plants store

energy in the form of starch

• Animals store energy in the form of glycogen

• Complete sentences

• P.96 section review 1-6

• P. 112 5a,6,12

PHOTOSYNTHESISsection 2

Using the Energy in Sunlight

Requirements for Photosynthesis• Sunlight – nearly all

organisms on Earth depend on sun for energy

• Pigments – colored substance that absorb or reflect light

• Energy-Storing Compounds – stored in the bonds of compounds

• Most important compound – one used by every living cell – ATP

• Adenosine triphosphate

• Inorganic substances – Water and Carbon Dioxide

• White Light – perceived as ”colorless”

• Actually a mixture of different wavelengths of light

• Visible spectrum – wavelengths visible to our eyes

• Infrared and ultraviolet – not visible to our eyes

• About 1 % of the energy in the sunlight is converted to chemical energy

• Three stages of Photosynthesis

• Stage 1: Energy is captured from sunlight.

• Stage 2: Conversion of Light Energy

• Stage 3: Storage of Energy

Stage 1Absorption of Light Energy

• First & second stages are sometimes called “light reactions”

• Light is a form of radiation – energy in the form of waves

• Pigments absorb only certain wavelengths and reflect all the others

• Chlorophyll absorbs mostly blue & red lights

• Plants contain two types of chlorophyll, a and b, a being the most important

• Carotenoids – pigments that produce yellow & orange colors – absorb wavelengths of light different from chlorophyll

• Most of the pigments reflect the color green, making the leaves appear green

Production of Oxygen• Thylakoids-

located in the chloroplasts & contain the pigments necessary for photosynthesis

• Light energy is transferred to electrons causing them to be “excited”

• Electrons jump to other molecules where they are used to power the second stage

• Replacement electrons come from water molecules

• Water molecules are split by enzymes, leaving H+ ions, and O atoms, forming Oxygen gas,

Stage Two: Conversion of Light Energy• Electron Transport

Chains (2)- series of molecules through which excited electrons are passed along a thylakoid membrane

• First, provides the energy needed to change ADP to ATP – needed by dark reaction

• A second electron transport chain provides energy used to make NADPH- which is needed by the dark reaction

• NADPH – electron carrier that provides the high-energy electrons needed to make carbon-hydrogen bonds in the third stage

• Excited electrons combine with hydrogen ions & NADP+ to form NADPH

Animated Light Reaction

• http://www.uic.edu/classes/bios/bios100/lectures/light_reaction.htm

Photosynthesis Problem

http://www.uic.edu/classes/bios/bios100/lectures/photorespiration.htm

Dark Reaction(Light Independent Reaction)

• Dark reactions generally take place in sunlight; light does not play a role in the dark reactions

• The simple inorganic molecule carbon dioxide is used to make a complex organic molecule

• Melvin Calvin, American, worked out cycle

Stage Three: Storage of Energy• CARBON DIOXIDE

FIXATION – transfer of carbon dioxide to organic compounds

• Considered light-independent “dark reactions”

• Most common method is the Calvin cycle

• Calvin cycle- a series of enzyme-assisted chemical reactions that produces a 3-C sugar

• The reactions are cyclic – they recycle the five-carbon compound needed to begin the cycle again

• The energy used in the Calvin cycle is supplied by ATP and NADPH made during the second stage of photosynthesis

Calvin Cycle Animated

http://www.uic.edu/classes/bios/bios100/lectures/calvin.htm

Light and Dark Reactions

• http://leavingbio.net/PHOTOSYNTHESIS.htm

Factors that Affect Photosynthesis• Light – photosynthesis

increases as light intensity increases until all the pigments are being used –limited by Calvin reaction which is the slowest step

• Carbon dioxide concentration – once a certain concentration is reached photosynthesis is limited

• Temperature- certain range is more efficient

• Water – the availability of water and the amount of rainfall

• Nutrients – how much organic matter that soil contains

• P. 103

• Section 2 review 1-6

• P. 112 1,2, 5c,8,9, 11

• Standardized Test Prep 1-3

Cellular Respiration• Food contains usable

energy in the form of protein, fat, & carbs (considered organic)

• Energy has to be transferred to ATP, which is done through cellular respiration

• AEROBIC respiration- metabolic processes that require oxygen, more efficient in making ATP

• ANAEROBIC-metabolic processes that do not require O2

Stages of Cellular Respiration• Stage I:

Breakdown of Glucose

• Stage II: Production of ATP

Stage I: Breakdown of Glucose• Glycolysis: takes place

in the cytoplasm- an enzyme-assisted anaerobic process that breaks down one 6-C molecule of glucose to 2 3-C pyruvic ions

• 4 Steps in the series on page 105 – you can copy them from the book

• Glycolysis uses two ATP but produces four ATP

Stage 2: Production of ATP• Krebs Cycle enzyme-

assisted reactions named for Hans Krebs, 1937

• 5 steps on p. 106 & 107

• Much of the energy that was stored in glucose & pyruvate is now stored in NADH and FADH2

Krebs Cycle

• http://www.1lecture.com/Biochemistry/How%20the%20Krebs%20Cycle%20Works/index.html

Electron Transport Chain• The electron

transport chain pumps hydrogen ions, H+, out of the inner compartment.

• At the end of the chain, electrons & hydrogen ions combine with oxygen, forming water.

• ATP is produced as hydrogen ions diffuse into the inner compartment through a channel protein.

Respiration in the Absence of Oxygen• Electron transport chain

does not function if oxygen is not available as final electron acceptor.

• Electrons in NADH are transferred to pyruvate; enables the recycling of NAD+ which is needed to make ATP

• Fermentation- recycling of NAD+ using an organic hydrogen acceptor

Lactic Acid Fermentation• Pyruvate is converted to

lactate• Lactate is the ion of lactic

acid• Vigorous exercise –

muscles must operate without enough O2 –

• ATP produces only while glucose supply lasts

• Blood removes excess lactate, but if not quickly-can cause muscle soreness

Alcoholic Fermentation• Two step process

a. Pyruvate is converted to 2-C compound, releasing CO2

b. Electrons are transferred from NADH to the two-C compound, producing ethanol

Yeast, a fungus, uses alcoholic fermentation. Yeast is used in bread industry and alcoholic beverages

Ethanol (12%) kills yeast

Production of ATP• Total of ATP

produced from glucose depends on the absence or presence of O2

• 2 ATP molecules are made during the Krebs cycle

• 34 ATP are produced by the electron transport chain

Types of chemical reactions

• An exothermic reaction is a chemical reaction that releases energy in the form of heat..

• An endothermic reaction is any chemical reaction that absorbs heat from its environment.

• These examples could be written as chemical reactions, but are more generally considered to be endothermic or heat-absorbing processes:

• melting ice cubes • melting solid salts • evaporating liquid water

• converting frost to water vapor (melting, boiling, and evaporation in general are endothermic processes)

• splitting a gas molecule

• cooking an egg

Homework

• Page 110 - section review 1-6

• Page 112 – 3,4, 5b, 5d,7,10,13,14,19

• Test Part 2 over section 3 Monday 8th

• 10 true false 14 multiple choice and discussion