Photosynthesis&

Cellular Respiration

Energy & Living Things, Photosynthesis and Cellular Respiration

Chapter 5

Energy in Living Things Building Molecules That Store Energy

Metabolism: builds and breaks molecules Photosynthesis: conversion of light energy into

chemical energy Autotrophs: organisms that use sunlight or

inorganic molecules to produce organic matter These organisms include:

Plants – use sunlightProkaryotes – use chemicals flowing out

of earth vents on the ocean floor

Breaking Down Food for Energy Chemical energy can also be transferred

from one organic compound to another Ex. Hydrolysis using water to break bonds

Heterotrophs: organisms who receive chemical energy from consuming organic matter

Cellular respiration: releases energy that is contained in food to convert it to ATP (another form of energy)

ATP is the source of energy for cells to carry out their daily activities for an organism to survive

Transfer of Energy to ATP Similar to burning coal or wood for heat Food energy is released in a series of

enzyme-assisted chemical reactions The product from the previous reaction

becomes the reactant in the next reaction until ATP is created

Example: Starch is broken down into glucose and

glucose is broken down into Carbon Dioxide & Water

During the reaction: heat is released

ATP Adenosine triphosphate Removal of a phosphate group = energy Equation:

Photosynthesis All the energy used by organisms is traced

back to the sun Stages of Photosynthesis:

Energy is captured from the sun Light Energy → Chemical Energy: temporarily

stored in ATP and NADPH ATP and NADPH powers the formation of

organic compounds with the use of CO2

Equation:

Stage One: Absorption of Light Energy Light –Dependent Reactions Pigments

Light absorbing substances Absorb only certain wavelengths and reflect

all others Chlorophyll: absorbs blue & red, reflects green

& yellow Plants contain chlorophyll, chlorophyll a &

chlorophyll b Carotenoids: produce yellow and orange colors

Absorbs and reflect different wavelengths than chlorophyll

Enables plants to absorb more light during photosynthesis

Stage One: Continued Production of Oxygen

Thylakoids: disk-shaped structure containing of clusters of pigments in the chloroplast of the cell

Light strikes the thylakoids, energy is transferred to electrons and electrons move to higher levels

Electrons move from chlorophyll to nearby molecules to initiate stage two of photosynthesis.

These electrons are replaced by water molecules

Stage Two: The Conversion of Light Energy Electron Transport Chain (ETC): a series of

molecules that electrons pass through along the thylakoid membrane

Works around a concentration gradient – Hydrogen ions lose energy when they channel through a protein when the concentration builds within the cell, the ions diffuse out

The ions are “recharged” when they assist in adding a phosphate group to ADP to make ATP (first ETC)

In the 2nd ETC, electrons combine with hydrogen ions to create NADPH from NADP+

NADPH: electron carrier that provides high-energy electrons for stage three of photosynthesis

Stage Three: Storage of Energy Purpose: production of organic compounds

from carbon atoms Carbon Dioxide Fixation: transfer of carbon

dioxide to organic compounds (light-independent reaction)

Calvin Cycle A CO2 molecule added to a five-carbon

compound (3) Three 6-C compounds split into six 3-C

compounds One 3-C sugar is used to make organic

compound Five 3-C compounds are cycled through

Factors That Affect Photosynthesis Increase

Light Intensity Increases (until saturation) Carbon Dioxide concentration (until max)

Decrease Slowed by the Calvin Cycle Unfavorable conditions for enzymes

Cellular Respiration – Cellular Energy Aerobic: metabolic processes that require O2

Anaerobic: metabolic processes that do not require O2

Equation of Cellular Respiration:

𝑪𝟔𝑯𝟏𝟐𝑶𝟔+𝟔𝑶𝟐𝒆𝒏𝒛𝒚𝒎𝒆𝒔→

𝟔𝐂𝐎𝟐+𝟔𝑯𝟐𝑶+𝑨𝑻𝑷

Stage One: Breakdown of Glucose Glycolysis: enzyme assisted anaerobic process

that breaks down 6-C glucose into two 3-C pyruvate ions

Step 1: In 3 rxns, phosphate groups from 2 ATP are transferred to a glucose molecule

Stage One: Breakdown of Glucose Step 2: In 2 rxns, glucose broken down into two 3-

carbon compounds each with a phosphate

Stage One: Breakdown of Glucose Step 3: Two NADH molecules are produced and

one more phosphate group is transferred to each 3-C compound

Stage One: Breakdown of Glucose Step 4: In 4 rxns, each 3-C compound →→pyruvate

ion and four ATP molecules are produced

Summary of Glycolysis Uses 2 ATP to begin

Produces 4 ATP Net gain: 2 ATP

Glucose (6-Carbons) → Two 3-C pyruvate ions NADH and NAD+ are recycled

Stage Two: Production of ATP Oxygen present – pyruvate is converted to a 2-

carbon compound in the mitochondrion Reaction produces:

One molecule of CO2

One molecule of NADH One 2-C acetyl group attached to form acetyl-CoA

Krebs Cycle A cycle beginning with acetyl-CoA to produce ATP

Step 1: Acetyl-CoA attached to a 4-C compound to form a 6-C compound and release

CoA

Step 2: CO2 is released from 6-C compound forming a 5-C compound Electrons transferred to NAD+ to make NADH

Krebs Cycle - Continued Step 3: Another CO2 is released forming a 4-C

compound, an ATP molecule and NADH are produced

Step 4: 4-C compound converted to a different 4-C compound. Electrons transferred to FAD to produce FADH2

Step 5: 4-C compound converted to the original 4-C compound that started the cycle NADH produced

Electron Transport Chain Electrons are donated from NADH & FADH2

Located in the inner membrane of mitochondrion The energy of electrons are used to pump

out hydrogen ions Concentration gradient is created - causes

hydrogen ions to be pumped into the membrane

The energy created adds a phosphate group to ADP to form ATP

Products include: ATP and water molecules

Respiration in the Absence of Oxygen ETC cannot function – oxygen is the final electron

acceptor NAD+ is recycled in other ways Fermentation: recycling of NAD+ using

another form of organic hydrogen acceptor Lactic Acid Alcoholic

Lactic Acid Fermentation 3-C pyruvate converted to 3-C lactate Lactate: ion of its organic acid lactic acid

Formed during intense workouts During the conversion:

NAD+ and NADH are recycled No FADH2

Lactate expelled from muscles

Alcohol Fermentation 3-C pyruvate broken down to ethanol (2-C

compound) Step 1: Pyruvate is converted to 2-C compound

Carbon dioxide expelled Step 2: 2-C compound converted to ethanol During break down:

NAD+ and NADH are recycled Carbon dioxide expelled