Chapters 6 & 7

Photosynthesis & Cellular Respiration

These processes are opposites!

The equation for photosynthesis:

6CO 2 + 6H 2 O + light energy C 6 H 12 O 6 + 6O 2 Carbon Dioxide + Water + sunlight –make Organic compounds (sugar) + Oxygen

Photosynthesis & Cellular Respiration are related:

• The oxygen (O 2 ) and some of the organic compounds produced by photosynthesis are used by cells in a process called

cellular respiration

.

In which organelles in cells do these process occur?

•

Photosynthesis occurs in the chloroplasts.

•

Cellular respiration occurs in the mitochondria.

Cellular Respiration is basically the opposite of Photosynthesis

•

Photosynthesis creates biomass (organic compounds) by converting light energy into chemical energy (stored as carbohydrate, ATP or other high energy molecule)

•

Cellular respiration is the process by which cells break down organic compounds to produce ATP (energy).

Cellular respiration is essentially photosynthesis in reverse

Photosynthesis

Energy from the sun:

Photosynthetic organisms are vital to the survival of all life on Earth.

For this slide show, Diagrams & information are from Holt biology text

Photosynthesis is vital- because it is beginning of almost all food chains

http://www.umaine.edu/umext/earthconnections/images/foodchain.gif

Discuss the following:

•

Name 3 foods you ate today & think about how this food is related to plants.

•

What is the difference between an organic compound and an inorganic compound?

•

What is a carbohydrate?

•

How does photosynthesis cause inorganic compounds to become organic?

Remember:

• •

Organic Compounds contain Carbon!

Carbohydrates:

– Molecules that are a source of

energy

– Example:

Glucose

–

General formula for a carbohydrate is [CH2O]n where n is a number between 3 and 6.

–

Glucose is C 6 H 12 O 6

Obtaining Energy from the sun to make inorganic compounds into organic compounds:

•

Photosynthesis

- converts

light energy

from the

sun

into

chemical energy

in the form of organic compounds through

a series of reactions called biochemical pathways

.

Part I.

The Light Reactions

A.

All organisms need energy to carry out the functions of life.

Where does this energy come from 1. Directly from the sun-

•

autotrophic organisms make sugar from sunlight, CO2 & H2O (examples- all plants, algae, cyanobacteria, plant-like protists) 2. Indirectly from the sun-

•

heterotrophic organisms – need to eat autotrophs )

There are 2 parts to photosynthesis

•

Light reactions

– Light energy is absorbed form the sun and is converted to chemical energy temporarily stored in the bonds of ATP and NADPH •

Calvin cycle

– organic compounds are formed using CO2 (now using the chemical energy stored from the light reactions)

B. Capturing Light Energy

•

The light reactions

– begin with the absorption of light in-

Chloroplasts

•

organelles found in the cells of plants, some bacteria, and algae.

•

Inside chloroplasts are Thylakoids , a system of membranes inside the chloroplast that look like flattened sacs

Light and Pigments

–

White light from the sun is composed of an array of colors called

th e vi si

ble s

pect rum .

–

Pigments

absorb certain colors of light and reflect or transmit the other colors.

•

Chlorophyll a & b

•

Carotenoids

The sun emits energy at a range of wavelengths: the visible spectrum is a small part of that range.

•

Chloroplast Pigments

– Located in membranes of the

thylakoids

of chloroplasts are several

pigments

, including

chlorophylls

(

chlorophyll a

and

chlorophyll b

) and

carotenoids.

How light is absorbed

Light Energy into Chemical Energy

•

Photosystems-

In the thykaloid membranes of chloroplasts- are the clusters of pigment molecules that harvest light energy for photosynthesis •

There are 2 photosystems:

–

Photosystem II

–

Photosystem I The 2 photosystems have similar pigments but different jobs in the chloroplast:

Photosystems II & I:

• •

Light Energy

is absorbed by

chlorophyll a molecules.

“Excited electrons”

in this higher energy level have enough energy to leave the chlorophyll

a

molecules.

• • the

primary electron acceptor

electrons to the donates the

electron transport chain.

NADPH is produced chemical energy!) . (now Energy is stored as

Water is needed:

•

The electrons are replaced by breaking down water

–

The Hydrogen is used to replace the H+ and the e used in the light reactions

–

Oxygen is a waste product.

Making ATP in Light Reactions

– An important part of the light reactions is the

synthesis of ATP.

–

Chemiosmosis

is the movement of protons through ATP synthase (an enzyme) & then into the stroma (This causes a concentration gradient. It releases energy, which is used to produce ATP.) –

Stroma

-the solution that surrounds the thykaloid membrane in chloroplasts.

II. Calvin Cycle

(The dark reactions) •

Carbon Fixation: The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis, the Calvin cycle.

•

In the Calvin cycle, CO 2 is incorporated into organic compounds, a process called carbon fixation.

The Calvin cycle is the most common way that plants fix carbon

• Occurs in the

stroma

of the

chloroplast

• Is a series of enzyme-assisted chemical reactions that produces

a three-carbon sugar called G3P

– Some G3P sugars are used to make

organic compounds

, (energy is stored for later use.) – Some G3P is converted to a

five-carbon sugar (RuBP) to keep the cycle going.

Alternative “Dark” Pathways

•

The C 4 Pathway

– Some plants that evolved in hot, dry climates fix carbon through the

C 4 pathway

.

These plants have their stomata partially closed during the

hottest

part of the day. •

The CAM Pathway

– Some plants in hot, dry climates fix carbon through the

CAM pathway

.

These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize

water loss

Summary photosynthesis

Chapter 7 is

Cellular Respiration

•

Cellular respiration is the process by which cells break down organic compounds to produce ATP .

• Products of cellular respiration are the reactants in photosynthesis;

they are opposites

!

Plants & Animals:

•

Both autotrophs and heterotrophs use cellular respiration to get energy from organic compounds and O 2 & produce waste products CO 2 and water

Cellular respiration can be divided into 2 stages:

•

glycolysis

•

aerobic respiration.

During

glycolysis

•

One six-carbon glucose

molecule is oxidized to form

two three-carbon pyruvic acid

molecules. • A

net yield of two ATP molecules

is produced for every molecule of glucose that undergoes glycolysis

Glycolysis takes a 6-carbon sugar & breaks it into 2 3-carbon sugars http://terravivida.com/vivida/glyintro/page01.htm

Remember: lysis means to break up

• Breaking up the glucose molecule into 2 smaller sugars (pyruvic acid) provides energy to make ATP which is the principle energy 'currency' in the cell http://terravivida.com/vivida/glyintro/page05.htm

What happens after glycolysis?

•

If no oxygen is available fermentation occurs

•

If oxygen is available the krebs cycle

1. Fermentation

.

• • •

Occurs if oxygen is not present convert pyruvic acid into other compounds For example: 1. Lactic Acid Fermentation

– an enzyme converts pyruvic acid into another three-carbon compound, called

lactic acid.

2. Alcoholic Fermentation

– Some plants and unicellular organisms, (like yeast) convert pyruvic acid to

ethyl alcohol & CO 2 .

2. Aerobic Respiration

• occurs in the

mitochondria.

• occurs

only if oxygen

is present in the cell.

•

Called the Krebs cycle

The Krebs cycle

• Also known as the

tricarboxylic acid cycle (TCA),

• was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs

Krebs happens in the mitochondria • After the glycolysis takes place in the cell's

cytoplasm,

• the pyruvic acid molecules travel into the interior of the

mitochondria.

The Krebs Cycle

: (There are actually 8 steps. Not all are show here) Each turn produces 1 ATP 2 CO2 3 NADH 1 ADH2 http://ncam.wgbh.org/publications/stemdx/images/krebs.jpg

The Krebs Cycle.

• • First,

pyruvic acid

(produced in glycolysis) reacts with coenzyme A to

form acetyl CoA.

Then, acetyl CoA enters the Krebs cycle. • The original glucose becomes completely broken down after

2 turns

of the Krebs cycle.

2 turns produce:

–

four CO 2 molecules,

–

two ATP molecules,

–

and hydrogen atoms that are used to make six NADH and two FADH 2 molecules.

Finally:

Electron Transport Chain

•

High-energy electrons in hydrogen atoms from NADH and FADH 2 are then passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane

Efficiency of Cellular Respiration

•

Cellular respiration can produce up to 38 ATP molecule s from the oxidation of a single molecule of glucose.

•

Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose.

•

Thus, cellular respiration is nearly 20 times more efficient than glycolysis alone

.

Summary of Cellular Respiration

•

Providing cells with energy in the form of ATP

is an important function of cellular respiration. • Also: Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

Summary diagram- cellular respiration: http://www.chem.uwec.edu/Webpapers2005/mintermm/pages/Intro_media/intro.gif