Photosynthesis

Chapter 8YouTube - MY FAVE SONG: THE PHOTOSYNTHESIS SONG

• 8-1 Energy of LifeAll living things depend on energy.

• Everything thing they do requires energy.

• To get energy, living things need food. The energy in food originally comes from the sun.

• Plants and some other organisms are able to use light energy from the sun to produce food.

• Organisms that make their own food are called autotrophs.

“Auto-” means self.

“-troph” means food.

• Organisms that cannot use the sun’s energy directly must obtain energy from the foods they consume (eat).

• Heterotrophs obtain energy from the foods they consume.

• Hetero- means other.

• Energy is stored in chemical compounds. One of the main chemical compounds that cells use to temporarily store and release energy is adenosine triphosphate (ATP).

• ATP consists of adenine, a 5-carbon sugar, and 3

phosphate groups.

These 3 phosphate groups are the key to ATP’s ability to store and release energy.

• The bonds between the phosphate groups of ATP can be broken. When the last phosphate bond is broken, a molecule of inorganic phosphate leaves ATP forming ADP (adenosine diphosphate).

ATP → ADP + Pi

This process releases energy that the cell can use to do work.

• When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, producing ATP.

• ATP has enough energy to power a variety of cellular activities.

• Any activity that requires energy can get what it needs by breaking down ATP.

• Even though ATP is a great source of energy, most cells have only a small amount of ATP, enough to only last them for a few seconds of activity.

• So what we need is a compound that can store lots of energy for long periods of time!!!

• Cells have many molecules that can store energy. One of it’s favorites is glucose (sugar).

• Glucose can store 90 times more energy than ATP.

• Cells can pull the energy from compounds like glucose to make more ATP.

8-2 Overview of Photosynthesis.The most important process for energy production is

photosynthesis.

Plants – YouTubeSpongebob photosynthesis - YouTube

• Plants (an other photoautotrophs) use the energy of sunlight to convert water and carbon dioxide into high-energy sugars (like glucose) and oxygen.

• The chemical equation for these reactions is…

6CO2 + 6H2O C6H12O6 + 6O2

All plants need is carbon dioxide from the air, water from the soil, and a little sunlight and they can make food (glucose) and release oxygen.

• The energy from the sun travels to Earth in the form of light.

• To us, the sunlight looks white but it is actually a mixture of wavelengths of light.

• We think sunlight is white because all these wavelengths blend together producing white.

• But each different wavelength produces different colors.

• By breaking up light into its different wavelengths we can see the visible light spectrum.

• The colors of the rainbow… ROY G BIV

• Let’s take a minute and break up some light into its different wavelengths (colors).

• Plants gather the sun’s energy with special chemicals called pigments.

• The main pigment in the leaves of plants is chlorophyll.

• Pigments absorb and get energy from certain wavelengths of light.

• Chlorophyll absorbs light in the blue-violet and red regions of the light spectrum.

• Chlorophyll cannot absorb the energy from the green region of the light spectrum so it reflects this wavelength…

• This is why leaves look green!!!

Plants also contain red and orange pigments (remember they reflect those wavelengths) called carotenes that help in absorbing light energy.

• The reason we don’t usually see these pigment colors in leaves is because there are so much more chlorophyll than these carotenes.

• We can usually only see them in the fall when chlorophyll moves out of the leaves.

• I feel another song coming on!!!

• Photosynthesis - They Might Be Giants - YouTube

8-3 The Reactions of Photosynthesis

Photosynthesis takes place inside cell organelles called chloroplasts.

The cells in the leaves is where you are going to find plenty of chloroplasts.

• If you look inside the double-membraned chloroplasts you will find flat saclike structures called thylakoids.

• These sacs are stacked up in a structure called grana.

• The space between the thylakoids is filled with a gel-like substances called the stroma.

• Photosythesis is a two-part process.

• Let’s look at the equation for photosynthesis again…

Sunlight

6CO2 + 6H2O C6H12O6 + 6O2

The goal is to make glucose. We are going to need water and carbon dioxide to pull this off (and of course, sunlight).

In the first part of photosynthesis we are going to get the energy from the sun and convert that to chemical energy.

It’s not until the second part of photosynthesis that we actually assemble glucose and store that trapped energy in that molecule.

• The first part takes place in the membrane of a thylakoid. Sunlight and water need to be added.

• Since light is needed, this part of photosynthesis is called light-dependent reactions.

• To understand the light-dependent reactions we need to become acquainted with what makes up the thylakoid membrane.

• The thylakoid membrane looks a lot like the cell membrane with embedded proteins. Two main proteins (called photosystems) are surrounded by chlorophyll.

• The photosystems are like solar panels that absorb sunlight.

When light hits the photosystems, the electrons in chlorophyll get excited and begin moving.

• The light-dependent reactions begin at Photosystem II.

• When the sunlight excites the electrons in chlorophyll, these moving electrons split two waters.

• Water is separated into oxygen gas and the hydrogen are split up

into hydrogen ions (H+) and the electrons.

• The hydrogen ions (H+) get dumped into the inside of the thylakoid and the electrons are sent to the electron transport chain. Oxygen is released out of the cell.

• The electron transport chain (ETC) contain carrier proteins that shuttle the electrons from Photosystem II to Photosystem I.

• By the time the electrons get to Photosystem I, they have run out of energy so it’s time to add more sunlight to get those electrons excited again.

• After the electrons are excited again they will continue down the electron transport chain.

• When the electrons get to the end of the chain, there is a molecule of NADP+ waiting to catch these electrons.

• When NADP+ catches the electrons and a H+, it becomes NADPH.

• This molecule is going to head to the second part of photosynthesis.

• In the meantime, a lot of H+ have built up inside the thylakoid. Because of diffusion, these H+ want to move from an area of

high concentration to low concentration (which would be the outside of the thylakoid.

• As H+ move out through a special protein called ATP synthase, ADP and Pi are driven together forming ATP. This ATP will head over to the second part of photosynthesis too.

• Let me explain… no it’s too much, let me sum up.

• During the light-dependent reactions in photosynthesis, light energy is used to split water, taking those electrons through the ETC and giving them to NADP+ forming NADPH.

• Also ATP is made by the movement of H+ from the thylakoid space to the stroma.

• Now we have two high-energy molecules moving over to the light-independent reactions.

ATP and NADPH are going to be needed in the second part of photosynthesis (Calvin cycle) where glucose (food) is going to finally be made.

• Clear as mud????

YouTube - Photosynthesis (Light Reactions)

• The second part of photosynthesis is called the light-independent reactions…

also known as the Calvin cycle.

• All the reactions involved in the Calvin cycle take place in the stroma (the jelly-like substance in the chloroplasts).

• The Calvin Cycle does not require light.

• It gets its energy from the ATP and NADPH (products of the light-dependent reactions).

• The Calvin cycle uses this energy to produce high-energy sugars (usually glucose).

• The Calvin cycle uses carbon dioxide from the air to build a 6-carbon sugar.

• It takes a total of 6 carbon dioxides to make one molecule

of sugar.

• Let’s watch the Calvin cycle in action!

• Calvin cycle - YouTube

• Let’s try tomodel whatis happening here!

• Plants use the sugars to meet their energy needs.

• When organisms eat plants, they can also use the energy stored in carbohydrates.

• The two sets of photosynthetic reactions work together to produce stable, high-energy sugars from carbon dioxide, water,

and sunlight.

• And in the process, release oxygen for animals!

• Many environmental factors can affect how well a plant can carry out photosynthesis.

• A shortage of water can slow or even stop photosynthesis.

• Many desert plants have adapted to dry conditions.

• Temperature can also be a factor. Because all the chemical reactions that take place in photosynthesis rely on enzymes, these enzymes must be within a certain temperature in order to do their job.

• Too hot or too cold and photosynthesis may stop all together!

• The intensity of light also affects the rate at which photosynthesis occurs.

Increasing sunlight increases the rate of photosynthesis (well, to a certain point).

http://www.youtube.com/watch?v=cX3Iev-JDgM

• Let’s Review!!

Let’s end with another song!

Photosynthesis Rap - YouTube