PhotosynthesisPhotosynthesis

• A great preparation for the Photosynthesis Web Quest.

• Science Grades 5 and 6• By: Laura Garrow

PhotosynthesisPhotosynthesis

The process in green plants and certain other The process in green plants and certain other organisms by which carbohydrates are organisms by which carbohydrates are

synthesized from carbon dioxide and water synthesized from carbon dioxide and water using light as an energy source. Most forms of using light as an energy source. Most forms of photosynthesis release oxygen as a byproduct.photosynthesis release oxygen as a byproduct.

What is photosynthesis?What is photosynthesis?

• Sunlight plays a large role in our world

• Photosynthesis is carried out by many different organisms, ranging from plants to bacteria.

• Name some ways that sunlight is useful on our planet.

PhotosynthesisPhotosynthesis

• This power for life that we call energy, flows into the food chain through our friends the busy plants.  The plants do something with that energy that seems miraculous.  They turn it into food. This is very nice of the plants because animals can't eat sunshine. They can only eat plants or each other.

PhotosynthesisPhotosynthesis

• Our mostly stationary green friends come to the Our mostly stationary green friends come to the rescue.  They take a little sunshine from the sky, rescue.  They take a little sunshine from the sky, a little carbon dioxide from the air around them, a little carbon dioxide from the air around them, a little water from the surroundings, and they a little water from the surroundings, and they turn those basic ingredients into little parts of turn those basic ingredients into little parts of themselves that we call plant cells.  This process themselves that we call plant cells.  This process is called photosynthesis. They also make and is called photosynthesis. They also make and release a useful little gas called oxygen during release a useful little gas called oxygen during photosynthesis.  photosynthesis.          

CO2 and OxygenCO2 and Oxygen

• Plants take in H2O from the ground.

• They take in CO2 through respiration

• They release Oxygen through respiration

QUIZ

• Pair up with your neighbor and answer these questions…

• How do plants use water?

• How do plants use CO2?

PhotosynthesisPhotosynthesis

• The basics of photosynthesis:

Parts of a leaf

• These parts of a leaf play a vital role in photosynthesis:

Leaf PartsLeaf Parts

• The chloroplasts, where photosynthesis occurs, are in the mesophyll cells.

• There are two kinds of mesophyll cells in our typical leaf.  Packed close together, are the palisade parenchyma region (I can't say it either - that's biologists for you).  This is where most photosynthesis is done.  The other region is called the spongy parenchyma region.  Here the cells aren't so close.  There are roomy air spaces between them. Jump on down to the leaf section below for the purpose of the air spaces.

Leaf PartsLeaf Parts

• Parts of the leaf:

LeavesLeaves

• It's amazing what's inside a leaf. The whole leaf looks green to us, but most of the cells and cell material are colorless or clear. The green color comes from the chlorophyll molecules in the chloroplasts.

Chlorophyll

• Chlorophyll is a complex molecule.

• All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll.

ChloroplastsChloroplasts

• Structure of a chloroplast:

ChloroplastsChloroplasts

• Now we're getting to some small plant parts.  But you can still see chloroplasts with a regular microscope. Inside the chloroplasts, in the stoma and the grana, is where photosynthesis happens.    

• Chloroplasts have fascinating little "organelles" with their own genetic material to make more of themselves.      

• Why are chloroplasts so important?     

Leaf SectionLeaf Section

• Leaf section

ThykaloidsThykaloids

• Now we have finally journeyed to the Now we have finally journeyed to the place where it all starts. The place where it all starts. The chlorophylls and other pigments that chlorophylls and other pigments that start the process are here, on the outer start the process are here, on the outer layer of the thylakoids. Photons from layer of the thylakoids. Photons from sunlight hit the pigments, electrons are sunlight hit the pigments, electrons are "knocked" loose, and off they go to "knocked" loose, and off they go to energize the complicated process of energize the complicated process of photosynthesis.photosynthesis.

Structural unitsStructural units

• The thylakoid is the structural unit of photosynthesis. Both photosynthetic prokaryotes and eukaryotes have these flattened sacs/vesicles containing photosynthetic chemicals. Only eukaryotes have chloroplasts with a surrounding membrane.

GranaGrana

• The little round flat pillow or pancake The little round flat pillow or pancake shaped things are called thylakoids. A shaped things are called thylakoids. A stack of them is called a granum. Two stack of them is called a granum. Two or more stacks are called grana.or more stacks are called grana.

• There can be from 2 to around 100 There can be from 2 to around 100 thylakoids in one granum. thylakoids in one granum.

Air SpacesAir Spaces

• You might call it breathing. Biologists like to call it gas exchange. We animals breath in oxygen and breath out carbon dioxide. Plants, and other autotrophs, do that too but they also need to do the opposite, get carbon dioxide in and oxygen out.

• All of these gas molecules get in and out through holes called stomas.  Then they flow into the roomy air passages of the spongy parenchyma region. These passages are all connected to each other and to the mesophyll cells.  So this is where the gas molecules get into and out of the photosynthesis "factory" cells.

StomaStoma

•  No air passes in or out unless the guard cells say so. Perhaps "Gate Keeper" cells would be a better name. They don't have muscles, but they can open and close. Fluid pressure is used to make the cells open and close the stoma.

Guard cellsGuard cells

• In a typical leaf, the guard cells are open during the day and closed at night. This can be a problem for the plants on hot dry days, because too much water is transpired, or evaporated, through the stomates. Loss of water slows down photosynthesis.

Glucose

• Gasoline is fuel for cars. Carbohydrates, made only by plants during photosynthesis, are the fuel for all living things.      

• A very important carbohydrate is a sugar (yes sugar is a carbohydrate) called glucose. Glucose is the basic fuel and basic building material for much of life.     

GlucoseGlucose• The picture below shows how glucose molecules are constructed. Notice that

they are made up only of Carbon (C), Hydrogen (H), and Oxygen (O).

Count each type of atom. How many carbon atoms are there?

SunlightSunlight

• All life needs energy to live, and the energy plants need comes from the sun.   

• We can stand in the sun all day, get warmed by it, even get a good sunburn, but we won't get nourished.

SunlightSunlight

• What the sunlight does:

SunlightSunlight

• White light is separated into the different colors (=wavelengths) of light by passing it through a prism.

• Wavelength is defined as the distance from peak to peak (or trough to trough). Longer wavelengths have less energy than shorter wavelengths.

Example of wavelengths

• Each wavelength represents how much energy and light is being used by the plant or autotroph.

Waves and rays

• The longer the wavelength of visible light, the more red the color. Likewise the shorter wavelengths are towards the violet side of the spectrum. Wavelengths longer than red are referred to as infrared, while those shorter than violet are ultraviolet.

Spectrum

• Remember that plants use only part of the spectrum.

• Blue, red, and blue-green light.

Pigment

• A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed).

• Chlorophyll, the green pigment common to all photosynthetic cells, absorbs all wavelengths of visible light except green, which it reflects to be detected by our eyes.

• Team up with your neighbor. • Why do we see the plants as green? Why do you think

we see some plants as red?

Why leaves are green

• We see green leaves because it is what our eyes can see from the light reflecting from the leaves.

Autotrophs

• Autotroph - Some living organisms can make their own food from inorganic material (stuff that does not come from living things) and sunlight.

• Autotrophs don't need to "eat" anything or anybody. All they have to do is sit around, or float around, catching some "rays", taking carbon from carbon dioxide in the air (if they are land plants), and absorbing a little water. Living organisms that can make their own food this way are called autotrophs. The process they use to make food is called photosynthesis.

Heterotrophs

• Heterotroph - The rest of us are heterotrophs. They could have called us "non-autotrophs", but we wanted our own name. Heterotrophs can't make their own food from sunlight, carbon, and water. Heterotrophs have to eat something. They have to eat an autotroph or another heterotroph. Then they digest what they ate and turn it into food. Animals are heterotrophs.

Quiz• Describe the process of photosynthesis.

• Name the parts of the leaf that are responsible for photosynthesis.

• What are Autotrophs?

• What are Heterotrophs?

Ready?Ready?

– I think you are ready to begin your Photosynthesis Web Quest!

• GOOD LUCK!!!