PHOTOSYNTHESISChapter 8

8-1: Energy & Life

• Energy is supplied to some things in the form of gasoline or electricity

• Cells need energy too!

• Where do plants gets the energy they need to produce food?

• What is the role of ATP in cellular activities?

Autotrophs & Heterotrophs

• Living things get their energy from food

• The energy in most food comes from the sun

• Organisms that can make their own food are called autotrophs

• Heterotrophs obtain energy from the food they consume (by eating plants directly, eating animal that ate autotrophs, or by decomposing other organisms)

• All organisms must release the energy stored in sugars and other compounds in order to survive

Autotrophs use light energy from the sun to produce food. These impalas get their energy by eating grass. In contrast, a leopard gets its energy by eating impalas and other animals.

Impalas and leopards are both heterotrophs.

Chemical Energy & ATP• Cells use ATP (Adenosine triphosphate) to store and

release energy• ATP consists of adenine, ribose, and three phosphate

groups• ADP (Adenosine diphosphate) is like ATP, but with

2 phosphates instead of three• The energy is stored with the addition of the third

phosphate• Energy is released by breaking the bonds that holds

the third phosphate – used for active transport, protein synthesis, muscle contraction, etc.

Chemical Energy & ATP

ATP Formation

Using Biochemical Energy• Cells use ATP to move sodium ions (Na+) out of

the cell and potassium ions (K+) into the cell with sodium-potassium pumps

• ATP is also used to move organelles throughout the cell

• ATP is also used for:– Making proteins & nucleic acids, response to chemical

signals, & even the light in a firefly

• There is very little ATP in a cell, only enough for a few seconds.

• ATP is not useful for long-term storage – glucose can store 90 times more chemical energy

The Sodium-Potassium pump uses ATP

8-2: Photosynthesis: An Overview• In the process of photosynthesis, plants use the

energy of sunlight to convert water and carbon dioxide into high energy carbohydrates (sugars and starches) and oxygen (a waste product)

– What did the experiments of van Helmont, Priestley, and Ingenhousz reveal about how plants grow?

– What is the overall equation for photosynthesis?– What is the role of light and chlorophyll in

photosynthesis?

Investigating Photosynthesis

• When a tiny seedling grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from?

• Van Helmont, Priestley, and Ingenhousz performed experiments to find out

Three additional slides accompany this section

* Van Helmont’s Experiment

• Van Helmont carefully measured the mass of soil and a small plant

• After 5 years, the mass of the plant increased significantly, but the mass of the soil did not change

• He concluded that the mass of the plant came from the water he added

• This conclusion was partially correct

* Van Helmont’s Experiment

* Priestley’s Experiment

• Priestley sealed a candle in a jar and noticed it slowly went out

• This was due to the consumption of all the oxygen

• He noticed that if he placed a sprig of mint in the jar, the candle could be relighted after a few days and would remain lit for a while

• He concluded that the plant was supplying the material that the candle needed to burn (oxygen)

* Priestley’s Experiment

* Ingenhousz Experiment

• Ingenhousz experiment showed that Priestley’s experiment would only work if the plant was exposed to light

• Therefore, they showed that light is necessary to produce oxygen

• These (and other) experiments showed that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen

The Photosynthesis Equation

• Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen

Light and Pigments• In addition to water and carbon dioxide,

photosynthesis requires light and chlorophyll, a molecule in chloroplasts

• Plants gather the energy in light with molecules called pigments

• Chlorophyll absorbs light very well in the blue-violet and red regions of the visible spectrum

• Plants do not absorb green light very well

• When chlorophyll absorbs light, the energy raises the energy levels of the electrons which allows photosynthesis to work

8-3: The Reactions of Photosynthesis

• Describe the structure of a chloroplast

• What factors may affect the rate of photosynthesis?

Inside a Chloroplast• In plants and other photosynthetic

eukaryotes, photosynthesis takes place inside the chloroplasts

• Chloroplasts contain saclike membranes called thylakoids, which are arranged in stacks called grana

• The two parts of photosynthesis include the light-dependent reactions (in thylakoid membranes) and light-independent reactions (Calvin Cycle) in the stroma (region outside the thylakoid membrane)

Factors Affecting Photosynthesis• Since water is needed for

photosynthesis, a shortage of water can slow or stop the process

• Photosynthesis works best at temperatures between 0 and 35 degrees C due to enzyme activity

• Increasing light intensity increases photosynthesis