12 - Polytech High School

12 Photosynthesis and cellular respiration

Every living cell needs a source of energy. Without energy, metabolism-- all of the chemical reactions that occur within cells--will not occur. In this activity, you will learn how the complex chemical reactions of photosynthesis and cellular respiration help meet the energy needs of living things. You will examine the organelles, molecules, and chemical reactions involved in these two processes. You will also learn how a microbe or chemical that disrupts one or more of the steps of photosynthesis or cellular respiration causes disease.

Challenge

solar energy sunlight

co2 h2o

photosynthesis in chloroplasts cellular respiration in mitochondria

car on containing molecules h2o

aTP

powers most cellular wor

Photosynthesis and

heat

cellular respiration

meet the energy needs

of organisms.

00how do photosynthesis and cellular respiration meet the energy needs of all organisms?

maTerials

sePuP s i cell sb igure cellsb 12 11 agenda medcond

For each student

Student Sheet 12.1, "Anticipation guide: photosynthesis and Cellular Respiration"

Procedure

1. Fill in only the Before column of Student Sheet 12.1, "Anticipation Guide: Photosynthesis and Cellular Respiration."

2. Visit the Science and Global Issues page of the SEPUP website at sgi. With your partner, go to "Photosynthesis and Cellular Respiration" and follow the simulation.

3. Complete the Reading.

4. Fill in the After column on Student Sheet 12.1, "Anticipation Guide: Photosynthesis and Cellular Respiration."

219

Science&GlobaliSSueS/bioloGy ? cellbioloGy

Reading

energy for life

every cell needs a source of energy

As you learned in the "Ecology: Living on Earth" unit of Science and Global Issues, all cells need energy if they are to function. Cellular respiration is the process by which cells break down complex molecules, such as sugars, to release energy. Some of the energy is released as heat while the rest is stored temporarily in other molecules, such as adenosine triphosphate (ATP). ATP is used when the cell needs energy. For example, whenever your muscles contract, ATP supplies the energy. As you also learned in the "Ecology" unit, photosynthesis is the process by which the cells of producers capture the sun's energy and store it in sugars. All producers and consumers ultimately depend on these sugars for their energy needs.

The following equations summarize the two processes.

Cellular respiration: sugars 1oxygen & carbon dioxide 1water 1 energy Photosynthesis: carbon dioxide 1water 1light energy & sugars 1oxygen

As you can see from the equations, the components of cellular respiration and photosynthesis are nearly identical. In fact, cellular respiration is often described as the opposite of photosynthesis. The two processes, however, are far more complex than the equations indicate.

photosynthesis

Photosynthesis only occurs in certain pigment-containing cells of producers. This differs from cellular respiration, which occurs in all types of cells in all organisms. A pigment is a molecule that absorbs light energy. All producers contain pigments, which are essential for photosynthesis. The most common pigment in producers is chlorophyll. Chlorophyll is what makes the stems and leaves of producers green. In most producers the chlorophyll is contained in chloroplasts.

PlanT

mitochondrion

PlanT cell

nucleus

chloroplast

sePuP s i cell sb igure cellsb 12 2 2a2g0enda medcond

cell wall cell mem rane

chloroplast

acuole

cytoplasm

Light micrograph of Elodea cells

PhoTosynThesis and cellular resPiraTion ? acTiviTy 12

Chloroplasts are relatively large organelles surrounded by two membranes. Chloroplasts absorb energy from sunlight, as shown in the diagram below. Inside the chloroplast is a fluid-filled space called the stroma and stacks of connected membrane sacs called thylakoids. The thylakoid membranes contain the chlorophyll, and the stacked structure greatly increases the membrane surface area that can absorb light.

PlanT cell

miTochondrion outer mem rane inner mem rane

animal cell

cristae

matri

chloroPlasT outer mem rane

inner mem rane stroma thyla oids

mitochondria

chloroplast Mitochondria are present in both plants and animal cells, while chloroplasts are present only in plant cells.

sePuP s i cell sb igure cellsb 12 agenda medcond

221

Science&GlobaliSSueS/bioloGy ? cellbioloGy

the reactions of photosynthesis

The reactions occurring in photosynthesis are grouped into two stages, lightdependent and light-independent reactions. The light-dependent reactions rely on chlorophyll and other pigments in the thylakoid membranes to harness the energy of light. In a complex series of reactions, water breaks down into oxygen, hydrogen ions (protons), and electrons. Each reaction requires a unique enzyme. The oxygen is released to the atmosphere, some of the energy from the reactions goes into making ATP from ADP, and the protons and electrons combine with the carrier molecule, NADP+, to form NADPH.

chloroPlasT outer mem rane inner mem rane stroma thyla oids

solar energy sunlight

li hT dePendenT reacTions

h2o

light dependent reactions

carrier molecule adP P

aTP

carrier

molecule

with

o2

hydrogen

co2 cal in cycle glucose

ThesNePAuPDsPiHceallnsbd ATP are important to the light-independent Calvin cycle, which

igure cellsb 12

isagaensdearimeesdocfonednzyme-catalyzed reactions that take place in the stroma of the chloroplast. During these reactions carbon dioxide combines with the hydrogen ions and electrons produced from water during the light-dependent reactions. This results in the production of the high-energy sugar glucose. The glucose is used in cellular respiration or is converted to another form, such as starch, and stored for later use. Starch is a type of carbohydrate. A starch macromolecule is made of many glucose molecules linked together.

h c

ho

ch2oh

c

o

h

oh

h

c

c

h

oh

glucose

h c

oh

starch molecule glucose

sePuP s i cell sb igure cellsb 12 agenda medcond

222 sePuP s i cell sb igure cellsb 12 a agenda medcond

PhoTosynThesis and cellular resPiraTion ? acTiviTy 12

The reactions in the Calvin cycle occur in the presence or absence of light and are referred to as light-independent reactions. During the Calvin cycle ATP and NADPH are converted back into ADP and NADP+. These will be used again in the light-dependent reactions in the thylakoid membranes.

chloroPlasT outer mem rane inner mem rane stroma thyla oids

solar energy sunlight

li hT indePendenT reacTions

h2o

light dependent reactions

carrier molecule adP P

aTP

carrier

molecule

with

o2

hydrogen

co2 cal in cycle glucose

sePuP s i cell sb

Tihguerereactcieollnsbs1o2 f the Calvin cycle continue as long as carbon dioxide, ATP, NagAenDdPa mHe,dacnondd enzymes are present. Certain plant diseases, such as the plum pox virus that attacks several kinds of fruit trees, inhibit enzymes involved in the Calvin cycle. This prevents the plant from making the sugar it needs to support cellular respiration. Trees infected with plum pox may eventually stop producing fruit. Organisms that feed off the fruit may need to find another food source, and communities that rely on fruit sales may suffer economically.

cellular respiration

Each reaction in cellular respiration also requires a unique enzyme, and, as in photosynthesis, diseases or poisons may reduce the activity of these enzymes. This can have serious consequences for an organism, since cellular respiration is the process by which energy is released for cells to use. It is important not to confuse cellular respiration with breathing, which is often called respiration. Breathing gets oxygen into your lungs, but the oxygen has no purpose until it enters your cells and plays its part in cellular respiration.

223

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download