Chapter 7 Lesson 2"How Plants Make Food"

Materials:

• How Plants make Food Sheet.
• A chemical heat pack and/or a chemical cold pack.
• Internet Research Word document

Objective:

• Students will describe where plants make food.
• Student will explain how plants make food.
• Students will discuss the meaning of the chemical equation for photosynthesis.

Alaska Content Standards:

• SCI A-10 Students will understand that living things are made up mostly of cells and that all life processes occur in Cells (Cells)
• SCI A-12 Students will distinguish the patterns of similarity and differences in the living world in order to understand the diversity of life and understand the theories that describe the importance of diversity for species and ecosystems.
• SCI A-13 Students will understand the theory of natural selection as an explanation for evidence of changes in life forms over time (Evolution and Natural Selection)
• SCI A-14 Students will understand the interdependence between living things and their environments; that living environments consists of individuals, populations, and communities; and that a small change in a portion of an environment may affect the entire environment (Interdependence);
• SCI A-15 Students will use science to understand and describe the local environment.

Anticipatory Set: Show student some pictures of two kinds of roots sent by other teachers. Refresh their memories of what was covered in the last lesson:

Mangrove rainforest trees require a different kind of support system. Mangroves grow in wet, muddy soil at the water's edge which can be subject to tides and flooding. As a means of support they develop several aerial pitchfork-like extensions from the trunk which grow downwards and anchor themselves in the soil trapping sediment which helps to stabilize the tree.

Most rainforest soil is very poor with all the nutrients available largely remaining at surface level. Because of this rainforest trees have very shallow roots. Some very tall trees have developed ways of obtaining much needed additional support by forming buttressed roots, which grow out from the base of the trunk sometimes as high as 15 ft above the ground. These extended roots also increase the area over which nutrients can be absorbed from the soil.

`Teacher will show the students the picture on Page 148 and discuss Photosynthesis. Here are some of the key points:

• photosynthesis is the link between the energy from the sun and almost all the energy available for living things on Earth.
• The energy of the sun is used to change Carbon Dioxide and water into simple sugars and oxygen. Show the students this formula:
• 6CO2 + 6H2O + Light Energy ---> C6H12O6 + 6O2 explain the formula and where the needed materials come from use the picture on Page 148 again.
• Chloroplasts use have a green pigment that absorbs certain types of light for energy. Define pigment and Chlorophyll.
• The chloroplasts use the energy to split H2O into H+ions and Oxygen.
• The oxygen leaves the plants through the stoma.
• The H+ ions combine with carbon (C) from the CO2 to form the sugars.
• The sugars are how the plants store the sun's energy.

Teacher Input: Teacher will discuss the different wavelengths of light and how they affect plants in photosynthesis.

• Show this picture and discuss the different wavelengths and how a prism can split light into its different colors. Note that the shorter the wavelength, the more energy it has.
• Show this picture of a chlorophyll molecule model and mention that there are many types of chlorophyll but the chlorophyll "a" pigment is found in ALL photosynthetic organisms. Chlorophyll"A" absorbs energy from the Violet-Blue and Reddish orange-Red wavelengths. How is that advantageous?
• Show this picture of how different pigments, "colors" absorb different wavelength of light. Ask how this can benefit different types of plants? Mention that short wavelengths do not penetrate water well. Which wave lengths would a plant living in the bottom of a lake use. Which pigments would you most likely fine in the leaves of those plants?
• Show this picture of a chloroplast and explain that inside the chloroplasts there are small structures called Thylakoids. The thylakoids is where photosynthesis occurs. An stacks of thylakoids are called Granum.
• Next show this picture and explain that photosynthesis takes place in two parts, light reactions and dark reactions. The light reactions use light energy to break apart water molecules. The H+ ion is used for chemical reactions that store energy and the O2 molecule is released through the stoma. The Dark or light independent reaction uses the energy stored in ATP and NADPH to bind the carbons from carbon dioxide together in the formation of sugar.
• Next, show this picture. This picture show a photosystem, which is an arrangement of chlorophyll and other pigments in the thylakoids. When this arrangement is hit by light of the proper wavelength it causes the electron to fly off. The photosystem then needs an electron so it steals one from nearby water. This causes the water molecule to break apart. The electron that flew off attaches to another an electron acceptor in another photosystem from there it causes a series of reaction that produces an energy molecule, ATP, and ends up attaching to a molecule in Photosystem I. When light hits the Photosystem I the electron is excited even more this time attaching to a different photosystem acceptor. This causes a different set of reactions which creates a molecule know as NADPH that has even more energy.
• Show a picture of the process he light reaction called Photophosphorylation has a continuous flow of electrons from water molecules to NADPH molecules, creating ATP in the process.
• Show this picture and explain that many very simple Prokaryotes have only this photosystem. It is called Photosystem II because it was discovered second. Even though it is probably the first system that existed.
• Show this picture to explain the light independent reaction. Better known as the Calvin Cycle for the man that discovered it. The formula for this reaction is: C5 + CO2 + ATP + NADPH ---> C6H12O6 since the 5 carbon atoms are attached to other atoms the actual reaction occurs like the picture.

Teacher Modeling: Remind students that, unlike animals, plants make their own food. What again do plants need to live? Do plants use any of the food they produce? Do plants then create carbon dioxide while they use that food?

Check for Understanding:

Students will complete the Workbook Activity, "How Plants Make Food."

(Day 2)

Guided Practice: Students will use an Internet (and this word document) as resource to learn and/or review what they have learned about photosynthesis.

Independent Practice: Students will take the quiz on Chapter 7 lesson 2.

Closure: Take out a cold pack and/or a heating pack and activate them. Explain to the students that they probably have learned that energy can not be created or destroyed, it only changes form. I heat is an energy then where the heat is coming from? Explain that it was stored in the form of a chemical. Much like energy is stored in ATP or in NADPH. Now discuss the cold pack. How come it feels cold? Tell the students that it too is a chemical reaction that needs energy to continue. It steals energy from the surrounding area so it feels cold. It is stealing heat energy from your hand. Which situation is most like the light reactions of photosynthesis? Which situation is most like the dark reactions of photosynthesis?

Duration:

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).