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12.2 Chemistry in Plants
• Plants are like a chemical factory that use energy from sunlight and raw materials from air and water.
• Some glucose made by the plant is changed into starch and stored for later.
• The rest of the glucose is transported throughout the plant to be used for energy so that the plant can convert soil nutrients to body tissues and grow larger.
• The chemical factory also produces hormones, which are complex chemicals that regulate growth and development.
• These hormones are what tells the plant which direction to grow.
Photosynthesis
• Light is absorbed by the green pigment chlorophyll. Chlorophyll is located inside the organelles called chloroplasts.
• Carbon dioxide from the air enters openings on the plant surface, called stomates .
• Carbon dioxide dissolves and travels into the cells that manufacture glucose.
• Oxygen is also produced.
• The oxygen not needed by the plant is released into the air through the stomates.
Chemical Equation
Carbon Dioxide & water – light -> yields Glucose, Oxygen, Water
First Stage
• A molecule of chlorophyll absorbs light and becomes energized.
• The energized chlorophyll is capable of transferring its energy in two ways.
• Some energy is used to split the water molecule (H2O) into hydrogen and oxygen.
• The rest of the energy is used to make ATP, a molecule used by cells of all organisms to store energy.
• The hydrogen stays in the chloroplasts to continue more chemical reactions.
• The oxygen passes out of the leaf through the stomates.
Second Stage
• Carbon dioxide is combined with the hydrogen and ATP made in the first stage.
• Unlike the first stage, the chemical reactions of the second stage do not require light.
• These chemical reactions, called the Calvin cycle, produce glucose and other simple sugars.
Respiration
• To release the energy stored in glucose, the plants, like animals, use the reverse process of respiration.
• Oxygen combines with glucose, releasing energy that is stored up in the form of ATP.
• Respiration takes place in the cell’s cytoplasm and mitochondria.
• Plants use less oxygen than they produce.
• This excess is released into the air.
End
Review Worksheet 12.2
Part A Review
• 1. What occurs in the first stage of photosynthesis?
• Chlorophyll absorbs light and becomes energized.
• Some of this energy splits water into hydrogen and oxygen, and some is used to make ATP
• 2. What occurs in the second stage of photosynthesis?
• Carbon dioxide is combined with hydrogen and ATP, producing glucose and other sugars.
• 3. What occurs during respiration?
• Oxygen combines with glucose, releasing energy in the form of A TP.
• 4. Name two other chemical interactions that occur in plants?
• Hormones cause plants to react to stimuli such as light, gravity, and change of season.
• Plants also produce chemicals that affect other plants and animals.
Part B – Skills Developement
Imagine that dust from an asteroid has killed all the plants on earth. Hypothesize how each of the
following would be affected.
1- Atmospheric gases
• a. Overabundance of carbon dioxide • b. Deficiency of oxygen
2- Grazing animals
• a. Lack of oxygen to breathe • b. Lack of food
3 - Topsoil
• Loss of fertility with no decomposing plant matter
• No roots to break up soil and spread nutrients
4 - Birds
• a. Lack of oxygen to breathe • b. Lack of food and shelter
End