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.

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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

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