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