Lesson 6 Understanding Plant Physiology
Next Generation Science/Common Core Standards Addressed! • HS‐LS1‐3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.] • HS‐LS1‐5. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy. [Clarification Statement: Emphasis is on illustrating inputs and outputs of matter and the transfer and transformation of energy in photosynthesis by plants and other photosynthesizing organisms. Examples of models could include diagrams, chemical equations, and conceptual models.] [Assessment Boundary: Assessment does not include specific biochemical steps.]
Agriculture, Food, and Natural Resource Standards Addressed • PS.02.03.01.a. Summarize the importance of photosynthesis to plant life on earth and the process of photosynthesis, including the types (c3, c4, Cam), its stages (e.g., light-dependent and light independent reactions), and its products and byproducts. • PS.02.03.02.a. Summarize the stages of cellular respiration including their products and byproducts.
Bell Work • Describe cellular respiration. • When these things are combined, what is produced as a result? • What are the ingredients needed for photosynthesis to take place? • Why are photosynthesis and Respiration important to humans? • Here is a glass of water. How can I add carbon dioxide to it?
Vocabulary • Cellular respiration • Chlorophyll • Chloroplast • Mitochondria • Photosynthesis • Transpiration
How Does Photosynthesis Work? • Photosynthesis is the process by which a plant turns the light energy from the sun into chemical energy in the form of sugar (glucose) • It is a complex series of chemical reactions that happens within the plant cells • It is the original source of all important fuels including oil, coal, wood, and natural gas • It is also the source of all foods
Most cells that carry on photosynthesis have organelles called chloroplasts • They contain a pigment known as chlorophyll • Chlorophylls are usually green because they absorb the red and blue wavelengths of light and reflect the green wavelengths • The pigment is responsible for trapping the sunlight for photosynthesis to occur
In photosynthesis, carbon dioxide and water are the raw materials • They are used to form glucose and oxygen • The formula for photosynthesis is: 6 CO2 + 12 H2O C6H12O6 + 6 H2O + 6 O2 Carbon dioxide Water Glucose Water Oxygen
Photosynthesis continued • Notice that water is both a raw material and a product • This is because there are two steps involved in photosynthesis: the light and dark reactions • Any excess water is removed through the stomata of the leaves by a process called transpiration • In the light reaction, light energy is converted to chemical energy and water is split into hydrogen and oxygen atoms • In the dark reaction, carbohydrates are formed from carbon dioxide and hydrogen atoms • Both processes occur within the chloroplast
Structure of a Chloroplast • A chloroplast contains stacks of membranes called grana which store the chlorophyll • Surrounding the grana are regions called stroma • The light reaction takes place in the grana while the dark reaction occurs in the stroma Chloroplast
Factors that Affect Photosynthesis • Photosynthesis is affected by six factors: • 1. Light quality – the best type of light should provide wavelengths in the blue and red range; This range is what works best with chlorophyll • 2. Light intensity – some plants need more light, others less; generally, the brighter the light, the more efficient the photosynthesis • 3. Light duration – the longer the day, the more photosynthesis takes place; Some plants need more light and some less
4. Carbon dioxide concentration – usually an increase in the amount of carbon dioxide in the atmosphere can double the rate of photosynthesis • 5. Temperature – the higher the temperatures the more photosynthesis occurs; Of course excessive temperatures will decrease the rate too • 6. Water availability – plants lacking water will close their stomata and decrease photosynthetic activity
How Does Respiration Work? • In many ways, cellular respiration is the opposite of photosynthesis: • Comparison of Photosynthesis & Respiration
In respiration, plants start with glucose which is broken down in the presence of oxygen • Water and carbon dioxide are released along with all the energy within the bonds • This is the formula for respiration: C6H12O6 + 6 H2O + 6 O2 6 CO2 + 12 H2O Glucose Water Oxygen Carbon dioxide Water
Factors Affecting Respiration • Respiration occurs in structures called mitochondria and are affected by five factors: • 1. Temperature – as temperature increases, so does the respiration rate • 2. Oxygen concentration – low concentrations of oxygen will decrease the respiration rate Mitochondrion
3. Soil Conditions – compacted or waterlogged soils exclude air, and therefore oxygen; Respiration is inhibited under these conditions • 4. Light – in low light, photosynthesis is reduced and therefore the rate of respiration is reduced because of a decrease in available glucose • 5. Growth rate & metabolic activity – when plants reach their full development, the rate of photosynthesis and respiration have reached their maximum; Age and availability of glucose affect respiration
How Are Photosynthesis & Respiration Important to Humans? • Photosynthesis and respiration are two of the most important chemical reactions to human beings • All of our food and nutrition comes either directly of indirectly from photosynthesis • All of our heat and electricity comes either directly or indirectly from by-products of photosynthesis in plants • All of the oxygen we breathe comes from the photosynthesis reactions • Transpiration puts thousands of tons of water into the air, cooling our environment and encouraging rainfall.
Summary • What is photosynthesis? • What are the two raw materials needed for photosynthesis? What are the products? • Where in a cell does photosynthesis take place? • Can humans produce food? Why or why not? • Where do the light and dark reactions occur in a chloroplast? • What is respiration?
Summary Continued • What are the raw materials needed for respiration? What are the products? • Where in a cell does respiration occur? • How is respiration the opposite of photosynthesis? • Why are these two processes necessary for humans? • What factors affect the rate of photosynthesis and respiration?