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Higher Biology. Effects of Chemicals and Light on Growth in Plants. Effects of chemicals and light on plants. By the end of this lesson you should be able to:. Know the symptoms of deficiency of nitrogen, potassium, phosphorus and magnesium in plants.
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Higher Biology Effects of Chemicals and Light on Growth in Plants
Effects of chemicals and light on plants By the end of this lesson you should be able to: • Know the symptoms of deficiency of nitrogen, potassium, phosphorus and magnesium in plants. • Describe the effect of light on shoot growth and development. • Understand what is meant by phototropism and etiolation. • Describe the effect of light on flowering in long day and short day plants.
Introduction • Elements play an important role in the growth and development of organisms. • If an element is missing then this can lead to nutrient deficiency. • In addition to carbon, oxygen and hydrogen for photosynthesis plants also need other elements. How do plants take up these minerals? • Through the root hairs in the soil- (remember?)
Macro-elements in plants • Macro-elements are required by plants in small but significant quantities for normal growth to occur. • Four of these elements are: • Nitrogen (N) • Phosphorus (P) • Potassium (K) • Magnesium (Mg)
Macro-elements in plants ATP & nucleic acid formation Phosphorus Growth reduced, death of older leaves Potassium Amino acids, proteins & nucleic acids formation Chlorotic leaves, leaf base red Growth reduced, chlorotic leaves Magnesium
Macro-elements in plants • Water culture experiments • Complete your “Macro-element Deficiency” Sheet from your diagram pack.
Effect of Light on Shoot Growth • Read page 273 of Torrance and then answer the following questions: • Name the term used to describe a plant which has grown in the dark. • Describe the appearance of such a plant in terms of: • Colour • Size of leaves • Internodes • Stem • Briefly describe the role of light in phototropism.
Effect of Light on Flowering • Many plants stop producing leaves and instead start to produce flowers at certain times of the year. • This occurs in response to changing periods of light and darkness. • Photoperiodism is a response (e.g. flowering) to changing daylength.
Long day plants • Also called short night plants. • Usually flower in spring. • Only flower when the numbers of hours of light is more than a critical level. • Critical length of light varies from species to species. • Normally 11-13 hours of light • E.g. spinach only flowers when there is more than 13 hours light.
Short day plants • Also called long night plants. • Usually flower in autumn or winter • Only flower when the numbers of hours of light is less than a critical level. • Critical length of light varies from species to species. • Can be less than 12 hours of light. • E.g. strawberry only flowers when there is less than 10 hours light. (i.e. must have at least 14 hours of darkness).
Practice Questions • Torrance • TYK page 270 Q1, p277 Q1-3
Effects of chemicals and light on plants Can you do it? • Know the symptoms of deficiency of nitrogen, potassium, phosphorus and magnesium in plants. • Describe the effect of light on shoot growth and development. • Understand what is meant by phototropism and etiolation. • Describe the effect of light on flowering in long day and short day plants.