Higher Biology

Effects of Chemicals and Light on Growth in Plants

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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 phototropismand etiolation.

Describe the effect of light on flowering inlong day and short day plants.

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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?)

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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)

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Macro-elements in plants

Element Function Deficiency

Growth reduced, leaf bases red

Role in transport of molecules

across membranes

Nitrogen

Required for chlorophyll formation

Magnesium

Potassium

Phosphorus

Growth reduced, death of older leaves

Chlorotic leaves, leaf base red

Amino acids, proteins & nucleic acids formation

ATP & nucleic acid formation

Growth reduced, chlorotic leaves

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Macro-elements in plants

Water culture experiments

Complete your “Macro-element Deficiency” Sheet from your diagram pack.

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Effect of Light on Shoot Growth1. Read page 273 of Torrance and then

answer the following questions:2. Name the term used to describe a plant

which has grown in the dark.3. Describe the appearance of such a

plant in terms of:a) Colourb) Size of leavesc) Internodesd) Stem

4. Briefly describe the role of light in phototropism.

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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.

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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.

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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).

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Practice Questions

Torrance1. TYK page 270 Q1, p277 Q1-3

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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 phototropismand etiolation.

Describe the effect of light on flowering inlong day and short day plants.