Higher Biology

1
Higher Biology

• Effects of Chemicals and Light on Growth in
  Plants

2
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.

3
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?)

4
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)

5
Macro-elements in plants
Element Function Deficiency
Growth reduced, leaf bases red
Role in transport of molecules across membranes
Nitrogen
Required for chlorophyll formation
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
6
Macro-elements in plants

• Water culture experiments
• Complete your Macro-element Deficiency Sheet
  from your diagram pack.

7
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.

8
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.

9
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.

10
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).

11
Practice Questions

• Torrance
• TYK page 270 Q1, p277 Q1-3

12
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.