IB Biology Review Chapter 38: Plant Reproduction Parts of a

1
IB Biology Review
Chapter 38 Plant Reproduction
2
Parts of a Flower

• Petal
• Sepal
• Stigma
• Style
• Ovary
• Anther
• Filament

3
What is the sequence of events from flowering to
germination?

• Pollination
• Fertilization
• Seed dispersal

4
How are flowers pollinated?

• Wind
• Animals
• Birds
• Insects
• Bats
• Self-pollinated

5
Self-Pollination

• Pollen from the anther is transferred to the
  stigma

6
Cross Pollination

• Pollen from the anther of one plant is
  transferred to the stigma of a different plant

7
What are some of the adaptations of
insect-pollinated flowers?

• large / colorful petals to attract insects
• petals release scent to attract insects
• nectaries secrete nectar that insects like
• sticky pollen grains that stick to insects
• sturdy filaments to hold anthers in position when
  brushed by insects

8
How do plants know when to flower?

• plants biological clock uses phytochrome to
  measure how long night lasts
• Long Day Plants (LDP)
• Pr converted to Pfr during the day by red light
• LDP needs a day length longer than night length
• Pfr converts back to Pr at night or in far red
  light
• Pfr is still in the phytochrome at the end of
  short nights
• left over Pfr stimulates flowering

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Pr and Pfr Conversions
10
How are plants manipulated in greenhouses to
flower out of season?

• plants respond to red light or far red light as a
  signal for flowering
• by shining either
• red light (long day plants)
• far red light (short day plants)
• flower production
• plants think it is time to flower
• only short bursts of light are needed to trick
  the plants

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How are seeds dispersed?

• Animals
• eaten (berries)
• stick to animal (burs)
• Wind
• blown around (dandelion seeds)
• Water
• float (coconuts)
• washed down stream

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Dicotyledonous Seed Structure

• Consists of
• Testa/seed coat
• Micropyle
• Epicotyl/embryonic shoot
• Hypocotyl/embryonic root
• Cotyledons
• This is a castor bean
• (REMEMBER NAME!)

13
How does a seed germinate?

• water is absorbed (imbibition)
• water triggers production of gibberellic acid
• gibberellic acid stimulates production of amylase
• amylase catalyses the breakdown of starch to
  maltose
• maltose diffuses into embryo
• used for energy production and growth

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IB Exam Question
1. Fertilization, pollination and seed dispersal
all occur during the reproduction of a flowering
plant. In what sequence do these processes occur?
(1 mark)

• A. seed dispersal -gt pollination -gt fertilization
• B. fertilization -gt pollination -gt seed
  dispersal
• C. pollination -gt fertilization -gt seed
  dispersal
• D. seed dispersal -gt fertilization -gt
  pollination
• Correct answer C

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IB Exam Question
2. Draw the structure of a dicotyledenous
animal-pollinated flower. (6
marks)

• Award 1 for each of the following structures
  clearly drawn and labelled correctly.
• petals
• sepal
• stigma
• style
• ovary
• stamen / anther and filament
• receptacle / nectary

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IB Exam Question
3. State two adaptations of insect-pollinated
flowers. (2 marks)

• large / colorful petals
• petals release scent
• nectaries secrete nectar
• sticky pollen grains
• sturdy filaments to hold anthers in position when
  brushed

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IB Exam Question
4. Draw and label a diagram showing the external
and internal structure of a named dicotyledonous
seed. (5 marks)

• Award 1 for each of the following structures
  clearly drawn and labelled correctly.
• Testa
• Micropyle
• Embryo root
• Embryo shoot
• Cotyledons

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IB Exam Question
5. Describe the metabolic events of germination
in a starchy seed. (5 marks)

• absorption of water / imbibition
• (embryo) increases respiration
• (embryo) secretes gibberellic acid
• (stimulates) production of amylase
• digestion of starch to smaller sugars / maltose
• mobilize to tissues / transport of foods /
  nutrients to embryo

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IB Exam Question
6. Describe how flowering is controlled in long
day plants (LDP). (4
marks)

• flowering in LDP controlled by the plant's
  biological clock
• uses phytochrome to measure dark period / Pr
  converted to Pfr during daylight
• LDP needs a day length longer than a critical
  period / night length shorter than a critical
  period
• Pfr remains at the end of short nights
• Pfr stimulates flowering
• phytochrome system / biological clock located in
  leaf

20
IB Exam Question
7. Explain how manipulation of day length is used
in the production of flowers. (6 marks)

• some flowering plants are short-day plants
• others are long-day plants
• important variable is length of darkness /
  photoperiod
• some plants grown in greenhouses with controlled
  light conditions
• short-day plants kept in the dark during daylight
  hours
• long-day plants artificially lit during the
  night
• using an appropriate wavelength / far-red light
• possible to expose only for brief periods to keep
  costs down
• but long enough to interrupt the dark period
• involves interaction of phytochromes with
  metabolic reactions
• controlled by the plant's biological clock