Transcript Sexual Reproduction in Flowering Plants

C40: Sexual
Reproduction in
Flowering Plants
Mr. E Murphy
Objectives
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Introduction
Structures and functions of a flower
Formation of sex cells or gametes
Pollination
Fertilisation
Fruit and Seed Dispersal
Dormancy
Germination
Stages in seedling growth
Introduction
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The ability to produce offspring of the same
species as the parent is one of the
characteristics of life
 Reproduction ensures that the traits of the
parent and species are transmitted to
succeeding generations
Introduction
Asexual and sexual reproduction
Asexual reproduction
•Asexual reproduction involves only one parent
•Does not require meiosis
Sexual reproduction
•Sexual reproduction involves two parents
•Each parent typically produces sex cells called
gametes
•Gametes are haploid cells capable of fusion
•Two gametes fuse to form a diploid cell called a
zygote
•Meiosis is essential for sexual reproduction
Structures of a flowering plant
Sketch this diagram into your notes
Activity/homework 25.10.11
P
257 Q 2 a-h
Solutions
P 257 Q 2 a-h
a)
Sexual Reproduction: Flower produces
gametes which fuse together to produce
a new individual
Asexual reproduction: Does not involve
gametes. Individuals are produced from
one parent plant. (clones)
Solutions
P 257 Q 2 a-h
b)
c)
Sepal: Green coverings that protect the
flower while it is still a bud
Petal: brightly coloured, they attract
animals to carry their pollen to other
flowers
Stamen: Male reproductive part, anther
produces pollen
Stigma: Tip of the carpel
Solutions
P 257 Q 2 a-h
d)
e)
Ovule: Where egg develops, fertilisation
occurs and seeds mature
Ovary: Swollen base of the carpel,
contains the ovule
Pollination: Transfer of pollen grains from
an anther to a stigma
Fertilisation: Uniting of a sperm nucleus
with an egg nucleus
Solutions
P 257 Q 2 a-h
f)
Self-pollination: Pollen is transferred to a
stigma of the same flower, or another
flower on the same plant
Cross pollination: pollen reaches the
stigma of a flower on a different plant (of
same species)
Solutions
P 257 Q 2 a-h
g)
h)
Zygote: What is formed when gametes fuse
together
Embryo: The growth of a zygote results into an
embryo
Seed: A miniature plant embryo) and its food
store
Fruit: Mature ovary or modified floral part that
contains seeds
Structures and functions of a
flowering plant
•Receptacle – part which the flower
grows from
•Sepals – Green, leaf-like structures,
protect flower when it is a bud
•Petals – Attract animals through
smell, (absent) in wind-pollinated
•Stamens – Male part of the flower
•Carpels – Female part of the flower
Formation of sex cells (gametes)
Male gamete formation
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Inside of anther is diploid
 Meiosis takes place in some of these cells producing
haploid pollen grains
 Each pollen grain divides by mitosis to form two
haploid sperm nuclei (male sex cells or gametes)
(40.3)
 Each pollen grain has a thick outer wall called the
exine
 Pollen grains are formed on the inside of the
anther(40.4, 40.6)
 When they are fully developed, the pollen grains are
exposed to the outside of the anther
Formation of sex cells (gametes)
Male gamete formation
Sketch into your notes
Formation of sex cells (gametes)
Male gamete formation
Homework 26.10.11
P
246 c 28
 Read p 246- 249
Formation of sex cells (gametes)
Male gamete formation
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Anther consists of four chambers called pollen sacs
Inside each pollen sac are a number of diploid microspore mother
cells
Cells divide by meiosis to produce a cluster of four haploid cells
called a tetrad
Each tetrad breaks up to form four separate haploid pollen grains
The pollen may divide by mitosis to produce two haploid nuclei , the
tube and degenerative nuclei
The tube nucleus will form the pollen tube and will then degenerate
Degenerative nucleus will form the male gametes
When the pollen grains have matured, the walls of the anther
become dry and shrivel
Results in splitting of the anther walls
The pollen grains are then exposed on the outside of the anther
Formation of sex cells (gametes)
Female gamete formation
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Each ovule is made up of a number of egg cells
One will divide by meiosis to form a single haploid cell
Cell undergoes mitosis three times to form a single large
cell, containing eight haploid nuclei (embryo sac)
Five of the 8 will later degenerate
One of the nuclei forms a haploid egg cell and 2 of them
form haploid polar nuclei in the centre of the embryo sac
Egg cell and polar nuclei = female gametes
Formation of sex cells (gametes)
Female gamete formation
Formation of sex cells (gametes)
Development of the embryo sac
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Each ovary contains one or more ovules
Ovule has two walls, called integuments, through which a pollen
tube can enter
One cell, in the ovule is called the megaspore mother cell
Cell is diploid and divides by meiosis to form four haploid cells
Three degenerate, the remaining one is called the embryo sac
Haploid nucleus of the embryo sac divides by mitosis three times to
form 8 haploid nuclei
Of the eight, 5 degenerate, the three remaining form the female
gametes
Two of the female gametes form the polar nuclei in the embryo sac,
the remaining gamete becomes the egg cell
When the embryo sac is mature it forms the carpel, as shown on the
next slide...
Formation of sex cells (gametes)
Development of the embryo sac
Formation of sex cells (gametes)
Carpel with mature embryo sac
Pollination
Pollination is the transfer of pollen from an anther to a stigma of a
flower from the same species
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Self-pollination involves the
transfer of pollen from an
anther to a stigma on the same
plant
Self-fertilisation
Cross-pollination involves the
transfer of pollen from an
anther to a stigma on a
different plant of the same
species
Cross-fertilisation
Pollination
Methods of pollination
 Wind
 Animal
(insect)
Hay fever
•Allergic reaction to the inhalation of
particles of certain harmless substances
•Most common allergens are pollen grains,
animal skin, house dust and dust mites
•Symptoms include inflammation of the
mucous membrane in the nose, sneezing
etc.
•Hay fever affects up to 10 % of the
population
•Treatments include decongestant drugs,
antihistamines
Fertilisation
Fertilisation is the union of the male and female gametes to form
a diploid zygote
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When a pollen grain lands on a stigma it is stimulated to grow
A pollen tube grows down through the style towards the ovule
Growth of a pollen tube is controlled by a nucleus, which
degenerates when the pollen tube reaches the opening of the ovule
Chemotropism
The haploid generative nucleus divides by mitosis as it moves down
the pollen tube, forming two haploid sperm nuclei (male gametes)
Two haploid sperm nuclei move down through the pollen tube
Presence of a pollen tube means that the male gametes of flowering
plants can move towards the egg without the need for external water
Adaptation for life on dry land
Fertilisation
Growth of a pollen tube
Double fertilisation
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Fertilisation
One sperm nucleus (n) joins with the egg nucleus (n) to form a
diploid (2n) zygote. Zygote will develop into an embryo (young
plant)
The second sperm nucleus (n) joins with the two polar nuclei
(both n) to form a triploid (3n) endosperm nucleus
Fertilisation
Seed Formation
Fertilisation
Seed Formation
•Fertilised ovule becomes the seed
•Walls of the ovule (integuments) dry up to become the wall of the seed
(testa)
•The zygote grows by mitosis giving rise to the embryo or young plant
•Embryo consists of the future root (radicle) or shoot (plumule)
•Some embryo cells grow to form the seed leaves (cotyledons), which
can store food
•The endosperm nucleus divides repeatedly by mitosis to produce many
endosperm cells, which act as a food store, storing fats and starch
•Cotyledons continue to grow absorbing the endosperm
•Non-endospermic (broad bean) and endospermic (maize)
Fertilisation
Seed Formation
Non-endospermic seed
Endospermic dicot seed
Monocots and dicot seeds
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Monocots have one cotyledon (cereals and grasses)
Dicots have two cotyledon seeds
Monocots differ in their method of storing food
Fruit formation
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Fertilisation
As the seed develops, the surrounding ovary becomes fruit (auxins)
Wall of the ovary becomes the wall of the fruit
Fruits are designed to protect the seed and to help dispersal
Once the fruit forms the rest of the flower parts die away and fall away
Fertilisation
False fruits
•False fruits develop from other parts of a flower besides the ovary
•Apple is formed when the base of a flower, join together and swell with stored
food
•Core of the apple is the ovary
•Strawberry is also a false fruit, as it develops from a swollen receptacle
Fertilisation
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The development of a fruit without a seed is called parthenocarpy
This is the form of virgin birth, as the egg is not fertilised
seedless fruit can be formed genetically, either naturally or by
special breeding programmes
Spraying with growth regulators can also produce seedless fruit
These growth regulators also cause fruits and vegetables to grow
larger
Fruit and seed dispersal
Dispersal is the transfer of a seed or fruit away from the parent plant
Fruit and seed dispersal
Dispersal is necessary to:
•Avoid competition
•Increase chance of survival for the plants
•Find new areas for growth
•Increase number of the species
Types of dispersal
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Wind
 Water
 Animal
 Self
Dormancy
Dormancy is a resting period when seeds undergo no growth and
have reduced cell activity or metabolism
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Onset of dormancy
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Growth inhibitors
The testa may be impermeable to
water or oxygen
The testa may be too tough to
allow the embryo to emerge
There may be lack of suitable
growth regulator needed to
stimulate growth
Dormancy
Advantages of dormancy
•Allows plant to avoid harsh
conditions
•Gives embryo time to develop
fully
•Provides time for the seed to be
dispersed
•Maximises the growing season for
the young seedling
•Helps survival of the species
because the duration of dormancy
varies
http://www.youtube.com/watch?v=r8Ff1
Xj_-eM
Germination
Germination is the regrowth of the embryo, after a period of
dormancy, if the environmental conditions are suitable
Conditions
•Water
•Oxygen
•Suitable
temperature
•Dormancy must be
complete
•Light may be
required
Germination
Events in seed germination
Germination
Changes in dry weights of
germinating seeds
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When weighing plant material, dry
weight is normally used
 This is weight without water
 Dry weight is measured by placing the
plant in an oven at 100 degrees until
the weight remains constant
The Stages in Seedling growth
Cotyledons remain below soil
The Stages in Seedling growth
Cotyledons move above the soil
Asexual reproduction
Vegetative reproduction is asexual reproduction, using
part of the parent plant to produce a new individual
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Propagation means
reproduction and vegetative
means the non-flower parts of
the plant
New roots and shoots grow
directly from part of the parent
plant
This occurs through mitosis,
offspring are identical
https://www.youtube.com/watch?v=3O
7icCqFfEo
Organs of Vegetative
reproduction
Stem
 Stem
tuber e.g. potato
 Runner e.g. strawberry
Root
 Root
tuber e.g. dahlia
Bud
 Bulb
e.g. onion
Organs of Vegetative
reproduction
Leaf
 Small
detachable
plantlets form along
the leaf
Artificial propagation
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Cuttings
Layering
Grafting
Tissue
culturing
Comparison of Seed and
vegetative Reproduction
Seed
Advantages
Produces offspring similar but not identical
Seeds are dispersed
Seeds can remain dormant
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3.
Disadvantages
1.
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Long, complicated series of events
necessary to produce adult plant
Plants grown from seeds take many year
to reach maturity
Comparison of Seed and
vegetative
Reproduction
Vegetative Reproduction
Advantages
Rapid spread over short distances
2. Simple and more reliable than
reproduction by seed
3. Useful to gardener
4. Identical plants
5. Quick growth at spring
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Disadvantages
Dispersal is limited and offspring grow in
clumps near parent plant
2. All plants identical, may be susceptible to
the same diseases
1.
Activity 8.11.11
 Revision
worksheet
Solutions
2010 HL Q13
Solutions
2010 HL Q13
Solutions
2009 HL Q15 a)
Solutions
2007 HL Q14 a)
Solutions
2006 HL Q14 a)
Experiments
 Mandatory
Activity 20: Investigate the
effect of water, oxygen and temperature
on germination
 Mandatory Activity 21: Investigate
digestive activity during germination using
starch agar or skimmed milk plates
Experiments
 Mandatory
Activity 20: Investigate the
effect of water, oxygen and temperature
on germination
 Will
complete next week
Experiments
 Mandatory
Activity 21: Investigate
digestive activity during germination using
starch agar or skimmed milk plates
 Today’s
class
Experiment
Experiments
Experiments
Experiments
Revision Test
 Topics
 Nervous
System
 The Senses
Activity/Homework 30.3.11
 Write
notes on:
 Pollen grain development (H)
 Development of embryo sac (H)
 Pollination
Experiment Questions
HL 2012 Q 7b v
Experiment Questions
HL 2006 Q 7b iv
Experiment Questions
HL 2012 Q 7b iii,iv
Experiment Questions
HL 2009 Q 8
Experiment Questions
HL 2006 Q 7 bii
Solutions
P410
a) to produce pollen, reproduction
b) a-filament, b- anther, c-stigma, d-ovary, estamen
c) wind: no bright colours, reproductive
organs are on the outside
d) anther, ovary
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Solutions
P410
4.
a) pollen, ovary