Transcript File

Sexual reproduction in
flowering plants
Lesson objectives
By the end of this lesson you should be
able to:
• Distinguish between sexual and asexual
reproduction with respect to plants
• Describe the structures and functions of
the parts of a flower
• Discuss the formation male and female
gametes
Introduction
•
The ability to produce
offspring is one of the
characteristics of life
• Reproduction ensures
that parental traits are
transmitted to
successive generations
• Reproduction has 2
main functions
1. Replacing organisms
that die
2. Allows for an increases
in numbers when
conditions are
favourable
Asexual and sexual reproduction
• Asexual reproduction
involves 1 parent and
requires no gametes –
does not require meiosis
– offspring are clones of
parent (genetically
identical)
• Sexual reproduction
involves 2 parents –
fusion of gametes
(fertilisation) – offspring
show variations as they
are a mixture of genes
from both parents (driving
force of evolution)
Structures and functions of a flower
Male gamete formation
Female gamete formation
What have you learned?
Can you. . .
• Distinguish between sexual and asexual
reproduction with respect to plants?
• Describe the structures and functions of
the parts of a flower?
• Discuss the formation male and female
gametes?
Lesson objectives
•
•
•
•
By the end of this lesson you should be
able to:
Distinguish between self and cross
pollination
Discuss methods of pollination
Discuss the causes, effects and
treatments for hay fever
Discuss fertilisation and seed formation I
flowering plants
Pollination
“Pollination is the
transfer of pollen
from an anther to a
stigma of a flower
from the same
species”
• There are 2 types of
pollination:
1. Self pollination
2. Cross pollination
Methods of pollination – 2 types
Animal
Wind pollination
pollination
Adaptations of flowers to wind or
animal pollination
Wind pollination
Animal pollination
Petals: small or absent,
not brightly coloured, no
scent, no nectaries
Pollen: large amounts,
light, small, dry, smooth
Anthers: large, outside
petals, loosely attached to
filament
Stigmas: large and
feathery, outside petals
Petals: large, brightly
coloured, have nectaries
Pollen: small amounts,
large, heavy, sticky, spiny
Anthers: usually small,
inside petals, firmly
attached to filament
Stigmas: usually small
and sticky, inside petals
Hay fever
• Is an allergic reaction to the inhalation of particles of
certain harmless substances
• The substance that triggers the reaction is known as the
allergen
• The most common allergens are pollen grains but
include fungal spores, animal skin or scales and house
dust
• The symptoms of hay fever include the inflammation of
the mucous membranes of the nose, sneezing, a
blocked and runny nose along with watery and irritated
eyes
• It affects 10% of the population and can be reduced by
limiting contact with the allergen
• Treatment include anti – histamine drugs and other
drugs that partially inhibit the allergic response
Fertilisation
“Fertilisation is the union of male and female
Growth of a pollen tube
gametes to form a diploid zygote”
Double fertilisation
•
Flowering plants are
unique in having a
double fertilisation:
1. 1st sperm nucleus (n)
joins with the egg
nucleus (n) to form a
diploid (2n) zygote) –
develops into the
embryo
2. 2nd sperm nucleus (n)
joins with the 2 polar
nuclei (both n) to form
a triploid (3n)
endosperm nucleus
Seed development
Types of seeds
Number of cotyledons
• Plants that form a seed with a single cotyledon
are called monocots, while plants with 2
cotyledons are called dicots
Presence or absence of endosperm
• In monocots the cotyledon absorbs food from
the endosperm and normally passes it onto the
embryo (i.e. the cotyledons do not store food) –
at maturity monocot seeds have an endosperm
– endospermic (grasses, cereals and maize)
• In dicots the cotyledons absorb food from the
endosperm and act as food stores – at maturity
dicot seeds do not have an endosperm – non endospermic
A non – endospermic seed (broadbean)
An
endospermic
dicot seed
(castor oil
bean)
LS of a monocot seed (maize). Note that maize
is not a typical monocot seed in that it stores food in
the cotyledon, as shown above.
What have you learned?
•
•
•
•
Can you. . .
Distinguish between self and cross
pollination?
Discuss methods of pollination?
Discuss the causes, effects and
treatments for hay fever?
Discuss fertilisation and seed formation I
flowering plants?
Lesson objectives
•
•
•
•
•
By the end of this lesson you should be
able to:
Discuss fruit formation
Distinguish between true and false fruits
Discuss the development of seedless fruit
Discuss fruit and seed dispersal
Discuss seed dormancy
Development of a fruit
Two types of fruit
Changes in a flower after
fertilisation
Before fertilisation
After fertilisation
1 Ovule
Seed
2 Integumants
Testa (seed coat)
3 Nucellus
Endosperm→Cotyledons
4 Egg
Zygote→Embryo
5 Polar nuclei
6 Ovary
Endosperm
Fruit
7 Ovary wall
Pericarp (fruit coat/wall)
Seedless fruit
•
The development of a fruit without a seed is
called parthenocarpy (or parthenocarpic
fruiting) – it can be formed in 2 ways
1. Genetically, either naturally or through special
breeding programmes – bananas, grapefruit,
pineapples, oranges and grapes
2. To spray plants with growth regulators e.g.
auxins – grapes, peppers, cherries and some
types of seedless tomatoes
Fruit and seed dispersal
“Dispersal is the transfer of a seed or a fruit
away from the parent plant”
Dispersal is necessary to :
• Avoid large numbers of seeds competing with
each other and the parent plant
• Increase the chance of survival for the plant
• Find new areas for growth
• Increase the numbers of species
The main methods of dispersal are wind, water,
animal and self - dispersal
Wind dispersal
Water dispersal
Animal dispersal
Edible,
Sticky fruits
fleshy- or
goosegrass
succulent fruits
Self - dispersal
Examples include peas, beans and gorse
Dormancy
“Dormancy is a resting period when seeds
undergo no growth and have reduced cell
activity or metabolism”
Dormancy is brought about by a number of ways:
1. Growth inhibitors (e.g. abscisic acid) may be
present in the outer part of the seed
2. The testa may be impermeable to water or
oxygen
3. The testa may be to tough to allow the embryo
to emerge
4. There may be a lack of suitable growth
regulator present to stimulate growth
Dormancy in agriculture or
horticulture
•
•
•
1.
2.
3.
4.
Many seeds need a cold break to break
dormancy – cause the breakdown of growth
inhibitors or the production of growth
promoters such as auxins
Special conditions are necessary to break
dormancy in seeds before they are planted for
agricultural or horticultural use
These conditions include:
Soaking seeds in water
Physical damage
Exposure to light or dark
Exposure to cold temperatures
Advantages of dormancy
• Allows the plant to avoid the harsh
conditions of winter
• Gives the embryo time to develop fully
• Provides time for the seed to be dispersed
• Maximises the growing season for the
young seedling, i.e. by starting growth in
the spring the plant is well developed by
the autumn
• Helps survival of the species because the
duration of the dormancy varies
What do you know?
•
•
•
•
•
Can you. . .
Discuss fruit formation?
Distinguish between true and false fruits?
Discuss the development of seedless
fruit?
Discuss fruit and seed dispersal?
Discuss seed dormancy?
Lesson objectives
•
•
•
•
•
•
By the end of this lesson you should be able to:
Discuss the conditions necessary for seed
germination
Discuss the events in seed germination
Account for changes in dry weights of
germinating seeds
Discuss the stages in seedling growth
MA: To investigate the effect of water, oxygen
and temperature on seed germination
MA: To use starch agar or skimmed milk plates
to show digestive activity during germination
Germination
“Germination is the
re - growth of the
embryo after a
period of dormancy
if the environmental
conditions are
suitable”
Conditions for germination
• Water is needed to allow enzyme
reactions to occur – the seeds absorb
water from the soil
• Oxygen is needed for aerobic respiration
• A suitable temperature is needed to allow
enzyme reactions to take place
• Dormancy must be complete
• Light may be required
Events in germination
1. Seeds store food in the form of oils, starch (especially
7.4.Dry
weight
(mass)
of the
falls
the food used
Products
of
digestion
areseed
moved
todue
theto
embryo
in
cereals
and grasses)
and
protein
(especially
in in
10.respiration
Thelegumes
plumulesuch
emerge
above
thebeans)
ground and leaves form
as peas
and
5.2.Glucose
and amino
acids
areseeds
used to
makewater
new structures
Germination
begins
when
absorb
through
11.Once
the
first
leaves
start
to
photosynthesize
the
dry
8. Weight
of
food
stores
falls,
the
weight
of
the
embryo
such
as cell
and
enzymes
a tiny
holewalls
called
the
micropyle allowing enzymes to be
weight
of the seedling increases again
increases
activated
6. Fats and some of the glucose are used in respiration
Oils bursts
are digested
fatty
acids and glycerol, starch to
9. 3.
Radicle
throughtothe
testa
glucose and proteins to amino acids
Changes in dry weights of germinating seed parts
The stages in seedling growth
Cotyledons remain below the soil – Broad beans
In radicle
this
type
of germination
seed
absorbs
water,
6.
4.1.
The
The
plumule
develops
grows
up
into
through
thethe
primary
the
soil
or
and
tap its
root
delicate
which
enzymes
become
active
the seed
begins
to grow
forms
leaves
many
are protected
lateral roots
by theand
plumule
being
hooked
over
Radicle
bursts
out through
the testa
and grows
down
7.
5.2.
Once
The
cotyledons
above
the (and
ground
endosperm,
the plumule
if present)
straightens
shrivel
up
and
as
produces
food
is transferred
the
first true
from
leaves
them
whichbetween
become the
green
and
3.
Plumule
emerges
and
the region
plumule
start
photosynthesize
andtocotyledon
(epicotyl) grows
The stages in seedling growth
Cotyledons move above the soil – Sunflower seeds
This form of germination is similar to the previous form
with the following differences:
The above
region the
between
thefruit
emerging
radicle and
2.• Once
soil, the
wall (pericarp)
fallsthe
to the
cotyledons
(hypocotyl)open
grows
the emerging
ground,
the cotyledons
outcausing
and become
green and
cotyledons to be
carried
above
the soil
photosynthetic.
The
plumule
emerges
from between the
cotyledons and forms the first foliage leaves
What do you know?
Can you . . .
• Discuss the conditions necessary for seed
germination?
• Discuss the events in seed germination?
• Account for changes in dry weights of
germinating seeds?
• Discuss the stages in seedling growth?
• MA: Describe an investigation of the effect of
water, oxygen and temperature on seed
germination
• MA: Describe an investigation to use starch agar
or skimmed milk plates to show digestive activity
during germination
Lesson Objectives - HL
By the end of this lesson you should know
how to:
• Discuss male gamete formation and pollen
grain development in detail
• Discuss female gamete formation and the
development of the embryo sac in detail
• Discuss the events of fertilisation in detail
Male gamete formation
Pollen grain development
Formation of a pollen grain
Development of
the embryo sac
Female gamete formation
LS of a carpal with mature
embryo sac
Fertilisation
“Fertilisation is the union of male and female
Growth of a pollen tube
gametes to form a diploid zygote”
What have you learned?
Can you. . .
• Discuss male gamete formation and pollen
grain development in detail?
• Discuss female gamete formation and the
development of the embryo sac in detail?
• Discuss the events of fertilisation in detail?