Lesson 5: Reproduction in Plants Flashcards
Sexual Reproduction
in Angiosperms
The flowers produced by
angiosperms contain the plant’s
reproductive organs.
The female reproductive
organs are called the carpel.
The male reproductive
organs are called the stamen.
The seeds form inside the flower.
When mature the seeds are
enclosed in a case.
Flower Structure
Sepals – when in the bud stage the
sepals protect the developing flower.
Petals – attract insects or other animals
for pollination
Pollen – contain the male gametes
Anthers – produce pollen
Filaments – hold anthers up to expose
pollen to insects and other animals
Stigma – receives pollen grains
Style – holds up the stigma to receive
pollen
Control of Flowering
Flowering involves a change in the
expression of genes in the cells of the shoot
apex.
New proteins are produced and the
cells and tissues that make up flowers
begin to develop from meristems
rather than leaves.
Plants flowering is influenced the amount of
light they receive. This is known as
photoperiodism.
In flowering, the critical factor is the
period of darkness the plant
experiences.
Plants respond to darkness using a leaf
pigment called phytochrome.
Phytochrome
This pigment exists in two forms inactive (Pr) and active (Pfr)
Active Pfr is rapidly produced from inactive Pr during daylight.
This conversion is in response to an increase in red light (660nm)
which is absorbed by Pr.
In darkness, the Pfr reverts slowly to the more stable Pr.
Long-day Plants
These plants flower when the days are
longest and nights are short.
These plants respond to increased amounts
of Pfr. Since the days are long more Pfr is
produced and the short nights only allow for
a small amount of Pfr to be converted back
into Pr.
These plants flower in the late spring and
early summer.
Examples of long-day plants include iris,
lettuce, wheat and radish.
Short-day Plants
These plants flower when as nights become
longer and days are shorter.
In short-day plants Pfr inhibits flowering. As the
days get shorter, less Pr is converted to Pfr and
during the longer nights more of the Pfr is
converted back into Pr allowing to flower.
These plants flower in late summer or autumn.
The amount of darkness must be over a critical
period unique to each species.
Examples of short-day plants include soybeans,
chrysanthemum, poinsettia and coffee.
Day-neutral Plants
Some are unaffected by the
photoperiod and will flower when
they reach a certain stage of
maturity, regardless of day length.
Examples of day-neutral plants
include tomatoes, rice and
dandelions
Pollination
For the seeds to develop, pollen grains
from the anthers must reach the stigma
of the carpel.
This process is called pollination
There are two types of pollination used
by angiosperms;
Self-pollination - the males and
female gametes come from the
same plant
Cross –pollination – the male and
female gametes come from two
different plants. The two most
common agents of
cross-pollination are wind and
insects.
Fertilization
Occurs when male and female gametes
meet and form a zygote.
Occurs in the ovule of the flower.
When pollen from the right species
arrive they germinate on the style
producing a pollen tube.
The pollen tube grows down the
style to the ovary
The pollen tube enters the ovary
and a pollen nucleus travels down
the tube to fuse with the ovule
nucleus.
Seed Structure (dicot)
Fertilized ovules develop into
seeds, which protect the
developing embryo.
Seeds are held within a seed pod,
fruit or nut.
Seeds have all the necessary
components to ensure successful
germination:
Embryo root (radicle) and
shoot (plumule)
Cotyledon
Testa (seed coat)
micropyle
Dicot plants seeds contain two cotyledons which store food reserves
(starches) for germination.
Cotyledons are surrounded by a hard protective seed coat called the testa.
The testa protects the tissues from the environment .
The testa contains a small pore called the micropyle through which water is
absorbed to begin germination.
Seed Dispersal
Seeds need to be moved to locations away
from the parents in order to minimize
competition.
There are many seed dispersal mechanisms:
Seed pods dry out and snap causing the
seeds to be ejected some distance from
the parent
Fruits are eaten by animals, which cannot
digest the tough seeds. The seeds are then
deposited in a rich fertilizer a long
distance from the parent to germinate.
Nuts are collected by animals which burry
them as reserve over winter. The animals
may not dig them up and they germinate.
Germination
Germination is the development of the
seed into a new plant.
Seeds remain dormant until conditions
are ideal
Temperature – suitable
temperatures activate enzymes
within the seed.
Water – most seeds contain about
10% water an therefore require
water to germinate.
Oxygen – Essential for aerobic
respiration
Process of Germination
Germination begins as water is absorbed through the micropyle in a process
called inbibition
Water rehydrates the stored food reserves and activates gibberellin
Gibberellin stimulates the release of amylase by the cells in the outer layer of
the seed (aleurone)
The amylase hydrolyses the starch in the cotyledon converting it into maltose.
Maltose is converted into glucose and transported to the embryo in order to
be used in respiration to create energy for growth.
Absorption of water by the seed splits the testa so that the embryo can
emerge and grow.
When the leaves of the seedling grow above ground, photosynthesis begins
and takes over energy production.
Gymnosperms
Gymnosperms do not produce
flowers
Produce seeds inside the cones
Seeds have a coat that
protects them but are not
inside a case
Sexual Reproduction in
Gymnosperms
Gymnosperms produce their seeds
inside cones. For this reason they
are called conifers.
In some species male and female
cones are produced on separate
trees.
In most conifers male and female
cones are produced by each tree.
