Botany - Flowers and Reproduction

1. LESSON IX. FLOWERS AND
REPRODUCTION

2. INTRODUCTION
Plants undergo alternation of generation during their life cycle. It is
called alternation of generation because their life cycle has two
multicellular stage: A halploid gametophyte and a diploid sporophyte.
This is different to animals that are diploid and mostly produce
haploid gametes that become diploid offspring after fertilization and
development.

3. IS THERE REALLY A MALE AND
FEMALE PAPAYA?

5. IX. 1. REPRODUCTION OF SIMPLE
PLANTS
 Ferns, mosses and liverworts are all plants that have spores.
 Spore plants have a different life cycle.
 A parent plant sends out tiny spores containing special sets of
chromosomes.
 These spores do not contain an embryo or food stores.
 Fertlization of the spores take place away from the parent, usually
in a damp place.
 An embryo is formed and a new plant grows from it.

12. IX. 2. FLOWER
 Angiosperm have flowers.
 The flowers are special structures for reproduction.
 They contain male parts that make pollen and female parts that contain
ovules.
 Some plants have these male and female parts in different flowers.
 Pollen is carried from a male part to a female part by wind, insects or
other animals (a process called pollination), where it releases male
gametes that fertilize the female gametes in the ovules.
 The ovules develop into seeds from which new plants will grow. In most
angiosperms, part of the flower develops into fruit, which protects the
seeds inside them.
 Fruit can be soft like oranges or hard like nuts.

14. The angiosperms are divided into three species that
are hermaphroditic (pistils and stamens are on the same flower),
monoecious (stamens and pistils are on the different flower but over
the same plant), and finally dioecious (both stamens and pistils are
found in different flowers in different plants)

15. The flowering plants which show hermaphroditism are known as
hermaphrodite flowers. They are also known as perfect or bisexual
flowers. Common examples of hermaphroditic flowers are roses,
lilies, mangoes, daffodil, petunia, etc. These plants can undergo self-
pollination, and are not dependent on pollinators

16. Monoecious plants have male flowers and female flowers in separate
structures on the same plant. "Mono" means one - and the term
"monoecious" is literally "one house". The same plant houses different
flowers, some being male the others being female. Squash is
monoecious

18. Dioecious
plants house the
male and female
flowers on different
plants. So not only
does the plant have
separate
male/female
flowers, they have
male plants (with
only male flowers)
and female plants
(with only female
flowers). Hollies and
asparagus are
dioecious.

22. IX. 3. POLLEN DEVELOPMENT
 Pollen is the male gametophyte of seed plants.
 Both gymnosperms (cone-bearing plants) and angiosperm
(flowering plants) produce pollen as part of sexual reproduction.
 In gymnosperms pollen is produced in microsporangiate cones
(male cones or pollen cones), while in angiosperms pollen is
produced in the anthers (part of the stamen within the flower).
 Each pollen grain typically consists of one to a few cells.

24. Schematic Diagram of Pollen Development in Maize.

25. Pollen development and growth. Pollen can be shed at either the two-celled or
three-celled stage; it varies from species to species.

26. Lilium anther cross-section. Lilium tetrads.
2-celled pollen grain of lily
Lilium – cross section of dehiscing anther
with two-nucleated pollen grains.

27. IX. 4. EGG DEVELOPMENT
 At the start of the process of egg cell development, a “mother cell”
in the ovule divides several times, in as sequence involving both
meiosis and mitotic divisions.
 These divisions result in the creation of an oblong, cell-like
structure called the embryo sac, which contains eight nuclei. Three
of which are clustered near the open end of the ovule.

29. Lilium – ovule with megaspore mother cell.
Composite of Lilium megagametophyte, 1. four-nucleated
embryo sac, 2. final mitotic division, and 3. mature eight-
nucleated, seven-celled embryo sac.
Mature embryo sac of Lilium.

30. IX. 5. MODES OF POLLINATION
 The process by which pollen grains are transferred from anthers to
stigma is referred as pollination.
 Pollination is of two types: viz.
1. Autogamy or self-pollination and
2. Allogamy or cross pollination

33. IX. 6. INFLORESCENCE
 Inflorescence are complex structures with many functions.
 At anthesis they present the flowers in ways that allow for the
transfer of pollen and optimization of the plant’s reproductive
success.
 During flower and fruit development they provide nutrients to the
developing flowers and fruits.
 At fruit maturity they support the fruits prior to dispersal, and
facilitate effective fruit and seed dispersal.
 From a structural point of view, inflorescences haves played
important roles in systematic and phylogenetic studies.
 As functional units they facilitate reproduction, and are largely
shaped by natural selection.

34. Inflorescence with labels.
Simple and compound umbels.