Plant Reproduction

Plant Reproduction
Chapter 22
Gymnosperm Reproduction
 Typically, the male pine cones are quite small and develop
near the tips of lower branches. Each scale of the male cone
has two or more microsporangia on the underside.
 Inside the microsporangia are microspore
cells that undergo meiosis and develop into
mature pollen grain, which is a spermbearing male gamete.
 The female pine cones are larger and located near the top of
the tree. Each scale of the female cone has two ovules that lie
on the upper surface.
 Within the ovule, a megaspore cell
undergoes meiosis and develops into mature
female gamete (egg), each containing a
single, large egg lying near the ovule.
 After pollination, the pollen tube discharges
two non-flagellated sperms. Only one of the
sperms fertilizes an egg in the ovule 15
months after pollination. The other sperm fertilizes
the endosperm to make a food source.
 After fertilization, the ovule matures and becomes the seed
composed of the embryo, its stored food, and a seed coat.
 Finally, in the third season, the female cone opens to release
its seeds, whose wings are formed from a thin, membranous
layer of the cone scale.
 When a seed germinates, the sporophyte embryo develops
into a new pine tree, and the cycle is complete
Angiosperm Reproduction
 In angiosperms, the reproductive structures
are located in the flower.
 The flower attracts insects and birds that aid
in pollination, and it produces seeds
enclosed by fruit.
 There are many different types of fruits,
some of which are fleshy (apple, tomato,
peach) and some of which are dry (pea in a
pod, nut, grain).
 Fruits provide protection for the seeds.
 Within a flower, there is a diploid megaspore mother cell in
each ovule of the ovary.
 The mother cell undergoes meiosis, producing one functional
megaspore, whose nucleus divides mitotically until there are
eight haploid nuclei.
 Male gametophytes are produced in the anther.
 An anther contains four pollen sacs with many microspore
mother cells, each of which undergoes meiosis to four
 Pollination is simply the transfer of pollen
from the anther to the stigma. It is brought
about by wind or with the assistance of a
particular pollinator.
 The plant uses the pollinator to ensure
 The pollinator uses the plant as a source of
food in the form of nectar.
 When a pollen grain lands on a stigma of the same species, it
germinates, forming a pollen tube.
 The pollen tube grows as it passes between the cells of the
stigma and the style to reach the female gametophyte.
 The outer layers (integuments) of the ovule
harden and become the seed coat.
 A seed is a structure formed by the
maturation of the ovule; it contains an
embryo plus stored food.
 The ovary and sometimes other floral parts
develop into the fruit.
 A fruit is a mature ovary that usually
contains seeds.
 Therefore, angiosperms are said to have
covered seeds.
Flowers and Pollinators
 Most flowering plants coevolved with
 Insects, birds, and other animals that
withdraw pollen from a flower and transfer
it to the female reproductive parts are