Transcript Chapter 24
Sexual Reproduction In Animals and Plants
Differences between sexual and asexual reproduction
Advantages and disadvantages of each type of reproduction
How plants reproduce
Reproduction can be asexual or
sexual
Asexual reproduction – single parent passes copies of all
its genes to offspring
Offspring is a clone of its parent
Prokaryotes and some eukaryotes can reproduce asexually
Sexual reproduction – two parents form reproductive
cells that have half the number of chromosomes of
parents
Offspring have traits of each parent but is genetically
different from each
Eukaryotes can reproduce asexually
Asexual Reproduction
Types
Fission
Fragmentation
Budding
Advantages/Disadvan
tages
Asexual reproduction
simplest and most primitive
form of reproduction
Produce many offspring in
short period of time
Little genetic variation –
problem in changing
environment
Sexual Reproduction
Evolution
Advantages/Disadvan
tages
May have evolved from
mechanisms used by early
life to repair DNA
Organism must use energy
to produce gametes and
find mate
Only diploid cells can do
DNA repair
Quickly makes different
combinations of genes –
creates genetic diversity
which is the raw material of
evolution
Many enzymes that are
involved in DNA repair are
also involved in meiosis
Sexual Life Cycles of Eukaryotes
Animals have a diploid life cycle – life cycle is dominated by
diploid stage – which produces haploid gametes – which
fuse to form diploid zygote
Plants have a life cycle that alternates between diploid and
haploid
Diploid phase in plants called sporophytes
Sporophytes produce haploid spores by meiosis
Spores develop into haploid multicellular individuals called
gametophytes without fusing with another cell
Gametophyte produces haploid gametes by mitosis.
Gametes fuse and give rise to the diploid phase
Plant Life Cycle
Complex plants have
sporophytes and
gametophytes that
appear very different
In mosses, the haploid
gametophyte is dominant
In flowering plants, the
diploid sporophyte
generation is dominant
Reproduction in Seed Plants
Seed plant gametophytes
are made up of only a few
cells
Male gametophytes
produce pollen
Ovule
Female gametophytes
develop within an ovule –
which is part of the
sporophyte. After
fertilization by pollen – the
ovule and its contents
develop into a seed
Seed plants can
reproduce sexually without
water –wind, insects and
birds carry pollen to the
female parts of the plant pollination
Seeds
Seeds contain the embryos
of plants
An embryo is a new
sporophyte
Outer layers of ovule harden
to form protective seed coat
Leaf-like structures called
cotyledons are part of plant
embryo – they provide
nutrients to embryo
Flowers
Gametophytes develop
within flowers
Outermost whorl = sepals
Second whorl = petals
(these are brightly colored
to attract birds and insects)
Stamen – produces pollen;
consists of anther and
filament
Pistil – produces ovules;
consists of ovary, style and
stigma (sticky part where
pollen sticks)
Fruit
Structure of the plant that
contains the seed
Develops from one or more
of the flower’s ovaries
Apples, tomatoes,
avocados, cucumbers,
pumpkins, okra – anything
that contains seed(s) is a
fruit
Vegetables
Other part of plant that we eat – leaf, root, stem…
Any part of the plant that we eat that does not contain the seed
Celery, carrots, potatoes, spinach, etc….
Parts of plant not directly involved in reproduction