Plants
• Plants evolved about 500 million years ago from
simple green algae that lived in the ocean.
• All plants are autotrophic and some, like the
famous Venus fly-trap, can also be heterotrophic.
• All plants are eukaryotic and multicellular.
• Their cells contain a nucleus and membrane
bound organelles, specifically chloroplasts.
• In addition, plant cells also contain a cell wall
composed of cellulose.
• The cell wall provides protection, structural
support and helps to regulate water pressure
within the plant cell.
• The diagram on the
right illustrates the
components of a plant
cell.
• You will notice the
presence of vacuoles
which help to store the
materials needed for
photosynthesis.
• Animal cells and plant
cells contain most of
the same organelles,
but it is important that
you note the
differences.
• Currently there are over 350 000 species of
plants.
• They include mosses, ferns, conifers and
flowering plants.
• Most plants live on land and can withstand a
wide variety of climates.
• Cacti live in arid, dry areas whereas mosses
need to be in moist environments to survive.
Evolution of Plants
• The transition from a mainly aquatic environment
to a terrestrial planet revolved around plants.
• The ability of plants to photosynthesize and
sustain themselves is a key factor in the
evolutionary process.
• Plants provided nutrition to other organisms and
they helped form soil.
• Taller trees helped to reduce temperatures by
providing shade and therefore promoted the
growth of other organisms previously affected by
hot and dry conditions.
• Trees and shrubs also provided habitats for many
other organisms.
• Plants evolved during this process.
• Surviving in an aquatic environment is much
different than living in a terrestrial environment.
• In water, plants were constantly provided with
water and minerals and were able to easily
release waste products.
• However, on land plants had to either live in
moist environments or develop a method that
allowed them to absorb and transport materials
within their cells.
• They would have to develop specialized cells to
carry out tasks and provide structural support.
• So, of course plants evolved too.
Classification
• Plants are classified based on the presence or
absence of vascular tissue.
• Vascular tissue can be compared to arteries
and veins.
• It is a network of specialized cells that allows
plants to transport water, minerals and sugar
throughout the plant.
• You will learn about the characteristics of
nonvascular plants and vascular plants.
A quick word from Hank
• https://www.youtube.com/watch?v=iWaX97p
6y9U&list=PL3EED4C1D684D3ADF&index=36
Nonvascular Plants
• Mosses, liverworts and hornworts are examples of
bryophytes.
• Bryophytes are nonvascular plants that lack specialized
transportation cells called xylem and phloem.
• In addition, they do not have distinct roots, stems or
leaves.
• As long as the environment is moist they can grow on
soil, dead trees, rocks and even buildings. However,
they cannot grow very tall.
Reproduction of Nonvascular Plants
• Bryophytes can reproduce asexually through
vegetative reproduction.
• This occurs when a part of the plant breaks off
and a new identical plant develops.
• To reproduce sexually, these plants require water
for the male reproductive cell to swim to the
female reproductive organ.
• Unlike animal cells that produce haploid sex cells
to produce a zygote, plant cells alternate the type
of cells they produce.
• In one generation, a plant produces haploid cells
called spores which develop into a haploid plant.
• The haploid plant, called a
gametophyte, produces and
releases haploid gametes.
• When two of these gametes
fuse together, a zygote forms.
• The zygote, which is diploid,
develops into a sporophyte
plant.
• The sporophyte plant then
releases haploid spores and
the cycle continues.
• The image on the right shows
two capsules that contain
many spores.
Moss reproduction
• Each of the spores can
develop into a new
plant.
Homework
• Watch the two videos:
• https://www.youtube.com/watch?v=iWaX97p
6y9U&list=PL3EED4C1D684D3ADF&index=36
• Moss reproduction
• And can you bring in a device that is capable
of reading a pdf tomorrow please.