22-1 Introduction to Plants

§    plants dominate the landscape

§    plants provide the base for food chains on land

§    plants provide shelter, shade and oxygen for animals

§    oldest fossiI evidence dates from about 470 million years ago

What is a Plant?

§    Plants are members of the kingdom Plantae

§    Multicellular eukaryotes with cell walls made of cellulose

§    Carry out photosynthesis using the green pigments chlorophyll a and b

§    Autotrophic, do not gather food, move about or directly struggle with predators

The Plant Life Cycle

§    Plants life cycles have alternation of generations

v    Gametophyte (N) or haploid, gamete-producing plant

v    Sporophyte (2N) or diploid, spore-producing plant

v    Gametes = egg & sperm (haploid cells) when fuse produce a new diploid individual

v    Spores are reproductive cells that produce a new individual by mitosis

v    Plants must be able to reproduce in dry environments where there is no water through which gametes move from plants to plant

What Plants Need To Survive

1.  Sunlight

w   Use energy from the sun to carry out photosynthesis

w   Photosynthetic organs such as leaves are broad and flat to maximize light absorption

2.  Water and Minerals

w   All cells require a constant supply of water

w   Water is a raw material of photosynthesis and is used up quickly when the sun is shining

w   Plants have developed structures that limit water loss

w   Minerals that plants absorb with water are nutrients needed for growth

3.  Gas Exchange

w   Plants need oxygen to support respiration and carbon dioxide to carry out photosynthesis

w   Gas exchange takes place with the atmosphere without losing excessive water

4.  Movement of Water and Nutrients

w   plants take up water and minerals through their roots

w   food is made in their leaves

w   plants have specialized tissues that carry the water and distribute the food throughout the plant body

Early Plants

Origins in the Water

§    first green plants evolved from an organism much like the multicellular green algae living today

§    algae have similar reproductive cycles to those of plants

§    green algae have cell walls and photosynthetic pigments identical to those in plants

The First Plants

§    The first true plants were still dependent on water to complete their life cycles

§    Early plants were similar to today's mosses in that they were simple and grew close to the ground

§    They were common in damp swampy regions

§    From these first plants others began to evolve:

v    mosses and their relatives

v    ferns

v    cone-bearing plants

v    flowering plants

Overview of the Plant Kingdom

§    Botanists divide the plant kingdom into four groups based on three important features:

►        water-conducting tissues

►        seeds

►        flowers

§    Today, plant scientists classify plants by their DNA sequences

§    Since 1994, the project known as "Deep Green" has provided evidence that first plants evolved from fresh water green algae instead of from the sea as had been thought