Introduction to Plants! Introduction to Plants!

Mrs. LambertMrs. Lambert

Plants

The Basics• Multicellular• Eukaryotes• Cell walls made of

cellulose• Autotrophs

An Early Scientist described plants as, “Stationary animals that eat sunlight.”

Life Cycle

• Plants have a life cycle that is characterized by alternation of generations.

• Two generations:– Gametophyte – plant that produces haploid

gametes (N).• Gametes – eggs and sperm that fuse to

produce diploid individual.– Sporophyte – plant that produces diploid spores

(2N).• Spores – reproductive cells that produce a

new individual by mitosis.

• All plants have gametophyte stage and sporophyte stage.

The lives of plants revolve around:

1. The need for sunlight, water and minerals.– Plants use water quickly when the sun is

shining.

2. Gas Exchange• Plants require oxygen to support respiration

as well as carbon dioxide for photosynthesis.

3. Movement of water and minerals.• Plants take up water and minerals through

their roots but make food in their leaves.

Early Plants

• Early plants lived in the water.

• When they moved to land, they changed the environment in ways that made it possible for other organisms to develop.

• Early plants probably looked like multicellular green algae.

Plants are divided into two categories:

• Bryophytes – Non-vascular plants.– No tissue to transport water and nutrients

throughout the plant.

• Tracheophytes– Vascular plants.– Tissue to transport water and nutrients.

Bryophytes

• Three divisions:– Mosses– Liverworts– Hornworts

• The simplest plants – no tissue to transport water and nutrients.– No true roots, stems, or leaves.

Mosses

• The most common bryophytes.• Live in wet habitats – swamps, bogs,

streams.• Can tolerate very low temperatures.

– Most abundant plants in polar region.

• Leaves of mosses are only one cell thick.

• Must be close to water – found in moist shaded environments.– Size is limited.

• Anchored to the ground by filaments called rhizoids.

• Obtain water and nutrients by absorbing them directly into plant cells.– Water seeps from one cell to the next.

Reproduction in bryophytes

• Reproduce with alternation of generations.

• Gametophyte is dominant stage of life cycle.

• Sperm must swim to egg.– Bryophytes must live in areas where water

is available.

Tracheophytes

• Contain vascular tissue.– Xylem – carries water upward from roots to

every part of the plant.• Tracheids – hollow cells with thick walls

that resist pressure.– Phloem – transports solutions of nutrients

and carbohydrates produced by photosynthesis downward from leaves to the roots.

• Produce lignin – a substance that makes cell walls rigid.

• Because of xylem, phloem and lignin, Tracheophytes can grow upright to reach great heights.

Tracheophytes are divided into two main groups

• Seedless plants– Club moss, horsetails and fern

• Seed plants– Gymnosperms– Angiosperms

Seedless plants - ferns

Seedless plants - ferns

• Have roots, stems and leaves.– Roots – underground organs that absorb

water and minerals.– Leaves – photosynthetic organs that

contains vascular tissue gathered into veins of xylem and phloem.

• The leaves of ferns are called fronds.– Stems – supporting structures that connect

roots and leaves, carrying water and nutrients.

Life Cycle of the Fern

• In ferns and other vascular plants, the diploid sporophyte is the dominant stage.

• Fern sporophytes produce haploid spores on the underside of their fronds in tiny containers called sporangia.

• Sporangia are grouped in clusters called sori.

• The spores germinate and develop into haploid gametophytes.

• Small heart-shaped plants that grow independently of the sporophyte.

• On the underside of the gametophyte:– Antheridia –

where sperm are produced.

– Archegonia – where eggs are produced.

• Fertilization requires a thin film of water, allowing the sperm to swim to the eggs.

• The diploid zygote produced by fertilization grows into a new sporophyte plant.

• Sporophyte fronds may die in the winter, but rhizomes live through the winter and sprout again in the spring.

Life cycle of fern

Seed Plants

• The dominant group of photosynthetic organisms on land.

Seed Plants are divided into two groups:

• Gymnosperms – bear seeds on the

surface of cones.– Conifers such as

pines and spruces.– Ancient ginkgoes.

Angiosperms

• Flowering plants that bear seeds within a layer of tissue that protects the seed.

• Include grass, flowering trees and shrubs, all flowers.

Reproduction in seed plants:

• Seed plants do not require water for fertilization of gametes.

• Adaptations that allow this:– Flowers or cones.– The transfer of sperm by pollination.– The protection of embryos in seeds.

Cones and Flowers

• Gametophytes of seed plants grow and develop in two types of sporophyte structures:– Cones – seed bearing structures of

gymnosperms.– Flowers – seed bearing structures of

angiosperms.

Pollen

• In seed plants, the male gametophyte is contained in a pollen grain.

• The pollen grain is carried to the female gametophyte by wind, insects, birds, or small animals.

• The female gametophyte is located in the ovary of the flower.

This transfer is called pollination.

Seeds

• After fertilization, the zygote develops into a tiny plant called an embryo.

• A seed is an embryo of a plant that is encased in a protective covering and surrounded by a food supply.– Embryo – the early developmental stage of

the sporophyte plant.– Seed coat – surrounds and protects the

embryo.

• The embryo can remain within the seed for years.

Gymnosperms

• Include gnetophytes, cycads, ginkgoes and conifers.

Ginkgoes

• Belong to phylum Ginkgophyta.

• Only one species: Ginkgo biloba.

• Common when dinosaurs were alive.

• One of the oldest seed plant species alive today.

Conifers

• Belong to phylum Coniferophyta.

• Includes pines, spruces, firs, cedars, sequoias, redwoods and yews.

• Some can live for more than 4,000 years.

• Most conifers are evergreens.

Some redwoods can grow more than 300 feet tall.Tallest is 397.1 feet tall!

Angiosperms – Flowering Plants

• Angiosperms have unique reproductive organs known as flowers.– The vast majority

of living plant species.

– 235,000 species.

.

• Flowers attract animals such as bees or hummingbirds, which transport pollen from flower to flower.– Much more efficient

than wind pollination used by gymnosperms

• Flowers contain ovaries, which surround and protect the seeds.

• After pollination, the ovary develops into a fruit. – A thick wall of tissue surrounding the seed.– Fruit protects the seed and aids in its

dispersal.– Animals eat fruit and the seeds leave the

digestive system ready to sprout.

• The animal disperses the seed when it travels.

• Plants use fruit to attract animals and increase the range of their habitat.

Diversity in Angiosperms

• Incredibly diverse with many different categories.

• Monocots and dicots.• Woody and herbaceous plants.• Annuals, biennials and perennials.• These categories overlap!

Two groups of angiosperms

• Named for the number of seed leaves or cotyledons in the plant embryo.

• Monocots and dicots.

Monocots

• One seed leaf or cotyledon.• Leaves: Parallel veins.• Floral parts in multiples of 3.• Stems: Vascular bundles scattered

throughout stem.• Fibrous roots.• Corn, wheat, lilies, orchids and palms.

Dicots

• Two cotyledons.• Leaves: Branched veins.• Floral parts in multiples of 4 or 5.• Stems: Vascular bundles arranged in a

ring.• Taproot.• Roses, clover, tomatoes, oaks and

daisies.

Monocots have fibrous roots, dicots have taproots

Woody and Herbaceous Plants

• Woody plants – made of cells with thick cell walls that support the cell body.– Trees, shrubs and vines.

• Herbaceous plants – do not produce wood as they grow.– Dandelions and sunflowers.

Classification of Angiosperms based on life

span:

• Annuals – complete life cycle within one growing season.

• Petunias, pansies, cucumbers.

Biennials

• Complete life cycle within two growing seasons.

• Parsley and celery.• Foxglove and Prince

William.

Perennials

• Plants that live for more than two years.– Grass, asparagus,

maple trees.