Plant Kingdom

Chapter 22

What Is A Plant?

• Plants are eukaryotic, multicellular organisms that have chlorophyll a and chlorophyll b and carry on photosynthesis.

• There cells have cellulose cell walls.

What Is A Plant?

• Plants are terrestrial organisms that can live in just about any environment, including deserts, arctic regions, swamps, shallow freshwater, and shallow oceans.

• There are more than 250,000 species of plants.

What Is A Plant?

• They range in size from the tiny floating duckweed the size of a pencil eraser to redwood trees over 100 meters tall.

• There are plants that lack chlorophyll and are parasites, plants that digest animals, and plants that have mutualistic relationships with animals.

Plant Cell

Alternation Of Generations

• The plant life cycle consists of two generations: the sporophyte generation and the gametophyte generation.

• This is referred to as alternation of generations.

Alternation Of Generations

• The sporophyte generation is diploid (2n). There are plant parts in which meiosis produces haploid (n) spores.

• In plants, the word spore refers to a haploid cell produced by meiosis that germinates to give rise to a multicellular haploid generation (gametophyte generation).

Gametophyte Generation

• The gametophyte generation is haploid and develops structures that produce gametes (eggs and sperm).

• Mitosis is utilized to produce eggs and sperm because the gametophyte is already haploid.

• When haploid gametes unite, a diploid zygote is formed.

Sporophyte Generation

• The zygote is the first new cell in the sporophyte generation.

• The zygote divides by mitosis, and a new multicellular sporophyte generation results.

Evolution Of Plants

• At one point in time, all life was aquatic.• Scientists believe that the ancestors of plants

were aquatic, photosynthetic algae.• Green algae have the same kind of chlorphyll

(chlorophyll a and chlorophyll b) and the same kinds of chloroplasts as plants.

• DNA comparison also supports this evolutionary conclusion.

Trends In Plant Evolution

• 1. Plants have become more specialized to live in a dry environment.

• 2. Plants have evolved toward a more prominent role for the sporophyte generation.

Trends In Plant Evolution

• Most primitive plants lack vascular tissue and are therefore limited to moist habitats.

• More advanced plants have vascular tissue to transport water and materials throughout the plant.

• Plants have also evolved seeds that can resist drying.

Evolution Of Plants

• In more primitive plants, the gametophyte generation is the dominant generation.

• In more advanced groups of plants, the sporophyte generation is dominant.

Nonvascular Plants

• The nonvascular plants include mosses, hornworts, and liverworts.

• They are commonly known as bryophytes.• Characteristics of nonvascular plants:– Lack vascular tissue.– Do not have true roots or leaves.– Gametophyte generation is most prominent.– Sperm swim to the egg.

Nonvascular Plants

• They rely on diffusion and osmosis to move dissolved materials through their bodies.

• Since the sperm swim to the egg, they must have water to reproduce sexually.

• Most are small and live in moist environments.

Moss Life Cycle

• The moss plant commonly recognized is the gametophyte generation.

• The cells of the gametophyte have the haploid number of chromosomes (same as gametes); however, not all of them function as gametes.

Moss Life Cycle

• At the top of the moss gametophyte are two kinds of structures that produce gametes:– The antheridium is made up of a jacket of cells

surrounding the developing sperm.– The archegonium is a flask shaped structure that

produces the egg.

• The archegonium usually only has one egg.

Moss Life Cycle

• When the sperm are mature, the outer jacket of the antheridium splits open, releasing the flagellated sperm.

• The sperm swims through a film of dew or rainwater to the archegonium.

Moss Life Cycle

• When the sperm and egg fuse, a diploid zygote is produced.

• The zygote is the first cell of the sporophyte generation.

• The mature sporophyte grows out of the top of the gametophyte.

Moss Life Cycle

Gametophyte Generation

Sporophyte Generation

Nonvascular Plants

• The mosses are the most common kind of nonvascular plant.

• Each moss plant is composed of a central stalk less than 5 centimeters tall.

• The gametophytes of liverworts and hornworts are flat sheets on a few layers of cells thick.

Nonvascular Plants

• Liverwort resembles the moist surface of a liver.

• Hornworts have a long slender sporophyte that protrudes from the gametophyte plant.

• Hornworts are unusual in that their cells contain only one long chloroplast per cell, whereas other plants have many per cell.

Moss

Liverwort

Hornwort

Significance Of Vascular Tissue

• Vascular tissue consists of tube-like cells that allow plants to efficiently transport water and nutrients about the plant.

• Vascular tissue is associated with the development of roots, leaves, and stems.

Vascular Tissue In Plants

Significance Of Vascular Tissue

• Roots are underground structures that anchor the plant and absorb water and minerals.

• Leaves are specialized structures for carrying out the process of photosynthesis.

• Stems are structures that connect the roots with the leaves and position the leaves so that they receive sunlight.

Vascular Plant Parts

Two Kinds Of Vascular Tissue

• There are two kinds of vascular tissue: xylem and phloem.

Vascular Tissue

Xylem

• Xylem consists of dead, hollow cells arranged end to end to form a tube.

• The walls of these “cells” are strengthened with extra deposits of cellulose and lignin.

• Xylem carries water and minerals up from the roots through the stem to the leaves.

Xylem

• There are two kinds of xylem cells: vessel elements and tracheids.

• Vessel elements are dead, hollow cells, up to .7mm in diameter, with endwalls missing. They forms long tubes.

Xylem

• Tracheids are smaller in diameter and consist of cells with overlapping, tapered ends.

• Holes in the walls allow minerals and water to move from one tracheid to the next.

Xylem

Phloem

• Phloem carries the organic molecules (sugars and amino acids) produced in the leaves to the other parts of the plant where growth and storage takes place.

• There are two kinds of phloem cells: sieve tube elements and companion cells.

Phloem

• Sieve tube elements lack a nucleus and most organelles, but have cytoplasm.

• Sieve tube elements have holes in the endwalls that allow the flow of water and dissolved nutrients.

Phloem

• Companion cells have direct connections to the sieve tube elements and assist in the movement of sugars and amino acids by active transport from cells in the leaves into the sieve tube elements.

Phloem

Xylem & Phloem

Growth And Storage

• Growth takes place at the tips of roots and stems and in the production of reproductive structures (cones, flowers, fruits).

• The roots are typically the place where food is stored, but some plants store food in their stems.

Roots

• Roots are the underground parts of plants that anchor the plant in the soil.

• Roots absorb water and nutrients, such as nitrogen, phosphorus, potassium, and other inorganic molecules from the soil.

Roots

• Vascular tissue distributes these substances to other parts of the plant.

• Roots grow from their tips to search for new water and nutrients.

• Most roots serve as a food storage place.

Roots

Root Types

Stems

• Stems have two main functions:– They support the leaves.– They transport raw materials from the roots to

the leaves and manufactured food from the leaves to the roots.

Stems

• The nature of plant cell walls provides the support in stems.

• Some plant cell walls thicken to provide additional support.

• Woody plants have especially thick cell walls.

Stem

Leaves

• Leaves are the major sites of photosynthesis.• Leaves have a large surface area to collect

light.• Leaves are relatively thin to allow the

penetration of light to the maximum number of cells.

• Leaves tend to be arranged so that they do not shade one another.

Leaves

Herbaceous Plants

• Herbaceous plants have few cells with thick cell walls.

• They are easily damaged.• Mosses, grasses, and many garden plants are

herbaceous.

Herbaceous Plants

Woody Plants

• Woody plants have a great deal of tissue with thick cell walls.

• There are ferns, gymnosperms, and angiosperms that are woody.

Woody Plants

Annual Plants

• Annual plants live one year.• They germinate from seeds, grow, produce

flowers and seeds, and die within 1 year.• The seeds they produce germinate the

following year and the cycle continues.

Perennial Plants

• Perennial plants live many years.• Most kinds of plants are perennials, including

mosses, ferns, horsetails, pines, and most flowering plants.

Perennial Plants

• Most perennial plants are woody, such as various kinds of trees.

• Some perennial plants produce above ground parts that die back at the end of the growing season. The plant grows the above ground parts from the roots each year. Tulips, daffodils, rhubarb, and ferns are examples.

Trees

• A tree is a large, woody plant that usually has a single main stem with branches.

• There are tree ferns, most gymnosperms are trees, and many flowering plants are trees.

Trees

Shrubs

• A shrub is a perennial woody plant that generally has several main stems and is relatively short.

Shrubs

Herbs

• Herbs are generally non-woody and small.

Herbs

Gymnosperms

• Several kinds of woody plants produce seeds that are not enclosed.

• Their seeds are produced in woody structures called cones.

• The seeds are said to be naked because they are not enclosed.

• The cone-producing plants, such as conifers, are called gymnosperms.

Gymnosperm

Cone

Angiosperms

• Angiosperms are plants that produce flowers and have their seeds enclosed in a fruit.

• A fruit is a modification of the ovary wall into a specialized structure that contains seeds.

Angiosperm

Angiosperm

Tropism

• Tropism is a growth or movement toward or away from a stimulus.

• Phototropism - plants orient themselves towards light.

• Thigmotropism – the ability of many vines to wrap stringlike tendrils around sturdy objects.

Thigmotropism