Plants Plant Diversity Chapter 19 The Origin of

Plants

Plant Diversity Chapter 19

The Origin of Plants from Algae Plants are multicellular autotrophs in which the embryo develops within the female parent. Based on molecular, cellular, and anatomical comparisons, the closest modern relatives of the ancestors of plants are the multicellular green algae called charophytes.

Charophyceans are the green algae most related to land plants Land plants evolved from this algae 500 million years ago. Plants are the major autotrophs of the terrestrial environments.

While algae live entirely in water, a plant lives in two environments: air and soil. A plant's organ systems are adapted to these two environments.

What adaptations were necessary for plants to invade the terrestrial habitat? • Absorb water • Prevent desiccation • Regulate gas exchange • Sexual reproduction without the advantage of water

Adaptations for Maintaining Moisture Cuticle of a fern stem (waxy layer provides waterproof protective layer)

Stomates regulate gas exchange and help maintaining moisture by regulating transpiration

Adaptations for Water Transport Xylem and Phloem of a Fern

Reproducing on Land • All plants produce their gametes in a "jacket" of protective cells. • In most plants, sperm reach the eggs by traveling within pollen grains, f • Fertilization and development of the embryo occurs within the female parent. • Embryos are eventually dispersed within a protective structure (seed).

An Overview of Plant Diversity Fossil evidence indicates that bryophytes are the oldest and angiosperms the youngest of the four major plant groups.

Highlights of plant evolution There are four main groups of Land Plants: 1. Bryophytes: nonvascular (moss) 2. Pteridophytes: vascular seedless (ferns) 3. Gymnosperms: vascular and seeded (conifers) 4. Angiosperms: vascular and flowering plants

Alternation of Generations Plant generations alternate between diploid (2 n) and haploid (n) forms A plant's life cycle alternates between the gametophyte and sporophyte generations.

The Diversity of Bryophytes

The Diversity of Bryophytes Liverworts Hornwort Moss

Mosses and other Bryophytes were the first land plants Nonvascular plants because they lack the lignin-hardened vascular tissue In the life cycle of a moss or other bryophyte, the sporophyte (2 n) remains attached to the gametophyte (1 n). The gametophyte provides water and nutrients to the sporophyte.

Life cycle of the Moss

Moss Life-cycle animation Which phase is dominant?

Peat bog Sphagnum or peat moss

Peat bogs

The Diversity of Vascular Plants (Tracheophytes)

The Diversity of Pteridophytes Club moss Horse tail Whisk Fern

Ferns and other Pteridophytes are seedless vascular plants During the Carboniferous period, 290 -363 million years ago, vast forests of seedless plants covered much of what is now Eurasia and North America. This is the source of our fossil fuels.

The sporophyte is the dominant generation in a fern's life cycle

Evolution of Vascular Plants: Fern Life Cycle: sporophyte-dominant life cycle Fern life-cycle animation

Carboniferous period 290 -363 million years ago Forests of seedless plants left materials for our fossil fuels

Pollen and Seeds evolve in Gymnosperms Important Reproductive Adaptations 1. Reduction of the Gametophyte 2. Advent of the Seed 3. Evolution of Pollen

Seeds are important means of dispersing offspring Bryophytes and ferns rely of spores How do seeds solve dispersal and survival in harsh environment issues? Seed consist of an embryo, protective coat and food supply

Pollen eliminated the requirement for aquatic environments for fertilization

The Diversity of Gymnosperms Coniferophyta: the most common gymnosperms Sequoia

The Diversity of Gymnosperms and Angiosperms

Ginkgophyta has only one living species: Ginkgo biloba

Phylum Cycadophyta: cycads Cycad cone

Gnetophyta Gnetum (tropical) Welwitschia (deserts of SW africa) Ephedra (arid regions)

Cypress Common juniper

In pines and other gymnosperms, the gametophytes develop inside cones. Airborne pollen grains (the male gametophytes) carry sperm to the female gametophytes.

Pine Life Cycle animation

The Diversity of Angiosperms

What are the major similarities and differences between the monocots and dicots?

MONOCOTS DICOTS Embryo with single cotyledon Embryo with two cotyledons Pollen with single furrow or pore Pollen with three furrows or pores Flower parts in multiples of three Flower parts in multiples of four or five Major leaf veins parallel Major leaf veins reticulated Stem vascular bundles scattered Stem vascular bundles in a ring Roots are adventitious Roots develop from radicle Secondary growth absent Secondary growth often present

What evolutionary “innovations” contributed to the success of angiosperms? Angiosperms also have both tracheids and vessels for more efficient transport of water.

Flower-pollinator relationships: Coevolution in action

Life of a Flowering Plant Chapter 20

Reproductive adaptations have lead to Angiosperms success. Label your diagram of the flower indicating the male and female parts.

Idealized flower Identify the functions of each of the structures: Complete flowers have: Sepals Petals Stamens Pistils

The flower is the defining reproductive adaptation How is the flower such a significant adaptation? Specific pollination (less random) Protected female gametes Ovaries develop into fruits

Angiosperm Life cycle

An angiosperm's life cycle includes development of male and female gametophytes, pollination, and fertilization. Click for detailed diagram

Development of angiosperm gametophytes Male Female

Pollen grains How is their structure of adaptive value?

Growth of pollen tubes from pollen grains

Growth of the pollen tube and Double Fertilization What do the two sperm fertilize? What is the value of the double fertilization?

Ovules are transformed into seeds and ovaries into fruits

Fruits aid in seed dispersal

Why is seed dispersal a great adaptive value?

Seed structure Typical dicot seed. Label the functions

Seed Germination The process where the seed begins to grow. What do you think seeds need to germinate? Seeds require: • water • oxygen • good temperatures

An advanced look at the activities that enhance seed germination 1. Seed takes in water 2. Gibberellin release signals 3. Amylase is released which hydrolyzes starch 4. Sugar is absorbed by embryo 5. Cellular respiration provides ATP

Seed germination A range of adaptations protect plants during germination. In some dicots, such as peas, the shoot tip avoids traveling "face-first" by being hooked downwards as it moves through the soil (left). In some monocots, such as corn, a protective sheath penetrates the soil ahead of the shoot (right).

Natural mechanisms of asexual reproduction Kalanchoe Aspen groves

Test-tube clones of carrots Just a few parenchyma cells can grow into a mass of undifferentiated cells. The callus differentiates into entire plant

Plant Structure and Function Chapter 20

Structure fits function in the plant body A plant has a root system below the ground a shoot system above. A shoot consists of stems, leaves, and flowers. New shoots grow from buds throughout a plant's life.

Plants have three basic organs: What are their general functions? Roots: Stems: Leaves:

Roots: absorb water and minerals Root hairs Fiberous roots Tap roots Plant Systems for Absorption video

A Plant's Main Tissue Systems Meristematic tissue continually produces the cells that will differentiate into three tissue types. The main tissue systems: the dermal, vascular, and ground tissue systems.

Tissues (cell types) of the plant

Plant Growth and begins with meristematic cells in growth regions Plants grow from these specialized regions Where are these growth regions?

Water is conducted through xylem: Xylem consists of two kinds of cells: Tracheids Vessel elements

Food made by the plant is conducted through Phloem consists of Sieve-tube elements and companion cells

Parenchyma cells are relatively unspecialized, thin, flexible and carry out many of the metabolic functons.

Collenchyma cells have thicker primary walls and provide support Lack secondary walls and hardening agent lignin

Sclerenchyma cells function as support with secondary walls and lignin. Fiber cells Sclereids: short fibers, irregular shape Give hardness to nutshells

Herbaceous stem cross-sections Look at the cross section for the tissues. How does the dicot differ from the monocot?

Modified shoots Stolons (strawberry) Rhizomes(ginger) Tubers (potatoes) Bulbs (onions)

Leaf Anatomy How is the leaf adapted for its function?

Modified Leaves Tendrils of pea plant Succulent (water storage) Cacti spines Pointsettia (attract pollinators)

Primary growth lengthens roots and shoots. New root cells are generated in the apical meristem. Those cells produced toward the bottom of the meristem replenish root cap cells. Those toward the top differentiate into cells of the dermal, ground, and vascular tissue, lengthening the root.

Primary Growth of Shoots As the apical meristem is pushed upward, new axillary buds have formed in each new axil.

Terminal bud and primary growth of shoot This is the region of growth for the stem

Secondary growth increases the thickness of woody plants. Cell division in the vascular cambium and cork cambium contributes to secondary growth.

Three-year-old woody stem What tissues are unique to the woody stem?

Tree Rings A cross section through a tree trunk reveals different layers of tissues. Sapwood is new xylem that is still actively transporting water. Heartwood is old xylem that no longer transports water. What can be learned by studying tree rings?

How old was this stem? Identify: Pith Phloem Springwood Summerwood Vascular rays Cork Vascular Cambium

Plant Nutrition Chapter 21

Plants acquire nutrients from the air and soil. Seeking the Source of a Plant's "Substance" 4 th century B. C. E. , Aristotle proposed that soil provides all the substance (mass) necessary for plant growth. Van Helmont (1648) grew a small willow tree in a pot containing 90 kilograms (kg) of soil. As the tree grew, he added nothing to the soil except water. Five years later, van Helmont found that the tree had gained nearly 75 kg while the soil had lost less than 0. 1 kg

Stephen Hales (1727), an English botanist, proposed a third hypothesis: Plants gain their substance from the air. Carbon dioxide and water are used to make sugar in photosynthesis.

The Mineral Requirements of Plants What do we do to make sure plants get enough nutrients? Nutrient deficiencies affect a plant's functioning. For example potato plants growing in magnesium-poor soil cannot make chlorophyll, which causes their leaves to yellow.

A Closer Look at Nitrogen What role does nitrogen play in plant metabolism? Plants must absorb nitrogen from the soil in the form of mineral ions

Bacteria help convert atmospheric nitrogen to ammonium and nitrate ions, forms of nitrogen that plants can use.

Transport in Plants Chapter 21

Vascular tissue transports sap within a plant Roots Absorb Water and Minerals Root hairs are tiny outgrowths of the root's epidermal cells. These root hairs grow into the spaces between soil particles. They greatly increase the surface area available for absorbing water and dissolved minerals.

Absorption and regulation of water and minerals by roots Endodermis surrounds stele and serves as checkpoint Casparian strip is a waxy zone impervious to water and minerals

Mycorrhizae are symbiotic fungi that increase surface area and absorb water and minerals and transport them to the host plant. Water absorption video

Transpiration: evaporation of water from leaves creates a force in leaves that pulls xylem sap up Water and minerals are transported as xylem sap Roots absorb water and dissolved minerals

Leaves exchange co 2 and o 2 through stomata during photosynthesis and respiration

Sugar is produced by photosynthesis in the leaves and transported in the phloem

Roots exchange gases within air spaces

Rise of water in a tree Water rises from high water potential in the soil to low water potential in the leaves. 1. Transpiration 2. Cohesion and adhesion 3. Root pressure Transport video

Xylem Both tracheids and vessel elements are stacked, forming hollow tubes that carry water through a plant.

Capillary action involves the adhesion and cohesion of water in the xylem.

Root Pressure forces water up the xylem Root pressure, helps push water up the xylem and usually operates at night. The root's epidermal cells and ground tissue cells use energy from ATP to accumulate certain minerals. The minerals can then move from cell to cell through cytoplasmic channels. Water and minerals move via this pathway into the xylem. In some plants, on windless nights, root pressure causes guttation.

Leaf Anatomy How is the leaf adapted for its function?

What is the role of the stomates?

Transport of the xylem sap Transpirational pull generated by the leaf.

Stomates Control of Transpiration Based on good conditions for photosynthesis and good water A leaf may transpire more than its weight in water in a day.

Regulating Water Loss Transpiration is required for the upward transport of water and minerals from the roots to the leaves. An average-sized maple tree, for instance, loses more than 220 liters of water per hour during the summer. Controlling water loss is essential. Water follows potassium ions from surrounding cells into guard cells, causing them to bulge and push apart at their centers. This forms a gap, opening the stoma. The flow of potassium ions and water out of the guard cells causes them to sag together, closing the stoma.

Regulation of Stomates Guard cells have microfibrils in the walls that cause them to elongate and open the stoma when turgid with lots of water and close when water is lost.

Phloem transport the foods synthesized by the plant.

Phloem Transports Organic Material (food) synthesized in the leaves. Pumps sucrose from cell walls into the phloem cells.

Pressure flow in a sieve tube Sucrose flows into sieve tube decreasing water potential. Water flows in from the xylem vessels Increase in pressure due to the increased water causing a flow from “source to sink”

The pressure-flow mechanism explains how sugar moves from source to sink.

Control Systems in Plants Chapter 22

Plant Responses to Internal and External Signals Chapter 39

Light-induced greening of dark-sprouted potatoes Dark grown After a week’s exposure to light What mechanism could be responsible for this?

What are some of the responses observed in plants that indicate plants respond to their environment. Phototropism Height growth Flowering Gravitropsm Leaf abscission Response to stress Thigmomorphogenesis Defense to herbivores

Discovery of a Plant Hormone The Darwins conducted a series of controlled experiments to determine the region of a seedling responsible for detecting light.

Early experiments on phototropism Enhanced Darwin’s work

The Went experiments Chemical auxin is responsible for the elongation of the cells in the stem

Auxins promote cell elongation (lengthening). The uneven growth rate on the two sides of the plant causes the shoot to bend toward the light. Cells on the shaded side of a plant grow faster than cells on the lighted side, causing the plant to bend toward the light.

Later experiments with phototropism: Plant growth responses to light is most significant in the blue light range (below 500 nm) Phototropin is the blue light receptor After 90 minutes

• Root gravitropism may be due to the settling of Statoliths in root cells • These plastids influence calcium and auxin concentration • High auxin in the root inhibits elongation

Thigmotropism is a plant response to touch Nastic movements of the mimosa and venus flytrap

Thigmotropism is a plant response to touch Tendrils of pea plants

Plant hormones help coordinate growth, development, and responses to environmental stimuli

Apical dominance: growth is up but if apical meristem is removed the lateral buds grow. Auxin from apical bud inhibits axillary buds Cytokinins from root counter auxin, when tip is removed cytokinins stimulate the axillary buds to form lateral branches

Cytokinins stimulate cell division and are produced by actively growing tissues. When tip was removed, cytokinin stimulates cell division and lateral buds grow.

Gibberellins: caused elongation in the “foolish seedling disease” from a fungus of the genus Giberella. More than 100 gibberellins have been discovered.

Treating dwarf plants with gibberelin

Gibberellin sprayed on Thompson seedless grapes makes grapes grow larger

Abscisic Acid (ABA) inhibits growth and induces dormancy in seeds (opposite to gibberellin) When would this regulator increase in concentration?

Ethylene produced under stress, fruit ripening and cell death Triple response: plants grow around obstacles 1. Slows stem elongation 2. Stem thickens 3. Grows horizontally 4. Touches upward until growth upward is possible

Leaf abscission is controlled by a balance of ethylene and auxin Ethylene increases and auxin decreases in response to short cooler days. Abscission zone

Flowering Response How does the plant time the flowering? Day length “sets the biological clock” Photoperiodism synchronizes plant responses to the season

Photoperiodism and Flowering: Plants fall into three types Long Day Plants flower during long days/short nights Short day Plants flower during short days/long nights Day Neutral How do plants monitor the period of day/night? Phytochrome

Phytochromes function as photoreceptors in flowering, seed germinations, biological clocks, etc. Red light (Inactive) Pr Pfr (active) Far-red light Seed germination: red light causes built up of Pfr and seed germinate, far red light reverses switch and inhibits germination

Phytochrome serves as a photoreceptor for many plant responses it is a molecular switch. Red light causes the Pr to change to Pfr (active form) The appearance of Pfr indicates sunlight Phytochrome is “switched” by 660 nm (red) and 730 nm (far-red) There exists a balance between the two forms.

(step in the signal transduction mechanisms in cells)

Short Day Plants flower short days but really long nights During the long night there is a conversion of Pfr to Pr Build up of Pfr inhibits the plant flowering What will happen if there is a brief exposure to light during the night?

Short day plants flower during uninterrupted long nights

Long day plants flower after long periods of light Build up of Pfr stimulates flowering What will happen if long day plants are exposed to periods of light at night even during short days?

During long days the Pfr accumulates or if during a long night there is an exposure to light

Is there a flowering hormone? Plant on left is induced to flower Grafted plant then flowers.

Rapid turgor movements by Mimosa pudica a sensitive plant Nastic movements Caused by changes in osmotic pressure