Plant Form and Function:Plant Form and Function:How Do Plants Live in the World?How Do Plants Live in the World?

What Important Events Define the History of Plant Life ?

• Photosynthesis changed the world

• Eukaryotic cells and multicellularity enabled plants to diversify

• Plants moved from water to land

• Vascular plants dominate the terrain

Important Events in Plant Evolution

Photosynthesis Changed the World

• Plants use chlorophyll to capture the energy of sunlight for use in photosynthesis

• Oxygen is the by-product and has accumulated over the past 2.5 billion years.

Evolution of Eukaryotic Cells

• Occurred before plants became multicellular.

• Evolution of eukaryotic cells due to endosymbiosis.– Evidence to support the theory: Mitochondria

and chloroplasts.– Many examples of living prokaryotes that

share features of mitochondria and chloroplasts found in eukaryotes.

Evolution of Multicellular Cells

• Advantages of multicellularity– Cellular organisms have opportunity for

cellular specialization.

– Decreased vulnerability to changes in temperature, humidity, and nutrient availability that comes with increased size

Origin of Multicellularity

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Plants Moved From Water To Land

• Several evolutionary adaptations made this possible:– Multicellularity.– To prevent water loss

• A waxy cuticle.• An epidermal layer.• Structures that protect and enclose the delicate

gametes and embryo.

Plants Moved From Water To Land

• Several evolutionary adaptations made this possible:– Alternation of

Generations• Their life cycle is

divided into two stages

Plants Moved From Water To Land

• Life cycle of vascular plants:– Have vascular tissues

for moving food and water.

– Includes evergreens and flowering plants.

Plants Moved From Water To Land

• Another evolutionary adaptation that occurred in most vascular plants is – Seed formation– Has helped contribute

to the success of vascular plants

Vascular Plants Dominate the Terrain

Vascular Plants Dominate the Terrain

• Most successful vascular plant are angiosperms.

– Most diverse

– Defining characteristic is the flower.

What Do Plants Need and How Do They Get It?

• Plant form and function is best understood in terms of their needs:– Light– Gases– Water– Nitrogen and other nutrients

Plants Need Light

• Needed for photosynthesis.– Asymmetric branch

pattern allows for greatest exposure to light.

– Leaf• Greatest amount of

photosynthesis.• Allow for maximum light

absorption• Can do solar tracking

Plants Need Light

• Leaf interior promotes light absorption

– Palisade layer

– Spongy mesophyll

Plants Need Gases

• Plants need carbon dioxide (CO2)– Raw material for

making sugar.

• Stomates allow CO2 to enter cells.– Water can be lost

through stomates

Stomata

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Plants Need Gases

• C4 plants

– Can trap CO2 on hot, dry days

– Trap CO2 in palisade or spongy cells

– Only about 3% of plants

Plants Need Gases

• CAM plants– Desert dwelling plants

• Stomates must be closed all day long to prevent water loss.

– Stomates only open at night• Carbon dioxide enters and is stored in 4-carbon

molecule .

– CO2 molecule is released during the day in order for photosynthesis to occur.

Plants Need Water

• Roots– Anchor plant to ground and absorb moisture and

minerals– Root structure specially designed for absorption

Plants Need Water

– Root hairs maximize absorption.

• Found on root surface

• Delicate extensions dramatically increase surface area

Plants Need Water

– Arrangement of cells in the root

• Water is absorbed at epidermal layer and moves from cell to cell through the cortex by diffusion

Plants Need Nitrogen

• Nitrogen-fixation– Process in which

certain microbes fix atmospheric nitrogen into organic compounds.

– Some plants have a symbiotic relationship with these microbes.

Plants Need Other Nutrients

• Plants obtain minerals through their roots.

• When water enters the plant roots, so do minerals.– Move up the body of the plant to the leaves

and stems.

Plants Need Nitrogen and Other Nutrients

How Do Higher Plants Transport Substances and Support Themselves?

• All large multicellular organisms must have some way of transporting substances through their bodies, including plants.

• In some plants, the same tissues are responsible for:– Moving water– Providing support

Translocation

• The movement of fluids within the plant body

• Phloem– Living vascular tissue near

the periphery of the stem– Made of columns of sieve

tubes– Sap (sugar-rich fluids made

by photosynthesis) moves through the phloem

Transpiration

• Evaporation of water through the stomates of plant leaves.– Creates a negative pressure

• Allows water to move upward plant from roots

• Also prevents plants from overheating.

Water and Minerals Move Through the Xylem

• Xylem– Vascular tissue usually

found nearer the core, or center, of the stem.

– Composed primarily of dead cells that form a hollow interconnected network of tubules.

Plants Need Mechanical Support

• Reaching for the sun means growing upward– Opposing gravity.

• In soft-stemmed plants, mechanical support provided by turgor pressure.

• In woody plants, mechanical support provide by xylem.– Reinforced with lignin.

How Do Plants Grow?

• Plant growth is indeterminate.– Occurs at the meristem

• Cells divide by mitosis within meristem tissue.

• Found at the – tip of shoots and roots– In periphery of the woody trees and shrubs

Three Main Tissue Types in Plants

How Do Plants Grow?

• Apical meristem– Found at tip of

shoots and roots.– Responsible for

lengthwise growth.• Called primary

growth.

How Do Plants Grow?

• Vascular cambium– Meristematic tissue

that produces new bundles of xylem and phloem.

– Increases the girth of the stem or roots.

• Called secondary growth.

How Do Plants Grow?

• Cork cambium– Layer of meristem

produced from cells of the ground tissues.

– Produces a new layer of cells called cork.

• Also contributes to secondary growth.

Plants Have Hormones

• Phototrophism– Growing plant will bend toward the light.– Due to the presence of auxins.

• Class of molecules.

Plants Have Hormones

• Auxins– Stimulate cell

elongation.– Play a role in causing

the growing plant root to bend down.

– Involved in fruit development.

Plants Have Hormones

• Gibberellins– Class of 100 similar chemical

compounds.

– Produced at tips of roots and stems.• Stimulates plant growth.

– Most concentrated in seeds.• Facilitates growth of embryo and

germination.

Plants Have Hormones

• Abscisic Acid (ABA)– Hormones that slow growth

• Needed on cold days or excessively hot days.

• Released when water is scarce.

• Plant growth is a balance between ABA and gibberellins.

Plants Have Hormones

• Ethylene– Causes fruit ripening

• As fruit ages, it releases more ethylene

– Activates enzymes that digest the cell walls of plants.

• Enables plant to respond to environment by by aging or planned cell death

Plants Reproduce Sexually

• Zygotes are formed by the fusion of male and female gametes

• In angiosperms, flowers are the sex organs that produce gametes.

Sexual Reproduction in Flowering Plants

• Male reproductive organs = stamens

– Have anthers

– Contain cells that give rise to pollen

Sexual Reproduction in Flowering Plants

• Female sex organ = carpel– First houses the

ovule,– Then the female

gametophyte– And finally, the

embryo

Fertilization in Flowering Plants

Fertilization in Flowering Plants

Pollination

• How does pollen get from the male anther to the female ovary?– Wind– Water– Animal pollinators

• Flowers attract animal pollinators.

Seeds and Fruits

• After fertilization, ovule develops into a seed.

• Seed remains dormant until conditions for growth are appropriate.

• Ovary that surrounds the seed, or some other parental structure, may develop into the fruit.