Plants

Mader-Chapters 24-28

Evolutionary History of Plants

Evolutionary Milestones• Embryo protection…This is what

separates plants from Green Algae and allowed them to become terrestrial (490 mya)

• Vascular tissue… Allowed plants to move away from water and grow taller (430 mya)

• Seeds…Allowed for embryo dispersal and protection (420 mya)

• Flowers and Fruit…Greatly increased the plants ability to sexually reproduce by attracting pollinators (200 mya)

Classification of Plants

Alternation of Generations

• All plants have a life cycle with an alternation of generations

• Two multicellular individuals alternate producing each other

• Sporophyte (2n) produces gametophyte (n) which then produces sporophyte…

Nonvascular Plants (bryophytes)

• Hornworts, liverworts, and mosses (Do not try to remember the differences)

• Do not have differentiated organs as seen in the plants with a dominant sporophytic life cycle stage… Instead have “rootlike, stemlike, and leaflike” tissue

• Lack vascular tissue (phloem and xylem)• The sperm must swim “nakedly” in a film of water

for fertilization to occur• Limited in height by previous two bullet points

Nonvascular plant life cycle

Seedless Vascular Plants

• Club Mosses, Ferns, and Horsetails• Were much larger in ancient times• Most are homosporous as opposed to the

heterosporous seeded plants that produce both male and female gametophytes

Fern Life Cycle

Seed Plants

• Gymnosperms (Naked Seeds) and Angiosperms (Seeds covered in Fruit that came from Flowers)

• Most plentiful plants in the world today• Seed-Sporophyte embryo plus stored food

(endosperm) inside of a seed coat• Seeds may lay dormant for years• All seed plants are heterosporous…. Pollen is the

male gametophyte which moves toward the female gametophyte in the ovule

Gymnosperms

• Conifers, cycads, ginkgoes, and gnetophytes

Conifer Life Cycle

Angiosperms

• Flowering and fruiting plants whose ovules are always enclosed in diploid tissue

•Classified as either Monocotyledons (monocots) or Eudicotyledons (dicots) based on either having one seed leaf or two

The Flower

Angiosperm Life Cycle

Plant Vegetative OrgansRoots

• Anchor plants in soil

• Absorb nutrients and water from soil

• Contains vascular tissue for transport of water and nutrients

• May store products of photosynthesis as vegetables in perennials as in carrots and sweet potatoes

Stems• Support leaves in

optimum position for photosynthesis

• Contains vascular tissue for transport of water and nutrients

Leaves• Where

photosynthesis occurs

• May be specialized such as cactus spines or tendrils for climbing

Monocot vs. Eudicot (dicot)

Plant Tissue

• Plants grow their entire life because of meristematic tissue

• The apical meristem continuously produces three types of meristem:

1.Protoderm forms epidermal tissue2.Ground meristem produces ground tissue3.Procambium produces vascular tissue

Plant Tissue: Epidermis

• Covers plant and creates cuticle… waxy covering that prevents water loss

Plant Tissue: Ground Tissue

• Forms the bulk of the plant… least specialized

Plant Tissue: Vascular Tissue

• Xylem and Phloem• Xylem, made from hollow dead tissue,

transports water • Phloem, made from a sieve tube (no nucleus

but does have cytoplasm and a companion cell that actively pumps sugars into sieve tube) transports sugars and other organic compounds… with the aid of water

Plant Tissue: Vascular Tissue

Organization of Roots

Root Tip

Zone of Cell Division

Zone of Elongation

Zone of Maturation

What is this, what does it do, and how does it work?

Monocot or Dicot? … and how do you know?

Which one of these is the dicot?

?

Organization of Stems

How do we know that this is either a conifer or a woody eudicot and not a herbaceous stem?

Organization of Stems

Organization of Stems

Leaves

How do you know that this leaf is from a C3 plant?

No chloroplasts in the bundle sheath cells and the mesophyll cells are not arranged concentrically around the vein.

Who can recall C3 from C4 photosynthesis?

In hot dry climates, the stomata close and limit the intake of CO2 . O2 builds up which combines with RuBP Carboxylase which limits 3PG production which limits G3P production which limits glucose production.

In C4, PEP combines with CO2 to form OOA which is pumped into the bundle sheath cells.

Plant Nutrition and Soil

• There are essential nutrients that a plant needs or it will die and there are beneficial nutrients that will help it grow

• Essential nutrients are divided into Macro and Micro depending on their concentrations in plant tissue

Soil

• All terrestrial life is based on soil!• Created through mechanical, chemical, and organic

erosion• Consists of mineral particles (sand, silt, and clay), decaying

organic material (humus), living organisms, air, and water• Soil profile with horizons can be analyzed • Takes a very long time to create (1cm/15yrs)• Soil erosion is happening at a very fast rate due to poor

agricultural practices and this is a serious threat to life on earth

Water Uptake•Water travels between cells, through the porous cell walls, until it get to the Casparian strip or it can enter the cell at the root hair and travel intracellularly •Water will enter root cells as long as they have lower osmotic pressure than surrounding soil or a lower water potential which is a combination of pressure potential and solute potential

The effects of Mycorrhizae

Mineral Uptake

• Plants absorb minerals in their ionic (charged) form and therefore these ions must pass through ion channels

• Plants expend energy to transport ions into the roots

• H+ is pumped out creating an electrochemical gradient which causes positive ions such as K+ to diffuse in

• H+ diffuses back down its concentration gradient along with negative ions

Transport Mechanisms•Xylem, consisting of tracheids and vessel elements move water and minerals from the roots to the leaves•Phloem, consisting of sieve-tube members and companion cells move sugars and organic nutrients, along with water, from the leaves to other tissue in the plant•Water potential and chemical properties of water such as cohesion allow these to occur

Water Transport by Cohesion-Tension Model

• Water is cohesive due to hydrogen bonds

• When stomata open, mesophyll cells are exposed to air and evaporation occurs

• There is a continuous column of water from roots to leaves through the xylem

• As each water molecule evaporates, it exerts a force, pulling up the water column

• Root pressure also contributes

Opening and Closing of Stomata

Water

Transport of sugars and other organic nutrients by the Pressure-Flow model

• Sugars and other organic nutrients are synthesized on the leaves

• Sieve-tube members connect leaves (source) to roots, developing leaves, and flowers (sink)

• Companion cells actively pump nutrients into sieve-tube members and water follows

• The water pressure creates a flow of nutrients form source to sink

Plant Responses

• Plant growth toward unidirectional stimulus is called tropism…. Toward stimulus is called positive tropism and away is negative tropism

• Examples… Phototropism (light), Gravitropims (gravity), Thigmotropism (touch)

Describe the following tropisms

How are they similar and how are they different?

Hint… I am a root!

Plant Responses

• Nastic Movements do not involve growth and occur even more rapidly than tropisms… almost as if there were a nerve impulse coordinating the movement

Nastic movement can be linked to touch, temperature, day cycles, or light cycles

Plant Hormones

• Almost all communication in plants in done by hormones

• Synthesized in one part of the plant and travel though phloem or intracellularly to target tissue

• Do not require large concentrations to be effective

Common Plant Hormones

1.Auxins-Promote many aspects of growth2.Gibberellins-Promotes many aspects of

growth such as stem elongation, break of dormancy in buds, and flower growth

3.Cytokinins- Promote cell division4.Abscisic Acid (ABA)- Prepares plant for

stressful period5.Ethylene-Prepares plant for abscission or the

dropping of leaves, flowers or fruit

Auxins-Promotes growth by weakening cell walls, creating cell

membrane, and turning on growth factors

Apical Dominance

Signal-Transduction-Response

Gibberellins-promotes amylase production which breaks down starch into sugar

for growth

What do we call this type of system where a hormone binds to an integral protein causing a cascading effect

Signal-Transduction-Response

• Cytokinins promote differentiation of tissue with the help of other hormones such as auxins

• Inhibit senescence, or the aging process in plants

Cytokinins-promotes cell division

• Maintains seed and bud dormancy so that energy will not be wasted on growth in unfavorable conditions, such as winter time

• Close stomata under water stress

Abscisic Acid (ABA)-Prepares plant for stress

• Ethylene is a gas that promotes the ripening of fruit by breaking down the cell wall

• Inhibits growth in roots, leaves, and stems• Promotes leaf abscission, or the dropping of

leaves

Ethylene-Promotes abscission

Photoperiodism• A physiological response prompted by a change in length of

day or night• Short day plants should really be called long night plants and

long day plants should really be called short night plants

Flowering Plants1. Long-Day- Plants flower in

spring or early summer when D.L. is increasing

2. Short-Day-Plants flower in late summer and early fall when D.L. is decreasing

3. Day-neutral

Flowering Plants• The life cycle of flowering plants

is adapted to a land existence• The microscopic gametophyte

develops within the sporophyte and are thereby protected from desiccation (drying out)

• Microspore (male),created through meiosis of microsporocyte, undergoes mitosis to become pollen

• Megaspore (female), created through meiosis of megasporocyte, undergoes mitosis to become an embryo sac within an ovule found in the ovary

Flowers*Not all flowers are “complete” or “Perfect” meaning hermaphroditic

Corn is monecious because it has both male and female flowers on the same plant

Life Cycle of Flowering PlantsInteresting Points to Remember

Seed Development

Fruits

• Simple fruit-derived from a simple ovary of a single carpel or from a compound ovary of several fused carpels

• Compound fruit is derived from several individual ovaries

…. Also, some fruit is fleshy (pear, orange, berry) and others are dry (Peas, beans, rice, oats)

I am fleshy!

Seed GerminationGermination

•During dormancy metabolism is slowed way down•Cells are dry and water is needed for germination•Fleshy fruit seeds need to be washed before they will germinate•For some seeds, bacterial action, mechanical abrasion, or even fire may be needed

Asexual Reproduction

• Plant cells are totipotent, meaning that each cell has the full genetic potential to makes a whole new organism

• This is done regularly in labs with the proper administration of various plant hormones such as Auxins and Cytokinins

• In nature, plants reproduce by vegetative propagation

• Vegetative propagation occurs from growth of meristematic tissue at nodes of stems or roots