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Plants. Definition of a Plant:.

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Definition of a plant

Definition of a Plant:

  • A multicellular, eukaryotic, photosynthetic autotroph. The cell walls contain cellulose and they store excess glucose as starch. They also exhibit alternation of generations – one will be dominant over the other. The sporophyte generation is 2n (diploid) and the gametophyte generation is n (haploid).

Evolution of plants

Evolution of Plants

  • Plants evolved from aquatic green algae about 500 mya.

    • Paleozoic era

    • Adaptations to dry land

    • Most plants are land plants today

Two groups of plants

Two Groups of Plants

  • Non-vascular – Bryophytes – no xylem or phloem

  • Vascular – Tracheophytes – contain xylem and phloem – conducting tissue

    • Xylem conducts – water

    • Phloem conducts – dissolved sugars

Primary functions of plants

Primary Functions of Plants

  • Absorb carbon dioxide

  • Release Oxygen

  • Hold soil in place

  • Provide for the transfer of energy from the sun to other organisms – AKA – Food

  • Provides habitats for animals

Division bryophyta

Division - Bryophyta

  • Non-vascular

  • Mosses, horn-worts, liverworts

  • They lack any lignin-fortified tissue so they can’t grow very tall.

  • The gametophyte generation is dominant in bryophytes (it is the green part that you see and the sporophyte is the stalk coming out of the gametophyte.)

Bryophyte continued

Bryophyte continued

  • Female gametophyte has an Archegonium that produces the egg (n)

  • Male gametophyte has Antheridia that produces sperm (n)- These are motile sperm and must have water in order to fertilize the egg.

  • Fertilization occurs within the archegonium and produces the zygote. The Sporophyte then grows from the zygote out of the gametophyte and produces sporangia that produce spores.

What do bryophytes do

What do Bryophytes do?

  • Stabilize and form soil from rocks – are pioneers in primary succession and are necessary to form the soil.

  • Used as fuel (peat moss)

  • Retains moisture when mixed with soil

Tracheophytes are

Tracheophytes are:

  • Vascular plants

  • Xylem and Phloem used for transport of water and sugars

  • Xylem and Phloem contain lignin that gives the plant support so that it can stand up against gravity

  • Roots absorb water and prevent desiccation (drying out), and anchor in the soil giving extra support

  • Leaves increase the photosynthetic area

  • Sporophyte is the dominant generation

Two groups of tracheophytes

Two Groups of Tracheophytes

  • Seedless Plants– Ferns – Pteridophytes

    • Homosporous– They produce only one type of spore

    • Stay fairly small because they must have water to reproduce due to the fact that sperm are flagellated and swim to get to the archegonium to fertilize the egg.

    • Ancient Ferns were tree size

    • They reabsorbed so much carbon dioxide during the Carboniferous period that the Earth experienced Global Cooling

    • Most turned into Coal that is now one of the causes of Global Warming


  • Life Cycle of a Fern

Seed plants

Seed Plants

  • Heterosporous – Produce megaspores – female gametophyte and microspores – male gametophyte

  • Male gametophyte does not have flagella so they don’t need water

  • Gymnosperms – Cone bearing – naked seed (conifers – pine, firs, redwoods, junipers, and sequoia) – long-lived organisms



  • First seed plants to appear

  • Seeds are not enclosed in a fruit

  • Replaced the ferns because they were better adapted for land

  • Have needle shaped leaves with a waxy covering that helps to prevent drying

  • Use the wind for pollination



  • Flowering plants – seeds are enclosed in a fruit

  • Most diverse and abundant of all plant species

  • Color and scent of flowers attracts animals for pollination and dispersal of seeds

  • Ovary becomes the fruit (fruit is ripened ovary)

  • Ovule becomes the seed

Seed fruit adaptations

Seed/Fruit adaptations

  • Maples have wings so that the wind can carry them

  • Fruit has burrs that stick to animal fur

  • Brightly colored and sweet so that animals eat them and then poop the seeds with fertilizer so it grows rapidly

  • Some float on water (coconut)

  • Fruit prevents drying out of seeds and protects them until they are ready to be dispersed.

Two types of angiosperms

Two types of Angiosperms

  • Monocots – have one cotyledon (seed leaf)

    • Scattered vascular bundles

    • Parallel veins in the leaves

    • Flower parts in 3s

    • Fibrous roots


  • Dicots – have two cotyledons (seed leaves)

    • Vascular bundle is arranged in a ring

    • Veins are netlike or branched

    • Flower parts are in 4s or 5s

    • Have taproots

Plants part ii how plants grow

Plants: Part II –How plants Grow

  • Plants can only grow from meristematic tissue (meristem) – it is embryonic tissue (stem cell)

  • Located at the tip of the roots and in the buds of shoots is apical meristem.

  • The plant’s roots grow down into the soil from this tissue and grow taller from the top of the plant.

Primary growth

Primary Growth

  • Zone of cell division – apical meristem: actively dividing cells

  • Zone of elongation – Cells are not dividing but are getting longer and push the root cap down deeper into the soil

  • Zone of differentiation: Cells become specialized into three tissue systems

    • A. The protderm becomes the epidermis

    • B. The ground meristem becomes the cortex for storage

    • C. The procambium becomes the primary xylem and phloem.

Vascular cambium is what makes woody plants thicker responsible for secondary growth

Vascular Cambium is what makes woody plants thicker. Responsible for secondary growth.

Types of plant tissue

Types of Plant Tissue:

  • 1. Dermal Tissue

  • 2. Vascular Tissue

  • 3. Ground Tissue

Dermal tissue

Dermal Tissue

  • 1. Covers and protects the plant.

    • Endodermis

    • Epidermis

    • Modified cells like guard cells, root hairs, and cells that make waxy cuticle

Vascular tissue

Vascular Tissue

  • Xylem – conducts water and dissolved minerals (cells are dead at maturity)

    • Consists of tracheids and vessel elements

    • Both types of cells are dead at maturity

    • Tracheids – long thin cells that overlap and are tapered at the ends. Water passes from one cell to another through pits.

    • Cells walls are hardened with lignin.

    • Xylem is what makes up wood.




  • Vessel Elements – wider than tracheids, but also shorter than tracheids.

  • Aligned end to end and the ends are perforated to allow free flow through the vessel tubes.

  • Seedless vascular plants and gymnosperms have only tracheids.

  • Seed plants have both tracheids and vessel elements.

Comparison of tracheid and vessel element

Comparison of Tracheid and Vessel Element



  • Carries sugars from the leaves to the rest of the plant by active transport.

  • Made of sieve tube members (elements) with sieve plates at the end to connect them.

  • These cells are alive at maturity but lack a nucleus, ribosomes and vacuoles.

  • Companion cells are connected to each sieve tube member and provides the sieve tube cells with what they need.

Ground tissue

Ground Tissue

  • Most common type of tissue in a plant

  • Functions in 1)support 2) storage 3) photosynthesis

  • Three types of ground tissue

    • Parenchyma

    • Sclerenchyma

    • Collenchyma

Parenchymal cells

Parenchymal Cells

  • They are like a regular plant cell but they lack secondary cell walls

  • Are totipotent

  • Many contain chloroplast and carry out photosynthesis – mesophyll cells in the leaf

Collenchymal cells

Collenchymal Cells

  • Unevenly thickened primary cell walls and lack secondary cell walls and lignin to harden them

  • They are alive at maturity and function in support of the growing stem.

  • They are the strings in celery

Sclerenchymal cells

Sclerenchymal Cells

  • Have thick primary and secondary cell walls

  • Function in support

  • Two types: 1) fibers 2) sclerids

  • Fibers – in bundles and are used in making rope

  • Sclerids – short and irregular and make up the rough seed coat and pits. They give fruit the gritty texture like in pears.

Roots and their function

Roots and their Function

  • 1) absorb water and nutrients

  • 2) anchor the plant in the soil

  • 3) store food

Dicot root

Dicot Root

Parts of the root and their fuctions

Parts of the Root and their Fuctions

  • Epidermis- covers and protects, absorbs

    • Root hairs – increase surface area

  • Cortex – Storage of starch and sugar

  • Stele – consists of vascular tissue and is surrounded by the pericycle (contains meristematic tissue)

    • Lateral roots arise from the stele

  • Endoderm – Surrounds the vascular cylinder


  • Casparian strip – a band of cell wall containing suberin and lignin, found in the endodermis. It restricts the movement of water across the endodermis.

  • Suberin – a waxy like substance that surrounds the casparian strip and acts as a barrier to water and solute movement across the casparian strip.

Types of roots

Types of Roots

  • 1) Drop – Type of aerial

  • 2) taproot

  • 3) fibrous

  • 4) Adventitious roots

  • 5) Prop

  • 6) Aerial – pneumatophores - snorkel

The leaf

The Leaf

Parts of the leaf

Parts of the leaf

  • Cuticle – covered with cutin(a wax) to prevent water loss

  • Guard Cells – modified epidermal cells that surround the stomata and help to control the opening and closing of the stomates. They do contain chloroplast.

  • Stomata – Openings on the underside of the leaf where gases, CO2 is taken in, O2 is released and water vapor is lost by transpiration. 90% of water escapes through the stomates


  • Pallisade and spongy mesophyll – pallisade is underneath the epidermis and the spongy is in the middle of the leaf. The primary function is photosynthesis.

  • Vascular bundles – veins – located in the mesophyll and carry water and nutrients from the soil to the leaves and carry sugars from the leaves to the rest of the plant.

Control of stomata by guard cells

Control of Stomata by Guard Cells

  • In the light, guard cells actively pump protons out, and this increases the uptake of potassium and chloride ions. (No light, potassium and chloride diffuse out of guard cells)

  • Higher concentrations of potassium and chloride gives guard cells a negative water potential.

  • This causes water to flow into the cells and increases the turgor pressure.

  • Increased turgor pressure stretches the cells and opens the stoma. (Decreased turgor pressure (flacid), the stomata closes.

  • Basically, the cellulose fibers are arranged radially so that when the cells absorb water they curve outward and open the stomata. They curve inward when flacid and close the stomata.

What will make the guard cells open

What will make the guard cells open?

  • Decreased carbon dioxide stimulates stomata to open. Happens when photosynthesis begins.

  • Increase in potassium ions in the guard cells which lowers the water potential

  • Stimulation of the blue light receptor

  • Active transport of H+ out of the guard cells

What will make stomates close

What will make stomates close?

  • 1. Lack of water

  • 2. High temperatures – stimulates cellular respiration and increases carbon dioxide

  • 3. Abscisic acid – produced by mesophyll cells in response to dehydration and guard cells close the stomata

Transport of water in plants through the xylem

Transport of Water in Plants through the Xylem

  • Water rises in the xylem against gravity.

    • 2 forces accomplish this:

      • 1) Root Pressure

      • 2) Transpirational Pull

Transpirational pull

Transpirational Pull

  • Transpiration is the evaporation of water through the stomates in the leaves.

    • Causes negative pressure as the water leaves. This negative pressure is also called tension.

    • Water molecules cling to each other due to hydrogen bonding. This is called cohesion and to the walls of the xylem which is called adhesion.

Transpirational pull cohesion theory

Transpirational pull-cohesion theory

  • The negative pressure created when water evaporates pulls other water molecules up the xylem. This is because the water molecules are clinging to each other.

  • 1)Water diffuses out of the stomata by evaporation. This is called transpiration.

  • 2)Water evaporates from mesophyll cell walls

  • 3)Tension pulls water from the veins into the apoplast surrounding the mesophyll cells

  • 4) This pulls water in the veins of the leaves upward and outward

  • 5)This pulls the water in the xylem of the shoot and root upward

  • 6)Cohesion between water molecules forms a continuous column of water from the roots to the leaves

  • 7)Water enters the root and moves into the xylem by osmosis


  • Apoplast and Symplast: The movement of water across a plant is called lateral movement and it occurs along symplast and apoplast.

  • The symplast is a continuous system of interconnected cells via plasmodesmata.

  • The apoplast is the network of cell walls and intercellular spaces within a plant body that allows extracellular movement of water within a plant.


  • When it gets to the endodermis it can continue to the xylem through the symplast, but water in the apoplast must pass across the endodermis by diffusion.



  • The movement of carbohydrates and other solutes through the plant in the phloem.

  • Moves from sources to sinks.

    • A source is an organ that produces by photosynthesis sugars

    • A sink is an organ that uses sugars such as a flower, fruit, etc.


Active transport of sugars


Sources and Sinks can change roles.

If photosynthesis is not occurring then sugars can be released from the roots or stems to the leaves for use in cellular respiration.

Plant reproduction

Plant Reproduction

  • Asexual – vegetative propagation

    • Stem

    • Leaf

    • Root

    • Produces an entirely new plant that is a clone

    • Used in grafting, cuttings, runners

Sexual reproduction

Sexual Reproduction

  • 1. Pollination

    • Pollen grain contains 3 monoploid nuclei, one tube nucleus and 2 sperm nuclei

    • Lands on stigma

    • Pollen absorbs moisture and sprouts a pollen tube that goes down the style

    • 2 sperm nuclei travel down the tube to the ovary

    • One sperm fertilizes the egg and becomes the embryo

Fertilization continued

Fertilization continued

  • The other sperm fertilizes the two polar bodies and becomes the triploid (3n) endosperm.

  • This is called double fertilization

  • The endosperm becomes the food for the developing embryo

  • The ovule becomes the seed

  • In dicots the food in the endosperm is transported to the cotyledons

  • In monocots the endosperm is liquid

The seed

The seed

Radicle – becomes the root

Embryo – hypocotyl, epicoltyl, and radicle

Hypocotyl becomes the lower stem and the epicotyl becomes the upper stem

Seed coat – protective outer layer

Seed germination

Seed Germination

Steps in germination

Steps in Germination

  • 1) Seed coat imbibes water, swells and ruptures

  • 2) Radicle emerges

  • 3) epicotyl elongates

  • 4) radicle grows down

  • 5) epicotyl pulls plumule out from between the cotyledons

  • 6)pulls plumule (first bud) backwards through the soil so leaves aren’t damaged

  • 7) epicotyl straightens and leaves open out

Plant hormones

Plant Hormones

  • Coordinate growth, development, and response to environmental stimuli

  • Auxins

  • 1) Auxin – IAA – Indoleacetic acid

  • 2) responsible for phototropism

  • 3)Enhances apical dominance – the preferrential growth upward rather than outward (terminal bud suppresses the lateral buds)

  • 4) stimulates stem elongation and growth by softening the cell wall


  • First hormone discovered

  • Synthetic Auxin is roundup a weed killer

  • Can also be used as a rooting powder

  • Sprayed on tomatoes causes fruit production without pollination – produces seedless tomatoes



  • Stimulates cytokinesis and cell division

  • Works with auxins to promote growth

  • Works against auxins in relation to apical dominance

  • Delays senescence (aging) by inhibiting protein breakdown

  • Produced in roots and travel upward in the plant



  • Promotes stem and leaf elongation

  • Works with auxins to promote growth

  • Induces bolting or rapid growth of stalk

Abscisic acid

Abscisic Acid

  • 1) inhibits growth

  • 2) Enables plants to withstand drought

  • 3)closes stomata during water stress

  • 4) works in opposition to growth promoting substances

  • 5)Promotes seed dormancy

Ethylene gas

Ethylene Gas

  • 1)Promotes fruit ripening

    • Positive feedback

  • 2) Is produced in times of stress in large amounts

  • 3) promotes apoptastic programmed cell death – cell reuses chemicals from the breakdown of cell parts to survive during stress ( drought, flood, injury, infection)


  • Promotes leaf abscission – leaf falling off –

  • A scar forms where the leaf falls off and prevents and prevents pathogens from entering. This is due to an increase in ethylene and a decrease in auxin.

  • Ethylene works in opposition to auxin.



  • The growth of a plant towards or away from a stimulus

    • Phototropism – towards light

    • Thigmotropism – towards touch

    • Geo/gravitropism – towards or away from gravity

    • Positive tropism – towards the stimulus

    • Negative tropism – away from the stimulus


  • Phototropism – due to unequal distriubution of auxins which accumulate on the side of the plant away from the light. This side grows longer while the top side doesn’t grow, causing it to bend toward the light.

  • Geotropisms occur due to interaction of auxins with statoliths which are specialized plastids with dense starch granules.

Signal transduction pathway

Signal Transduction Pathway

  • 1) Reception

  • 2) Transduction

  • 3) Response

    • A receptor is stimulated which undergoes a conformation change and is known as a ligand

    • This activates a second messenger (cyclic AMP, or cyclic GMP) and this messenger goes to the nucleus where transcription occurs.

    • The gene is then translated into a response for the plant.

Adaptations to land

Adaptations to Land

  • 1) Cell walls – support

  • 2) Roots and root hairs – absorption of water and nutrients

  • 3) Stomates – gas exchange

  • 4) Waxy Cuticle

  • 5) Gametangia – prevents drying of zygote

  • 6) Sporopollenin – a tough polymer that is resistant to environmental damage and protects the plants in a harsh terrestrial environment and is found in the walls of spores and pollen

  • 7) Seeds and Pollen – protective coat that prevents drying and are how offspring are dispersed.

  • 8) Reduced gametophyte generation

  • 9) xylem and phloem

  • 10) Lignin for support



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