OAT Biol 10: Plants

What is a seed?

A plant reproductive unit that contains all the materials required to produce a new independent plant.

Seed coat

Hard outer layer which covers and protects the seed

Endosperm

Storage which provides nutrients to the seed

Embryo (plants)

An early plant which develops within the seed

Radicle

First portion to emerge, develops into the root and anchors the plant to the soil

Hypocotyl

Hypocotyl: Bottom region of the young shoot

Plumule

Plumule: Develops into the leaves

Epicotyl

Top region (shoot tip)

Germination

Process of a seed sprouting into a seedling when conditions are optimal

• Water is the most important condition to initiate

Meristems

Place where plant cell growth takes place. It is made of plant stem cells.

Primary Growth

• Where does it occur

• When does it occur comparatively.

Vertical growth

Occurring at apical meristems

• Occurs before secondary growth

Secondary Growth

• Where does it occur

• When does it occur comparatively.

• Secondary growth: Horizontal growth occurring at lateral meristems

  • Lateral meristems include the vascular cambium and cork cambium

  • Mainly occurs in woody plants

Vascular Cambium

Lateral Meristems.

Vascular cambium

• A ring of meristematic tissue located between the primary xylem and primary phloem

Primary Xylem

Transports water and dissolved minerals from the roots to the shoot and leaves in young plants.

Primary Phloem

Transports nutrients from the leaves to the shoot and roots in young plants

What happens to cells produced in the vascular cambium?

They can become a secondary xylem or the secondary phloem.

Secondary Xylem

Secondary xylem: Cells on the inside of the ring form the wood

Secondary Phloem

Secondary phloem: Cells on the outside of the ring form the inner bark

What happens over time with wood plants?

New xylem is produced yearly, giving them growth rings. New phloem replaces old phloem.

Cork Cambium

Cork cambium: A ring of meristematic tissue located outside the phloem.

• Produces cork,which is the outermost protective layer

Cork

• Cork: Dead bark cells, which waterproof the outside of the woody plant

Ground Tissue:

Provides structural support and accounts for most of the plant’s mass

• All non-vascular and non-dermal tissue

Vascular Tissue:

Transports water and nutrients from source to sink

Phloem

Transports sugars from the leaves to the roots and other areas

Sieve cells:

Elongated, organelle-lacking cells that connect to form continuous channels for nutrient transport

Companion Cells:

Organelle-containing cells that connect to sieve cells and support their metabolic functions

Xylem

Transports water and dissolved minerals from the roots to the leaves while providing structural support.

Tracheids

Long, thin cells that transport water through pits in their tapered ends

Vessel Elements

Short, stout cells that transport water through cell wall perforations

Dermal Tissue

• Dermal tissue: The outer layer of the plant which provides protection and regulation

• Waxy cuticle: Outer layer which limits water evaporation

Casparian Strip

Casparian strip:

• An impenetrable substance in the cell walls of root endodermis

  • Made of fat and wax

• Water passage from roots to vascular tissue:

  • Water cannot penetrate the Casparian strip

  • Water is forced out of the cell walls and into the endodermal cell cytoplasm where it is filtered

What are leaves covered by?

Epidermal Layer and a waxy cuticle.

Stomata

• Role in gas exchange

Pores in the lower epidermis that open and close for gas exchange

• Low CO2 concentration causes stomata to open, allowing for new CO2 influx for photosynthesis

Guard cells

• Role in gas exchange

Become turgid (swollen) due to water influx, causing the stomata to open

• Low CO2 concentration causes stomata to open, allowing for new CO2 influx for photosynthesis

When do stomata close?

• Stomata close when:

  • CO2 concentrations are high

  • Temperatures are high (prevent transpiration)

What is transpiration?

• Why is it an important factor in energy production?

Transpiration: Loss of water vapor through the stomata

• A balance is needed between stomata opening for food production and closing to prevent water loss

Mesophyll Cells

Involved in photosynthesis and gas exchange

• Situated between the upper and lower epidermis

Bundle Sheath Cells

Surround and protect the vascular bundles.

What allows the movement of water in plants?

• Cohesion-tension theory

• Capillary Action

• Root Pressure

Cohesion Tension Theory

• Cohesion-tension theory: Transpiration (loss of water vapor through open stomata) leads to transpiration pull

  • Transpiration pull: Cohesive force (attraction between like molecules) pulls the water column upward

Transpiration pull:

Cohesive force (attraction between like molecules) pulls the water column upward

Capillary Action

• Capillary action: Adhesive force (between dissimilar molecules) allows the water to interact with the xylem walls and climb upward

Root pressure

• Water enters the roots osmotically from the soil

  • An osmotic gradient in the roots then drives water into the xylem

Pressure Flow Hypothesis:

Source cells produce sugar and load it into the phloem

• Increased sugar concentration creates a gradient that pulls water into the phloem

• Turgor pressure in the phloem increases

• Bulk flow movement of sugar from leaves down to roots

Ethylene

Plant Hormone

• Gaseous hormone that promotes fruit ripening

Auxins

• 4 examples of these

• Def

Plant Hormones that stimulate cell growth

• Plant tropisms

• Phototropism

• Gravitotropism

• Thigmotropism

Plant tropism

Growth in a particular direction. Auxins concentrated on one side of a plant cause asymmetric growth

Phototropism:

Growth Toward Light

Gravitotropism:

Growth in response to gravity

Thigmotropism

Growth in response to contact

Cytokinins

Plant Hormone

Regulates cell differentiation and division in coordination with auxins

Gibberellins

Plant hormone

Promotes

• stem and shoot elongation

• elimination of seed dormancy

• plant flowering

• fruit production

• leaf and fruit death

Abscisic Acid

Plant Hormone

Promotes

• seed dormancy

• closes stomata

• inhibits growth

Functions during stress.

What is alternation of generations in plants?

Plants alternate between reproductive states during their life cycle

• Gametophyte Stage

• Sporophyte Stage

Gametophyte Stage

Gaemtophyte Stage:

Haploid phase

• Cells have one set of chromosomes

• Haploid gametophytes produce haploid gametes

• Haploid Gametes form two separate organisms fuse, forming a diploid zygote.

• Diploid zygotes undergo mitosis, eventually forming a diploid sporophyte.

Sporophyte Stage

Sporophyte Stage

Diploid phase

• Cells have two sets of chromosomes

• Diploid sporophytes can produce haploid spores via meiosis

• Haploid spores eventually produce a haploid gametophyte via mitosis

Homosporous plants

Homosporous plants:

• Produce only one type of spore

• Spores will eventually develop into a bisexual gametophyte

• Bisexual gametophytes are capable of producing both sperm and egg

Heterosporous

• What does this mean

• What are the types

• Heterosporous plants: Produce two types of spores

  • Megaspores

  • Microspores:

Megaspores

Develop into the embryo sac (female gametophyte). Embryo sacs will produce an egg

Microspores

Develop into pollen grains (male gametophyte). Pollen grains will produce sperm

Bryophytes

• Def

• Examples

• Locations where they are found

• Special part that they contain.

• What part of the life cycle are they mainly in

• Nonvascular plants that are short in stature

• Examples include liverworts, hornworts, and mosses

• Found in moist environments and grow horizontally to remain in close contact with water sources

• Contain: Rhizoids (no roots)

• Most of their life cycle is spent in the gametophyte stage

• Sporophytes are dependent on and attached to the gametophytes

Rhizoids

• Hair-like projections that aid in water absorption and provide minor anchorage

Tracheophytes

• Def

• What makes them unique

• What part of the life cycle are they mainly in

• Vascular plants capable of growing vertically due to the presence of a root system that provides anchorage

• Contain xylem and phloem

• Most of the life cycle is spent in the sporophyte stage

Seedless tracheophyes

• Ex

• Def

• Sperm types

• Seedless: Mostly homosporous plants with independent gametophyte and sporophyte life cycles

  • Produce motile, flagellated sperm

  • EX: Lycophytes and pteridophytes; club moss, quillworts, fern, horsetail

Seed-bearing plant types

Heterosporous plants that are classified into gymnosperms and angiosperms

Gymnosperms:

• Def

• Ex’s

• Sperm Type

Produce unprotected seeds and non-flagellated sperm, which are dispersed by the wind

• The first seeded plants, including conifers such as firs, spruce, pines, redwood

Angiosperm

• Angiosperm: Flowering plants that produce fruits with seeds enclosed in an ovary

• Non-flagellated sperm is carried in pollen and dispersed by wind or animals

• The most abundant plant type.

• Double fertilization: A single female gamete is fertilized by two male sperm

Double ferilization

A female gamete is fertilized twice (two male sperm).

Flower Structures (8)

• Petals

• Stamen

• Anther

• Filament

• Pistil

• Stigma

• Style

• Ovary

Petals

• Petals: Attract animals to achieve pollination

Stamen

• Stamen: Male plant sex organ

Anther

• Anther: Site of microspore production

Filament

• Filament: Supports the anther

Pistil

• Pistil: Female Plant sex organs

Stigma

• Stigma: The top of the pistil where pollen lands for germination

Style

• Style: Tube connecting the stigma to the ovary

Ovary and Ovary

• Ovary: Stores the ovule, which houses the embryo sac (female gametophyte containing eggs)

Double fertilzation: in depth

Pollen Lands on the stigma and forms a pollen tube down the style.

• Two sperm cells are released

• One sperm nucleus fuses with an egg in the ovule to form the embryo. The surrounding ovary later develops into the fruit

• The other sperm nucleus combines with the ovule’s polar nuclei to form the endosperm

Cotyledons

The first leaves to appear on a seedling

• Contain nutrients from the seed to feed the growing seedling.

Monocotyledons (monocots)

Singly cotyledon

• Floral parts in multiples of 3

• Long, narrow leaf and parallel veins

• Vascular bundles scattered

• Fibrous, fine root system near the surface

Dicotyledon (dicots)

• Two cotyledons

• Floral parts in multiples of 4 or 5

• Broad leaf with network of veins

• Vascular bundles in a ring

• Single taproot with branching

Nitrogen Fixation

• Atmospheric nitrogen (N2) is converted into ammonia (NH3) and ammonium (NH4+), which organisms can use

  • Plants form a symbiotic relationship with nitrogen-fixing bacteria

  • The bacteria fix atmospheric nitrogen into forms usable by plants

  • Plants produce food for the bacteria via photosynthesis

Nitrogen Fixing Steps

1. Nitrogen-fixing bacteria in root nodules convert atmospheric nitrogen (N2) into ammonia (NH3) and ammonium (NH4+)

2. Nitrifying bacteria convert ammonia and ammonium into nitrites (NO2-), and then into nitrates (NO3-)

3. Nitrates are taken up by plants (nitrogen assimilation) and incorporated into amino acids and chlorophyll

   1. Animals acquire nitrogen by eating plants (producers)

4. Detritus of dead, decaying plants and animals provides soil with nitrogen

5. Denitrifying bacteria convert nitrates back into atmospheric nitrogen

What is the specific plant structure where spores are formed?

Sporangia

What is reduced in a bryophyte?

Sporophyte