BIOLOGY EXAM 2!!

All green algae and land plants shared a common ancestor? T or F

All green algae and land plants shared a common ancestor? T or F

True

Not all photoautotrophs are plants? T or F

True. ( excludes red and brown algae)

3 mains issues plants had to overcome on land:

-water loss

-protection from the sun

-ability to effectively disseminate gametes

During colonization of the land there were…

• no soil on the land (488 MYA)

• No insects or land animals

• Fungi present, along with bacteria

• Fungi helped to make nutrients and water available for plants

Brytophytes

• Mosses

• Limited in size due to lack of vasculature

• Lack tracheids, but have other conducting cells

Vascular tissue in Tracheophytes

Xylem and phloem

Xylem

Conducts water and minerals from roots

Phloem

Transports sugars from leaves

What features do plants have to protect themselves from desiccation and harmful effects of the sun?

• waxy cuticle and stoma

• Shift to dominant diploid generation

Haplodiplontic life cycle

• multicellular haploid and diploid life stages; alternation of generations

• All land plants are haplodiplontic

Haplodiplontic life cycle includes:

A multicellular haploid stage where gametophyte is formed, within gametangia gametes are produced by mitosis, gametes from other plants fuse to form a zygote, the zygote is the first cell of the sporophyte generation. Multicellular diploid stage then produces a sporophyte, within the sporangia diploid mother cells undergo meiosis, to then produce 4 haploid spores by meiosis.

Female gametangia

Archegonia

Male gametangia

Antheridia

Vascular tissue in Tracheophytes and their function.

Xylem and phloem; enhance height and hormones throughout the plant.

Roots

Provide transport and support

Leaves

Increased surface area for photosynthesis

Seed plants

• maintain dormancy under poor conditions

• Protect the young plant

• Provide food for the embryo

• Facilitate dispersal of the embryo

Conifers

Pines; leaves have thick cuticle and recessed stomata to retard water loss, canals with resin deter insects and fungi.

Angiosperm features that aided abundance

• flower production

• Insect pollination

• Broad leaves with thick veins

Root system (vascular plants)

• anchors the plant

• Absorbs water and ions from the soil

Shoot system (vascular plants)

• supporting stems

• Photosynthetic leaves

• Productive flowers

• Consists of internode, node, leaf, axillary bud

Meristems locations

Tips of the stems and roots

Plant meristems

Produce hormones that repress the development of lateral bud, if meristem removed plant can not grow from that tip.

Lateral meristems

• produce an increase in shoot and root diameter

• Found in plants that exhibit secondary growth

Three main types of plant tissue and their functions.

• dermal: external surface; serve as protective function.

• Ground: participates in photosynthesis, storage function, structural support.

• Vascular: conducts water and nutrients

Dermal tissue specifics

• forms epidermis

• One cell layer thick

• Protective covering of the plant

• Covered in fatty cutin layer

• Contains special cells, including guard cells, trichomes, and root hairs

Guard cells

Open and close stomata.

Trichomes (dermal tissue)

Hair-like outgrowths; keep leaf surfaces cool and reduce evaporation by covering stomatal opening.

Root hairs (dermal tissue)

• greatly increase the roots surface area and efficiency of absorption.

3 ground tissue cell type and their function:

• parenchyma: storage, photosynthesis, secretion.

• Collenchyma: support and protection

• Sclerenchyma: support and protection

Xylem (vascular tissue)

Conducts water and mineral, supports plant body

Phloem ( vascular tissue)

Conducts carbohydrates , transports hormones, amino acids, and other substances needed for growth.

2 types of water conducting cells ( xylem)

Vessels: cells are joined butt-ended; water passes through cell to cell through perforated plates.

tracheids: cells are joined at an angle; water passes through from cell to cell through pits.

4 regions of root structure:

• root cap

• Zone of cell division

• Zone of elongation

• Zone of maturation

Monocot stems vascular tissue

Bundles scattered through ground tissue systems.

Eudicot stems vascular tissue

Arranged in a ring with internal ground tissue and external ground tissue.

2 different morphological groups ( leaves)

Microphyll: leaf with one vein

Megaphyll: leaf with many veins

Transport mechanism in plants

Water and minerals enter the roots, move to the xylem and innermost vascular tissue, water rises through xylem, most of the water exits through the stomata in leaves.

osmotic concentration

When two solutions have a different concentration

Hypertonic

Higher solute concentration

Hypotonic

Lower solute concentration

Isotonic

Two solutions have the same concentration

Turgid

High concentration of water within cells due to osmosis

Plasmolysis

Cell shrinks due to water leaving the cell.

Increase in solute concentration causes a…

Decrease in water potential

Increase in turgor pressure causes a…

Increase in water potential.

Most water absorbed by plants enter through the…

Roots and root hairs

Three transport routes through cells:

• apoplast route:movement through cell walls and the space between cells; avoids membrane transport

• Symplast route: cytoplasm continuum between cells connected by plasmodesmata

• Transmembrane route: membrane transport between cells and across the membranes of vacuole within cells; permits the greatest control

Guttation

The loss of water from leaves when root pressure is high.

Root pressure

• Caused by the accumulation of ions in the roots at times when transpiration from leaves is low or absent

-        At night

Causes water to move into plant and up the xylem despite the absence of transpiration.

Abundant in xylem

Phosphorus, potassium, nitrogen and sometimes iron.

Mineral that can not be transported elsewhere once deposited in a particular plant part:

Calcium

Rate of transpiration

• Over 90% of water taken by the plants roots is lost to the atmosphere

• Photosynthesis requires carbon dioxide supply from the atmosphere

• Closing the stomata can control water loss on a short term basis

• Stomata must open to allow carbon dioxide entry

Stomatal opening and closing

• Closed when carbon dioxide concentrations are high

• Open when blue wavelengths of light promote uptake of potassium by the guard cells

• Closed when temperature exceeds 34 degrees and water relations are unfavourable

• CAM plants conserve water in dry environments by opening the stomata and taking in carbon dioxide at night.

 Plant adaptions to drought

• Dormancy

• Loss of leaves

• Covering leaves with cuticle and wooly trichomes

• Reducing the number of stomata

• Having stomata in pits on the leaf surface

Halophytes

Halophytes are plants that can tolerate soils with high salt concentrations.

Soil

• Highly weathered out layer of the earths crust

• The earths crust includes about 92 naturally occurring elements

• Full of microorganisms

Topsoil

Mixture of mineral particles of varying sizes, living organisms, and humus.

If topsoil is lost, soils water holding capacity and nutrient content is adversely affected.

Measures to prevent erosion include:

• Intercropping

• Conservation tillage

• No-till

Plant nutrients

• Photosynthesis; CO2 into sugar

• Also need:

• Macronutrients (9)

• Micronutrients (7)

Hydroponics

• soil provides nutrients and support but these functions can be replaced in hydroponic systems to maximize growth

• Allows plants to be grown all year around

Mycorrhizae

• Symbiotic associations with mycorrhizal fungi are found in about 90% of vascular plants

-        Expand surface area available for nutrient uptake

• Enhances phosphate transfer to the plant

Carnivorous plants

• Often grow in acidic soils that lack nitrogen

• Trap and digest small animals, primarily insects, to obtain adequate nitrogen supplies

• Having modified leaves adapted for luring and trapping prey

• Prey is digested with enzymes secreted from specialized glands

Photorespiration

• If CO2 levels are low then O2 may bind to rubisco

• This causes photorespiration

• Which results in neither nutrients or energy storage

• Plants must keep O2 away from rubisco

C3 Photosynthesis

• Occurs in mesophyll cells   

• In C3 plants, as CO2 increases, the Calvin cycle becomes more efficient

• But the C3 plants have less nitrogen and minerals per unit mass

• Which results in lower nutritional value for herbivores

• Meaning more plant must be eaten

C4 Photosynthesis

• This photosynthesis uses an extra pathway to shuttle carbon deep within the leaf

• This reduces photorespiration

Increasing CO2 levels

Less nitrogen and other macronutrients found in leaves, so herbivores must eat more to meet requirements.

Phytoremediation

Use of plants to break down pollutants.

Phytodegradation

contaminant is taken up from soil and broken down.

Phytovolatilization

 contaminant is taken up from soil and released through the stomata.

Phytoaccumulation

contaminant is taken up from soil and concentrated in shoots

Dermal tissue system ( plant defence)

• First line of defence

• Epidermal cells throughout the plant secrete wax to protect plant surfaces from water loss and attack

• Above ground parts also covered with cutin.

Damage to the dermal surface can…

Create an entry site for pathogens. Parasitic nematodes use their sharp mouth parts to get through the plant cell walls, some form tumors.

Fungal invasion and phases:

Fungi seek out weak spot in the dermal system or stomata to enter the plant.

Phases include:

• windblown spore lands on leaves

• Spore then germinates and forms adhesion pad

• Hyphae grow through cell wall and press against cell membrane

• Hyphae differentiate into haustoria

Chemical defences

Many plants employ toxins to kill herbivores or deter their grazing behaviour.

Secondary metabolites

Metabolic pathways needed to sustain life are modified to produce chemicals that adversely affect herbivores.

Such as:

• alkaloids

• Tannins

• Plant oils

Allelopathic plants

Plants that secret chemicals to block seed germination or inhibit growth of nearby plants; minimizes competition for resources.

Very little vegetation grows under black walnut trees due to allelopathy.

Ricin

Poison, produced by the castor bean plant, very deadly, protects plants from aphids.

Photomorphogenesis

Non-directional, light triggered development.

Phototropism

Directional growth response to light.

Phytochrome

Pigment containing protein, that has two interconvertible forms: Pr and Pfr

Involved in many signalling pathways that lead to gene expression.

Blue light receptors

Blue light receptor phototropin 1.

Blue light stimulates PHOT1 To autophosphorylate

Regulates the flux of auxin in shoots

Gravitropism

Plants response to the gravitational field of the earth.

Shoot exhibits negative gravitropism

Roots have a positive gravitropic response

4 general steps lead to gravitropic response:

1.         Gravity is perceived by the cell; falling amyloplasts

2.         A mechanical signal is transduced into a physiological signal; amyloplasts touch ER membranes

3.         Physiological signal is transduced inside the cell and to other cells

4. Differential cell elongation occurs in the “up” and “down” sides of root and shoot

Amyloplasts

• Starch storing organelles

• Modified chloroplasts, have no chlorophyll

Roots response to gravity

• In roots, the cap is the site of gravity perception

• Signalling triggers differential cell elongation and division in the elongation zone

What is auxin?

A plant hormone that promotes cell growth.

Indoleacetic acid

4 genetically regulated pathways to flowering have been identified:

1.         The light dependent pathway

2.         The temperature dependent pathway

3.         The gibberellin dependent pathway

4.         The autonomous pathway

Plants rely primarily on one pathway, but all four pathways can present.

Light dependent pathway is also known as…

The photoperiodic pathway.

Long day plants…

Flower when daylight becomes longer than critical

Short day plants

Flower when daylight becomes shorter than critical length.

Day neutral plants

Flower when mature regardless of day length.

CONSTANS (CO)

• Turns on genes that are needed for flowering.

• Leads to expression of LFY

• Phytochrome regulates the transcription of CO

• Produced day and night

• Levels are maintained by circadian clock

Vernalization (temperature dependant pathway)

Plants that require a period of chilling before flowering.

Gibberellin dependent pathway

Plant hormone; decreased levels have shown to delay flowering in some species.

Autonomous pathway

Balance between floral promoting and inhibiting signals, delays flowering .

Flowering pathways

Lead to adult meristem becoming a floral meristem.

The sepals, petals, stamen, and carpel.

The four whirls

Calyx: consists of flattened sepals

Corolla: consists of petals

Androecium: all the stamens; filament and anther

Gynoecium: all the carpels; ovary, style, stigma, ovule.

Germination

Emergence of the radical through the seed coat requires light warmth in time.

Ethology

Study of the natural history of behaviour.

• Emphasis on innate behaviour

• Instinctive, does not require learning

• Preset paths in nervous system

• Genetic- fixed action pattern