PLANT SCIENCE

Plant Classification

Examples 4 common plant divisions

-Bryophyta: mosses and liverworts

-Filicinophyta: ferns

-Coniferophyta: coniferous plants

-Angiospermatophyta: flowering plants

A. Bryophytes=mosses, liverworts, hornworts

1. have no true roots, leaves or stems

2. have structures called rhizoids

(rhizoids are root like structures that look like long hairs)

rhizoids

3. mosses have simple leaves and stems4. liverworts consist of a flattened thallus5. a thallus is a plant body not divided into true

roots, stems and leaves

6. bryophytes can grow up to 0.5 m7. they do not produce flowers

8. bryophyte reproduction

-can be sexual or asexual

-often involves alteration of generations

-spores are developed in capsules that are found at the end of stalks

9. bryophytes are often homosporous (the gametophytes contain male and female sex organs)

10.most common in damp habitats

B. Filicinophytes (ferns)

1. have, roots, leaves and short non-woody stems

2. leaves are often curled up in buds and are often pinnate

3. pinnate=leaves divided into pairs

4. ferns are vascular plants

-they have transport tissue called vascular bundles (xylem and phloem)

5. can grow up to 15m

6. filicinophyte reproduction-

-spores are produced by sporangia, usually found on the underside of the leaves

7. ferns can be heterosporous or homosporous

8. ferns do not produce flowers

C. Coniferophytes (conifers)

1. conifers are shrubs of trees with roots, leaves and woody stems

2. leaves are often narrow with thick, waxy cuticles

3. they are vascular plants

4. can grow up to 100m

5. reproduction-

-seeds are produced

-they develop in the ovules on the surface of the scales of the female cones

-male cones produce pollen

6. coniferophyta are heterosporous

7. they do not produce flowers

Male cone

Immature female cone

Mature female cone

D. Angiospermatophyta-flowering plants

1. usually have true roots, leaves and stems

2. stems that develop into shrubs and trees are woody

3. can grow up to 100m

4. reproduction

-seeds are produced

-they develop in the ovary

-ovaries are part of the flowers

-fruits develop from ovaries to disperse the seeds

5. angiospermatophytes are heterosporous

Xerophyte adaptationsA. Xerophytes are plants adapted to dry environments

--their adaptations allow them to obtain the maximum amount of water from their environmentB. Xerophyte=‘dry plants’

Xerophytes (cont)C. The adaptations

1. reduced leaves (reduced surface area)2. thick waxy cuticle-reduces water loss3. reduced number of stomata-reduces water loss, gas exchange and photosynthesis4. Water storage tissue-helps in long dry periods

Xerophyte adaptations (cont)5. Stomata in pits and/or surrounded by hair

-reduces air flow past pore-water that has diffused out will stay near-this reduces the concentration gradient

and reduces the diffusion of water out of the plant

Xerophyte adaptations (continued)

6. Vertical stems

-allow absorption of light early and late in the day (not at midday when light is most intense)

-reduces transpiration

Xerophyte adaptations (cont.)

7. Wide-spreading shallow root network

-allow immediate absorption of extensive amounts of water immediately after rain

8. CAM physiology

-stomata open at night and stay closed during the day

Hydrophyte Adaptations

A. Hydrophyte= ‘water plant’

B. The adaptations

1. Air spaces

-allow the plant to float on top of the water to absorb the most sunlight

2. Stomata found in upper epidermis (not in lower epidermis)

-open to air

Hydrophyte adaptations (continued)

3. Small amount of xylem in stems and leaves

-xylem conducts water

4. Surrounded by water

-roots serve mainly as anchorage (not water absorption

Plant Leaf Structure and Function

A. Leaf function=to produce food via photosynthesis (C3, C4, CAM)

B. Leaves are adapted to their environments (C3, C4, CAM)

C. Photosynthesis depends on gas exchange over a moist surface

Plant Leaf Structure and Function

D. Cross section of a leaf

Upper epidermisCuticle

Palisade mesophyllXylem

Phloem Spongy mesophyll

Lower epidermis

StomaGuard cell

Plant Leaf Structure and FunctionE. Leaf anatomy

1. Upper epidermis-layer of cells covered by a thick waxy cuticle

-prevents water loss from the upper surface

2. Palisade mesophyll-densely packed cylindrical cells

-contain many chloroplasts-main photosynthetic tissue-positioned near top of leaf for

maximum light absorption

Plant Leaf Structure and Function

E. Leaf anatomy

3. Xylem-vascular tissue responsible for water transport

-replaces water lost during transpiration

4. Phloem-vascular tissue that transports minerals

-transports photosynthetic products out of leaves

5. Spongy mesophyll-cells that provide a means for gas exchange

-have fewer chloroplasts than the palisade mesophyll

-found near stomata and lower epidermis

Plant Leaf Structure and Function

E. Leaf anatomy

6. Stoma (stomata =pl.)

-pore that allows carbon dioxide to diffuse in and oxygen to diffuse out

-also responsible for water loss

7. Guard cells-cells that open and close the stomata

-control transpiration

Xylem

Phloem

Pericycle

Cortex of parenchyma cells

Endodermis

EpidermisSpecial layer with rootHairs (protoderm)

Root hairs

Root Anatomy (dicot)

Stem anatomy

(dicot)

Xylem

Phloem

Cambium

Epidermis

Pith of parenchyma

cells

Cuticle (outside layer)

Cortex ofParenchyma

cells

13.2 Transport in AngiospermsRoots

A. Plants take in water and minerals through their roots

B. Roots have large surface area to allow for adequate uptake of water and minerals

-they are branched and they have root hairs

C. Function of the cortex=to facilitate water uptake

D. Roots also act as anchorage to ground

Roots and active transportA. Mineral concentrations are often higher in the root than in the soil

B. This suggests active transport (going against the concentration gradient)

C. Cortex cells can absorb ions that are dissolved in the water that is drawn by capillary action through the cortex cell walls

Water Uptake By Roots

A. Roots take in water via osmosis

-Water in the soil contains a lower concentration of solutes than the cytoplasm of root cells

-This causes water to diffuse in to the roots

High solute Low solute

Root cell Soil

H2OH2O

Water Uptake by Roots

**Water diffuses (osmosis) to an area of high solute concentration to reach equilibrium between the roots and the soil **Minerals are taken in via active transport because the roots have higher solute concentration than the soil

Water Uptake By Roots (continued)

B. Most absorbed water is eventually drawn to the rest of the plant because of transpiration

-as water leaves the leaves it must be replaced

C. To get water from the root hairs to the xylem, there are three possible methods

-apoplast, symplast or vacuolar pathways

Water Uptake By Roots (continued)D. Apoplast pathway

-water does not enter the root cells-it travels by capillary action through the cell walls of the cortex until it reaches the endodermis-cells of the endodermis have Casparian strips around them that are impermeable to water-to pass through the endodermis the water must follow the symplast pathway (the apoplast pathway stops at the endodermis)

Water Uptake By Roots (continued)

E. Casparian Strips

-found in endodermis

-thought to be a protective measure

-prevent water from seeping between cells

-forces water to enter the endodermis before passing to the vascular tissue

-forces water to go through cell walls (not between them

Cellmembrane

Cell wall

Vacuole

Casparian strip

Cellmembrane

Cell wall

VacuoleWater flow (cannot flow between cells when Casparian strips are present)

Water flow

Water flow without Casparian strips

Water flow with Casparian strips

Water Uptake By Roots (continued)

F. Symplast Pathway

-water enters the cytoplasm of the cells, but not the vacuole

-water passes from cell to cell via the plasmodesmata (connections of cytoplasm between cells)

-the water eventually enters the xylem

Movement Through Roots

Water Uptake By Roots (continued)

G. Vacuolar Pathway

-water enters the cells and moves to the vacuole

-when necessary the water will travel through the cytoplasm and cell wall to the vacuole of the next cell

Assignment: Make a chart to compare apoplast, symplast

and vacuolar pathways

The Xylem

A. Function-to transport water and dissolved minerals from the roots to other parts of the plant

B. Mature xylem cells are dead

C. Made of two components

1. tracheids

2. xylem vessels

The Xylem (continued)D. Tracheids

-narrow cells, arranged in columns

-overlap at tapered ends

-function as support

-overlapping ends have pits that allow water to move rapidly between cells

-all plants have tracheids

-not as efficient as xylem vessels

The Xylem (continued)

E. Xylem vessels

-most water travels through vessels

-composed of columns of cells

-when the cells die the walls between them disappear partly or completely (leads to more efficient transport)

-diameter is wider than tracheid diameter

-side walls are reinforced with lignin (this helps with structural support)

Tracheid Xylem vessel

Water Transport Through Plant Tissue

A. Transpiration=loss of water vapor from leaves and stems

B. Transpiration causes water flow from roots, through stems and to the leaves

C. Transpiration stream = describes the transpiration flow through the plant

D. The process begins with evaporation of water from the leaves (through the spongy mesophyll)

Water Transport Through Plant Tissue (continued)

E. Evaporated water is replaced with more water from the xylem

F. Capillary action allows the water to move from the xylem to the spongy mesophyll

G. The capillary action creates transpiration pull

-transpiration pull= low pressure or suction within the xylem

H. Water molecules have strong cohesion forces

Water Transport Through Plant Tissue (continued)

I. As water moves out of the vessel, other molecules will want to replace it

J. All water will move up a little (toward the leaves), at the other end of the plant (the roots) water will move from the soil to the plant

Water Cohesion

A. Water molecules are attracted to each other

B. These are intermolecular forces

C. This is created by hydrogen bonding

The whole point:

EVAPORATION CAUSES TRANSPIRATION PULL. THIS PULLS WATER INTO THE ROOTS AND TO THE REST OF THE PLANT BECAUSE OF THE STRONG COHESION OF WATER MOLECULES.

Phloem

A. Primary function= translocation

B. Translocation-movement of substances from one part of a plant to another in the phloem

C. Sugars, amino acids and other organic compounds produced by photosynthesis are transported away from the leaf

-materials sprayed on the plant can also be transported from the leaves via the phloem

Phloem

D. Found in all leaf veins

E. Materials can be transported in both directions

**Remember xylem only transports one way (up)

Ex: In summer trees transport sugars from leaves to roots

-In spring transport sugar from roots (where it is stored) to the new branches

Food storage in plants

A. Many perennial plants have food storage for dormant seasons

B. The food is transported when necessary by the phloem from the root to the rest of the plant for new growth

C. Examples:

1. Carrots-carrots store food in the cortex of their roots

-may be used to allow the growth of stems and

leaves after winter

Food storage in plantsC. Examples (continued)

2. Seeds-seeds need a certain amount of food to

allow them to grow a stem and a few leaves-this food usually lasts until photosynthesis takes over

3. Tubers (potatoes)-tubers are swollen underground stems that store food

Other plant modifications

A. Tendrils-used for climbing

-modified leaves or stems

-Example: grape vine or ivy

B. Bulb - any plant that stores its complete life cycle in an underground storage structure

-usually perennial flowers have this type of structure

Classwork (in your notebook)Explain the relationship between the distribution of

tissues in the leaf and the functions of these tissue. [8]

Draw and annotate a diagram showing the structure of a dicotyledonous animal-pollinated flower.-Include: 1. sepal 2. petal 3. anther 4. filament 5. stigma 6. style 7. ovary

Draw and annotate a diagram showing the external and internal structure of a named dicotyledonous seed.-Include: 1. testa 2. micropyle 3. embryo root 4. embryo shoot 5. cotyledons

Plant support

A. No skeleton

B. Xylem vessels have some support tissue that help keep the plant upright

-xylem alone is inefficient (think about wilting plants)

C. Trees and shrubs have woody stems

D. Herbaceous (non-woody) plants use turgor for support

Plant support

E. Turgor

-vacuoles take up water

-the cell swells up

-the cell wall is stretched to the limit

-the vacuole still has less water potential than the cytoplasm and continues to draw in water

-the force of the cell wall forces water out at the same rate

More on guard cells

A. Plants maintain large surface areas to capture sunlight

B. To avoid water loss their surfaces are covered with waxy cuticle layers

-cuticle also is impermeable to gases

(oxygen and carbon dioxide)

C. Pores in the cuticle and lower epidermis allow gas exchange within the spongy mesophyll

More on guard cells

D. When the plant is at risk of drying out the guard cells lose turgor and sag together, closing the stomata

E. This reduces water loss and photosynthesis

F. Because photosynthesis is reduced guard cells only close the stomata when the plant is at risk

G.Guard cells regulate transpiration by opening and closing the stomata.

-A plant hormone called abscisic acid causes the stomata to close. (This is helpful during times of drought or stress.)

Anatomy of stomata and guard cells

Pea leaf stomata and guard cells

Four abiotic factors that affect the rate of transpiration in typical mesophytes

Mesophytes-plants adapted to conditions of average water supply (not xerophytes or hydrophytes

A. Light

-plants generally open stomata in day to allow carbon dioxide to diffuse in and allow photosynthesis to occur

-this increases transpiration

Four abiotic factors that affect the rate of transpiration in typical mesophytes

B. Temperature

-as temperature increases transpiration also increases because high temperatures increase the rate of diffusion and decrease relative humidity

-the rate of transpiration doubles for every 10 degree C increase in temperature

Four abiotic factors that affect the rate of transpiration in typical mesophytes

C. Humidity-Decrease in humidity = increase in transpiration-Increase in humidity=decrease in transpiration**This is directly related to concentration gradients

PlantIncrease

transpiration

AirLow humidityLow moisture

PlantDecrease

transpiration

AirHigh humidityHigh moisture

H2O

Four abiotic factors that affect the rate of transpiration in typical mesophytes

D. Wind

-High winds increase transpiration

-When the wind blows it moves moist air away from the stomata

-When the air is still there is no current to move the water saturated air away from the stomata (moist air stays above the stomata and reduces transpiration)

Questions to Consider

1. When a farmer sprays a chemical on to crop plants, how does the chemical travel to the roots of the plants?

a. In the phloem, by active translocation

b. In the phloem, by transpiration pull

c. In the xylem, by active translocation

d. In the xylem, by transpiration pull

2. Roots take up minerals from the soil by:

a. osmosis b. facilitated diffusion

c. active transport d. diffusion

3. What causes movement of water through the xylem?

a. active transport in the root tissue c. active translocation

b. evaporation of water from the leaves d. gravity

4. Describe how water is transported in a plant. [4]

Questions to consider (and turn in)

1. Draw a labeled diagram to show the arrangement of tissues in a leaf.

2. Explain how roots absorb water and then transport it to the xylem, noting any special adaptations that help these processes to occur.

Reproduction in flowering plantsPollination, fertilization and seed dispersal

A. Pollination -the transfer of pollen grains from the anther to the stigma

1.self pollination

-the plant pollinates itself

2. cross pollination

-one plant pollinates another

-the plant’s genes are spread

3. Male gametes must use an external force to transfer the pollen (wind, animals)

Pollination, fertilization and seed dispersal

B. Fertilization1. The fusion of male and female gametes to form a zygote (happens inside the ovule)

2. Pollen develops from the anthers (male gamete)

3. Female gametes are found in the ovules in the ovaries of the flowers

4. Ovules that become fertilized develop into seeds

5. Ovaries with fertilized ovules develop into fruits

**Pollination does not always lead to fertilization

Path of pollen to fertilization

Anatomy of a flower

Draw, Label and Annotate

Anatomy of a flower

Pollination, fertilization and seed dispersal

C. Seed dispersal

1. One of the primary functions of fruits is seed dispersal

2. Seeds are often dispersed by animals or insects

-Ex: The seeds pass through animal intestines and are released

3. Seeds can be carried by wind

4. Fruits can explode and disperse the seeds

5. Seeds can be dispersed by moving water

Wind dispersal

Exploding fruit

This plant grows near water. The fruit bursts, the seeds fall in the water and the river carries them away.

Pond Iris

Impatiens capensis (orange spotted touch me not)

Carduus nutans (nodding plumeless thistle)

Dicotyledonous and monocotyledonous seed structure

A. Dicots-have 2 seed leaves(two cotyledons)

1. Mature plants have broader and shorter leaves with net-like veins

2. Examples: Oak trees Buttercups

3. Dicotyledonous seed internal anatomy

Phaseolus multiflorus (a bean seed)

DICOT SEED ANATOMY

B. Monocots -have one seed leaf (one cotyledon)

1. Mature plants tend to have long, narrow leaves with parallel veins

2. Examples:

Grasses Palm trees

A typical monocot seed

Required conditions for seed germination

A. Seeds are normally in a dormant condition

(they grow in the parent plant and become dormant when they leave)

B. The dormancy must be broken for the seed to germinate

C. Germination=the resuming of growth or development from the seed

Required conditions for seed germinationD. Breaking the dormancy

-water must be available for hydration of tissues inside the seed-oxygen must be available for cellular respiration-suitable temperatures (seeds stay dormant at temperatures that are too low or too high because enzyme activities are altered)-ideal light conditions (to ensure photosynthesis will be possible)-wearing down of the testa (seed coat)

Metabolic events during germinationA. Absorption of water

-presence of water activate hydrolytic enzymes

-the seed will become metabolically activated B. Gibberellins are produced

- Gibberellins are plant growth hormones produced by the cotyledons-Gibberellins stimulate the production of amylase which breaks down stored

starches into maltose

Metabolic events during germination

D. Maltose is moved to the embryo and eventually converted into glucose

E. Glucose is used in cellular respiration to produce energy or it is used to make cellulose for cell walls

F. Stored proteins and lipids are hydrolyzed

-The amino acids produced will be used to make new proteins or used as enzymes

-The fatty acids and glycerol produced will be used in the cell membrane as phospholipids

Metabolic events during germination

F. Continued

-The food reserves are stored as large insoluble macromolecules in seed.

Not useful Useful

G. When the leaves of the seedlings reach sunlight photosynthesis will begin to supply the necessary nutrients (seed energy stores are no longer needed

Phaseolus multiflorus seedling (after about two weeks)

Work ahead

1. Explain how flowering is controlled in plants.

2. What is a photoperiod?

3. Distinguish between long and short day plants.

4. Explain the experiment dealing with red and far red light and plant flowering.

Flowering in plants

A. Phytochrome-a photoreceptor that plants use to detect light

B. Photoperiod-relative lengths of night and day

C. Photoperiodism-physiological response to photoperiods

D. Flowering in plants is related to A, B and C

Flowering in plants

A. Three types of plants (you should be able to figure out which plants need longer/shorter photoperiods)

-short-day (ex: poinsettas)

-long day (ex: spinach)

-day neutral (ex: tomatoes)

B. Each type of plant has a defined photoperiod

The experiments indicated that flowering of each species was determined by a critical period of darkness (“critical night length”) for that species, not by a specific period of light. Therefore, “short-day” plants are more properly called “long-night” plants, and “long-day” plants are really “short-night” plants.

(a) “Short-day” plantsflowered only if a period ofcontinuous darkness waslonger than a critical darkperiod for that particularspecies (13 hours in thisexample). A period ofdarkness can be ended by abrief exposure to light.

During the 1940s, researchers conducted experiments in which periods of darkness were interrupted with brief exposure to light to test how the light and dark portions of a photoperiod affected flowering in “short-day” and “long-day” plants.

EXPERIMENT

RESULTS

CONCLUSION

24 h

ours

DarknessFlash oflight

Critical dark period

Light

(b) “Long-day” plantsflowered only if aperiod of continuousdarkness was shorterthan a critical darkperiod for thatparticular species (13hours in this example).

Flowering in plants

A. There are two types of red light-Pfr-far red absorbing

-Pr-red absorbing

B. Pfr promotes flowering in short-day plants

C. Pr promotes flowering in long-day plants

Action spectra and photoreversibility experiments– Show that phytochrome is the pigment that receives red light,

which can interrupt the nighttime portion of the photoperiod

A unique characteristic of phytochrome is reversibility in response to red and far-red light. To test whether phytochrome is the pigment measuring interruption of dark periods,researchers observed how flashes of red light and far-red light affected flowering in “short-day” and “long-day” plants.

EXPERIMENT

RESULTS

CONCLUSION

A flash of red light shortened the dark period. A subsequent flash of far-redlight canceled the red light’s effect. If a red flash followed a far-red flash, the effect of the far-red light was canceled. This reversibility indicated that it is phytochrome that measures the interruption of dark periods.

24

20

16

12

8

4

0

Hou

rsShort-day (long-night) plant

Long-day (short-night) plant

R RFR FR

RR RFR

RFR

Crit

ical

dar

k pe

riod

Distinguishing between monocots and dicots

Monocots Dicots

Leaf venation Parallel Net-like

Vascular tissue distribution

Number of cotyledons

Floral organs

Root types Adventitious rootsTap roots w/ lateral branching

Apical vs. Lateral Meristems in Dicots

A. Apical meristems allow primary growth-found in buds and tips of shoots-allows plants to grow organs and develop

the shape of a plantB. Lateral meristems are responsible for

secondary growth-make the stem grow thicker and/or develop new vascular bundles-found in cambium

Auxin and plant growth

A. Auxin-a plant growth hormoneB. Best known auxin is IAAC. Produced by apical buds and transported down

stem (towards the end)D. Accumulates at shaded side of plantE. Stimulates cell divisions and stretchingF. Activity is related to phototropism (growth

response in response to light)G. Auxin allows positive photropism (the plants

grow towards the lightH. Read p. 152 of the green IB textbook.

Compare growth due to apical and lateral meristems in dicotyledonous plants. [6]

Explain the role of auxin in phototropism as an example of the control of plant growth. [6]

Distinguish between monocots and dicots.

Monocots Dicots

Leaf venation

Vascular tissue distribution

Number of cotyledons

Floral organs

Root types

Review

1. Draw and label a flowering plant (from memory).

2. Describe the metabolic events of germination in a starchy seed.

3. Explain how abiotic factors affect the rate of transpiration.