Plant Life CyclesCHAPTER 30

Animals vs. PlantsPlant Reproduction

Animal Reproduction

Life cycleAlternation of generations

No alternation of generations

Gametes Haploid gametes Haploid gametes

Spores Haploid spores No spores

Gametes made by

Haploid gametophyte, by mitosis

Diploid organism, by meiosis

Spores made by

Diploid sporophyte, by meiosis

No spores

Alternation of Generations

• Plants have a double life cycle with two distinct forms:– Sporophyte: diploid, produce haploid spores

by meiosis.– Gametophyte: haploid, produce gametes by

mitosis.

Non-flowering plants

• Mosses, ferns, and related plants have motile, swimming sperm.

• What kind of environmental conditions would be required for reproduction in these plants?

• What kinds of limits does external reproduction impose on these plants?

Life cycle of mosses

• Follow the link and write down in your notes 1 page on the life cycle of mosses

http://www.microview.org.uk/millennium/pages/moss_lifecycle.htm

http://www.sumanasinc.com/webcontent/animations/content/moss.html

Moss Life Cycle

Life cycle of ferns

• Ferns, unlike some other plants, do not flower in order to propagate. Instead, they reproduce sexually from spores.

• The life cycle of a fern is very different from the life cycle of many other plants.

• While many plants grow a mature adult form straight out of the seed, ferns have an intermediate stage, called a gametophyte, which then grows into a mature fern.

•

• There are two distinct stages in the life cycle of ferns. The first stage is that of the gametophyte.

• Spores are produced on the underside of mature plants. These will germinate and grow into small, heart-shaped plants called gametophytes.

• The gametophytes produce both sperm and egg cells, and will fertilize itself, or others. Once the fertilization occurs, the adult fern will begin growing.

• The second stage in the life cycle of a fern is the adult stage. The fertilized gametophytes begin to look like a mossy growth.

Conifers

• Conifers (also non-flowering plants) have reduced gametophytes.– Male gametophyte is contained in a dry pollen

grain.– Female gametophyte is a few cells inside of

the structures that become the seed.

Conifer life cycle

Conifer pollination

• Conifers are wind-pollinated plants.

• Chance allows some pollen to land on the scales of female cones.

• Pollen germinates, grows a pollen tube into the egg to allow sperm to fertilize the egg.

• What are some advantages and disadvantages to wind pollination?

Flowering Plant Reproduction

Angiosperms (flowering plants)• Plants that protect their seeds within the body

of a fruit.

• Make up ¾’s of all plants, including:

– Trees, shrubs, herbs,

grasses, water plants…

Structure of a Flower1. Pistil

2. Stigma

3. Style

4. Ovary

5. Stamen

6. Filament

7. Anther

8. Petal

9. Sepal

10. Receptacle

11. Stem

Male Reproductive Structure

The stamen consists of two parts: Anther and Filament

The anther is where meiosis occurs to produce haploid pollen

The filament is a stalk that supports the anther

Female Reproductive StructureThe pistil consists of

the stigma, style and ovary

The sticky stigma receives the pollen from the anther

The pollen grows a tube down through the style

Meiosis occurs in the ovary to produce haploid ovules

Reproductive Structures

• Petals: colourful

structures that attract pollinators.

• Sepals: surround and protect the flower bud.

Pollination

Wind, insects or other animals transfer pollen from the anther of one flower to the stigma of another

Flowers vary depending on pollination mechanism

Pollination Animation

Pollination VectorsWind Pollination: Dull, scentless flowers with reduced petalsBees/Butterfly Pollination: Brightcolor, nectaries, scent. They sip nectar, get pollen on coats, transfer pollen from flower to flower

Bird Pollination: Nectaries, brightcolors, tube-like flowers

Moth Pollination: White petals, open at night

Fly Pollination:Rank odor, fleshcolored petals

• Pollen Grain • Anther Sac

Pollen grains contain two haploid cells produced through meiosis.

1- The Tube cell – will grow the pollen tube. 2- The Generative cell – will go through mitosis to create two sperm cells.

OvaryEach ovule within an ovary has a micropyle (an opening for the pollen tube). The ovules’ megasporangium undergo meiosis to produce four haploid cells (3 die leaving 1 megaspore)The megaspore undergoes mitosis 3 times to produce 8 haploid cells within the embryo sac.

Fertilization

After pollen lands on the stigma, a pollen tube grows down through the style to ovary

Generative cell creates the two sperm nuclei Double fertilization occurs:

one sperm fertilizes the egg one sperm the two polar nuclei together

Result of Double Fertilization

The sperm nucleus and egg nucleus join to form a 2n (diploid) embryo

The other sperm nucleus and the two polar nuclei join to form a 3n (triploid) endosperm. The endosperm is the food supply for the embryo.

First link

Seed and Fruit Development After fertilization,

the petals and sepals fall off flower

Ovary “ripens” into a fruit

The ovule develops into a seed

Seed Dispersal Mechanisms-Allow plants to colonize new areas and avoid

shade of parent plant

Wind Dispersal - Flight mechanisms, like parachutes, wings, etc. Ex. Dandelion, maples, birch

Animal Dispersal - Fleshy fruits which animals eat, drop undigested seeds in feces or burrs which stick to animals’ coats

Gravity Dispersal - Heavy nuts fall to ground and rollex. acorns

Water Dispersal - Plantsnear water create floating fruitsex. coconuts

Plant ResponsesCHAPTER 31

• How plants move and communicate

Plant Hormones

Plant Hormones

• Plant hormones can be divided into two classes:– Growth promoters: Auxins, Gibberellins,

Cytokinins– Growth inhibitors: Ethylene gas, Abscisic acid

Growth promoters

• Hormones can promote plant growth in two ways:– Stimulating cell division in meristems to

produce new cells.– Stimulating elongation in cells.

Auxins

Auxin activityAuxins stimulate genes in cells associated with plant growth.

Auxin roles

• Auxins carry out multiple roles having to do with plant growth including:– Tropisms– Apical dominance– Growth of adventitious roots– Fruit growth

Tropisms

• Tropisms are the growth of a plant toward or away from a stimulus, including:– Phototropism: in response to light– Gravitropism: in response to gravity– Thigmotropism: in response to touch

Nastic Movements

Nastic movement in the sensitive plant (Mimosa pudica)

Hinge control in Venus Fly Trap - Nastic movement

How it works

• Nastic movements are rapid, reversible movements in a plant.

• Electrical potentials across cell membranes, similar to those in our nerve cells, signal plant cells at the base of the Mimosa leaf to rapidly lose water. This causes the leaf to droop.

Movies• Sensitive Plant:

http://www.youtube.com/watch?v=BVU1YuDjwd8

• Venus Fly Trap: http://www.youtube.com/watch?v=ktIGVtKdgwo&feature=related

Other examples

• Sunflowers follow the sun during the day.

• Leaves of many plants turn to follow the sun.

Day/Night length

• Some plants flower in response to the length of periods of darkness.

• Spring-blooming flowers are long night (short day) plants, while summer-blooming flowers are short night (long day) plants.

• Some plants are day-neutral.

Plant Communication

• Plants communicate chemically.

• Injured plants send out chemical signals that may– signal other plants to prepare for an attack.– attract other insects that eat the insects that are

attacking the plant.