L earning Objective 6

a. Describe the events involving flowers: pollination, fertilization, relationship of ovule to seed formation, and relationship of pistil to fruit formation.

b. Describe patterns of plant life cycles: annual, biennial and perennial.

c. Understand the basics of plant reproduction: sexual and asexual, vegetative propagation, tissue culture and cloning.

Plant Organs: Root, Stem, Leaf. Flower and Fruit.

1) Made up of specialized cells and tissues.
2) Has a particular function in the organism.

For further discussion amd diagrams, it is recommended that the student refers to a introductory botony or biology text, which can be found in most libraries.

A.  Function:  Absorption, anchorage and storage. B.  Internal Structure:  root cap, root hairs, meristem, region of elongation and maturation, vascular tissue. C.  Systems:  fibrous and taproot. D.  A true root's origin is from the seedling.  Adventitious roots originate from the stem.

A. Stem functions: support and transport.      B. Parts of a woody twig:      1. terminal and lateral buds      2. node and internode  C. Leaf arrangement:      1. opposite and alternate     2. whorled

Opposite leaflet

Opposite leaflet

Alternate

Whorled

Whorled

1.  Herbaceous  Stem:
a.  A herbaceous stem is typically soft, succulent and  green.
b.  It is produced by a plant in its first year of growth the stem may remain herbaceous or develop into a woody stem.

'Uala

2. Woody stem:      a. A woody stem is produced only in second and subsequent years of certain plants, usually trees, shrubs and some vines.      b. Many dicots produce wood.     c. A few monocots, like palm trees, bamboo and the hala tree, produce a woody-type growth differing structurally from dicot wood.     d. wood is primarily composed of plant cells called xylem which also conduct water in the plant.

1. The epidermis or bark:

a. Both are outer coverings on stems.

b. The epidermis is a single layer found on herbaceous stems.

c. Bark is a multi-layered woody covering on woody stems.

2. The cambium

a. is found directly under the epidermis or bark

b. is composed of a single row of cells which divide and produce all new cells, increasing the thickness of the stem.

c. may be damaged if too much bark is scraped away in the same area (called girdling).

 

Diagrams of the epidermis, bark, and cambium appear at this site.

3. The vascular system is a very complex tissue found on either side of the cambium. It is composed of two primary cell types:

a. Phloem is just outside the cambium. In it sugar and other substances move upwards in it.

b. Xylem is non-living cells which function as a pipeline moving water upwards in the plant.

F. Formation of wood:

1. Wood is formed in woody stems of dicots and is composed of many bands of xylem cells produced annually in temperate climates and more frequently in tropical plants.

2. Wood functions as a system for support and water movement in the plant. By supporting many leaves, the plant produces more food and eventually more offspring.

Wauke

A. Function: To photosynthesize and produce food in form of sugar for the plant. (More detail on photosynthesis to follow). The only way plants get food is to make it.

1. Palisade cells form two or three rows on the upper surface of a leaf where most of photosynthesis takes place.

2. Stomates:

a. are openings mostly found on the lower side of leaf.

b. Stomates control water movement out of leaf and allow CO2 inside leaf for photosynthesis.  Water loss through the open stomates is called transpiration.

C. External Features (will be observed in lab, review as needed).

1. petiole and blade.

2. compound (pinnately or palmately).

3. venation:

a. Dicots have a fine venation which is netted. The pattern of venation is either pinnate or palmate.

b. Monocots have primarily parallel venation.

4. leaf shapes, edges and surface characteristics: (see lab handout).

Visit this excellent site for more images.

A. Function of flower is plant reproduction.      B. Major parts and their function (From the lower parts of the flower to the upper parts).      1. Sepals protect the bud and are sometimes very petal-like.     2. Petals      a. are often large and brightly-colored, but can be small and inconspicuous.     b. attract pollinators by color, shape or markings.     c. BRACTS are not petals but function and appear as petals. Their origin is from a leaf and not the floral structure. Examples of flowers having bracts are poinsettia and bougainvillea.

Poinsettia

a. are the male reproductive parts of the flower.

b. consist of filament (stalk) and anther.

1) The anther has 4 chambers in which thousands of tiny pollen grains are formed.

2) Pollen grains are nuclei functioning like sperm in higher animals containing 1/2 the genetic information needed by the offspring. They fuse physically with the egg cellnucleus in the event of fertilization.

Visit this excellent site     for more images.

a. The stigma.      1) is located at the very tip of the pistil.     2) Is the only place where pollen grains will become active and start growing into the pistil for fertilization. b. The style is a long or short neck linking the stigma to the ovary.     c. The ovary      1) is located at the base of the pistil.     2) Contains one or more ovules each with a single egg cell.     d. Ovules within the ovary contain one eggcell. Potentially each egg cell may be fertilized by sperm nucleus (transferred by the pollen tube) and produce one offspring plant

a. Are the different arrangements of flowers on the stem of plants, either singly or in groups.

b. One striking example is the composite in which many flowers give the appearance of a single one. The daisy, sunflowers and Wedelia are examples.

1. bisexual flowers:

a. are like the flower described above. They are the most common.

b. They have functional stamens and pistils in the same flower.

2. unisexual flowers:

a. Each flower has ONLY one functional reproductive structure:
pistil (female) or stamens (male).

b. The male and female flowers may be on same plant.

[for example, 'ulu, or breadfruit tree. (technical name: monoecy)]; or male and female flowers may be on different plants [example is hala which results in seperate male and female plants. (technical name: dioecy)]
'ulu, , hala

D. Reproduction (sexual) of flowering plants is as follows: (Be able to describe this event.)    

1. Pollination:

a. Pollination is the transfer of the pollen grain from stamen to stigma of pistil.    

b. It is always the first step in reproduction.

2. Fertilization:

a. Fertilization is an event that can only follow pollination.    

b. It involves the growth of the pollen tube down the style and into the ovary.    

1) The pollen tube finds the ovule where the egg cell is located and releases a sperm nucleus which joins with the egg cell nucleus.    

2) This single cell, called either fertilized egg or plant zygote, is the beginning of a new individual plant (See figure 6-A).

3. Ovule to seed formation:

a. The fertilized egg inside ovule develops into a plant embryo.

b. Simultaneously the entire ovule develops into the seed.

4. Pistil to fruit formation:

a. After fertilization, parts of the flower dry up and fall off: the sepals, petals, stamens and top parts of pistil. (Why?)

b. The base of pistil, the ovary, grows and swells and develops into the fruit.

c. The seed develops from an ovule (containing fertilized egg cell) which is located in the developing fruit (See Fig. 6-B).

5. Functions of the parts of a seed:

a. The seed coat protects the embryo until conditions are favorable for germination.

b. The plant embryo will become the new plant.

c. The stored food (endosperm) will nourish the embryo as it develops into a seedling and is large enough to make its own food by photosynthesis.

 

6. Seed germination:

a. Seed germination is initiated by water and favorable conditions such as temperature.

b. Germination stimulates the plant embryo to begin cell division.

1) The embryo first develops the first root (radicle).

2) Second, cotyledons, often called "seed leaves", emerge with a tiny apical bud in the center.

E. Plant Life Cycles

1. In an annual cycle, a plant grows and reproduces in one growing season or within a year. This is rare among Hawaiian native plants.

2. In a biennial cycle, a plants takes two growing seasons, or years, to reproduce. Very few Hawaiian native plants are biennial.

3. In a perennial plant, the plant grows for three or more years, reproducing a number of times in its life span. This is the most common life cycle for Hawaiian native plants.

F. Other Aspects of Plant Reproduction:
 

Comparison of Sexual and Asexual Reproduction

1. Sexual reproduction:

a. Sexual reproduction occurs when a sperm nucleus from the pollen grain fuses with egg cell from ovary of pistil.

b. Each brings a complete set of genes and produces genetically unique organisms.

c. The resulting plant embryo develops inside the seed and grows when seed is germinated.

2. Asexual reproduction:

a. Asexual reproduction occurs when a vegetative part of a plant, root, stem or leaf, gives rise to new offspring plant whose genetic content is identical to the "parent plant". An example would be a plant reproducing by root suckers, shoots that come from the root system. The breadfruit tree, or 'ulu((Artocarpus altilis)), is an example.

b. Asexual reproduction is also called vegetative propagation. It is an important way for plant growers to get many identical plants from one very quickly .

c. By asexual reproduction plants can spread and colonize an area quickly.
For example: crab grass (Digitaria spp. ) or Arrowhead vine (Syngonium podophyllum, a common groundcover plant in Hawaii .)
 

Applications of Asexual Reproduction in plants 1. Vegetative Propagation: is a type of asexual reproduction found in plants.

a.  It is widely used by gardeners and the nursery trade.  Pieces of the original plant, usually stems, but leaves and roots can also be used in some cases, are treated and grown so that they will eventually form a new plant with roots, stems and leaves.  This offspring plant will be gentically identical to the mother plant.

b.  Cultivars are propagated in this way.  For example, it's the main way to get new banana plants, from the sprouts at the base of the banana clump.

Cultivated bananas, like a number of cultivars, inlcuding seedless grapes and navel oranges, produce no viable seeds, so vegetative reproduction is the only way to propagate them.

 

3. Tissue culture, Micro-propagation and cloning:

a. These are techniques used by botanists and horticulturists to produce many plants asexually from cells, or from meristems found in leaf and flower buds.

b. These techniques involve growing cells in sterile cultures on petri dishes.  They require special labrotary equipment and training in the techniques

c. At Lyon Arboretum, Dr. Greg Koob has been using micro-propagation in culturing rare native Hawaiian plants.  He has been able to save a number of highly endangered plants from extinction which could not be repoduced in any other way. (See video: Preventing Extinction of Hawaii's Endangered Plants for a visit to Dr. Koob's laboratory.)

d.  A clone is a term that can be applied to any plant resulting from vegetative reproduction.  A clone is always genetically identical to the single parent plant from which it came.

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