Unit A3-1

Horticultural Science

Horticulture CD

Problem Area 3

Plant Propagation

Lesson 1

Understanding Sexual Reproduction

Interest ApproachLook at the sample of plants that I have brought in for you. What are the two categories of plants that are displayed?How important do you think flowers are to a plant?How are plants more successful at reproduction than animals?

VocabularyCotyledon

Cross pollination

Diploid

Embryo

Endosperm

Epicotyl (plumule)

Fertilization

Gametes

Genes

HaploidHybridsHypocotylPollinationRadicleSeedSeed coatSelf pollinationSexual reproductionZygote

Student Objectives1. Discuss the importance of plant propagation

2. Explain the difference between sexual and asexual reproduction

3. Identify the major parts of a seed

4. List the function of each major part of a seed

What Would Happen if Plants Did Not Have the Ability to Reproduce?Plants are essential for life as we know it on earth

They are the ecological producers of our planetThey produce food and shelter for other organisms, produce oxygen to support animal respiration, and enrich our environment

Throughout history people have relied on seeds and plant parts to grow new plants for food and fiber

In more recent times, knowledge of plant reproduction has resulted in the development of plant hybrids that have enabled large scale agricultural production of food and fiber plants

Courtesy of Interstate Publishers

How Is Sexual Reproduction Different From Asexual Reproduction?

Sexual reproduction occurs when the male sperm carried in the pollen unites with the female egg within a flower

Most plants reproduce their own kind in nature by seeds that are the result of sexual reproduction

The male sex cell (sperm) and the female sex cell (egg) are known as gametes

The union of gametes produces the seed that contains the embryo plant and stores food

Both the male sperm and the female egg contribute genetic information to the new embryo plant

This results in new combinations of genes producing new traits that add vigor to the offspring

The offspring resulting from this new combination of genes is known as a hybrid

People have greatly improved agricultural crops through hundreds of years of hybridization

The genes, made from DNA, are located in chromosomes

Normal cells contain a pair of chromosomes and are said to be diploid

Reproductive cells, the egg and sperm, contain a single chromosome and are said to be haploid

Fertilization unites the single chromosome in the sperm nucleus with the single chromosome in the egg nucleus

This enables the fertilized egg or zygote to have a complete pair of chromosomes (diploid)

Plant fertilization is unique because the sperm contains two nuclei

Causes the plant to become double fertilizedOne sperm nucleus unites with the egg nuclei to produce a zygote

The second sperm nucleus unites with the nuclei of the embryo sac that develops into the endosperm

Fertilization Process

PollenStigma

Ovary

Egg

Two sperm nuclei

Pollen tube

Second nucleus

Egg nucleus

One sperm fertilizes egg

One sperm fertilizes second nucleus to form endosperm

Courtesy of Interstate Publishers

Pollination is the transfer of the male sperm carried in the pollen to the female part of the flower, the stigma

Plants rely on wind and water to transfer the pollen to the stigmaIn addition, plants depend on animals to help with this process

Birds, insects, bats and other animals are attracted to brightly colored, scented flowersThese animals transfer pollen from the anthers of the flowers they visit to the stigmas of other flowers

PollinationPollen grains (contain sperm)

Stigma

Ovule

OvaryEgg cell

Courtesy of Interstate Publishers

A bat is covered with pollen from this flower. It will transfer this pollen to another flower when it searches for more nectar.

Courtesy of McGraw Hill Publishers

Types of PollinationA. When the pollen of a plant pollinates a flower on the same plant, it is called self-pollination

Many plants have this ability, others do not

B. When the pollen of a plant pollinates the flower on another plant of the same species, it is said to be cross-pollination

What Are the Major Parts of a Seed & Where Are They Located?

A seed is a living entity that serves as a bridge between generations of a plant

It is formed in the pistil of the flower and develops from the ovule following fertilization

As the fertilized egg (zygote) grows and develops, it becomes the embryo of the seed

Parts of the EmbryoThe embryo contains the root, stem and leaf of a complete plant

In addition to this, it also contains stored food to support development and growth of the embryo

The seeds of dicot plants have food stored cotyledons. In monocot seeds, most food is found in the endosperm

The embryo’s root is called the radicle, the stem the hypocotyl and the leaf the epicotyl

Surrounding the embryo & endosperm is a protective seed coat

Embryo Parts

Seed coat

Epicotyl

Cotyledons

Hypocotyl

Seed coatEndosperm

Epicotyl

Hypocotyl

RadicleCotyledon

Courtesy of Wm. C. Brown Publishers

What Is the Function of Each Major Part of a Seed?

Each part of the seed has a specific function to help ensure that a healthy new plant will emerge from the seedThe seed is a living entity which contains the embryo plant & everything necessary for its growth & development

Dicot plants (soybean, pea, oak) have two cotyledons while monocots (corn, coconut, lilies) have only one cotyledon in its seed

Seed Parts & FunctionsRadicle Lower part of the hypocotyl; forms the

first root; first to emerge from the seed

Hypocotyl Develops into the true stem

Epicotyl Above the hypocotyl; develops into a pair of small leaves

Tip is sometimes called the plumule – it is the terminal bud of the first shoot to emerge form the seed

Endosperm Found in monocots in an area of high concentration of food; food source for the embryo

Cotyledon Stores food absorbed from the endosperm when the seed is formed; provides energy until the plant produces its own food

Seed coat Surrounds the seed and protects it from injury and dehydration

SummaryWhy are plants essential on earth?How is sexual reproduction different from asexual reproduction?What is another name for the sex cells of a plant?How is a haploid gene different from a diploid gene?Explain the process of pollination. What are the two types?

Summary ContinuedHow does fertilization in a plant occur?

What part of the seed is the primary root?

What is the function of a cotyledon?

What part of the plant develops into the true stem?

How is a monocot different from a dicot?

What protects the seed before it germinates?