Chapter 24Reproduction of Seed Plants

Gametophytes

Sporophytes

Gametophytes are the gametes (egg and sperm)

Sporophytes are the plants

Life Cycle of Gymnosperms

Life cycle of gymnosperms takes place in cones which are produced by the mature sporophyte plant.

Turn to page 611, Figure 24-4

Pollen cones – produce male gametophytesSeed cones – produce female gametophytes

Ovules – found at the base of each scale, this is where the female gametophyte develops

Cone scale

Ovule

Ovules

Fertilization and DevelopmentText page 611

Pollen tube – structure containing two haploid sperm nuclei

Zygote – new diploid sporophyte plant

Zygote grows into an embryo, and becomes encased in a what will soon become a seed. Pollen grain

has 2 nuclei!

Generally takes 2 years to complete

Structure of flowersSpecialized leaves:NOT involved in reproduction...1. Sepals – outermost circle of floral parts;

protects flower bud

2. Petals – found just inside the sepal; often brightly colored; attract

insects

Text page 612

Structure in Flowers:Reproduction

Specialized leaves:ARE involved in reproduction...

3. Stamen – contains the male parts of the flower

Anther – oval sac producing pollen grainsFilament – stalk that supports the anther

Structure in FlowersReproduction

Specialized leaves:ARE involved in reproduction...

4. Carpel (Pistils) – makes up the female part of the flower; stigma, style, and ovary

Ovary – contains ovules where the female gametophyte are produced

Style – stalk leading to the ovaryStigma – top of the style; sticky

Flower variety

Flowers vary greatly in shape, color, and size.

Flower VarietyThe typical flower produces both male and female gametophytes.

But, sometimes, male and female gametophytes are produced in separate flowers on the same plant... Like on corn!

Tassel = flower that produces male gametophytesSilk = style of a flower that contains the female gametophyte

Composite Flowers

A compound flower is a whole colony of flowers with their own petals, and multiple reproductive systems.

A sunflower is not a single flower, but arow of outer petals around many small flowers

A simple flower has one reproductive system...

Other examples:•Dandelion•Zinnia•Aster•Black-eyed Susan•Chrysanthemum...

Often called compound flowers

Life Cycle of AngiospermsReproduction takes place within the flower

Seeds develop inside protectivestructures.

1. 4 haploid cells are produced in the anther2. Each cell becomes a pollen grain3. In the ovary, 4 haploid cells form, but three

disintegrate. 4. Remaining cell divides into 8 nuclei within a

membrane called a embryo sac. One of the 8 nuclei is the egg nucleus.

This is the gametophyte of the flowering plant

PollinationMost angiosperms are pollinated by animals,

not wind...

Advantage?

Animals carry pollen from one flower to another.

What is the advantage to the animal?

Double Fertilization

A pollen grain lands on the stigma and begins to grow a pollen tube.The pollen tube grows into the style, eventually reaching the ovary and entering the ovule.

Two distinct fertilizations take place:• sperm and egg nuclei fuse together new plant embryo• other nuclei form endosperm, a rich food supply for plant

Text page 616

Practice your flower parts!

24-2: Seed Development & GerminationDevelopment of the seed was a major factor in the success of plants on land

A seed enclosed within a fruit offers something else...A better start to its new life!

As Angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds.

Fruit – applies to any seed that is enclosed within its embryo walls

Seed & Fruit Development

Which of these foods are fruits?

Plant Ovary (fruit) Lab

Assignment:

Bring in a plant ovary for our lab. You may choose any ovary, from the grocery store or out of your yard. We will dissect the plant ovaries...

and possibly eat a few

Seed DispersalDispersal by Animals:

Seeds are covered with a tough coating enabling them to pass through the digestive system unharmed

Seeds dispersed by animals are typically contained in fleshy, nutritious fruits

Dispersal by Wind and Water

Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water

Seed Dormancy

Environmental factors such as temperature, and moisture can cause a seed to end dormancy and germinate

Dormancy – time in which an embryo is alive, but not growing

Seed Germination

MonocotsUsually, the single cotyledon

remains underground

Dicots (one of two ways)• cotyledons emerge above ground and protect early leaves• cotyledons remain below the soil, providing food for the growing seedling

Germination – the early growth stage of the plant embryo

24-3: Plant Propagation & AgricultureSeed plants are essential to human life

The earliest humans gathered plants for food, shelter, and medicine

Vegetative ReproductionVegetative reproduction - the production of new plants from horizontal stems, plantlets, or underground roots

Occurs when plants are well adapted to an area

Can reproduce very quickly!

Stolen – long, trailing horizontal stems that produce roots

Plantlets

Plant Propagation

Cuttings – cut a length of stem that includes buds (meristematic tissue)

When a plant has a desired characteristic, we want copies. There are a variety of methods...

Text p. 622

Plant Propagation

Grafts – stems are usedBudding – buds are used

Other methods...

To reproduce seedless or woody plants without strong root systems, we use grafting or budding.

Scion – the stem or bud of a plantStock – root plant to which scion is attached

Text p. 623

Agriculture

Worldwide Patterns of Agriculture

Most of the people in the world depend on a few crop plants for the bulk of their food supply...• Wheat• Rice• Corn

Agriculture - the systematic cultivation of plants

North America has some of the richest, most productive cropland in the world.

Changes in Agriculture

Increases in crop yields has lowered prices, and fed more people on less land.

As our population on Earth increases,what else can we do?

Up?