Roots, Stems and Leaves

Roots, Stems, and Leaves The three principal organs of seed plants are roots, stems, and leaves. –Perform functions such as the transport of nutrients, protection, and coordination of plant activities.

Roots, Stems, and Leaves Roots –absorb water and dissolved nutrients. –anchor plants in the ground. –protect the plant from harmful soil bacteria and fungi. –Two types: Fibrous –Highly branched (most monocots) Tap –Large central roots (most dicots)

Roots, Stems, and Leaves Stems –a support system for the plant body. –a transport system that carries nutrients. –a defense system that protects the plant against predators and disease. –Two types: Herbaceous –Green, fairly bendable –Die down at the end of the growing season Woody –Covered by bark, hard, thick –Stems of plants that have been growing for 2+ years

Roots, Stems, and Leaves Leaves –Main photosynthetic organ. –Increase the amount of sunlight plants absorb. –Epidermis Covers the top and bottom of the leaf –Cuticle Covers the epidermis to protect from water loss (transpiration) –Mesophyll Specialized ground tissue where photosynthesis takes place

Plant Reproduction

Early Plants Dependent on water to complete their life cycle. However, demands of life on land favored plants that were resistant to drying rays of the sun and were more capable of conserving water.

Seeds Ability to form seeds is a trait that now is the most dominant group of photosynthetic organisms on land. An embryo of a plant encased in a protective seed coat. –the early development stage.

Seed Plants Seed plants are divided into two groups: –Gymnosperms: bear their seeds on the surface of cones –Angiosperms: flowering plants that have seeds within a layer of tissue that protects the seed.

Angiosperms have unique reproductive organs known as flowers. –Contain ovaries, which surround and protect the seeds. Seed Plants

The unique angiosperm fruit (thick wall of tissue surrounding the seed) is another reason for the success of these plants. –Attracts animals –When the animal eats the fruit, seeds from the core generally enter the animal’s digestive system. –Seeds leave the digestive tract ready to sprout and can be spread many miles. Seed Plants

Life Cycle Annuals: –Life cycle that is one year long Biennials: –Complete life cycle in two years. Perennials: –Live for more than two years.

Flowers are reproductive organs Specialized structures: –Sepals –Petals –Stamen –Carpel (AKA: Pistil) Complete vs. Incomplete Flower –Complete flowers have all four specialized structures (ex: hibiscus, lily) –Incomplete do not (ex: zuchinni)!

Flowers are reproductive organs

Sepals The outermost circle of floral parts Enclose the bud before it opens Protects the flower while it’s developing

Petals Brightly colored to attract pollinators and found inside the sepals

Stamen Male parts Anther –oval sac where meiosis takes place –Covered with a yellow dust called pollen (sperm). Filament –long stalk that supports the anther.

Carpel Female parts Ovary –produces female gametophytes Stigma –sticky portion where pollen grains land. –supported by a stalk called the style.

Fertilization (Pollination!) Fertilization in plants happens when a pollen grain is released from the anther and deposited on the stigma.

Angiosperms often rely on animals and insects to carry pollen from one plant to another. –Beneficial to animals because plants can produce nectar (a sugar rich liquid) that animals can eat. –Beneficial to plants because pollen is taken directly from flower to flower. Mutual symbiotic relationship. Fertilization (Pollination!)

Steps in Fertilization 1. When the pollen grain lands on the stigma, it grows a pollen tube. The pollen tube grows into the style and enters the ovule. 2. The nucleus in the pollen grain divides and forms two sperm nuclei. 3. One sperm fuses with the egg to make a diploid zygote. This will become the plant embryo. –The other sperm nuclei fuses with two polar nuclei and makes a TRIPLOID 3N cell. This becomes the endosperm which will be the food supply for the seed.

Fertilization Animation Because the endosperm and zygote are fertilized, this is called double fertilization.

Flower to Fruit! As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. The term “fruit” applies to any seed that is enclosed within its embryo wall. –Also includes beans, peas, and tomatoes.

Plant Responses Tropism –Response of a plant to an environmental stimulus –Controlled by hormones Chemical produced in one part of an organism that affects another part (target cells) of the same organism

Plant Responses Tropism –Controlled by hormones Auxin: Stimulate cell elongation Cytokinin: Stimulate cell division, the growth of lateral buds, and cause dormant seed to sprout

Plant Responses Tropism –Controlled by hormones Gibberellin: Produce dramatic increases in size, particularly in the stems and fruit Ethylene: In response to the presence of auxins, fruit tissues release small amount of ethylene, which ripens fruits

Plant Responses –Phototropism Response of plants to light When light hits one side of the stem of a plant, a high concentration of auxins is produced in the shaded side –Cells on the dark side elongate, causing the stem to bend away from the shaded side and toward the light

Plant Responses –Gravitropism Response of plant to gravity Auxins build up on lower sides of roots and stems –These cell elongate in the stems, which helps to turn the trunk upright –In roots, auxins actually inhibit cell growth and elongation, which causes roots to grow downward Result: the shoots of a germinating seed grow out of soil, against the force of gravity, while roots grow down

Plant Responses –Thigmotropism Response of plants to touch Vines, climbing plants, animals