Chapter 22-25

Plant Characteristics §Multicellular §Eukaryotic §Cell walls made of cellulose §Autotrophic §Carries out photosynthesis using green pigment called chlorophyll §Usually have large central vacuoles

Non Vascular Plants – Mosses (Bryophytes) §Require damp environment §Require water for reproduction §Do not have true roots (have rhizoids instead)

Vascular Seedless Plants – Ferns (Pteridophytes) §Largest group §Usually live in moist environment §Need water for fertilization §Have true leaves, stems, and roots

Vascular Seed Plants- GYMNOSPERMS §Conifers do not require water for fertilization §Wind carries the pollen from male cones to female cone where egg is fertilized. §Zygote becomes embryo and ovule becomes seed §Seeds produced in cones

White Pine Fir Cypress Spruce EXAMPLES

The giant redwoods (Notice the person in the tree to your right.)

Ancient Gynmnosperm Welwitschia spp.

 Other types of Gymnosperms… Cycad Ginko Gnetae

 While some gymnosperms lose their leaves, most have needle-like leaves that they keep all year. This is why they are referred to as evergreens.

Vascular Seed Plants- ANGIOSPERMS

§The most abundant and recent type of plants on Earth §Have seeds that are protected by a fruit. Passion flower and fruit

§Divided into two groups: monocots and dicots. §Monocot seeds have one cotyledon (seed leaf). These are seeds that cannot be split in half, like a piece of corn. §Dicots have two cotyledons. These seeds can be split in half like peanuts and beans.

Monocots vs. Dicots

EXAMPLES OF MONOCOTS Flower parts usually in groups of three Lily

EXAMPLES OF DICOTS Chrysanthemum Petunia Trenia Rose Sunflower Flower parts usually in groups of four or five

Vascular Tissue §Xylem carries water and minerals upward in a plant. §Water always moves in only one direction: from the roots to the stems and leaves. §Water evaporates from the plant through structures on the leaves called stomata (singular = stoma).

§Phloem carries the “food” of the plant. §A plant’s food is sugar dissolved in a solution called sap. §It carries sugars in two directions. §Sugar can be carried from where it is made (usually the leaves) to where it is stored (usually stems and roots).

ROOTS There are two kinds of roots: §Taproots - a large, main, primary root. § Example= carrot §Fibrous - branching, secondary roots. § Example = grasses

§Water is absorbed into the plant by the process of osmosis. §Water enters the root through the root hairs. §Root hairs give the root more surface area so that it can absorb more water. §The amount of water that is absorbed is dependent upon the amount of water in the soil.

STEMS §Stems typically have two main functions: l Supporting leaves and flowers l Transporting water and food §Some plant stems have the additional job of food storage. EX: The potato is a special stem that stores starch.

§Secondary growth is when the plant grows wider.. §Cambium is the meristem tissue that allows plants to get wider. §This secondary growth creates a layer of dead cells called wood.

 The secondary phloem, cork cambium and the cork combine to form the bark of a tree.

Trunk of an Oak Tree Notice the splits in the bark

§As the xylem gets older, it becomes clogged and can no longer carry water. These dark-colored layers are known as heartwood. Heartwood is stronger and more resistant to decay than sapwood.

§The alternation of spring and summer wood is what forms the tree’s growth rings. §The wider the rings, the more favorable the conditions were for growth. §The more narrow the rings, the poorer the conditions.

Summer Wood Spring Wood

Annual Rings

LEAVES §The blade is the actual leaf. §It attached to the stem by a thin structure called a petiole. §The vascular tissue enters the leaf through the petiole and forms the veins of the leaf.

§The top and the bottom of the leaf is covered by epidermis. §The upper layer usually has a waxy layer known as a cuticle to prevent water loss.

§Guard cells in the lower epidermis take in water and swell unevenly. §This causes an opening to form between the guard cells. §This opening is called the stoma. §Stomata allow carbon dioxide to enter the leaf and oxygen and water vapor to diffuse out.

§The mesophyll (middle layer) is where most of the photosynthesis takes place.

Leaf Cross-Section

§The most common sexual reproductive structure is the flower. A perfect flower contains both male and female parts. Flowers

§The male part of a flower is called the stamen. §Formed by a filament which holds anther. §The anther produces the pollen, which in flowers is the male gamete or sperm.

§The female flower parts form the pistil, which is composed of a sticky top called the stigma, a neck called the style and a base called the ovary. §The ovary contains the female gametes - egg or ovules.

§The petals are usually colorful to attract pollinators. §The sepals are protective green leaves at the base of a flower. They protect the bud before the flower blooms.

§During pollination, pollen is transferred from the anther to the stigma. When a pollen grain lands on a stigma, it sends out a pollen tube that grows through the style to the ovary. Ovule fertilized by sperm. Pollen Tube

§The ovary will eventually develop into a fruit. §The ovules will develop into seeds.

§The job of a fruit is to protect the seeds and to sometimes help them be spread. §The spreading of seeds is known as seed dispersal. §Seeds can also be dispersed by wind, water, animals, and being carried away on fur or clothes.

Modes of Seed Dispersal Gravity Animals Force Wind Water

PLANT RESPONSES §Phototropism is the response of plants toward light.

§Gravitropism is a plant’s response to gravity. This assures that roots grow down and stems grow up.

§Thigmotropism is a response to touch. This allows a plant to grow on a surface that can support it. Whenever the stem touches the support, the cells on the opposite side of the stem grow longer, causing the stem to coil around or grasp a hold of the support.

§The response of a plant to daylight length is called photoperiodism. It is actually a response to the hours of continuous darkness. A single flash of light during darkness can upset the cycle of some plants. Long Night Short Night Long Night Short Night

Importance of plants? §Food §Fiber §Fuel §Construction §Transport §Medicine