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Plants What is a Plant? • Plants are – Autotrophs – Eukaryotes – Multi-cellular What is a Plant? • Most plants are autotrophs, which means that they make their own food. • Sunlight provides the energy for the plant food-making process, which is known as photosynthesis. – During photosynthesis, plants use carbon dioxide and sunlight to produce food and oxygen. What is a Plant? • Plants are eukaryotes, which means that they have a nucleus. • Although plants vary greatly in size, they all contain multiple cells, which are organized into tissues. What is a Plant? • Unlike animal cells, plant cells contain a cell wall which protects the cell. • Plant cells also contain chloroplasts which capture sunlight and undergo photosynthesis. This is what gives plants their green color. Living on Land • Most plants live on land. • In order to be able to live on land, plants must be able to – Obtain water and nutrients – Retain water – Transport materials – Support their bodies – Reproduce Living on Land • Most plants use their roots to suck water and nutrients up from the ground. Living on Land • Most plants retain water by having a waxy, waterproof layer that covers their leaves called a cuticle. Living on Land • Like all organisms, plants must be able to transport materials to different parts of its body. • Larger plants have transporting tissue called vascular tissue. Vascular tissue is a system of tubelike structures where water and other substances are transported through the plant. Living on Land • For small plants, support is not an issue, but for larger plants, rigid cells walls and vascular tissue strengthen and support the plant’s bodies. Living on Land • All plants undergo sexual reproduction. • Fertilization occurs when the sperm cell unites with an egg cell creating a fertilized egg, or zygote. The Origin of Plants • The oldest plant fossils are about 400 million years old. • These fossils already had many adaptations for land life, including vascular tissue. The Origin of Plants • Land plants and green algae have very similar forms of chlorophyll, and their genetic material is similar. • Because of this, many biologists believe plants evolved from ancient green algae. Plant Life Cycles • Plants have complex life cycles that include two different stages: – The sporophyte stage – The gametophyte stage Plant Life Cycles • The sporophyte stage – The plant produces spores, which are tiny cells that can grow into new organisms. – The spore then develops and enters the gametophyte stage. Plant Life Cycles • The gametophyte stage – The plant produces two kinds of sex cells: sperm cells and egg cells. – These cells then join and create a zygote. – The zygote grows and develops into a sporophyte, which creates more spores, starting the cycle over again. Classification of Plants • Scientists classify plants into two major groups: – Nonvascular plants – Vascular plants Nonvascular Plants • Nonvascular plants do not have a welldeveloped system of tubes for transporting water and other materials. • They are low-growing and do not have roots for absorbing water from the ground. Nonvascular Plants • Nonvascular plants obtain water and materials directly from their surroundings. • The materials then pass from one cell directly to another. • This type of transport is slow and does not go very far. Nonvascular Plants • Nonvascular plants normally live in damp, shady places so that they can easily access water. • Nonvascular plants have very thin cell walls and cannot grow more than a few centimeters tall. Nonvascular Plants • There are three major groups of nonvascular plants: – Mosses – Liverworts – Hornworts Mosses • Mosses are the most diverse group of nonvascular plants, with more than 10,000 species. Mosses • The familiar green, fuzzy moss is the gametophyte generation of the plant. • Thin, rootlike structures called rhizoids hold the moss and absorb water and nutrients. • The sporophyte generation then grows up out of this in long, slender stalks, with a capsule at the end that contains spores. Liverworts • There are more than 8,000 species of liverworts. • Liverworts are named because they grow in the shape of a human liver. – Wort means “plant”. • Liverworts grow as a thick crust on moist rocks or soil along the sides of streams. Hornworts • There are less than 100 species of hornworts. • Hornworts are named after the sporophyte generation that appear as slender, curved structures that look like horns. • Hornworts are found in moist soil, normally mixed with grass plants. Vascular Plants • Vascular plants have true vascular tissue, which allows transport of materials quickly and efficiently through the plant’s body. • Vascular tissue also provides strength, stability, and support allowing vascular plants to grow tall. Vascular Plants • Vascular plants can be broken down into two groups: – Seedless plants – Seed Plants Seedless Plants • Seedless vascular plants do not produce seeds. Instead they produce spores. • Because they produce spores instead of seeds, these plants must live in moist surroundings, so that the sperm can swim toward the egg during the gametophyte stage. Seedless Plants • Seedless vascular plants have very strong cell walls, which gives them strength and stability. • This allows them to grow much taller than nonvascular plants. Seedless Plants • Seedless plants are broken down into three groups: – Ferns – Club Mosses – Horsetails Ferns • There are more than 12,000 species of ferns, making them the most diverse seedless vascular plant. • Ferns range in size from a few millimeters to 5 meters tall. Ferns • Like all vascular plants, ferns have stems, roots, and leaves. • The stems of most ferns are underground, while the leaves grow upward from the top of the stems and the roots grow downward from the bottom of the stems. Ferns • The fern’s leaves, or fronds, are divided into many smaller parts, that look like small leaves. Ferns • The regular fern is the sporophyte generation of ferns and develops spores on the underside of its fronds. • The gametophyte generation appears as tiny plants low to the ground. Club Mosses • There are very few species of club mosses. • Club mosses are not the same as regular moss because it has vascular tissue. • Club mosses grow in moist woodlands and near streams. Horsetails • There are only about 20 species of horsetails on Earth today. • The stems of horsetails are jointed and have needlelike branches coming out of the joints. • Horsetails get their name because they resemble a horse’s tail.