What Is a Plant? Page 574 Read the lesson title aloud to students.

Come to the board and list plants that are common to our area. Name some plant characteristics that could be used to classify them into a few large groups. For example, you can use flower or leave characteristic, or size to describe.

At the end of the lesson, you should be able to explain what plants need to survive and how the first plants evolved. You should also be able to explain the process of alternation of generations.

Learning Objectives List the basic needs of plants. Explain how plants adapted to life on land. Identify the features that defines most plant life cycles.

Vocabulary Plant Cuticle Stomata Vascular system Lignin Pollen grain Seed Alternation of generations: life cycle that has 2 alternating cycles: sporophyte (2n) and gametophyte (n). Sporophyte: spore-producing plant. Gametophyte: gamete-producing plant.

What Do Plants Need to Survive Sunlight Sunlight Gas exchange Water Minerals Carbon dioxide Oxygen Minerals Water

What Do Plants Need to Survive Plants also absorb minerals. Minerals are nutrients in the soil needed for plant growth. Many plants have specialized tissues that carry water and nutrients upward from the soil and distribute the products of photosynthesis throughout the plant body. Simpler types of plants carry out these functions by diffusion. Plants use the energy from sunlight to carry out photosynthesis. Every plant displays adaptations shaped by the need to gather sunlight. Photosynthetic organs such as leaves are typically broad and flat and are arranged on the stem so as to maximize light absorption. Explain that plants require oxygen to support cellular respiration and require carbon dioxide to carry out photosynthesis. They also need to release excess oxygen made during photosynthesis. Plants must exchange these gases with the atmosphere and the soil without losing excessive amounts of water through evaporation. What can be the role of CO2?

What Do Plants Need to Survive Copy this chart in your notebook and fill it with a summary of the information provided.

The History and Evolution of Plants Modern land plants evolved from water-dwelling organisms. For most of Earth’s history, land plants simply did not exist. Life was concentrated in oceans, lakes, and streams. Although photosynthetic prokaryotes added oxygen to Earth’s atmosphere and provided food for animals and microorganisms, true plants had not yet appeared on the planet. The fossil record indicates that the ancestors of today’s land plants were water-dwelling organisms similar to today’s green algae. Fossil spores of land plants occur in rocks 475 million years old, but the plants themselves from this time period left no fossils. The oldest fossils of land plants themselves are found roughly 50 million years later in the fossil record. One of the earliest fossil vascular plants was Cooksonia.

The History and Evolution of Plants The greatest challenge that early land plants faced was obtaining water, which they achieved by growing close to the ground in damp locations. Fossils also suggest that the first true land plants were still dependent on water to complete their life cycles

The First Land Plants How did plants adapt to life on land? Answer: Over time, the demands of life on land favored the evolution of plants more resistant to the drying rays of the sun and more capable of conserving water. Life on land favored plants: resistant to drying capable of conserving water capable of reproducing without water

An Overview of the Plant Kingdom Green algae Mosses Ferns Cone-bearing Flowering Do you remember how to read a cladogram?

Analyze the cladogram an answer In the ancestor to which plant group did seeds first evolve? What key feature does a fern have in common with a flowering plant? To what taxonomic group to do the vast majority of plants belong? To what taxonomic group do the fewest plants belong?

Cone-bearing plants Both have true water-conducting tissue. The vast majority of plant species are flowering plants. The cone-bearing plants have the fewest species.

The Plant Life Cycle Meiosis Spores (N) Gametophyte plant (N) Sporophyte plant (2N) Sperm (N) What feature defines most plant life cycles? The life cycle of land plants has two alternating phases, a diploid (2N) phase and a haploid (N) phase. This shift between haploid and diploid is known as the alternation of generations. Explain that the multicellular diploid (2N) phase is known as the sporophyte, or spore-producing plant. The multicellular haploid (N) phase is known as the gametophyte, or gamete-producing plant. Haploid (N) organisms carry a single set of chromosomes in their cell nuclei, while diploid (2N) organisms have two sets of chromosomes. A sporophyte produces haploid spores through meiosis. These spores grow into multicellular structures called gametophytes. Each gametophyte produces reproductive cells called gametes—sperm and egg cells. During fertilization, a sperm and egg fuse with each other, producing a diploid zygote. Explain to students that the zygote develops into a new sporophyte, and the cycle begins again. To make sure that students have a firm grasp of this information, ask the following questions. Ask: Which generation of a plant is diploid, and which is haploid? Answer: The sporophyte generation is diploid, and the gametophyte generation is haploid. Ask: Why does it make sense that the sporophyte generation is diploid? Answer: because sporophytes form when two haploid gametes fuse Ask: What does the sporophyte produce? Answer: spores Ask: What process produces spores? Answer: meiosis Ask: Are the spores diploid or haploid? Answer: haploid Fertilization Eggs (N)

Based on the diagram, answer the following questions. The Plant Life Cycle Based on the diagram, answer the following questions. 1. During the alternation of generations, which stage is diploid? ________________________ 2. How many sets of chromosomes does a plant have when it is in its diploid phase? _________________ 3. What happens during fertilization? __________________

Trends in Plant Evolution How does the relative size of the haploid and diploid stages differ between mosses and seed plants? Gametophyte size: reduces Sporophyte size: increases This illustration shows an important trend in plant evolution—the decreasing size of the gametophyte and the increasing size of the sporophyte. Although many green algae do have a diploid sporophyte phase, some do not; their only multicellular bodies are gametophytes. Mosses and their relatives consist of a relatively large gametophyte and smaller sporophytes. Ferns and their relatives have a small gametophyte and a larger sporophyte. Seed plants have an even smaller gametophyte than ferns, which is contained within sporophyte tissues.

Mosses have a relatively large gametophyte (N), while seed plants have the smallest gametophyte (N) of all plant groups. Mosses have smaller sporophytes (2N) than seed plants.

Plants have adaptations that allow them to live on land. Challenges of living on land have selected for certain plant adaptations. A cuticle allows plants to retain moisture. waxy, waterproof layer Hold moisture in

Stomata are tiny holes in the cuticle. can open and close allow air to move in and out

collection of specialized tissues A vascular system allows resources to move to different parts of the plant. collection of specialized tissues brings water and mineral nutrients up from roots disperses sugars from the leaves allows plants to grow higher off the ground sugars water and mineral nutrients

hardens cell walls of some vascular tissues Lignin allows plants to grow upright. plant cells lignin hardens cell walls of some vascular tissues provides stiffness to stems

pollen grains contain a cell that divides to form sperm Pollen grains allow for reproduction without free-standing water. pollen grains contain a cell that divides to form sperm pollen can be carried by wind or animals to female structures

seed coats protect embryos from drying wind and sunlight A seed is a storage device for a plant embryo. seed coats protect embryos from drying wind and sunlight embryo develops when environment is favorable

Plants evolve with other organisms in their environment. Plants and other organisms can share a mutualistic relationship. a mutualism is an interaction in which two species benefit plant roots and certain fungi and bacteria flowering plants and their animal pollinators

Plants have adaptations that prevent animals from eating them Plants have adaptations that prevent animals from eating them. (plant-herbivore interactions) spines and thorns defensive chemicals

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