Lesson Overview 22.1 What is a Plant?

Characteristics of Plants What do plants need to survive?

Characteristics of Plants What do plants need to survive?   The lives of plants center on the need for sunlight, gas exchange, water, and minerals.

The Plant Kingdom Plants are classified as members of the kingdom Plantae.   Plants are eukaryotes that have cell walls containing cellulose and carry out photosynthesis using chlorophyll a and b. Photosynthesis – The process of using light energy to power a series of chemical reactions that combine water and carbon dioxide to form carbohydrates, such as glucose

Cellulose – The tough fiber that makes up the cell wall of plants Cell Wall – The outer layer of a plant cell that gives structure and protection to the cell

What Plants Need All plants have the same basic needs: sunlight, a way to exchange gases with the surrounding air, water, and minerals.

Sunlight Plants use the energy from sunlight to carry out photosynthesis.   Leaves are typically broad and flat and are arranged on the stem so as to maximize light absorption.

Gas Exchange Plants require oxygen to support cellular respiration, as well as carbon dioxide to carry out photosynthesis.   Plants must exchange these gases with the atmosphere and the soil without losing excessive amounts of water through evaporation. Cellular Respiration – The breakdown of sugars into useable energy for the cell

Water and Minerals Land plants have evolved structures that limit water loss and speed the uptake of water from the ground.   Minerals are nutrients in the soil that are 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.

The History and Evolution of Plants How did plants adapt to life on land?

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

Origins in the Water The ancestors of today’s land plants were water-dwelling organisms similar to today’s green algae.   Although not as large and complex as many plants, green algae have cell walls and photosynthetic pigments that are identical to those of plants. Green algae also have reproductive cycles that are similar to plants. Studies of the genomes of green algae suggest that they are so closely related to other plants that they should be considered part of the plant kingdom.

The First Land Plants The greatest challenge that early land plants faced was obtaining water. They met this challenge by growing close to the ground in damp locations.   Fossils suggest the first true plants were still dependent on water to complete their life cycles. One of the earliest fossil vascular plants was Cooksonia, shown here.

The First Land Plants Several groups of plants evolved from the first land plants.   One group developed into mosses. Another lineage gave rise to ferns, cone-bearing plants, and flowering plants.

An Overview of the Plant Kingdom The relationship of plant groups is shown below Algae Moss Ferns Cone- Flowering Bearing Plants