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Lesson Overview
What is a Plant?
Lesson Overview
22.1 What is a Plant?
Lesson Overview
What is a Plant?
Characteristics of Plants
What do plants need to survive?
Lesson Overview
What is a Plant?
Characteristics of Plants
What do plants need to survive?
The lives of plants center on the need for sunlight, gas exchange, water, and
minerals.
Lesson Overview
What is a Plant?
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
Lesson Overview
What is a Plant?
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
Lesson Overview
What is a Plant?
What Plants Need
All plants have the same
basic needs: sunlight, a
way to exchange gases
with the surrounding air,
water, and minerals.
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
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
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
Many plants have specialized
tissues that carry water and
nutrients upward from the
soil and distribute the
products of photosynthesis
throughout the plant body.
Lesson Overview
What is a Plant?
The History and Evolution of Plants
How did plants adapt to life on land?
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
An Overview of the Plant Kingdom
The relationship of plant groups is shown below
Algae
Moss
Ferns
Cone- Flowering
Bearing Plants