Plants dominate life on Earth, and are typically green.
What Do Plants Need to Survive?
Plants are rooted and need adaptations to survive.
The lives of plants depend upon sunlight, gas exchange, water, and minerals.
Sunlight
Plants use sunlight for energy through photosynthesis.
All plants show adaptations for gathering sunlight.
Without sunlight, they can’t make food, so sunlight is essential to a plant’s life.
Gas Exchange
Plants need oxygen for cellular respiration.
They also need carbon dioxide for photosynthesis.
Plants exchange gases with the atmosphere to survive and grow.
Water and Minerals
Water is a key material for photosynthesis.
Plants absorb water and minerals from the soil using special tissues to carry water and minerals throughout the plant.
These structures allow plants to thrive on land.
Checkpoint: Why are plants not found in deep underground caves?
Caves usually lack sunlight.
The History and Evolution of Plants
Early life was mostly in oceans, lakes, and streams.
Photosynthetic prokaryotes added oxygen to the atmosphere and provided food for other life forms.
Land plants came much later in Earth’s history.
Origins in the Water
Ancestors of land plants lived in water and were similar to today’s green algae.
Some were unicellular, others multicellular.
Green algae are now classified in the plant kingdom.
The First Land Plants
First land plants appeared 472 million years ago.
Plants like Cooksonia were small and leafless.
They grew close to the ground in damp places.
They adapted to draw water and resist drying out.
The demands of life on land favored the evolution of plants that were able to draw water from the soil, resist drying out, and reproduce without water.
How Plants Changed Earth
Land plants created new ecosystems.
Organic matter from plants helped form soil.
Mosses evolved from early land plants.
Other plants gave rise to ferns, cone-bearing plants, and flowering plants.
An Overview of the Plant Kingdom
All plants are eukaryotes with cellulose cell walls.
They use chlorophyll a and b for photosynthesis.
The plant kingdom has five major groups, based on embryos, tissues, seeds, and flowers.
Importance of Four Key Features
Embryos develop within plants for protection.
Water-conducting tissues allow plants to grow taller.
Seeds protect embryos and help them spread.
Flowers and fruits give flowering plants a reproductive advantage.
Checkpoint: What are the five major groups in the plant kingdom?
Green algae, mosses and relatives, ferns and relatives, cone-bearing plants, and flowering plants.
The Plant Life Cycle
Plants alternate between diploid and haploid phases.
The life cycle of plants has two alternating phases – a diploid (2N) phase and a haploid (N) phase.
This cycle is called alternation of generations.
Alternation of generations: life cycle that has two alternating phases – a haploid (N) phase and a diploid (2N) phase.
Sporophytes and Gametophytes
Diploid sporophytes produce spores by meiosis.
Sporophyte: spore-producing plant; the multicellular diploid phase of a plant life cycle.
Haploid gametophytes produce eggs and sperm.
Gametophyte: gamete-producing plant; multicellular haploid phase of a plant life cycle.
Fertilization and New Sporophytes
Gametes fuse during fertilization to form a zygote.
The zygote develops into a new sporophyte.
The life cycle then repeats itself.
Trends in Plant Evolution
Gametophytes have become smaller over time.
Sporophytes have increased in size.
Mosses have large gametophytes, small sporophytes.
Seed plants have tiny gametophytes and large sporophytes.
Ch 22.2 - Plant Diversity
Key Questions
What are the characteristics of green algae?
What factor limits the size of bryophytes?
How is vascular tissue important?
What adaptations allow seed plants to reproduce without standing water?
Vocabulary
Bryophyte
Vascular tissue
Archegonium
Antheridium
Sporangium
Tracheophyte
Tracheid
Xylem
Phloem
Seed
Gymnosperm
Angiosperm
Pollination
Ovule
Early Seedless Plants
Earliest land plants were seedless and small.
Restricted to damp environments for reproduction.
Many groups of seedless plants still exist today, thriving through unique adaptations.
Green Algae
Algae aren't a single group of organisms.
Green algae are part of the plant kingdom, sharing features with larger plants: photosynthetic pigments \& cell walls.
Mostly aquatic, found in fresh/salt water or moist areas.
The First Plants
Green algae appeared well before land plants.
Fossils from 550 million years ago show mats of green algae, dating to the Cambrian Period.
Early green algae shared traits with complex plants.
Life Cycle of Green Algae
Switch between haploid and diploid phases.
Chlamydomonas reproduces asexually by mitosis when conditions are good.
Switches to sexual reproduction in unfavorable environments.
Haploid and diploid stages alternate like land plants.
Multicellularity in Green Algae
Spirogyra:
Forms threadlike colonies with stacked cells.
Volvox:
Forms hollow spheres with up to 50,000 cells.
Colonial Algae gives insight into multicellular plant evolution.
Checkpoint: How do green algae get moisture and nutrients?
They absorb water and nutrients directly from their surroundings.
Mosses and Other Bryophytes
Mosses grow in cool, damp forests, forming green carpets.
They have waxy coatings and rhizoids to resist drying out.
Rhizoids anchor mosses and absorb nutrients from soil.
Bryophytes include mosses, hornworts, and liverworts.
Bryophytes: group of plants that have specialized reproductive organs but lack vascular tissue; includes mosses and their relatives.
Bryophyte Characteristics
Among the first land plants to evolve.
Grow from embryos and have reproductive organs.
Lack vascular tissue, limiting their size and distribution.
Vascular tissue: specialized tissue in plants that carries water and nutrients.
Found mainly in damp environments due to water dependence.
The lack of vascular tissue limits the height of most bryophytes to just a few centimeters.
Life Cycle of Bryophytes
Display alternation of generations.
Gametophyte is dominant and performs most photosynthesis.
Sporophyte grows from gametophyte and depends on it.
Sporophyte contains a capsule (sporangium) that produces spores.
Sporangium: spore capsule in which haploid spores are produced by meiosis.
Reproduction in Bryophytes
Spores grow into green filaments that form gametophytes.
Gametophytes produce eggs in archegonia and sperm in antheridia.
Archegonia: structure in plants that produces egg cells.
Antheridia: male reproductive structure in some plants; produces sperm.
Sperm can swim through water to reach eggs.
Fusion forms a diploid zygote that grows into a sporophyte.
Sporophyte Development in Bryophytes
Zygote develops into a sporophyte attached to gametophyte.
Sporophyte produces spores in the sporangium by meiosis.
When mature, the capsule opens and releases spores.
Spores are dispersed by wind, starting the cycle again.
Checkpoint: Identify evidence that supports the claim that the gametophyte carries out most of a bryophyte’s photosynthesis.
The sporophyte grows out of the body of the gametophyte and is dependent on it for water and nutrients, indicating this cannot be the primary source of photosynthesis.
Ferns and Their Relatives
Early plants lacked vascular tissue and were short.
About 420 million years ago, vascular tissue evolved.
Allowed plants to grow much taller than before.
Ferns, horsetails, and club mosses are examples of vascular plants.
Evolution of a Transport System
Tracheophyte: vascular plant.
Named after tracheids, specialized water- conducting cells.
Tracheid: hollow plant cell in xylem with thick cell walls strengthened by lignin.
First true vascular plants could grow high above the ground.
Vascular Tissues
Xylem: vascular tissue that carries water upward from the roots to every part of a plant.
Phloem: vascular tissue that transports solutions of nutrients and carbohydrates produced by photosynthesis through the plant.
Importance of Vascular Tissues
Vascular tissues enable plants to move fluids against gravity.
Vascular tissues–xylem and phloem–make it possible for vascular plants to move fluids through their bodies against the force of gravity.
Limits on water transport cap plant height at about 130 meters.
Seedless Vascular Plants
Include ferns, horsetails, and club mosses.
Ferns are most numerous with around 11,000 species.
Ferns have roots, rhizomes, and large leaves called fronds.
Prefer wet or seasonally wet habitats and low light areas.
Life Cycle of Ferns
Diploid sporophyte is the large fern plant we recognize.
Spores form on the underside of fronds and grow into gametophytes.
Gametophytes are heart-shaped and independent from sporophyte.
Fertilization requires water for sperm to swim to eggs.
Checkpoint: Why are ferns able to grow so much taller than bryophytes?
Ferns have vascular systems that provide structural support and allow for water to be moved from roots throughout the plant against gravity. Bryophytes do not have vascular systems.
Seed Plants
Seeds contain a plant embryo and food supply in a protective coat.
Allow plants to colonize dry environments on land.
Seed: plant embryo and a food supply encased in a protective covering
The embryo is a young diploid sporophyte.
Seeds enable long-term survival until conditions are right.
The First Seed Plants
Seed plants first appeared about 360 million years ago.
Fossils show several evolutionary stages in seed development.
DNA evidence links modern seed plants to common ancestors.
Adaptations that allow seed plants to reproduce without standing water include a reproductive process that takes place in cones or flowers, the transfer of sperm by pollination, and the protection of embryos in seeds.
Seed Plant Adaptations
Seed plants use cones or flowers for reproduction.
Pollination replaces water-based fertilization.
Sperm are transferred by wind or animals, not swimming.
Embryos are protected inside seeds from drying out.
Cones and Flowers
Male and female gametophytes mature inside cones or flowers.
Cones:
Gymnosperms produce seeds on cone scales.
Flowers:
Angiosperms bear seeds inside flowers with protective tissue.
Angiosperms include most crop and fruit plants.
Gymnosperms
Gymnosperms mean 'naked seeds', exposed on cone scales.
Gymnosperm: group of seed plants that bear their seeds directly on the scales of cones.
Include pines, spruces, firs, and cycads.
First seed-bearing plants in the fossil record, dominating large forests of North America today.
Angiosperms
Angiosperm: any of a group of seed plants that bear their seeds within a layer of tissue that protects the seed; also called flowering plant.
Flowering plants that protect seeds inside fruits.
Include grasses, fruit trees, and crop plants like wheat and corn.
Reproductive structures include flowers and fruits.
Flowers attract pollinators, aiding reproduction.
Pollen
Pollen grains contain the male gametophyte.
Sperm do not swim; they are carried by wind or animals.
Pollination transfers pollen to female structures.
Fertilization leads to the formation of seeds.
Pollination: transfer of pollen from the male reproductive structure to the female reproductive structure.
Seeds
Seeds protect embryos with a tough outer coat.
Allow survival through extreme conditions like cold and drought.
Contain food supply for the developing embryo.
Sprout when conditions are favorable for growth.
The Life Cycle of a Gymnosperm
Gymnosperms produce pollen cones (male) and seed cones (female).
Male cones produce pollen grains via meiosis.
Female cones develop ovules with female gametophytes.
Fertilization produces a zygote that becomes a seed.
Pollen Cones and Seed Cones
Pollen cones release pollen in large quantities in spring.
Pollen grains land on female cones and grow pollen tubes.
One sperm fertilizes the egg inside a female gametophyte.
Ovules: structure in seed cones in which female gametophytes develop.
Fertilized egg develops into an embryo within the seed.
Pollination and Fertilization in Conifers
Pollination involves pollen capture by female cones.
Pollen tube grows to female gametophyte for fertilization.
Zygote forms into an embryo, protected by the seed coat.
The seed is eventually dispersed to grow a new plant.
Ch 22.3 - Flowers, Fruits, and Seeds
Key Questions
How are different angiosperms classified?
What are flowers?
How does fertilization in angiosperms differ from fertilization in other plants?
What is vegetative reproduction?
How do fruits form?
Vocabulary
Ovary
Fruit
Cotyledon
Monocot
Dicot
Embryo sac
Pollination
Double fertilization
Endosperm
Vegetative reproduction
Dormancy
Germination
Flowering Plants Dominate the Land
Flowering plants dominate the land and are the most abundant in the plant kingdom.
Their reproductive strategy contributes to their success.
Angiosperms
First appeared during the Cretaceous Period (135 million years ago).
They originated on land and dominate Earth's plant life.
They produce reproductive organs called flowers.
Their ovaries develop into fruits after fertilization.
Ovaries: in plants, the structure that surrounds and protects seeds.
Fruit: structure in angiosperms that contains one or more matured ovaries.
Angiosperm Classification
Originally classified by number of seed leaves (cotyledons).
Cotyledons: first leaf or first pair of leaves produced by the embryo of a seed plant.
Monocots: angiosperm with one seed leaf in its ovary.
Dicots: angiosperm with two seed leaves in its ovary.
Recent studies reveal more complex relationships. Amborella and water lilies are basal angiosperms.
Angiosperm Diversity
Differ in number of seed leaves and stem structures.
Angiosperms differ in the number of their seed leaves, the strength and composition of their stems, and the number of growing seasons they live.
Can live for one or more growing seasons.
Farmers and botanists classify them by physical traits. Iris is a monocot; nonwoody and long- lived.
Monocots and Dicots
Monocots include corn, wheat, lilies, orchids, and palms.
Dicots include roses, clover, tomatoes, oaks, and daisies.
Differ in flower parts, leaf veins, and vascular bundles.
Monocots are especially important for food crops.
Woody and Herbaceous Plants
Woody Plants:
Have thick cell walls (trees, shrubs, vines)
Provide structural support
Herbaceous Plants:
Have nonwoody stems (dandelions, petunias)
Typically smaller and flexible
Annuals, Biennials, and Perennials
Annuals complete their life cycle in one season.
Biennials take two years to complete their life cycle.
Perennials live and grow for many years.
Life spans depend on genetics and the environment.
Checkpoint: How do woody plants differ from herbaceous plants?
Woody plants are made primarily of cells with thick cell walls that support the plant body. Herbaceous plants do not produce true wood, and therefore have non- woody stems.
Flower Structure
Flowers bring gametes together and protect embryos.
Attract pollinators with color, scent, and shape.
Pollinators carry pollen from flower to flower.
Pollination increases reproductive efficiency.
Flowers are reproductive organs that are composed of four different kinds of specialized leaves: sepals, petals, stamens, and carpels.
Sepals
Sepals protect the flower bud before it opens.
Petals attract pollinators with bright colors and petals usually fall off after pollination.
Losing petals can aid reproduction by focusing on seeds.
Stamens
Stamens are the male parts of flowers.
Each stamen has a filament and an anther.
Anthers produce pollen grains, the male gametophytes, which are the yellow dust seen on flowers.
Carpels
Carpels produce female gametophytes and seeds, forming a broad base called the ovary, which contains ovules.
Style connects ovary to stigma, which captures pollen.
Single or multiple carpels form pistils.
Checkpoint: Make a two-column table with the columns labeled Male and Female. Then list and define the structures that make up a flower in the appropriate column.
Male Female
Stamen Carpel
Anthers Style
Filaments Stigma
Ovary
Ovule
Both:
Sepal, petal
Variety in Flowers
Flowers vary in color, size, and shape.
Some plants have separate male and female flowers.
Composite structures can mimic single flowers, attracting a wide variety of pollinators.
Checkpoint: How might it be an advantage for a plant to have many flowers clustered in a single structure?
Sample Answer: Having many flowers clustered together might improve each flower's chance of being pollinated by a pollen-carrying insect that touches the cluster.
The Angiosperm Life Cycle
Alternation of generations: diploid sporophyte and haploid gametophyte.
Male gametophytes (pollen grains) develop in anthers and female gametophytes develop in carpels’ ovules.
Sporophyte generation dominates life cycle.
Male Gametophytes
Pollen grains develop inside anthers.
Meiosis produces haploid spore cells.
Generative and tube cells form the gametophyte.
Protected by a thick wall from damage.
Female Gametophytes
Develop inside ovules within carpels.
Meiosis produces four haploid cells; three disintegrate, and the remaining cell forms an embryo sac with seven cells and eight nuclei.
Embryo sac: female gametophyte within the ovule of a flowering plant.
Egg cell becomes the zygote if fertilized.
Pollination
Pollen transfer to female flower parts.
Pollination: transfer of pollen from the male reproductive structure to the female reproductive structure.
Most angiosperms rely on animal pollinators with adaptations attract animals (bright colors, nectar).
Insects and animals ensure efficient pollination.
Pollination Adaptations
Hummingbirds have long beaks for deep flowers.
Bees collect pollen and nectar for food.
Plants benefit from targeted pollen transfer.
Pollination dependency can make plants vulnerable.
Fertilization
Pollen grain grows pollen tube into ovary.
Generative cell divides into two sperm cells.
One sperm fertilizes egg; other forms endosperm.
Double fertilization produces zygote and endosperm.
Double Fertilization
Double fertilization: process of fertilization in angiosperms in which the first event produces the zygote, and the second produces the endosperm within the seed.
Zygote forms new plant embryo and triploid endosperm nourishes developing seed.
Endosperm: food-rich tissue that nourishes a seedling as it grows.
Efficient use of energy—no seed without fertilization, which is a key reason for angiosperms’ evolutionary success.
The process of fertilization in angiosperms is distinct from that found in other plants. Two fertilization events take place–one that produces the zygote and the other that produces the endosperm within the seed.
Checkpoint: What are the products of double fertilization?
The endosperm nucleus and the zygote.
Vegetative Reproduction
Vegetative reproduction: method of asexual reproduction in plants, that enables a single plant to produce offspring that are genetically identical to itself.
Vegetative reproduction is the formation of new individuals by mitosis.
It does not require gametes, flowers, or fertilization, and produces genetically identical offspring quickly.
Used by horticulturists for cloning plants.
Natural Vegetative Reproduction
Occurs in many plants like strawberries and potatoes.
Offspring grow from runners, tubers, or cuttings. Allows rapid colonization of favorable environments because there is no need for seed formation.
Grafting
Used to reproduce seedless or difficult plants.
Stem or bud attached to another plant’s stem, and works best with closely related plants.
Combines desirable traits from different plants.
Checkpoint: Describe how asexual reproduction might allow a plant to become rapidly established in a new area.
Answer: Plants that reproduce asexually can grow quickly because they do not follow the complex life cycle of pollination, fertilization, and development from seeds.
Fruits and Seeds
Angiosperm seeds protected by fruit, and fruit develops from thickened ovary walls.
Fruits can be fleshy (grapes) or dry (peanuts).
Seeds develop inside fruits, often with animals aiding dispersal.
Fruit and Seed Development
Fertilization triggers nutrient flow to support the embryo. As angiosperm seeds mature, ovary walls thicken to form a fruit that encloses the developing seeds.
Ovary wall thickens into a fruit, and fruits may be sweet or tough, attracting animals at ripening.
Seeds develop and mature inside fruits.
Seed Dispersal
Fleshy fruits attract animals to eat them, and seeds pass through digestive systems unharmed.
Dispersal reduces competition with parent plant, and animals help distribute seeds to new areas.
Seed Dispersal by Wind and Water
Wind Dispersal:
Dandelions use parachute structures.
Spreads seeds far from parent plants
Water Dispersal:
Coconuts float for long-distance travel
Adaptations ensure dispersal over wide areas
Seed Germination
Embryos in seeds stay dormant until conditions are right.
Dormancy: period of time during which a plant embryo is alive but not growing.
Germination: resumption of growth of the plant embryo following dormancy.
Resumes growth and starts the plant life cycle.
Dormancy allows seeds to wait for ideal conditions.
First leaves (cotyledons) unfold and provide nutrients.
Germination Conditions
Some seeds require cold periods to break dormancy, and timing is crucial for successful growth.
Seeds germinate when temperature and moisture are optimal, ensuring seedlings grow at the right time of year.
Monocot and Dicot Germination
Monocots (grasses) and dicots (beans) have different germination strategies.