• Land plants evolved from green algae.

• Seedless, Nonvascular Plants– They grow close to the ground or on surfaces

where they can absorb water and nutrients and also rely on free-standing water for reproduction.

– Examples: liverworts, hornworts, and mosses

• Seedless, Vascular Plants– They depend on water for reproduction. – A vascular system allows these plants to grow

higher above the ground and still get materials they need from the soil.

– Examples: club mosses, whisk ferns, horsetails, and ferns

• Seed-bearing, Vascular Plants– From an evolutionary viewpoint, seed plants have

several great advantages over their ancestors.• Seed plants can reproduce without free-standing water.

They instead rely on the process of pollination.• Seeds nourish and protect plant embryos.• Seeds allow plants to disperse to new places.

• Two basic types of seed-bearing plants:– Cone-bearing Plants

• A gymnosperm is a seed plant whose seeds are not enclosed in fruit.

– A cone is the reproductive structure of most gymnosperms. It contains hard protective scales.

– Examples: cycads, ginkgo, and conifers (pines, redwood, spruce, cedar, fir, and juniper)

• Flowering Plants– An angiosperm or a

flowering plant is a seed plant that has seeds enclosed in some type of fruit.

• Classification by Seeds– A cotyledon is an embryonic leaf inside a seed. – Monocots

• Characteristics:– one cotyledon– have parallel veins in long, narrow leaves– flower parts usually occur in multiples of three– bundles of vascular tissues are scattered throughout the stem.– Examples: corn, wheat, rice, grasses, irises, and lilies

– Dicots• Characteristics:

– two cotyledons

– have leaves with netlike veins

– flower usually occur in multiples of four or five

– bundles of vascular tissue are arranged in rings

– Examples: most deciduous trees and peanuts are also dicots

• Classification by Stems– Woody Stems

• Wood is a fibrous material made up of dead cells that are part of the vascular system of some plants. Examples: Trees, shrubs, and most vines

– Herbaceous• Do not have stems made of wood.• Examples: cucumbers, cacti, and marigolds.

• Classification by Lifespan – Annual Flowering

• Plants that mature from seeds, produce flowers, and die all in one year are called annuals.

• Examples: Corn and lettuce are common annuals, as are some garden flowers such as zinnias.

– Biennial Flowering• Plants that take two years to complete their life cycle are called

biennials. • Example: Carrots

– Perennial• Any flowering plant that lives for more than two years is a

perennial.• Examples: Most woody plants, some grasses and dandelions.

• Plant tissues are made of three basic cell types.– Parenchyma Cells

• Stores starch, oils, and water for the plant.

• Help heal wounds of the plant.

• Have thin flexible walls.

• Collenchyma Cells– Provide support to a

growing plant.– Strong and flexible.

• Sclerenchyma Cells– Sclerenchyma cells are the strongest. – These cells have a second cell wall made of lignin, which

makes these cells very tough and durable, but rigid.– Die when they reach maturity.

• Plant organs are made of three tissue systems.– Dermal Tissue System– Covers the outside of a plant– protects the plant

– secretes cuticle of leaves – forms outer bark of trees

• Ground Tissue System– Ground tissue provides

support and stores materials in roots and stems.

– In leaves, ground tissue is packed with chloroplasts, where photosynthesis makes food for the plant.

• Vascular Tissue System– The system of vascular tissue

transports water, mineral nutrients, and organic compounds to all parts of the plant.

• Made up of two networks of hollow tubes.– Xylem:carries

water and dissolved mineral nutrients.

• The cohesion-tension theory proposes that the physical properties of water allow the rise of water through a plant.

• Phloem: carries minerals and sugars out of the leaves to stems and roots.

• Parts of Plants– Roots

• Roots support the plant and absorb, transport, and store nutrients.

• root cap covers the tip• apical meristem is an area

of growth• vascular cylinder contains

xylem and phloem

– Fibrous root systems have fine branches.

Fibrous root Taproot

• There are two main types of roots.

– Taproot systems have one main root.

• Stems have many functions. – support leaves and flowers – house most of the vascular system – store water – Grow underground for storage– Form new plants

• Secondary growth increases a plant’s width.

• Primary growth increases a plant’s length.

• Tree Rings– Tree rings form due to uneven growth over the

seasons. In spring, if water is plentiful, new xylem cells are wide and have thin walls. These cells appear light in color. When water becomes more limited in the following months, xylem cells are smaller and have thicker walls, so they appear darker in color. These two growth together make up one ring. The age of a tree can be determined by counting these annual rings.

• Leaves– The blade is usually broad and flat, and it

collects the sunlight for the plant. – The blade connects to the stem by a thin stalk

called the petiole.

• The dermal tissue of many leaves is covered a cuticle, a waxy, waterproof layer that helps hold in moisture.

• In most plants, the top and undersides of leaves have different functions.– The upper portion of the leaf has

most of the chloroplasts and is where most photosynthesis takes place.

– The underside portion of a leaf has tiny holes in the cuticle, called stomata. Guard cells allow stomata to close to prevent water loss, or to open to allow air to move in and out. Without stomata, the movement of air would be prevented by the cuticle.

• Plants complete their life cycle by alternating between two phases. – Diploid Phase: plant produces

spores. – Haploid Phase: plant produces

gametes.

• Life cycle phases look different among various plant groups.– Life Cycle of Nonvascular Plants: Moss

• Nonvascular plants have a dominant gametophyte (haploid) phase is dominant and require water to reproduce.

• Life Cycle of Seedless Vascular Plants: Ferns– The sporophyte (diploid) phase is dominant phase.

• Sori are clusters of sporangia (spore-producing sacs) that are found on the underside of the fern leaf.

• A mature sporophyte is called a fiddle head.

– Life Cycle of Seed Plants: Conifers• The sporophyte (diploid phase) is the dominant

phase.– Produce two types of spores that develop into male and

female gametophytes (pollen is produced in male cones, while eggs are produced in female cones).

» Pollination occurs in a cone-bearing plant when a pollen grain reaches the small opening of an ovule in the female cone. After pollination, eggs are produced inside the ovule and a pollen tube begins

• Life Cycle of Seed Plants: Flowering Plants– Flowers contain reproductive

organs protected by specialized leaves.

• The outermost layer of a flower is made up of sepals. Sepals are modified leaves that protect the developing flower.

• Petals are the modified leaves inside of sepals. Their bright colors often help to attract animal pollinators.

• Flowers can be a single sex or contain both.• A stamen is the male structure of a flower.

– The stamen includes:• filament (holds up anther)• anther (produce pollen)

stamen

anther

filament

– The female structure is called a carpel.• Flowers can have several carpels fused together called

a pistil.• Structure of pistil:

– stigma (sticky; where pollen lands)– style (tube that leads to ovary)– ovary (female reproductive structure)

pistil

stigma

style

ovary

• Flowers allow for more efficient pollination than occurs in most gymnosperms, which rely on wind for pollination.

» Insects and other animals feed on pollen or nectar and transfer pollen when feeding.

• Fertilization takes place within the flower.– Pollination– One cell in the pollen grain grows into a pollen tube

that extends toward the ovule.– The other cell in the pollen grain divides by mitosis,

producing two sperm that travel down the pollen tube. One fertilizes the egg.

– The other sperm combines with the polar nuclei to become a cell with a triploid (3n) nucleus that will become the endosperm, a food supply for the developing plant embryo.

• The process is called double fertilization which only happens in flowering plants.

• Fruits and Seed Dispersal– The function of fruit in flowering plants is to help

disperse seeds to eliminate competition with parents.

• Animals, wind, and water can spread seeds.– Examples:

» Bird eats a blackberry and defecates out the seed away from the bush.

» Dog gets burr in fur and scratches it off in a new location.

» Dandelion fluff is actually a fruit with a seed attached and is spread by the wind.

» Coconuts float thousands of miles across oceans and arrive on different islands.

• Seeds will not grow until conditions are favorable. This period before growth is called dormancy.– Examples: Strawberry seeds remain dormant until their

seed coats are weakened in the digestive tract of an animal. Other seeds have waterproof seed coats that can only be cracked by winter ice.

• When a seed begins to grow it is called germination.– Embryo takes up water and

breaks out of seed coat.– Seedling growth begins.– Enzymes are activated

inside the seed to help digest the endosperm.

• Plants can reproduce asexually with from a fragment of a stem, leaf, or root.– Example: prickly pear

cactus

• Vegetative reproduction is a type of asexual reproduction in which stems, leaves, or roots attached to the parent plant produce new individuals. – Example: aspen trees

• A hormone is a chemical messenger produced in one part of an organism that stimulates or suppresses the activity of cells in another part. When a hormone meets the right receptor, it triggers a response.– Gibberellins are plant hormones that

produce dramatic increases in size. – Ethylene a plant hormone that

causes ripening and is naturally produced by fruits.

– Auxins are plant hormones involved in the lengthening of plant cells.

• Plants can respond to light, touch, gravity, and seasonal changes. These responses are called tropisms.– Phototropism is the tendency of a plant to

grow toward light.

– Thigmotropism is the response of plants to touch.

– Gravitropism is the response to Earth’s gravitational pull.

• Plants take signals from the changing lengths of day and night throughout the year, in a response called photoperiodism. – Shorter days and longer nights during the fall help trigger

the leaves of many deciduous trees to change color. This response is part of the preparation for winter, when these trees enter a stage of dormancy.

• Mutualisms– A mutualism is an interaction

between two species in which both species benefit.

• Examples: – plant roots and fungi (mycorrhizae)– plant roots and bacteria (legumes)– plants and pollinators (orchid and

moth).

• Commensalism– Symbiosis where 1 species

benefits.

• Plant-Herbivore Interactions– Plants have a variety of adaptations that

discourage animals from eating them.• spines (cacti, roses)• defensive chemicals (poison ivy, natural

pesticides).

• Leaf Adaptations– In desert climates

leaves are adapted to minimize water loss.

• Cacti leaves are actually the sharp spines that protect them from predators and help minimize water loss due to transpiration.

• Agave plants store water in their leaves.

– In cold, dry climates, leaves are minimized to prevent damage from the cold.

• Pine needles are leaves with a small surface area and a thick, waxy epidermis that protects them from cold damage.

– In aquatic environments, plant leaves are adapted for gas exchange or movement of water.

• The water lily has stomata on the upper surface of its leaves.

• Many aquatic plants also have flexible petioles adapted to wave action.

– In tropical climates, plants leaves are adapted to combat the competition for light, space, and nutrients.

• Many tropical plants have very large, broad leaves to allow for more photosynthesis.

• A few plants are actually predators to supplement nitrogen in low nutrient environments.