Plants

Unit 7 Chapters 22-25

Biology

Origin of Plants Evolved from organisms similar to

green algae First evidence in the fossil record was

around 500 million years ago Did not have any leaves Psilophytes – earliest known plant

fossil

Plant Characteristics A multicellular eukaryote Produce its own food (glucose) by way

of photosynthesis– Use chlorophyll (green pigment)

Thick cell walls made of cellulose Cuticle – waxy waterproof coating on

the stems and leaves

Needed for survival Sunlight

– Used in photosynthesis to produce food Water and Minerals Gas exchange

– Require oxygen for cellular respiration and carbon dioxide for photosynthesis

Movement of water and nutrients– Use specialized tissues (vascular tissue)

Plant Life Cycle Alternation of generation

– Two alternating phases, a diploid phase and a haploid phase

– Sporophyte Diploid phase that reproduces by asexual

spores

– Gametophyte Haploid phase that reproduces sexually by

producing gametes that fuse together by fertilization

Classification of Plants 4 groups that are based on:

– Water-conducting tissues– Seeds– Flowers

Bryophyte (Nonvascular) Ferns and allies (Seedless vascular ) Gymnosperm (Seed vascular) Angiosperm (Seed vascular flowering plant)

Bryophytes Nonvascular Plants Life cycle depends on water for

reproduction Draws up water by osmosis Include: mosses, liverworts, and

hornworts

Bryophyte Types Mosses

– Most common bryophyte– Rhizoids – long, thin cells that anchor

them in the ground and absorb water and minerals from the soil

Liverworts– Gemmae – small multicellular

reproductive structures used in asexual reproduction

Bryophyte Life Cycle Gametophytes

– Dominant recognizable stage– Carries out most of the plant’s

photosynthesis– Antheridia – produce the sperm (male)– Archegonia – produce the egg (female)

Sporophyte– Depends on the gametophyte for water

and nutrients

Vascular Plants Contain specialized tissue that conducts water and

nutrients throughout the plant (vascular tissue) Tracheids – tubular cells that are specialized to

conduct water; dead at maturity Xylem – transport subsystem that carries water

upward from the roots Phloem – transports solutions of nutrients and

carbohydrates produced in photosynthesis– Sieve tube element – main phloem cells that are

surrounded by companion cells

Vascular Plants Roots – underground organs that

absorb water and minerals Stems – supporting structures that

connect roots and leaves; carry water and nutrients between them

Leaves – photosynthetic organs that contain one or more bundles of vascular tissue (veins)

Ferns and Allies: Seedless Vascular Plants

Include club mosses, horsetails, and ferns Ferns

– Rhizomes – creeping or underground stems– Fronds – large leaves of ferns.

Life cycle of ferns– Diploid sporophyte is the dominant stage– Sporangia – tiny containers of haploid spores– Sori – group or cluster of sporangia

Seed Plants Divided into 2 groups

– Gymnosperms Bear their seeds directly on the surfaces of

cones Include: conifers, cycads and ginkgoes

– Angiosperms (Flowering plants) Bear their seeds within a layer of tissue that

protects the seed Include: grasses, flowering trees and shrubs,

and all wildflowers and cultivated flowers

Adaptations of Seed Plants

Reproduce free from water by the use of:– Flowers and cones

Cones are the seed bearing structure of gymnosperms

Flowers are the seed bearing structures of angiosperms

– Transfer of sperm by pollination Pollen grain – tiny structure that contains the entire

male gametophyte Pollination – transfer of pollen to the female

structure; can be transferred by wind, insects or small animals

Adaptations of Seed Plants

– Protection of embryos in seeds Seed – an embryo of a plant that is encased

in a protective covering (seed coat) and food supply (cotyledons); may have structures that aid in its dispersal

Embryo – an organism in its early stage of development

Angiosperms – Flowering Plants

Flowers– Reproductive organ; contains ovaries that

surround and protect the seed Fruit

– Wall of tissue surrounding the seed– Used to attract animals to disperse their

seeds

Parts of a Flower Sepals and Petals

– Outermost floral parts that protect the developing bud– Petals – brightly colored to attract vectors

Stamens – Male reproductive part– Consists of a thin stalk (filament) and an oval sac that

consist of pollen grains at the top (anther) Pistil (carpels)

– Female reproductive part– Consist of a broad base (ovary) that contain one or more

ovules, the stalk that comes from the ovary (style), and a sticky portion at the top (stigma) where pollen grains land

Diversity of Angiosperms 2 types: named for the number of

cotyledons in the plants embryo– Monocots (monocotyledon)

Corn, wheat, lilies, orchids, and palms

– Dicots (dicotyledon) Roses, clover, tomatoes, oaks, and daisies

Comparison of Monocots and Dicots

Monocots– Single cotyledon– Parallel veins– Flower parts are

multiples of 3– Vascular bundles

are scattered– Fibrous roots

Dicots– Two cotyledon– Branched veins– Flower parts are

multiples of 4 or 5– Vascular bundles

are arranged in rings

– Taproot

Diversity of Angiosperms Life spans are divided into 3 categories:

– Annuals Flowering plant that complete a life cycle within one

growing season Marigolds, petunias, and pansies

– Biennials Complete their life cycle in two years Primrose, parsley, and celery

– Perennials Flowering plants that live for more than two years Asparagus, many grasses, palm trees, maple trees,

and honeysuckle

Seed Plant Structure 3 principal organs:

– Roots absorb water and dissolved nutrients anchor plants in the ground Protect the plants against bacteria and fungi Hold plant upright against wind and rain

– Stems Transports nutrients between the leaves and the roots

– Leaves Photosynthetic systems of the plant

Seed Plant Structure 3 plant tissue systems:

– Dermal tissue Outer covering of a plant Consist of a single layer of epidermal cells

– Vascular tissue transport system composed of xylem and phloem

– Ground tissue Cells that lie between the dermal and vascular tissues Functions in storage, adds flexibility and strengthens

the plant

Plant Growth Most plants have an open or indeterminate

type of growth– i.e. they grow as long as they live

Meristems – clusters of tissue that are responsible for growth throughout the plants life

Meristematic tissue – undifferentiated cell that are produced by the meristems

Apical meristem – increase the length of stems and roots

Roots Function: anchor the plant and absorb water

and dissolved nutrients from the soil 2 main types of roots:

– Taproot Found mainly in dicots Primary root is long and thick Secondary roots remain small Example: oak and hickory trees

– Fibrous root No single root grows larger than the rest Help prevent erosion Example: grasses

Roots Root structure and growth

– Root hairs – tiny cellular projections that increase the surface area through which water can be absorbed

– Cortex – spongy layer of ground tissue underneath the epidermis

– Root cap – protects the root as it forces its way through the soil

Stems 3 important functions:

– Produce leaves, branches, and flowers– Hold leaves up to the sunlight– Transport substances between roots and leaves

Nodes – point of leaf attachment Internodes – regions between nodes Buds – contain undeveloped tissue that can

produce new stems and leaves

Stems Monocot and Dicot Stems

Stems Growth of stems:

– Primary growth – growth in which the plant increase in height; occurs at the apical meristems; takes place in all seed plants

– Secondary growth – growth in which the stem increases in width; occurs in the lateral meristem

Vascular cambium – produces vascular tissue Cork cambium – produces the outer covering of stems

(bark)

Leaves Structure is optimal for absorbing light

and carrying out photosynthesis Blade – thin, flattened sections of the

leaf that is attached to the stem by a thin stalk (petiole)

Functions: – Photosynthesis, transpiration, and gas

exchange

Leaves Transpiration – the loss of water

through the leaves Gas exchange occurs in the

– Stomata – porelike opening in the underside of the leaf

– Each stoma consist of two guard cells that control the opening and closing of the stomata

Transport in Plants Capillary action

– The tendency of water to rise in a thin tube

– Adhesion – is the attraction between unlike molecules; property that causes capillary action

Plant Hormones Auxins – stimulate cell elongation Cytokinins – stimulate cell division

(growth) Gibberellins – produce dramatic

increases in size in the stems and fruit Ethylene – stimulates fruits to ripen

Plant Responses Tropisms – plant responses to external

stimuli– Gravitropism – plant responses to the

forces of gravity– Phototropism – tendency of a plant to

grow toward light– Thigmotropism – response of plants to

touch

Plant Adapted for Specific Habitats

Xerophytes – plants that live in the desert biome

Epiphytes – plants that are not rooted in soil but grow directly on other plants