Plants Chapters 21-23

Evolution of Plants Adapting to Land Nothing lived on land until an ozone layer formed – the ozone layer offered protection from the sun’s intense UV radiation. With life on land came adaptations for survival: Preventing water loss Reproducing by spores & seeds Abilities to transport materials throughout the plant

Preventing Water Loss Cuticle – a waxy protective covering that prevents water loss The cuticle kept water in, but kept O2 and CO2 out. Plants developed a stomata (little mouth) – a small opening in the leaf that allows for gas exchange.

Reproduction Reproduction by spores and seeds helps protect reproductive cells from drying out. spore – haploid (n) reproductive cell surrounded by a hard outer wall Seed – embryo, diploid (2n) surrounded by a protective coat endosperm – tissue that provides nourishment for the developing embryo

Transporting materials throughout the plant Vascular tissue – transports water and dissolved substances from one part of the plant to another Xylem – carries water and inorganic nutrients from the roots to the stems and leaves Phloem – carries organic compounds and some inorganic nutrients in any direction

Some plants developed woody tissue and grew to great heights This gave them an advantage in gathering light. Woody tissue Several layers of xylem Usually brown, woody stems Non-woody plants Herbaceous Soft, green stems

Classifying Plants

A Cladogram of Plant Groups Flowering plants Cone-bearing plants Ferns and their relatives Mosses and their relatives Green algae ancestor Flowers; Seeds Enclosed in Fruit Seeds Water-Conducting (Vascular) Tissue Go to Section:

Bryophytes, Seedless Plants, Gymnosperms & Angiosperms When we classify plants, what question do we first ask? Vascular or non-vascular? Let’s look at non-vascular first Bryophytes do not have vascular tissue

Bryophytes – Non-Vascular Bryophytes include: Mosses (most common) Liverworts Hornworts Help! I Need Water!!! Bryophytes have life cycles that depend on water for reproduction Since they don’t have vascular tissue, the plants draw up water by osmosis.

Dependence on water keeps bryophytes small in size Bryophytes are low-growing plants found in moist, shaded areas. Lack of vascular tissue means that bryophytes do not have true roots. Bryophytes have rhizoids – long, thin cells that anchor them to the ground and absorb water and minerals from the soil (by osmosis).

The gametophyte stage of moss Hornworts Liverworts

Reproduction For fertilization to occur, the sperm must swim to an egg. Because of this limiting factor, bryophytes must live near water. Remember, bryophytes need water to reproduce !!!

Vascular Plants Vascular plants have vascular tissue Xylem – carries water upward from the roots to every part of the plant Phloem – transports solutions of nutrients and carbohydrates produce by photosynthesis (all directions) Produce lignin – makes cell walls rigid. Allows vascular plants to grow upright and reach great heights

Vascular plants have true roots, leaves and stems Roots – underground organs that anchor plants, and absorb water and minerals Leaves – photosynthetic organs – one or more bundles of vascular tissue gathered into veins made of xylem and phloem

Stems – supporting structures that connect roots and leaves, carrying water and nutrients between them. Vascular plants have a life cycle in which the sporophyte is the dominant stage. Remember, first we ask vascular or non-vascular? Next, we ask seeds or seedless?

Seedless vascular plants Include: Whisk ferns Club mosses Horsetails Ferns (most common) Seedless vascular plants have true vascular tissue, strong roots, rhizomes (underground stems), fronds (large leaves)

The whisk fern are rare. They are usually found in tropical and subtropical regions.

The club moss is sometimes known as a ground pine.

Horsetails Tree ferns

Seed Plants We have asked vascular or not-vascular? We then asked seeds or seedless? Seed plants can be further classified: Gymnosperms (unprotected seeds on cones) Includes conifers, cycads, ginkoes, gnetophytes Angiosperms (flowering plants with protected seeds) Includes grasses, flowering trees and shrubs, wildflowers and cultivated flowers

Reproduction free from water Adaptations that allow reproduction without water Flowers or cones Transfer of sperm by pollination Protection of embryos in seeds A seed coat surrounds the embryo. It also contains a stored food supply for the embryo.

Angiosperms can be further classified: Named for the number of seed leaves (cotyledons) in the plant embryo Monocots have one seed leaf Dicots have two seed leaves

Comparison of Monocots and Dicots Single cotyledon Parallel veins Floral parts often in multiples of 3 Vascular bundles scattered throughout stem Fibrous roots Two cotyledons Branched veins Floral parts often in multiples of 4 or 5 Vascular bundles arranged in a ring Taproot Seeds Leaves Flowers Stems Roots Go to Section:

Roots, Stems and Leaves The three principle organs of seed plants are: Roots Stems Leaves

Roots Two main types of roots Taproots – found mainly in dicots Fibrous roots – found mainly in monocots Two functions of roots Anchor a plant in the ground Absorb water and dissolved nutrients from the soil

Stems Three functions of stems: Produce leaves, branches and flowers Hold leaves up in the sunlight Transport substances between roots and leaves The vascular tissue of stems lifts water from the roots to the leaves (xylem) and sends the products of photosynthesis from the leaves to other parts of the plant (phloem)

Leaves Main function is photosynthesis The broad, flat surface of leaves helps increase the amount of sunlight absorbed by plants Other functions of leaves: Transpiration Gas exchange

Connects with exterior through stomata – allows CO2 and O2 to diffuse in and out of the leaf Each stoma consists of two guard cells that control the opening and closing of the stomata by responding to changes in water pressure.

Transpiration Transpiration is the loss of water from a plant through its leaves. The water is replaced by water drawn into the leaf through the xylem vessels in the vascular tissue.

A B Evaporation of water molecules out of leaves. Pull of water molecules upward from the roots.

Gas Exchange Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water. Guard cells control the stomata through changes in water pressure. when water pressure in guard cells is high, stoma is open When water pressure in guard cells is low, stoma is closed.

In general, stomata open in the daytime, when photosynthesis is active, and close at night to prevent water loss. A plant will close its stomata any time water conservation is an issue.

Reproduction of Seed Plants Reproduction in gymnosperms takes place in cones. Pollen cones – male cone – produce pollen grains (male gametophytes) Seed cones – female cone – produce female gametophytes Gymnosperm pollen is carried by the wind to female cones (pollination)

Angiosperms Flowers are reproductive organs composed of four kinds of specialized leaves: Sepals Petals Stamen Carpels

Sepals – resemble leaves Sepals – resemble leaves. Enclose the bud before it opens; protect the flower while it is developing. Petals – often brightly colored (the pretty part). It attracts insects and other pollinators. Stamen (boy parts) anther – produce male gametophytes (pollen) filament – supports anther

Carpel (girl parts) sometimes called pistils ovary – produces female gametophytes style – stalk stigma – sticky portion where pollen lands

The Structure of a Flower Filament Anther Stigma Style Ovary Carpel Petal Sepal Ovule Stamen

Pollination Most gymnosperms and some angiosperms are wind pollinated Most angiosperms are pollinated by animals (beneficial to both plant and animal) For fertilization to occur, pollen grains land (or are carried) on the stigma of an appropriate flower. Pollen (male gametes) reach the ovary (where female gametes are made) and fertilization occurs

Seed Development & Germination Once fertilization occurs, nutrients flow into the flower tissue to support the growing embryo within the seed. As seeds mature, ovary walls thicken to form a fruit that encloses developing seeds A fruit is a ripened ovary that contains angiosperm seeds. The term “fruit” applies to any seed (even vegetables) enclosed within its embryo wall

Why do angiosperms produce fruit? Two ways seeds can be dispersed To disperse seeds Two ways seeds can be dispersed animals Typically contained in fleshy, nutritious fruits wind and water Typically lightweight Allows them to be carried in the air or float on the surface of the water

Some plants develop right away, others “wait” Environmental factors like temperature and moisture determine when a seed develops dormancy – embryo is alive but not growing germination – early growth stage of the plant embryo

Seed Germination Seed absorbs water Absorbed water causes the endosperm to swell, cracking open the seed coat Through the cracked seed coat, the young root emerges and begins to grow

Three categories of plant life spans annuals – flowering plants that complete a life cycle within one growing season biennials – complete their life cycle in two years perennials – flowering plants that live for more than two years

Concept Map Plants are categorized as Annuals Biennials Perennials that complete their life cycle in that complete their life cycle in that complete their life cycle in 1 growing season 2 years More than 2 years Go to Section:

Plant Responses The response of plants to environmental stimuli are called tropisms. Tropisms demonstrate the ability of plants to respond effectively to conditions in which they live

Light & Gravity The response of a plant to light is known as phototropism Phototropism causes a plant to grow toward a light source The response of a plant to gravity is known as gravitropism

Gravitropism Gravitropism causes the shoots of a germinating seed to grow out of the soil - against the force of gravity It also causes the roots of a plant to grow with the force of gravity and into the soil

Response to Touch The response of plants to touch is called thigmotropism. An example of thigmotropism is the growth of vines and climbing plants.

Any Questions ???