20.1 Origins of Plant Life UNIT 16: PLANTS Chapters 20-22 L.14.7

20.1 Origins of Plant Life

• UNIT 16: PLANTS

• Chapters 20-22

• L.14.7


KEY CONCEPT Plant life began in the water and became adapted to land.


Land plants evolved from green algae. • Plants and green algae have many common traits.

– both are photosynthetic eukaryotes – both have the same types of chlorophyll – both use starch as a storage product – both have cell walls with cellulose


• Genetic analysis points to the common ancestor of all plants.

– extinct green algae species– modern species are still common in lakes and ponds


• Important plant characteristics likely originated in algae

– multicellular body allowing for specialization of cells and tissues


– Ancestral algae lived in areas of shallow water.

• True plants evolved through natural selection.

– Those that could survive longer dry periods were favored.

– First true plants probably grew at edges of water.– True plants have embryos that develop while attached

to female parent. (seeds!)


• True plants evolved through natural selection.


Plants have adaptations that allow them to live on land. • Challenges of living on land have selected for certain

plant adaptations.• A cuticle allows plants to retain moisture.

– waxy, waterproof layer

– holds moisture in


• Stomata are tiny holes in the cuticle.

stoma

– can open and close– allow air to move in and out


• A vascular system allows resources to move to different parts of the plant.

sugars

water and mineral nutrients

– specialized tissues– brings water and mineral nutrients up from roots

– disperses sugars from the leaves – allows plants to grow higher off the ground


• Lignin allows plants to grow upright.

– hardens cell walls of some vascular tissues– provides stiffness to stems

plant cells

lignin


• Pollen grains allow for reproduction without free-standing water.

– pollen grains contain a cell that divides to form sperm

– pollen can be carried by wind or animals to female structures


• A seed is a storage device for a plant embryo. – seed coats protect

embryos from drying wind and sunlight

– embryo develops when environment is favorable

– (moisture, temperature, etc just right)


KEY CONCEPT Plants have specialized cells and tissue systems.

21.1: Plant Cells & Tissues


Plant organs are made of three tissue systems.

• Dermal tissue covers the outside of a plant. – protects the plant – secretes cuticle of leaves – forms outer bark of trees



– provides support – stores materials in roots and stems

• Ground tissue is found inside a plant.



stem

leaf

root

– two networks of hollow tubes – xylem transports water and

minerals UP from the roots to the rest of the plant

– phloem transports photosynthetic products DOWN from the leaves to the stems & roots

• Vascular tissue transports water, minerals and organic compounds.



KEY CONCEPT The vascular system allows for the transport of water, minerals, and sugars.

21.2: The Vascular System


– water vapor exits leaf stomata– helps pull water to the top

branches

• Transpiration is the loss of water vapor through leaves.

21.2: The Vascular System


KEY CONCEPT Roots and stems form the support system of vascular plants.

21.3: Roots & Stems


Roots anchor plants and absorb mineral nutrients from soil. • Roots provide many

functions.– support the plant– absorb, transport,

and store nutrients

21.3: Roots & Stems


Stems support plants, transport materials, and provide storage. • Stems have many functions.

– support leaves and flowers – house most of the vascular system – store water

Baobab trees

Cactus

21.3: Roots & Stems


– grow underground for storage

Ginger rhizomes

Potato tubers



21.3: Roots & Stems


– grow underground for storage



– form new plants

Strawberry stolons

21.3: Roots & Stems


• Some stems are herbaceous and conduct photosynthesis.

21.3: Roots & Stems


• Some stems can be woody, and form protective bark.


KEY CONCEPT Leaves absorb light and carry out photosynthesis.

21.4: Leaves


– Stomata open and close when guard cells change shape.

– When stomata are open, water evaporates and gas exchanges.

– Stomata close at night and when plant loses too much water.

guard cells stoma

• Guard cells surround each stoma.21.4: Leaves


• READ BUT DON’T COPY• Leaves may be simple, compound, or double compound.

Simple leaf Compound leaf Double compound leaf


• READ BUT DON’T COPY• Leaf veins may be parallel or pinnate.

Pinnate veinsParallel veins

21.4: Leaves


• READ BUT DON’T COPY• Leaf margins may be toothed, entire, or lobed.

Toothed margin Entire margin Lobed margin

21.4: Leaves


– for extreme temperatures, ex: pine needles

READ BUT DON’T COPY•Leaves have many adaptations.

21.4: Leaves


• READ BUT DON’T COPY• Leaves have many adaptations.


– for water loss,ex: cactus spines

21.4: Leaves


– for aquatic environments, ex: water lily

– for getting food,ex: Venus’ flytrap

• Leaves have many adaptations.


– for water loss,ex: cactus spines

21.4: Leaves


KEY CONCEPT Reproduction of flowering plants takes place within flowers.

22.2: Reproduction in Plants


sepal

Flowers contain reproductive organs protected by specialized leaves. • Sepals and petals are modified leaves.

– Sepals are outermostlayer that protectsdeveloping flower



• A stamen is the male structure of the flower.

– produces pollen grains

stamen

filament anther



carpel style

stigma

ovary

• The innermost layer of a flower is the female part (carpel).

– ovary produces female gametophyte (“egg”)



Flowering plants can be pollinated by wind or animals.

• Flowering plants pollinated when pollen grains land on stigma.

• Wind pollinated flowers have small flowers and large amounts of pollen.



• Pollination occurs when a pollen grain lands on a stigma.

pollen tubepollen tube

spermsperm

stigmastigma

– one cell from pollen grain forms pollen tube– other cell forms two sperm that travel down tube



endosperm

seed coat

embryo

– one sperm fertilizes the egg

– other sperm unites with polar nuclei, forming endosperm

– endosperm provides food supply for embryo

• Flowering plants go through the process of double fertilization.


• Each ovule becomes a seed.

• The surrounding ovary grows into a fruit.


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20.1 Origins of Plant Life UNIT 16: PLANTS Chapters 20-22 L.14.7