Plants

What are Plants?

• Multicellular eukaryotes• Have cell walls made of cellulose• Develop from multicellular embyros• Carry out photosynthesis

Evolution of Plants

• Started in water– Evolved from an organism similar to multi-cellular

algae living today

Mosses

Ferns

Cone-bearing plants

Green algae ancestor

Flowering plants

Vascular Tissue

Seeds Flowers; seeds enclosed in fruit

Nonvascular Plants

• Called bryophytes• Depend on water to

reproduce• Lack vascular tissue

(draw up water by osmosis)

• Mosses, liverworts, and hornworts

Vascular Plants• Have vascular tissue

(tissues that conduct water and nutrients throughout the plant)– Xylem: transports

water – Phloem: transports

sugar

Vascular Plants - Tracheophytes

• Ferns• Seedless plants ~ Reproduce with spores;

Need water for reproduction.• Have roots, stems, and leaves

Gymnosperms

• Vascular• Seed bearing plant• Conifers ~ Seeds are in cones.

Angiosperms

• The flowering plants.• Vascular• Bear seeds in fruits.

Vascular Plants

• 3 basic organs:– Roots– Stems– Leaves

Figure 35.2

Reproductive shoot (flower)

Terminal bud

Node

Internode

Terminalbud

Vegetativeshoot

BladePetiole

Stem

Leaf

Taproot

Lateral roots Rootsystem

Shootsystem

Axillarybud

Root

• Organ that anchors the vascular plant

• Absorbs minerals and water

• Often stores organic nutrients

Root Anatomy(cross-section)

Stem

• Organ that consists of an alternating system of nodes, the points at which leaves are attached

Stem

Leaves

• Is the main photosynthetic organ of most vascular plants

• Leaves generally consist of:– A flattened blade and a stalk– The petiole, which joins the leaf to a node of the

stem

Leaf Anatomy

• Cuticle – Waxy layer that protects leaf.

• Epidermis – Outermost layer of cells. Upper and lower.

• Palisade mesophyll ~ Hot dog shaped cells lined up like Popsicle sticks under the epidermis. Have lots of chloroplasts, and carry out most of the photosynthesis.

• Spongy mesophyll ~ Rounded, loosely arranged cells under the palisade mesophyll. Spaces between the cells allow oxygen and CO2 to circulate.

Leaf Anatomy

• Vein ~ A bundle of phloem and xylem surrounded by protective cells. This vascular tissue carries water to and from the leaf for photosynthesis

VEIN

Gas Exchange in Leaves

• Stomata – Holes in lower epidermis that allow CO2 to enter and O2 to leave.

• Guard cells – Pickle-shaped cells on each side of stoma that open and close the hole.

Plant cross-section

Turgor Pressure – Plant vocabulary

• Turgor Pressure – The pressure of water against the inside of plant cell walls.

• Turgor pressure maintains a plants shape and stiffness. As water is lost, turgor pressure decreases the plant wilts.

Nonvascular Plant ReproductionMosses produce sperm that must swim to meet the egg. Once egg and sperm meet, a spore is produced. Spores do not have a coat to protect them like seeds do, so they need moisture!

Gymnosperms

• Gymnosperms – “Naked seeds”

• Produce seeds in cones

• Leaves are needle-like

• Evergreens – don’t shed leaves seasonally.

• Pines, cedar

Gymnosperm Reproduction

1. The diploid sporophyte generation (pine tree) produces male and female cones (gametophytes)

2. The male cone produces pollen3. The female cone holds the eggs4. Pollen travels by the wind to the female cone5. The pollen and the egg meet and form a seed6. The seed grows into the sporophyte generation

(pine cone)

Angiosperms

• Angiosperms - “covered seeds”• Flowering plants• Produce seeds in fruits.• Leaves are broad• Deciduous – Lose and replace leaves

seasonally.

Flowers

• Flowers are the main reproductive organ of the plant.

• Flowers produce egg and sperm cells

• Some flowers are hermaphroditic

• Parts of the flower eventually become seeds and fruits.

Flower Anatomy

Flower Anatomy

• Pistil - Female1. Stigma: sticky portion

where pollen grains land

2. Style: stalk; pollen tube forms inside the style

3. Ovary: contains ovules

4. Ovules: produces female gametophytes

Flower Anatomy

• Stamen - Male 1. Anther: produces

pollen grains (male gametophytes)

2. Filament: supports anther

Flower Anatomy

Angiosperm Reproduction

1. The plant produces flowers 2. Flowers contain both male and female structures3. The male part of the flower releases pollen4. The pollen is carried by a pollinator to the female part of

the flower5. The pollen lands on the female part and grows a pollen

tube6. The pollen meets the egg and fertilization takes place7. The egg and sperm make a seed8. The ovary of the flower becomes a fruit to protect the seed

until it is planted

Pollination

• Process by which pollen is transferred to plants– Wind pollination: pollen is transferred via wind– Animal pollination: pollen is transferred via

animals

Seeds and Seed Dispersal

• Purpose is to protect and provide nutrition for a developing plant embryo

• Seeds are dispersed by:– Animals (contained in fleshy, nutritious fruits; pass

through animals digestive system)– Wind and water (seeds are generally lightweight)

Fruit

• As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seed