Biology II

Vascular plants have 3 tissue systems:

Dermal

Protective outer layer of plant

Vascular

Forms strands that conduct water, minerals, and

organic compounds

Ground

Much of the inside of nonwoody parts of plants

Includes roots, stems, and leaves

Green – Ground

Purple – Vascular

Tan - Dermal

Covers outside of plant’s body

Forms “skin” called epidermis

Made up of single layer of flat cells in most

plants

Often have hair-like extensions to slow water

loss by trapping moisture

Called root hairs – help increase water

absorption

Waxy cuticle protects epidermis of stems and leaves

Also prevents water loss

Made it possible for plants to live in drier

environments

Water lilies also have cuticle – protects leaves and repel

water

Cork – on woody stems and roots

Several layers of dead cells

Contains a waterproof material – not covered by cuticle

Functions in gas exchange and absorption of mineral

nutrients in addition to protection

Stomata, singular stoma permits plants to exchange

oxygen and carbon dioxide (since the cuticle does not)

Extend through cuticle and outer layer of cells

Found on at least some parts of most plants

Guard cells border each stoma

Stomata open to gain CO2 from air – also loses water

this way

When closed, plant conserves water, but photosynthesis

slows (shortage of CO2)

Why does photosynthesis

slow down when stomata

are closed?

Two kinds of vascular tissue

Xylem

Phloem

Composed of cells that are stacked end to

end like sections of pipe

Allow most vascular plants to grow much

larger than nonvascular plants

Composed of thick-walled cells that conduct water and mineral

nutrients from a plant’s roots through its stems to its leaves

At maturity, cells are dead – still has strong cell walls

Conducting cells

Tracheids

Water flows from one to the next through pits, or thin

areas in cell walls

Vessel elements

Link to form vessels

Have large perforation in ends that allow water to flow

quickly between elements

Made up of cells that conduct sugars and nutrients throughout a

plant’s body

Cells have cell wall, cell membrane, and cytoplasm

Lack organelles or have modified organelles

Conducting cells

Sieve-tube members

Link to form sieve tubes

Pores in walls connect the cytoplasms and allow

substances to pass from cell to cell

Companion cells

Contain organelles

Carry out cellular respiration, protein synthesis, and

other metabolic functions

Makes up much of the inside of nonwoody plants

Surrounds and supports vascular tissue

Most consists of thin-walled cells that remain alive and keep

their nucleus after maturity

Also contains some that do the opposite (die, thick-walled cells)

Contain many specialized structures

In leaves – packed with chloroplasts

In stems and roots – vacuoles (water storage)

In angiosperms, makes up flesh of fruits

Largely absent in woody parts of plants

Roots, stems, and leaves contain all

three tissue types

Anchor plants

Absorb water and nutrient minerals

Can function in storage of sugar and starch (organic)

Monocots – highly branched, fibrous roots

Dicots – central root, called taproot system

Has central core of vascular tissue surrounded by ground tissue

Ground tissue surrounding vascular tissue called cortex

Roots covered by dermal tissue

Epidermis covers all of root except root tip

Epidermal cells behind root tip often produce root hairs

Increase surface area

Roots hairs = extensions of epidermal cells

Mass of calls called root cap covers and protects root tip

Stems support leaves and house vascular tissue

Can be specialized for other functions

Stems of cacti store water

Potatoes stores nutrients

Leaves attach to stems at nodes

Internode – space between two nodes

Herbaceous plants – have stems that are flexible and usually

green

Vascular bundles – bundles of xylem and phloem

Surrounded by ground tissue

In dicots, bundles are in a ring

Ground tissue outside of bundles is called cortex

Pith = ground tissue inside bundles

Covered by epidermis

Stiff and nongreen

Buds produce new growth, are found at the tips of nodes

Young has central core of pith and a ring of vascular bundles

Fuse into solid cylinders as stem matures

Layers of xylem form innermost cylinder – major component of wood

Phloem lies outside cylinder of xylem

Covered by cork – protect from damage and water loss

Cork and phloem make of layers(bark) of woody stem

Wood in center is called heartwood

Provides support but no longer conducts water

Sapwood outside heartwood

Contain vessel elements that can conduct water

Primary photosynthetic organs of plants

Most have flattened portion called blade

Attached to stem by a stalk, called petiole

can be divided into 2+ sections called leaflets

Undivided leaves are simple leaves

2+ leaflets are compound leaves

Leaf is mass of ground tissue covered by epidermis

Cuticle coats upper and lower

Xylem and phloem found in veins of leaves

Veins are extensions of vascular bundles that run from tips of roots to

edges of leaves

In leaves, ground tissue is called mesophyll

Packed with chloroplasts

Most plants have 2 layers of mesophyll

Palisade layer – closely packed, columnar cells

Spongy layer – loosely packed cells

Stomata usually located in lower epidermis of leaf

Water lily – specialized for floating

Stomata on upper surface

Cactus – modified as spines

Protect plant from herbivores

Garden pea – form tendrils that climb

Venus flytrap – can catch insects

Seed develops from ovule and contains a plant embryo

Embryo contains embryonic root and embryonic shoot

Cotyledons, or seed leaves are attached to embryonic shoot

Gymnosperm embryos =2+ cotyledons

Angiosperms = monocot 1, dicot 2

Embryo within seed is in dormancy

Can remain in dormancy for thousands of years

Germination – process of plant embryo resuming growth

1st sign – emergence of root

Sprout in response to certain changes in environment

Rising temp, soil moisture, sometimes cold, fire, passing through

digestive system of animal, falling onto a rock

Must have water and oxygen penetrate seed coat

Allows seed to swell and breaks seed coat

Part of plant’s body that grows mostly

upward is shoot

Part that grows down = root

Meristems – active regions of growth

Made of undifferentiated cells, develop

into specialized tissues

Primary growth – increases length of

height

Result in primary tissues

Secondary growth – increases width of

stems and roots

Result in secondary tissues

Apical meristems – located at the tips of stems and roots

Produce primary growth via cell division

Differentiate into roots, stems, and leaves

Each plant has 2 – one at the tip of the embryonic root, and one at tip of

embryonic shoot

Makes stems and roots get longer, not wider

Primary growth would end if all cells in apical meristem

differentiated

Undifferentiated cells are left behind to produce new meristems

New meristems found at buds at base of leaves and within roots

Some undifferentiated cells left behind as stems and roots

lengthen to produce lateral meristems

Responsible for increase in width of stems and roots

Called secondary growth

Most dramatic in woody plants

Produced by cell division in two lateral meristems

Form thin cylinders near outside of woody stems and roots

Cork cambium – lies within the bark and produces cork cells

Vascular cambium

Lies just under bark and produces secondary xylem and

secondary phloem