Selected Plant Topics

Chapters 23 – 25

Specialized Tissues in Plants

23 -1

Seed Plant Structure • Three of the principal organs of

seed plants are roots, stems, and leaves

Roots• Absorb water and dissolved

nutrients

• Anchor plants in the ground

• Hold soil into place and prevent erosion

Stems• Support above ground parts of plant

• Transports nutrients

Leaves• Main photosynthetic systems

• Let in oxygen and carbon dioxide

Vascular Tissue• Forms a transport system that

moves water and nutrients throughout the plant

Types of vascular tissue

• Xylem – brings water and nutrients up from the roots

• Phloem – brings food down from the leaves

Leaf Structures and Functions

• Mesophyll – where photosynthesis happens

• Palisade mesophyll – closely packed, lots of chloroplasts

• Spongy mesophyll – loose tissue with many airspaces

• Stomata – pore-like openings in the underside of the leaf

• Allow CO2 and O2 to diffuse in and out of the leaf

Guard Cells• Control the opening and closing of

the stomata by responding to changes in water pressure

Transpiration• The loss of water through its

leaves

Gas Exchange• If stomata were kept open all the time, water

loss due to transpiration would so great that few plants would be able to take in enough water to survive.

• Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose too much water.

• The stomata open and close in response to changes in water pressure in the guard cells

• When pressure is high – stomata open

• When pressure is low – stomata close

Q: What time of day do you think stomata are open and why?

A: Daytime, cause that’s when photosynthesis happens

24 – 1 Reproduction with Cones and Flowers

Life Cycle of Gymnosperms

• Reproduction in gymnosperms takes place in cones

• Male cones produce – pollen grains

• Female cones produce – ovules

Structure of Flowers• Flowers are reproductive organs

that are composed of 4 kinds of specialized leaves

Sepals• Enclose the

bud before it opens, leaf-like

Petals• Brightly colored, attract insects to

flower

Stamen• Male reproductive

structure of flower, made of 2 parts

• Filament – long, thin, stalk that supports the anther

• Anther – makes pollen grains

Anther

Filament

Anther + Filament = Stamen

Pistil• Female reproductive structure,

made of 3 parts

Stigma• where pollen

grains land, sticky

Style• Connects stigma to ovary

Style

Ovary• swollen base of

the pistil where ovules are formed

Ovary

Pollination• Most gymnosperms and some

angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals

• Insect pollination is beneficial to insects and other animals because it provides them with food

• Plants also benefit because this method of pollination is more efficient

Q: What kind of symbiotic relationship is this?A: Mutualism

25 – 1 Hormones and Plant Growth

• In plants, the division, maturation, and development of cells are controlled by a group of chemicals called hormones

Hormones

• A substance that is produced in one part of the organism and affects another part of the same organism

Target Cell• The portion of an

organism affected by a particular hormone

Auxins• Discovered by Charles Darwin

and his son

• They were trying to explain phototropism

Phototropism• The tendency for plants to grow

toward light

• Auxins are produced in the apical meristem and are transported downward into the rest of the plant

• They stimulate cell elongation

Gravitropism• The response of a plant to gravity

Auxin Like Weed Killers• High concentrations of auxins can

inhibit growth, so scientists have produced many auxin like compounds to be used as herbicide

• Ex.) Agent Orange

Cytokins• Plant hormones that stimulate cell

division, the growth of lateral buds and cause dormant seeds to sprout

• Cytokins often produce effects opposite to those of auxins

Gibberellins• Promote growth, particularly in

stems and fruits

Ethylene• Stimulate fruits to ripen

25 – 2 Plant Responses

tropisms• The response of plants to external

stimuli

• Ex.) gravitropism and photoperiodism

Thigmotropism• Growth in response to touch

Rapid Responses• Some plant responses do not

involve growth, they are so rapid it would be a mistake to call them tropisms

• Ex.) sensitive plant, venus fly trap

Sensitive Plant

Venus Fly trap

Photoperiodism• The way a plant responds to periods of

light and darkness• Short day plants – flower when days

are short• Long day plants – flower when days

are long• Photoperiodism in plants is responsible

for the timing of seasonal activities of plants

Dormancy • The period during which an

organism’s growth and activity decrease or stop

• As cold weather approaches deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves from the rest of the plant