Transcript What is a Plant? - Jordan High School

UNIT 11 – BOTANY
Chapters 22 – 24
22.1: What is a Plant?
Characteristics of Plants
• Plants are eukaryotes with cell walls
containing cellulose
• Plants carry out photosynthesis
– Need sunlight, CO2, H2O, & minerals
History & Evolution of Plants
• Ancestors of modern plants were waterdwelling organisms similar to algae
• Early land plants were centimeters tall
– Grew close to the ground to obtain water
• Plant evolution:
– Became more resistant to drying out
– Capable of conserving water
22.2: Seedless Plants
Green Algae
• Fossil evidence suggests green algae were
the first plants
• Algae are in fresh or salt water, or moist
areas on land
– Most are single-celled
– Some form multicellular colonies
Mosses & Other Bryophytes
• Bryophytes—a group of plants that lack
vascular tissue
– Includes mosses, hornworts & liverworts
• Vascular tissue—tissues in plants that
carries water & nutrients
• Mosses & bryophytes are small so they can
draw up water
– Are found only in damp environments
22.3: Seed Plants
The Importance of Seeds
• Seed—plant embryo and a food supply
covered in a protective coating
• Seeds enabled plants to survive in many
environments on dry land
• Seed plants are divided into two groups:
– Gymnosperms—have seeds in cones (pines &
fir trees)
– Angiosperms—have seeds in flowers (most
plant species)
• The male gamete of plants is carried in a
pollen grain
• Pollination—transfer of pollen grain to
female ovule
• Embryo of plant contained within the seed
is protected by the seed coat
• Seeds can survive drought, cold/heat
– Embryo begins growing when conditions are
right
22.4: Flowering Plants
Angiosperm Diversity
• Angiosperms reproduce using flowers
– Flower develops into fruit to protect seeds
• Monocot—angiosperm with one seed leaf
– Ex: grasses, lilies, corn
• Dicot—angiosperm with two seed leaves
– Ex: roses, tomatoes, oak trees
• Woody plants—have thick cell walls in
stems to support plant
– Ex: trees, shrubs
• Herbaceous plants—do not have woody
stems or tissues
– Ex: dandelions, daisies
23.2: Roots
• Plant vascular tissues consist of long,
slender cells
– Xylem—vascular tissue that carries water
– Phloem—vascular tissue that carries nutrients
& carbohydrates
Root Structure &
Growth
• Root systems in
plants:
– Taproot—large
primary root (trees,
carrots)
– Fibrous root—many
roots branching from
base of plant
(grasses)
Root Anatomy
• Dermal tissue
– Epidermis protects
root
– Root hairs absorb
nutrients
• Ground tissue
– Water & minerals
move through cortex
• Vascular tissue
– Contains xylem &
phloem in the
vascular cylinder
• Root cap covers &
protects root tip
23.3: Stems
Stem Structure & Function
• Stems produce leaves, branches & flowers
• Stems transport substances throughout the
plant using xylem & phloem
• Growing stems contain nodes where leaves
are attached
• Buds—produce new stems & leaves
• Vascular bundle—clusters of xylem &
phloem in a stem
• Dicots have vascular bundles arranged in a
ring
• Monocots have vascular bundles scattered
throughout the stem
23.4: Leaves
Leaf Structure & Function
• Leaves carry out photosynthesis
• Blade—thin, flattened portion of leaf
– Attached to stem by the petiole
• Epidermis of
leaves covered
by a waxy
cuticle to limit
water loss
• Xylem & phloem
bundled in veins
of leaf
• Underside of leaf has stomata—small
openings for gas & water exchange
– Allows for transpiration—loss of water
through the leaves
Gas Exchange & Homeostasis
• Leaves take in CO2 & give off O2 during
photosynthesis
• Plants maintain homeostasis by keeping
stomata open enough for photosynthesis
while not losing water
– Guard cells—open & close stomata
24.1: Flowers
The Structure of Flowers
• Flowers bring male & female gametes
together for reproduction
• Sepals enclose the flower bud
• Petals are the colored portion of the flower
• Stamen—male parts of the flower
– Anthers—on tip of stamen; contain pollen
grains
• Carpel—female parts of the flower
– Ovary—base of carpel; contains ovules
• Pistil—tubelike structure leading from
ovary; guides pollen to ovule
– Stigma—sticky end of pistil
24.2: Fruit & Seeds
Seed & Fruit Development
• Ovaries thicken to produce fruit that
encloses seeds
• Fruits may be fleshy (ex: strawberries) or
tough & dry (ex: peanuts)
Seed Dispersal
• Dispersal by animals
– Seeds enclosed in sweet, fleshy fruit are eaten
by animals
– Seeds in animals’ feces grow in new areas
– Dry fruits with burs or hooks catch on animal’s
fur
• Dispersal by wind & water
– Seeds dispersed by wind are contained in
lightweight fruits
– Seeds dispersed by water are contained in
fruits that float
24.3: Plant Hormones
Hormones
• Hormones—chemical signals produced by
organisms that affect the growth, activity &
development of cells & tissues
• Plant hormones control development of
cells, tissues, & organs
• Auxins—hormones that stimulate cell
elongation & growth of new roots
– Auxins collect on shaded side of stem
– Cells on shaded side lengthen the stem
towards the light
Tropisms & Rapid Movements
• Phototropism—plant grows toward light
• Gravitropism—plant bends upright; roots
grow downward
• Thigmotropism—plants respond to touch
• Some plants have rapid leaf movements
(ex: Venus flytrap)