Transcript Plant Unit: part 2

Plantae 2
Botany –the study of plants
This unit primarily a study of Angiosperms
- Plant parts and tissues (roots, stems and leaves)
- Flowering Plant Reproduction
Meristematic Tissue
Unlike animals, plants only
divide in specific areas called
meristems
 Meristems found at the
tips of roots and stems
are called apical meristems
and produce the most rapid growth
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Root and stem lengthening is
called primary growth
More Meristematic Tissue
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Cork cambium produces the outer covering of
stems
Vascular cambium produces vascular tissue
and increases the thickness of stems over time.
Pericycle enables roots to grow thicker and
makes it possible for roots to branch
Secondary growth is the increase in diameter
Most herbaceous monocots don’t experience
secondary growth while all woody plants do
Plant Tissue Types

Plant cells differentiate into
three kinds of tissue :
epidermal, vascular and
ground
There are also three main types of
cells used to make these tissues
 Parenchyma is the thin walled cell
found throughout a plant
 Sclerenchyma cells have tough thick
walls and are used to strengthen and
support plant tissues
Collenchyma is mainly a developmental
support cell and we won’t address it
in this unit
Epidermal tissue
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Epidermal tissue,
like the skin on us,
protects plants
from parasites
and from water
loss, except in the
roots were it
facilitates water
entry.
Tightly packed epidermal cells
Vascular Tissue
Vascular tissues
include xylem and
phloem
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Xylem consists of
tracheids and vessel
elements (usually dead
when mature)
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Phloem cells are
called sieve tube
members ( alive when
mature, no nucleus)
Ground tissue
Ground tissue is usually
made up of parenchyma.
 When found at the
center of roots and
stems it’s called pith.
 Important functions of
ground tissue is to
support vascular tissue
and store food and
water.
CS of stem
Roots, Stems and Leaves
Sun Energy
6CO2 + H2O
C6H12O6 + 6O2
Every developmental adaptation of roots, stems and
leaves is a slave to this formula.
Roots gather water, stems hold up leaves to the sun
that have adapted to take in carbon dioxide to
produce the energy the rest of us need to live.
Roots
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Anchor the plant
Absorb water and minerals
from the soil
Store food that is produced
in the leaves
Two types : fibrous and
taproot
Roots
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Roots are
composed of
three structures :
epidermis,
cortex and
vascular cylinder
Roots
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The epidermis contains
root hairs which greatly
increase the surface area
of the root system and
increase the plants
capacity to absorb water
Roots
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The cortex is mostly parenchyma with an inside layer
of endodermis that controls water flow into the
vascular cylinder using active transport of minerals
Vascular Cylinder
Monocots and Dicot roots have different vascular
cylinders
MONOCOT
DICOT
Stems
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Stems transport food,
water, and minerals
between the roots and
leaves and support
plant growth above
ground, exposing
leaves to the sun.
Stems have four types of
tissue : Parenchyma (pith),
vascular, cambium (vascular
and cork), and cork tissue
(bark)
The arrangement of vascular
tissue differs between
monocots and dicots
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Herbaceous stems- with
little or no secondary
growth these stems are
partially supported by
turgor pressure, the
pressure of water in the
vacuoles.
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Woody stems exhibit
secondary growth
adding another ring of
xylem each year
Leaves
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Leaves are the original
solar collectors
They need sun, water
and CO2 to make our
food and so they
maximize their surface
area (thin and flat) to
maximize the result.
Leaves
Leaves are made up of epidermis, vascular tissue and
ground tissue ( mesophyll) like all plant parts.
Epidermis
The epidermis is
responsible for
balancing the need for
water in the leaf with
the need for air, which
evaporates the water.
 Cutin, a waxy
substance, is secreted
to slow evaporation
 Stomata, openings
found on the bottom of
the leaf, control gas
exchange and water
loss.
Epidermis
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Guard cells control the opening of the stomata,
closing and opening as needed.
Mesophyll
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The mesophyll, or middle part of the leaf ,contains the most important
factory on the planet.
The vascular bundle is also found in the mesophyll
The mesophyll is made up of two kinds of parenchyma , the palisade
layer and the spongy layer.
Leaves and Water Loss
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Transpiration is evaporation of water through
the stomata .
Temperature ,humidity and wind speed all
affect the rate of transpiration
The unique polar characteristics of water
causes it to exhibit both cohesion and adhesion
This transpiration pull allows water to move
up large trees at the rate of as much as 100
gallons a day with little energy use.
Reproduction in Flowering Plants
Flowers come in a variety of
shapes ,smells ,colors and
odors designed to attract
pollinators of all kinds.
Fertile Flower Parts
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Stamens are the male part
of a flower. They consist of
two parts called the
filament which holds up the
anther were pollen is
produced.
The pistil is the female part
and is made up of the style,
stigma and ovary which
contains the ovules where
the egg cells are produced.
Sterile Flower Parts
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The receptacle is the base of
the flower.
The sepals enclose the flower
bud and collectively form the
calyx which protects the
ovary.
Petals are the colorful
fragrant part that protect the
pistil and stamens.
Collectively the petals form
the corolla.
Kinds of Flowers
Fertilization
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The tube cell forms the pollen tube , while the
generative cell divides and in a process called
double fertilization forms a zygote and a
triploid (3N) endosperm.
The endosperm normally provides food for the
embryo unless we eat it in the form of corn or
wheat or rice.
Seeds and Fruit
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When fertilized the
ovule becomes a seed
As the seeds mature
inside it the ovary
ripens.
A ripened ovary is a
fruit which contains
seeds.
Fruits
Fruits can be dry (nuts,
burrs or winged) or fleshy
( peaches apples and berries)
 Simple fruits form from a
single ovary
 Aggregate fruits form from
flowers that have many
pistils on the same flower.
 Multiple fruits are single
fruits that grow so close
together they form a single
structure.
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Seed Dispersal
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Fleshy fruits attract
animals and are
dispersed by them
Dry fruits can be food
for animals or they can
have hooks or claws that
facilitate their dispersal
Some seeds are
dispersed by air or
water
Environmental Influences
Many plants are photoperiodic-they respond
through pigment called phytochrome to a
critical dark period.
A long day plant produces flowers in the
summer
A short day plant produce flowers in the spring
and fall
Plant Hormones
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Auxins stimulate elongation of cells
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Gibberellins stimulate rapid growth
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Cytokinins stimulate cell division
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Ethylene (a gas) stimulates fruit ripening
Tropisms and Nastic Movements
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Phototropism is the
movement toward or away
from light
Geotropism is the positive
or negative response to
gravity
Nastic movements are
rapid turgor pressure
movements caused by a
stimulus