Transcript plant form and function

PLANT FORM AND FUNCTION
Angiosperm Structure
– Monocotyledons a.k.a. monocots
(newer still)
Have a single seed leaf
- Dicotyledons and/or
Eudicotyledons a.k.a. eudicots
(newest)
Have double seed leaves
Palms and Bananas are Monocots
Rice, wheat, corn – all monocots
Monocots vs. Dicots
Basic Angiosperm Morphology
• Reproductive structures in order simplest to
most complex- sperm, pollen, anther, flower,
and plant.
• Seeds-seed coat protects and keeps seed
from drying out.
• Fruit-protects seeds, helps with seed
dispersal, and is a food source for many
organisms. (do not aid in pollination).
• Shoot system= stems and leaves
• Root system= tap root and lateral roots
Plant Morphology
•Stems consist of alternating “nodes”, the
site of leaf attachment
•The angle created where the leaf
attaches to the stem is called the axil
•The axil contains an axillary bud, which
can give rise to a lateral shoot or a branch
•The tip of the shoot is called the apex
and holds the terminal bud
•The terminal bud and the apex is where
the elongation of the shoot occurs
•The apical bud inhibits the growth of the
axillary buds - therefore the advent of the
practice of pruning
Purpose of roots
• The entire root structure
serves to anchor the
plant/tree in the soil
• Absorption of water and
nutrients from the soil
actually occurs only at the
tips of each root fiber
• Millions of tiny roots hairs
in these tip areas help
absorption by increasing
surface area
Fibrous vs. Tap Roots
• Seedless vascular
plants (ferns) and
Moncot angiosperms
such as grasses
have fibrous roots
• Dicot angiosperm
have tap roots
Adventitious Roots
Roots that grow out of the stem or trunk - sometimes for
extra support, sometimes for vegetative reproduction
Other modified roots
• Aerating roots (or
pneumatophores): roots
rising above the ground,
have a large number
pores for exchange of
gases.
• Buttress roots are large
roots on all sides of a tall
or shallowly rooted tree.
Typically they are found in
rainforests where soils are
poor so roots don't go
deep. They prevent the
tree from falling over and
help gather more
nutrients.
More modified roots
• Storage Roots:
Beets, radish, turnip,
horseradish, sweet
potato, and cassava
(tapioca).
Types of leaves
Single and double compound leaves
Compound Leaves
Simple Leaves
Modified leaves
• Spines on cacti
are actually
leaves. The
photosynthesis is
carried out by the
green stems
• Bracts on
poinsettias are
actually not
petals, but leaves
around the tiny
yellow flowers
Tendrils for grasping
LEAF STRUCTURE
Where most
photosynthesis occurs.
Review of the typical Plant Cell
Major Plant Cells
• Parenchyma cells
• Collenchyma cells
• Sclerenchyma cells
– Fibers
– Schlereids
• Water-conducting cells of the Xylem
– Tracheids
– Vessel elements
• Food-conducting cells of the Phloem
– Sieve-tube members
– Companion cells
Parenchyma cells
• Typical plant cell – most abundant in plants
• Thin walled (Walls contain cellulose, not lignin)
• Unspecialized – can either photosynthesize, or store starch
– Can be found in leaves – contain chloroplasts and carry out
photosynthesis (mesophyll cells are an example)
– Can also be found in roots and other non-photosynthesizing parts and
store starch in amyloplasts (related to chloroplasts) – in stems they are
called the pith
amyloplasts
chloroplasts
Collenchyma cells
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•
•
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These cells are usually just under the epidermis of leaves, stems and roots
Collenchyma cells are collectively also called the cortex
Cells are columnar in shape
Also lack lignin in their cell walls, but have thicker walls than parenchyma
cells
Give younger plants or plant parts support
Because they have thick walls but lack lignin, they are able to provide support
without restricting growth – hence found in young, growing parts
Parenchyma
Columnar
Collenchyma
Collenchyma
Epidermis
Sclerenchyma cells
• Thick walls that are fortified with lignin
(secondary wall) making them much more
rigid than collenchyma walls
• Mature sclerenchyma cells usually do not
contain protoplasts and cannot
grow/elongate, so these cells are located
in regions of the plant that have stopped
growing
Sclerenchyma cont’d.
•
Two types of sclerenchyma cells:
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Fibers - long and thin, exist in bundles in stems,
right above above vascular tissue
Sclereids – shorter than fibers and give nutshells
and seed coats their hardness. The gritty texture of
certain fruit like pears is basically due to sclereids
scattered among the parenchyma tissue
Xylem Cells
• Xylem conducts water and minerals
up from the roots
• Elongated
• Produce lignin-containing secondary
walls
• Lack protoplasts after maturity
• Two types:
– Tracheid cell – spindle-shape, with
pits in which water passes from
tracheid cell to tracheid cell.
– Vessel element cells are broader
and lie end to end and form
continuous hollow tubes for water to
flow through
Phloem Cells
• Transports sugar down from the leaves.
• Two types:
– Sieve-tube cells –conducting cells of the phloem
tissue.
– Companion cells – connected to sieve-tube cells,
contain nuclei and ribosomes, so help maintain sievetube cells
Sieve-tube elements and companion
cells of the Phloem
Three Tissue System
• The cells we have learned about in the
past slides such as parenchyma, sieve
tube cells, etc. can be placed into 3 main
tissue categories or systems:
– Dermal tissue system
– Vascular tissue system
– Ground tissue system
Three Tissue System, cont’d.
Tissue System
and Its Functions
Dermal Tissue System
• protection
• prevention of water loss
Ground Tissue System
• photosynthesis
• food storage
• regeneration
• support
• protection
Vascular Tissue System
• transport of water and
minerals
• transport of food
Component Tissues
Epidermis
Periderm (in older
stems and roots)
Parenchyma tissue
Collenchyma tissue
Sclerenchyma tissue
Xylem tissue (Tracheids
and vessel elements)
Phloem tissue (Sievetube members and
companion cells)
Location of Tissue
Systems
Cross Section of a Monocot Stem
CROSS SECTION OF AN HERBACEOUS DICOT STEM
 Epidermis
Sclerenchyma
Phloem
 Collenchyma (also called
the cortex – which is ground
tissue between the epidermis
and the vascular bundles)
Vascular bundle
Xylem
A thin layer of cells called the
vascular cambium separates the
xylem and phloem
 Parenchyma or pith
Also known as the Pith in stems – stores food (amyloplasts) and water (central vacuoles)
Summary of dicot & monocot stems
(Parenchyma)
(Collenchyma)
Vascular bundles in celery
Summary of Monocot vs. Dicot Stems
Summary of monocot & dicot roots
Growth in Plants
• Animals undergo determinate growth –
they stop growing after they reach a
certain size.
• Plants on the other hand have
indeterminate growth – they continue to
grow throughout their life.
Annual, Biennials, Perennials
• Botanically, an annual plant is a plant that usually
germinates, flowers and dies in one year. (Impatiens,
sunflower, gerbera daisies)
• A perennial plant is a plant that lives for more than two
years. Perennial plants are divided into two large groups,
those that are woody and those that are Herbaceous.
(Roses, sage, peonies)
• A biennial plant is a flowering plant that takes between
twelve and twenty-four months to complete its lifecycle.
(Parsley, foxglove, sweet William)
How can plants have constant growth?
• They can have indeterminate growth
because they have perpetual embryonic
tissues (like stem cells in animals)
• These embryonic tissues are called
Meristems or cambiums.
Meristems
•
There are 2 main types of meristems (embryonic
tissues):
1. Apical meristems – they are located in the
terminal and axillary buds of shoots and root
tips
– Parenchyma cells, collenchyma cells and sclerenchyma
cells all come from apical meristems
– Herbaceous plants (non-woody) the entire plant
develops due to primary growth from apical meristems
Meristems, cont’d.
2.
Lateral meristems (also called Cambiums) – are also located
in shoots and roots, but are responsible for secondary growth
or lateral growth – they make the stems and roots thicker by
growing sideways Woody plants and trees grow in thickness in
areas where primary growth has stopped.
There are 2 types of lateral meristems:
a. Vascular cambiums: this produces secondary xylem and
phloems which are actually wood. The vascular cambium
is the source of both the secondary xylem the
secondary phloem.
b. Cork cambiums – replace the epidermis with peridermis
which is bark or cork in some trees
The main component of
Bark in terrestrial
Plants is
Phloem and cork cells
Meristems, cont’d.
Vertical growth
Vertical growth
Lateral growth 
Stomata
• Located on the ventral side of the leaf.
• Function regulation of water loss.
Plant Movement
• Tropism-are directional movement responses that occur in response
to a directional stimulus
• Phototropism – movement toward light – caused by photoreceptors
on shoot tips and auxins
• Gravitropism – response to gravity (seeds always germinate in the
right direction) – caused by plastids called statoliths that contain
dense grains of starch, in root tips and auxins
• Thigmotropism – response to touch (ivy grasping supports), caused
by ethylene
• Nastic response-plant movements that occur in response to
environmental stimuli but unlike tropic movements, the direction of
the response is not dependent on the direction of the stimulus.
These include the closing of the carnivorous Venus Flytrap leaf
when it captures prey or the folding of the mimosa leaf when it is
disturbed.
Photoperiodism
• When a plant responds to amount to light available e.g. by flowering
• Controlled by proteins called phytochromes
• Phytochrome is a photoreceptor, a pigment that plants
use to detect light. It is sensitive to light in the red and
far-red region of the visible spectrum. Many flowering
plants use it to regulate the time of flowering based on
the length of day and night (photoperiodism) and to set
circadian rhythms. It also regulates other responses
including the
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germination of seeds,
elongation of seedlings,
the size, shape and number of leaves, and
the synthesis of chlorophyll.
• Plants make several different phytochromes
Epiphytes
• Plants that attach to other plants
• Epiphytes usually derive only physical
support and not nutrition from their host,
though they may sometimes damage
the host. Hence, they are NOT parasitic
• They do this to get more light and rain
water in a rainforest canopy
Bromeliad
Orchid
Parasitic Plants
• Derive all or some nutrients from host
plant
• Parasitic plants have a modified root, the
haustorium, that penetrates the host plant
and connects to the xylem, phloem, or
both, in stems or roots of the host plant.
• Examples: Mistletoe, Dodder, Rafflesia
Parasitic Plants
Mistletoe
Japanese Dodder
Rafflesia
Carnivorous Plants
• Grow in nutrient poor soil such as bogs.
• High acidity in bogs prevents growth of muchneeded nitrogen cycle bacteria
• Most plants cannot grow in such soil
• Carnivorous plants evolved a mechanism to trap
and digest insects
• This adaptation helped them overcome the
nitrate dilemma
• Examples: Pitcher plants, sundews, Venus flytrap
Carnivorous Plants
Venus Flytrap
Sundews
Pitcher Plant
THE END