Transcript Plant Structure

Lecture # 16
Date _____
• Chapter #35~
Plant Structure and
Growth
Seed Plants
• There are two categories of seed producing
plants:
▫ Gymnosperms (conifers)
▫ Angiosperms (flowering plants)
Angiosperms
• Angiosperms (flowering plants) can also be
divided into two groups based on the amount of
cotyledons
▫ Monocots (1 cotyledon)
▫ Dicots (2 cotyledons)
Monocot vs. Dicot
• Cotyledons – storage tissue that provides nutrition to
the developing seed
Monocot
Dicot
- one cotyledon
- 2 cotyledons
Monocot vs. Dicot
• Leaf Venation – the pattern of veins on leaves
Monocot
Dicot
- parallel
- netted (branching
pattern)
Monocot vs. Dicot
• Flower Parts– number of petals, sepals, stamen, and
other flowering parts
Monocot
Dicot
- in multiples of 3s
- in multiples of 4s & 5s
Monocot vs. Dicot
• Vascular Bundles– arrangement of bundles of
vascular tissue (xylem & phloem) in stems
Monocot
Dicot
- scattered
- organized in a circle
Monocot vs. Dicot
• Root– form of root
Monocot
Dicot
- fibrous system
(a cluster of many fine roots)
- taproot
(a large single root)
Plant Tissues
The entire plant (leaf, stem and root) are composed of 3 major
types of tissue groups:
• 1) Ground Tissues – includes 3 types of cells that differ
only by their cell walls
▫ Parenchyma cells are the most common and have thin walls and
serve in a variety of roles including storage, photosynthesis, and
secretion
▫ Collenchyma cells have thicker walls and provide support for the
plant
▫ Sclerenchyma cells have the thickest walls and provide support
Plant tissues
• 2) Dermal Tissues – consist of epidermis cells
that cover the outside of plant parts and protect
it from water loss and bacterial invasion. These
cells can also secrete waxy protective substance
called cuticle
Plant Tissues
• 3) Vascular Tissues – is a network of cells that run from
root to shoot. It consists of two major tissues, xylem
and phloem. They usually occur together as a vascular
bundle.
▫ Xylem
 Tubes that draw water UP from roots to
the entire plant
 has two types of cells for conducting water
(tracheids & vessels)
 has 2 cell walls for added support
 Most xylem are “dead” at maturity,
essentially they are just the left over cell
walls
Plant Tissues
• 3) Vascular Tissues – is a network of cells that run from root
to shoot. It consists of two major tissues, xylem and
phloem. They usually occur together as a vascular bundle.
▫ Phloem
 Tubes that draw sugar down from leaves
to the entire plant
 has two types of cells for conducting sugar
sieve tubes & companion cells)
 The sieve tubes are chains of cells that
allow materials to be transported
 Companion cells lie parallel to sieve tubes
and provide the molecular needs of the
sieve tube
The seed
• A seed consists of an embryo, a seed coat, and
some type of storage material (endosperm or
cotyledons
•The top part of the embryo (epicotyl)
becomes shoot tip
•Attached to the epicotyl are tiny leaves
called plumule
•The hypocotyl is the shoot that connects
epicotyl to the cotyledons
•sometimes a radicle is present, which
becomes the roots
*in monocots, there is an extra protective
layer for epicotyl called the coleoptile
Germination
• Most seeds reach maturity and remain dormant until cues are
encountered
• The most common cue is water
• Others may be temperature, light, etc.
•Germination begins with absorption of
water
•The water initiates enzymes, which activate
cellular respiration
•Water also cracks open the seed coat
•Hypocotyl and radicle starts to eloongate
creating the shoot and roots
•This vertical growth is termed primary
growth
•Plants can also go through secondary
growth which is growth horizontally
creating layers of cork and bark
Roots
•Primary growth in roots leads to specialized tissues
1) epidermis lines the outside surface of the roots. this layer has hairs that
help absorb water. As it grows, older layer protect the root
2) cortex cells formt eh bulk of the root. It functions to store starch. It also
has a spaces between cells to allow for oxygen to reach cells for cellular
respiration
3) endodermis is a ring of cells called the Casparian Strip which creates a
waterproof layer to control water entering the plant
4) vascular cylinder AKA stele in the endodermis and is made of xylem
and phloem. The very center is called the pith
Stems
•The tissues in the stem are similar to the root, with the
Casparian Strip missing (for water absorption)
•Epidermis contains cells covered in cuticle (waxy
substance)
•Cortex contains cells that contain a lot of chloroplasts
•Vascular Cylinder contains xylem, phloem and pith
(arrangement differs between dicots and monocots).
Generally the xylem and phloem come in bundles with the
xylem being inner and phloem being outer. A layer of cells
separate the xylem and phloem called the cambium
Leaves
• A typical leaf is made of several layers of cells
•Epidermis protects the outside by producing cuticle (waxy). The cuticle may
also function to reduce transpiration (loss of water due to evaporation)
•Palisade mesophyll is made of parenchyma cells with a ton of chloroplasts.
This layer has the most surface area and is where photosynthesis primarily
occurs
•spongy mesophyll is parenchyma cells with air pockets to provide CO2 to
photosynthesizing cells
•Guard cells are epidermal cells that control the openign and closing of the
stomata
•Vascular bundles consist of xylem and phloem.
Transport of Water
•Water and dissolved minerals enter the root by osmosis
•The movement of water to the center of the root follows two pathways
•Apoplast is when water moves between cell walls
•Symplast is when water moves through cells (when water reaches the
endoplast, this is the only way to travel through xylem
•In general, there are 3 mechanisms for water to move
through plant:
•Osmosis is the movement of water through
membranes of high concentration to lower
concentration. This creates root pressure which
forces water up through xylem
•Capillary action is caused by adhesion in a tube
(forcing water up)
•Cohesion-Tension Theory is the idea where water is
transpired, which creates a pressure. This pressure is
relieved by water being cohesive and pulling up
neighboring molecules, creating an entire bulk flow
Transport of Sugar
•Translocation is the movement of carbohydrates through
the phloem from source (leaves) to sink (site of utilization)
•Translocation is described by pressure-flow hypothesis
•Sugar enters sieve-tube members
•Water enters sieve-tube members
•Pressure builds from water entering,
forcing water and sugar to move in
bulk flow
•When sink is reached, the sugars are
used, relieving pressure and
diffusing water out
Control of Stomata
•The opening an closing of stomata controls gas exchange, sap
production, and photosynthesis rate.
•Each stomata (hole) is surrounded by guard cells that swell to
close the stomata and shrink to open the stomata
•OPEN: transpiration, loses water, CO2 can enter
photosynthesis occurs
•CLOSED: keeps water, no CO2 entering, “technically” no
photosynthesis occurs
•Some factors control the opening and closing
•Closed when temperatures are high
•Open when CO2 levels are low
•Closed at night
•Open in the day
Plant Hormones
Hormones are substances produced by specialized cells to
influence the physiology of target cells
•Auxin promotes plant growth by facilitating the
elongation of developing cells
•Gibberellins promotes plant growth in the roots and
shoots
•Cytokinins are a group of hormones that stimulate
cytokinesis (cell division)
•Ethylene is a gas that promotes the ripening of fruit
•Abscisic Acid is a growth inhibitor. It delays growth and
causes scales in preparation for winter
Plant Response to Stimuli
•Tropsim is a growht pattern in response to environmental
stimuli
•There are 3 types of Tropism in plants
•Phototropism is a plant’s response to light. It uses the
hormone Auxin to grow in the direction of light
•Gravitropism is the response to gravity by stems and
roots. It uses Auxin and Gibberellins to always grow
roots and shoots in a vertical direction
•Thigmotropism is response to touch. This stimuli is
what allows vines to climb object
Photoperiodism
•Photoperiodism is th plant’s response to photoperiod
(legnth of daylight and night)
•Many flowering plants initiate flowering in response to the
photoperiod
•Long-day plants flower in the spring and early
summer (when daylight is incerasing)
•Short-day plants flower in the late summer and early
fall (when daylight is decreasing)
•Day-neutral plants do not flower in response to
daylight. They respond to other cues like water and