Transcript Plant Structure - GLENEAGLESBIOLOGY

VCE BIOLOGY UNIT ONE
Chapter Four
Plants
Dr Adrian Mascia
Plant Structure
Plants can be divided into 2
systems
1.
The Shoot system (above
ground) – stem, leaves,
reproductive organs
2.
The Root system (below the
ground) – roots and root hairs
Inputs and outputs
Plant Tissues
•
There are 4 main types of plant tissues
1.
2.
3.
Meristematic Tissues (tissue undergoing mitosis)
Dermal tissue (Outer layer)
Vascular Tissue (Tissues responsible for transport of
water and nutrients)
Ground Tissue (All internal cells other than vascular
tissue)
4.
Meristematic tissue
•Meristematic tissue is composed of cells undergoing
Mitosis
•These cells are found at the tips of roots and shoots in a
plant and in a ring around the inside of stems and branches
•Meristems are the only places that growth occurs in a
plant
•Some meristem cells differentiate after divison and make
up the other 3 primary tissues
Dermal Tissue
• Outer most layer of the
plant
• Acts as a skin preventing
abrasion, invasion from
other organisms and
controlling water loss
• On leaves and stems
usually produce a waxy
cuticle to prevent water
loss
Ground Tissue
• Consist of a variety of cells
• Functions include storage, support and
photosynthesis
• Examples include fleshy portions of
apples, pears, potatoes
Vascular Tissues
• Transport tissues including xylem and
phloem
• Xylem = Water transport
• Phloem = Nutrient transport
• Circulatory system of the plant
Xylem
• Xylem is water conducting tissue that carries
water from the roots to the rest of the plant
• When the cells mature, they die, leaving behind
hollow cells
• In some flowering plants xylem vessels have
open ends and are arranged end to end forming
long continuous tubes
• Wood is composed entirely of xylem tissue and
provides the main support for most large plants
• (Figure 4.11, Nelson, Pg 89)
Phloem
• Unlike Xylem cells, mature phloem cells
are living
• Form sieve tubes (long thin cells with large
pores arranging themselves end to end)
• Used for the transport of sugars from the
roots to the tips of the plant
• (figure 4.11, Nelson, Pg 89)
Interactions between Xylem and Phloem
• Sucrose moves into the
sieve cells, causing water
to move across from the
xylem to the Phloem via
osmosis
• Sieve cells a re controlled
by companion cells as
they have no nucleus or
mitochondria
ROOTS
2 Types of roots
1. Tap roots: Large
tapering main root with
only slender, short side
branches. Capable of
burrowing very deep
into the ground e.g.
Eucalypts, daisies,
orchids
2. Fibrous roots: Many
small roots of about
equal size, do not grow
deeply, rather spread
out e.g. Grasses
Purpose of roots
• Anchorage
• Provide large surface
area to collect water
and nutrients from the
soil (presence of root
hairs greatly increases
this surface area (by up
to 130 times)
Root Hairs
• Root hairs penetrate
between soil particles,
coming in close contact
with the soil water
• Water from the soil is able
to pass from the soil
through the plasma
membrane of the root hair
through osmosis
• Minerals enter through
the plasma membrane
through diffusion and
active transport
Root Pressure
• How does the water
make its way all the way
to the top of the tree?
• As the water is taken in
by the roots it moves
into the xylem. As the
thin tubes of the xylem
fills, that water column
within the plant goes
higher and higher
• The thin yet strong
structure of the tubules
in the xylem allow a
‘water columns’ or
transpiration streams to
form
Leaf Structure
• Location / shape
/ orientation are
all designed to
take in
maximum
amount of
sunlight
• (large surface
area to volume
ratio, at the top
of the plant, lean
towards the sun)
INTERNAL LEAF STRUCTURE
•
•
•
•
•
Xylem and phloem
Cuticle: waxy covering which is
impermeable to water. Prevents water loss
through evaporation
Upper Epidermal layer: several stomata
pores present in this layer. Protective
function
Palisade cells: Type of chloroplast,
elongated cells directly beneath the
epidermis, collectively called the palisade
mesophyll (site of photosynthesis)
Spongy mesophyll: Fills the leaf from the
palisades down to the lower epidermis,
contains large amounts of free space which
can be used for water storage, some
chlorophyll present (usually moisture
saturated)
Large amount of space within the mesophyll
means that there are large areas of cell walls
exposed for diffusion
Stomata: Small opening through the
epidermis and cuticle
Allows the diffusion of CO2 into photo
synthetic tissue
Stomata & Guard Cells
• Guard cells: border the stomata. When they
swell with water the stomata opening becomes
exposed, when low in water they constrict closing
the stomata opening
• A greater number of stomata are found on the
underside of a leaf as this prevents exposure to
sunlight, thus lowering water loss.
Special ways of obtaining nutrients
in plants
•
As spoken about earlier, most plants actively transport minerals into their
systems through the root hairs, however some soils are mineral deficient, so
plants have adapted other means of getting these nutrients.
•
Nitrogen Fixing Bacteria can often work in a relationship with plants, The
plant provides a home for the bacteria, whilst the waste product of the
bacteria (nitrogen) is supplied to the plant
•
Plants living in Humus rich soil have developed an association with a
fungus, causing increased surface area to absorb nutrients
•
Others have the ability to break down Humus into soluble nutrients, some
of which can be used by the plant.
•
Other plants are Carnivorous and devour insects as a means of obtaining
vital nutrients not supplied by soil
Distributing energy around a plant
•
Energy made from photosynthesis is
stored as sugars. These sugars need
to be distributed from the leaves where
it is made, to the rest of the plant.
•
This process is called Translocation
•
Sugars are actively pumped (energy
comes from mitochondria in companion
cells) from their storage site into the
phloem, causing water from the xylem
to move via Osmosis into the phloem.
•
This creates a sugary solution that can
travel around the plant via the phloem
to areas which require energy
Removing Waste in plants
• There are several methods plants use to dispose of waste
• Transported to the leaves or bark, which are then dropped off,
removing the substance from the plant
• Store as crystals or dissolved in the vacuoles.
• Store in non living tissue
• Exude resins, fats, waxes- e.g. latex from rubber tree (Other
substances include excess salt, gases, etc)