Download Chapter 11 Plant Structure and Function

Chapter 11 Plant Structure and Function
Introduction: Cell Specialization
1. Life in general
In order to carry out the basic processes of life:
• Food production (photosynthesis)
• Intake of water and nutrients
• Exchange (CO2 and O2) gases
• Distribute and store food
• Reproduction
…each organism is made up of
Specialized systems
Which are composed of
Specialized organs
Which are composed of
Specialized tissues
Which are composed of
Specialized cells
This is sometimes referred to as an Organizational Hierarchy
1
2. Plants in particular
In plants growth (cell division) occurs only in three places:
• Root apical meristem – at the tip of the root
• Shoot apical meristem – at the tip of the shoot
• Lateral meristem – an area arranged in a ring in the stem
Immediately after division, the daughter cells are undifferentiated –
that is, their fate hasn’t been decided about what kind of cell it will
become. At some point it will receive chemical messages which will
initiate differentiation. Once that has happened, its fate is
determined. (Sorta’ like stem cells)
Diagram
SILENT READING p280 -290
Seed Growth and Development
Every seed is made up of
embryo - dormant, primitive plant
cotyledons - storage
endosperm - storage
testa - seed coat
2
In each pollen grain contains two sperm to accommodate two fusion
events:
1) fertilization of egg to produce zygote
2) fusion with the polar nuclei to produce endosperm
Following fertilization, the zygote germinates rapidly but halts and
becomes dormant at some point in its embryonic stage. Meanwhile,
the cotyledons and endosperm have grown and the seed has
produced a tough, protective coat (testa). This dormancy can last
many years, with growth restarting once conditions are favourable
and the testa has softened (water presence). The embryo uses the
nutrient supply in the cotyledons/endosperm to fuel its renewed
growth. It emerges from the testa by pushing through a primary root
and shoot. The nutrient reserves continue to be used until the shoot
has pushed its way through the soil surface. Two criteria must be met
before the plant is able to start producing food on its own.
leaves must have enough chlorophyll to trap light.
roots must have enough root hairs to absorb water and nutrients.
Diagram of germinating bean.
3
Plant Tissues
There are three basic kinds of plant tissues
• ground tissues
• vascular tissues
• dermal tissues
Ground tissues
• there are three types of ground tissues:
Picture
Parenchyma
Cell Description
Function
Distribution
healing
Living
Large, thin-walled regeneration of
parts
photosynthesis
storage (food/H2O)
Throughout plant:
most common type
Collenchyma
Flexible support
Living
Long, thickened
walls
Moderately flexible
Stalks
Sclerenchyma
Dead
Stalks and testa
Strength and
support
in primary plants
Long, fibrous,
rigid
Ground tissue distribution in the roots and stem
4
Vascular tissues
• there are two systems which conduct water, nutrients and food
throughout the plant
XYLEM
PHLOEM
- water conduction
- dead at maturity
- tracheids and vessels
Tracheids
- sugars and other dissolved substances
- living cells
- seive tubes
Vessels
Seive Tubes
Dermal Tissue
epidermis - the outermost layer of cells; is similar to skin cells
• often has specialized cells embedded in it
• root hair cells
• guard cells (gas exchange)
• above ground is coated with cuticle (a waxy coat which prevents
water loss)
5
Roots
¾ taproots - large central core which grows downward with
lateral roots
¾ fibrous roots - surface roots arising from adventitious roots
(roots that grow from unusual places)
Root Growth
Figure 11.7 Nelson
6
Root Structure
Figure 11.8 Nelson
Shoots
The shoot system is made up of:
• stems
• leaves
Stems
Functions of stems:
¾ support - to hold the leaves in order to get maximum exposure
to sunlight
¾ transport - ‘trafficking’ of chemicals (and water) between roots
and leaves
¾ storage - of food for later use.
Herbaceous stems ¾ soft, green, flexible
¾ plants under 1 meter tall
7
Woody stems
¾ hard, rigid
¾ trees
Vascular Bundle Distribution
Monocot
Dicot
Stem Structure
Figure 1.14 Hopkins
8
Stem Development -The Terminal Bud
Stem Development - Trees
• primary growth - increase in height by elongation at the root
and shoot apical meristems.
• secondary growth - increase in stem thickness by addition at
the lateral meristem. (a.k.a. vascular cambium)
Figure: Hayden’s Mock-up
9
Leaf
Figure 1.16 Hopkins
Guard cell function
• Osmosis (again)
Start
100% water
Finish
Salt solution
100% water
Start
100% water
Salt solution
Finish
Salt solution
100% water
Salt solution
10
• Photosynthesis (Again)
CO2
+ H2O + sunlight ⎯→ C6H12O6
+ O2
carbon dioxide + water + sunlight ⎯→ glucose (sugar) + oxygen
Terrestrial plant leaves are faced with a huge problem. They must be
able to bring carbon dioxide into the leaf without loosing so much
water in the process that they shrivel up and die. On the underside of
leaves are specialised cells which are located on either side of tiny
holes. The holes are called stomata and these specialised cells are
guard cells.
In sunlight two things happen
1.) CO2 and H2O are converted into sugar…
…SO the concentrations of those tend to decrease within all
photosynthetic cells including the guard cells, but because the
guard cells have more chlorophyll, they tend to run out of water
faster than the rest of the leaf.
2.) Blue light from the sun causes potassium ions ( K+ ) to be pumped
into the guard cells. This causes an osmotic imbalance and H2O
follows the K+ into the sausage shape guard cells causing them to
swell. This swelling causes the guard cells to open.
At night the plant cells respire (producing CO2) which causes K+ to
leave the guard cells and again H2O leaves as well. Guard cells
shrink and close.
Figure
11
Leaf Adaptations
Environmental
Condition
Shade
Adaptation
Dry
Need for storage
Pollination
Bud protection
Transportation
Water can be transported against the force of gravity to great heights
(100 m +) This incredible feat is accomplished by a combination of
three processes.
1.) Transpiration - 90% of plant water loss is through stomatal
openings. Water is lost from leaf cells and causes an osmotic
imbalance (low water) this is replaced by the next cell, and the next,
12
and the next…A negative internal root pressure (vacuum-like) occurs.
This produces an effect quite like sucking on a straw.
2.) Capillary action - the attraction of water to surfaces. This is
caused by water tends to travel up fine tubes under this force.
3.) Cohesion - the attraction of water molecules to other water
molecules.
Together called transpiration - cohesion theory.
Food can be translocated from the leaf cells through the phloem to
the roots or any other part via osmotic imbalance. Although poorly
understood it is believed that food travels from source (where it is
made) to sink (where it is used) by the pressure - flow theory. As
food is produced at the source, there is an increase in osmotic
pressure. As food is used up at the sink, there is a drop in osmotic
pressure. Flow between the two points is due to this imbalance.
13
Plant Responses
¾ Hormonal
Hormones are powerful chemicals which are produced in one part of
an organism but cause a change in another part.
The most common plant hormones are:
Hormone
Response
auxins
inhibit/stimulate plant growth
cell elongation
apical bud growth fruit ripening
gibberellins
stem elongation and 'bolting'
cytokinins
promotes cell division especially in leaves, endosperm and fruit
abscissic acid
stomatal closure
regulates seed and bud dormancy
resistance to water stress
ethylene
fruit ripening
conversion of starches and acids to sugars
¾ Tropism
Tropism - growth or movement of a plant in response to an
environmental stimulus
Tropisms are easy to remember and understand if you remember the
following definitions and word parts:
14
positive - toward the stimulus
negative - away from
nastic - neither; a response that is independent of stimulus direction
photoperiodism - day length
vernalization - some seeds have to go through a freeze cycle before
they can germinate.
photo - light
geo - gravity
thigmo - touch (like vines)
chemo – chemical
hydro - water
15