plants make up over 50% of the living organisms on this planet they belong to the kingdom plantae ...
TRANSCRIPT
TOPIC 9 – PLANT SCIENCE
Introduction to Plants
Plants make up over 50% of the living organisms on this planet
They belong to the kingdom Plantae There are five phylum:
Bryophyta Filicinophyta Coniferophyta Angiospermophyta
Introduction to Plants (cont)
Angiosperms are the most dominant phylum
Angiosperms, or flowering plants, produce seeds enclosed inside fruits.
Angiosperm comes from the word angerion – a container sperma – a seed phyton – a plant.
Introduction to Plants (cont)
Angiosperms are divided into two large groups: Monocotyledons (Monocots) Dicotyledons (Dicots)
These names refer to the number of leaves contained in the embryo, called cotyledons.
Typical Monocot
Monocots vs. Dicots
Typical Dicot
Shoot Apical Meristems
Lateral Meristems
Comparison of Growth for Apical and Lateral Meristems
APICAL MERISTEMS LATERAL MERISTEMS
Primary growth Allows plant to grow
longer (upwards) Forms leaves and
branches Increases
photosynthetic capacity
Found in both monocots and dicots
Secondary Growth Allows plant to grow
in width Widening of main
trunk for support and depositing of vascular tissue and bark
Found only in dicots
Stems
Supports the leaves for photosynthesis Transports water and nutrients from roots
to leaves Support is achieved by:
Tugor Cellulose walls Lignin reinforcing the xylem
Stems
Consist of an epidermis which surrounds the vascular tissue, composed of xylem (water transport, up the stem) and phloem (mineral and sugar transport, up and down the stem to sinks for storage)
Meristems deposit secondary xylem and phloem, which will grow outwards to become primary xylem and phloem.
Plan Diagram of the Stem
Leaf Structure
Consists of a: Leaf Blade Leaf stalk
Leaves have a large surface area and a small space between layers
Designed for photosynthesis
Leaf Structure (cont)
Leaves consist of: Outer structure - Epidermis
Tough, transparent layer Upper – waxy Cuticle Lower – specialized cells called guard cells, that
form openings in the bottom, called Stoma Inner Structure – Specialized Cells
Mesophyll cells
Leaf Structure (cont)
Upper Surface – Palisade Mesophyll Tightly packed Contain chloroplasts
Lower Surface – Spongy Mesophyll Loosely packed with air spaces
Vascular Bundles Consist of xylem and phloem Bring water to and transport sugars and
minerals away and to leaves Support the leaves along with cellulose and
turgor
Plan Diagram of the Leaf
Roots
First stage of development for the seed when it germinates
Tap Roots Lateral Roots
Roles Absorption Anchors Support Storage
Roots (cont)
Roots have an outer coat, called the epidermis, and the inner portion is called the cortex
In the root, there is a vascular bundle, of xylem and phloem
Branching of roots allow for a greater surface area
Root hairs off of growing roots, increase the surface area as well.
Diagram of Roots and tissue Plan Diagram
Modifications of Stems, Roots and Leaves
Roots
Prop Roots
Storage Roots
Pneumatophores
Buttress Roots
Examples of Root Modifications
Modifications of Stems, Roots and Leaves
Stems
Bulbs
Tubers
Rhizomes
Stolons
Examples of Stem Modifications
Modifications of Stems, Roots and Leaves
Leaves
Tendrils
Reproductive Leaves
Bracts or floral leaves
Spines
Control of Plant Growth - Phototropism
Plant growth is controlled by gravity and light Plant grows against gravity Plants grow towards the light
Responses to the above stimuli, called tropisms
Growth towards light called phototropism Controlled by a hormone called auxin Produced in the tip of the shoot
Control of Plant Growth - Phototropism
Steps of phototropism Photoreceptors in the tip of the plant sense the
light Stimulate the production of auxin Auxin will travel to the “shady side” of the plant, as
detected by the phototropins Promotes the elongation of cells in stems, by
loosening the connections between the cell walls and cellulose microfibrils
Promotes the stem to grow more on the shadier side and go towards the light.
Allows the leaves on the sunny side to get more light and photosynthesize at a greater rate.
Control of Plant Growth - Phototropism
Transport in Angiosperms
Root System
Transpiration Water uptake Factors affecting Transpiration
Translocation
Transport in Angiosperms
Roots – Absorption and uptake Provide large surface area for uptake of water
and minerals Water is absorbed by osmosis Amount of water absorbed is increased by root
hairs, on ends of growing roots Minerals absorbed by active transport
Water uptake
Occurs by osmosis
Flows through epidermis, into cortex by mass flow, as the cells are interconnected
Three possible routes for uptake of water: Apoplast Pathway (Mass Flow) Symplast Pathway Vacuolar Pathway
Water uptake
Apoplast Pathway (Mass Flow) Most common way for water to move (faster) Water does not enter the cell Moves through the cell walls until it reached
the endodermis Cells of the endodermis have a Casparian
Strip around them that is impermeable to water
The water is diverted to the spaces of dead cells, eventually to the xylem
Water uptake
Symplast Pathway Water enters the cytoplasm but not the
vacuole It passes from cell to cell via connections
between cellular cytoplasm of adjacent cells, called plasmodesmata
The organelles are packed together in cells, and as a result, block significant progress of water
It is not the major pathway for water. Minerals mainly move through this pathway.
Water uptake
Vacuolar Pathway
Water enters the cell and move into the vacuole It can be stored in the cells It can also travel through the cytoplasm and the
cell wall to the next cell, to move into cortex
Once in the endodermis, water can move into the xylem and pulled via transpiration forces.
Pathways for water uptake
Uptake of Minerals
Minerals are important to build cells walls, carbohydrate storage and protein synthesis
Processes for mineral uptake: Active transport Mass flow (in water) Fungal hyphae
Transpiration
Transpiration the loss of water vapour from the leaves and
stems of plants. Like perspiration
As water is lost, the amount of water in
the plant decreases. A pull is created in the plant to “pull” water up the plant. This is similar to maintaining homeostasis.
Transpiration (cont)
Water moves from root to leaf by transpiration pull
Water moves up the stem to leaves in the xylem Dead material Made of tracheids and xylem vessels
Xylem Tissue
Mechanism of Movement of Water – Transpiration Pull
Controlled by stomata Stomata open and close depending on
the amount of water in the plant If there is a lot of water – high turgor
pressure in guard cells and stomata are open
If there is a deficiency of water – low turgor pressure in guard cells and stomata close
If water drops, abscisic acid is released, overriding all variables and stomata close
Mechanism of Movement of Water – Transpiration Pull
When stomata are open, water vapour is lost to the external environment
Concentration gradient is created The lost water needs to be replaced Water moves from the high concentration
(roots) to lower concentration (leaves) and moves up the plant
Cohesive forces of water allow water to move in a continuous flow
Transpiration
Factors that affect Transpiration
Biotic Factors
Size of the plant The thickness of the cuticle How widely spaced the stomata are Whether the stomata are open or closed
Factors that affect Transpiration
Abiotic Factors Temperature
Humidity
Wind
Light
All of these can be over ridden by abscisic acid
Translocation
Movement of manufactured food (sugars and amino acids).
Occurs in the phloem tissues of the vascular bundles.
Moves sugars from source to sink (leaves to storage) and from source to areas of new growth, like ends of shoots and new leaves.
Phloem tissue allows movement up and down the stem of the plant
Translocation
Phloem Tissue, is living tissue, and consists of: Sieve tubes
Flow of sugars and minerals Companion cells
Control flow / Active transport
Theory of Translocation is by mass flow, from source to sink
Source and sink can change, depending on use and season
Translocation
Transpiration and Adaptations of Xerophytes
Small, thick leaves Reducing the number of stomata Stomata located in crypts or pits
on the leaf surface Thickened, waxy cuticle Hair-like cells on the surface to
trap water vapour Become dormant in the dry
months Store water in the fleshy stems
and restore the water in the rainy season
Using alternative photosynthetic processes called CAM photosynthesis (Crassulacean acid metabolism) and C4 photosynthesis
Reproduction in Flowering Plants
Parts of the flower Pollination Fertilization Seed formation and
dispersal Seed germination Control of flowering
- Photoperiodism
Typical Dicotyledonous Flower
Sepal enclose and protect the flower in the bud, and are
small, green and leaf like.
Petals (together called the corolla) coloured and used to attract insects or other small
animals to pollinate the flower.
Stamen – male part of the flower, which consists of:
Anthers – produces the male sex cells house the pollen grains
Filament or stalk – holds up the anther
Typical Dicotyledonous Flower
Carpels – female part of the flower, and they may be on their own or fused together. Each carpel consists or:
Ovary – at the base of the carpel which contains the female sex cells (containing many ovules)
Stigma – sticky top of the carpel (to receive the pollen)
Connecting style – supports the stigma
Pollination and Fertilization
Pollination the transfer of pollen from a mature anther to
a receptive stigma.
Fertilization occurs after the pollen grain has landed on a
stigma, and germinated there. It is the fusion of the male and female gametes.
Pollination and Fertilization
Process of Fertilization
The pollen produces a tube, which grows down between the cells of the style, and through the ovule.
The pollen tube delivers two male
nuclei. One of these male nuclei then fuses with the egg
nucleus in the embryo sac, forming a diploid zygote.
The other fuses with the other nucleus, which triggers formation of the food store for the developing embryo.
Seed Formation and Dispersal
Seed contains the developing embryo and the food store
The zygote grows by mitosis, forming the embryonic plant, consisting of an embryo root and stem.
A seed leaf or cotyledon forms. The seed leaf has two
forms, as angiosperms have two classes. Monocotyledons – have a single seed leaf Dicotyledons – have two seed leaves
The formation of stored food reserves is triggered. In many seeds the food store is absorbed into the cotyledons.
Seed Formation and Dispersal
The outer layers of the ovule become the protective seed coat, or testa.
The micropyle is a small hole through the testa,
where it was attached to the parent plant.
The whole ovary develops into the fruit.
The water content decreases and the seed moves into a dormancy period, assisted by the formation of abscisic acid.
Seed Formation and Dispersal
Seeds are dispersed when “fruit” ripens Seeds are dispersed in such a way as to
eliminate many seeds in one place and around the base of the parent plant (population dynamics)
Dispersed by: Wind Animals Explosive
Seed Germination
Seeds are in suspended animation When metabolic activity starts, this is
germination
Seeds are dormant because: Incomplete seed development Presence of a plant growth regulator – abscisic
acid Impervious seed coat
Seed Germination
In order for germination to occur, the proper conditions are needed
Water – hydrates plant and activates amylase and removes the abscisic acid
Oxygen – for Cellular respiration Period of warm temperatures as this is
important for enzyme production.
Seed Germination The metabolic processes during the germination of a seed
are as follows: The seed absorbs water.
Gibberellin, or gibberellic acid, is released after the uptake of water and is a plant hormone
Gibberellin triggers the production of amylase.
Amylase causes the hydrolysis of starch into maltose. The starch is present in the seed’s endosperm or food reserve.
Maltose is then further hydrolysed into glucose that can be used for cellular respiration or may be converted into cellulose by condensation reactions.
Cellulose is used to produce the cell walls of new cells.
The seed coat cracks and out comes the plant.
Control of Flowering of Angiosperms - Photoperiodism
Photoperiodism Plant’s response to light involving the lengths of day
and night. It is the length of day and night that controls flowers
Plants that respond to large amounts of sunlight, and short periods of darkness are called long day plants (late spring, summer)
Plants that respond to small amounts of sunlight, and long periods of darkness are called short day plants (early spring, late fall)
Control of Flowering of Angiosperms - Photoperiodism It is actually the length of night that
controls the flowering process
The control by light is brought about by a special blue-green pigment called phytochrome.
Phytochrome is a large protein that is
not a plant growth hormone, but a photoreceptor pigment.
Control of Flowering of Angiosperms - Photoperiodism
There are two forms of phytochrome: inactive form Pr
active form Pfr
In light, the Pr is converted to Pfr.
In darkness, the active form (Pfr) slowly converts back to Pr
The slow conversion allows the plant to time the dark period and controls the flowering in short-day and long-day plants.
Process of Photoperiodism A long day in the summer:
A lot of Pr is made into Pfr during the day.
In the night, because the night is short, little Pfr is converted back to Pr, and when the sun rises, there is still a lot of active phytochrome (Pfr) left
This signals a long day, short night, and promotes flowering in long day plants
This does not signal a short day, long night and inhibits flowering in short day plants
Process of Photoperiodism A short day in the spring or fall:
A small amount of Pr is made into Pfr during the day.
In the night, because the night is long, almost all Pfr is converted back to Pr, and when the sun rises, there is minimal active phytochrome (Pfr) left and lots of inactive (Pr)
This does not signal a long day, short night, and inhibits flowering in long day plants
This does signal a short day, long night and promotes flowering in short day plants
Summary of Photoperiodism
Long day plants need active phytochrome (Pfr) Pfr acts as a promoter Need a short night
Short day plants do not need active phytochrome (Pfr) Pfr acts as an inhibitor Need a long night
Experiment for Photoperiodism