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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).

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introduction to plants
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
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 cont1
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.
comparison of growth for apical and 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
  • Supports the leaves for photosynthesis
  • Transports water and nutrients from roots to leaves
  • Support is achieved by:
    • Tugor
    • Cellulose walls
    • Lignin reinforcing the xylem
  • 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.
leaf structure
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
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 cont1
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
  • First stage of development for the seed when it germinates
  • Tap Roots
  • Lateral Roots
  • Roles
    • Absorption
    • Anchors
    • Support
    • Storage
roots cont
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.
modifications of stems roots and leaves
Modifications of Stems, Roots and Leaves
  • Roots
    • Prop Roots
    • Storage Roots
    • Pneumatophores
    • Buttress Roots
modifications of stems roots and leaves1
Modifications of Stems, Roots and Leaves
  • Stems
    • Bulbs
    • Tubers
    • Rhizomes
    • Stolons
modifications of stems roots and leaves2
Modifications of Stems, Roots and Leaves
  • Leaves
    • Tendrils
    • Reproductive Leaves
    • Bracts or floral leaves
    • Spines
control of plant growth phototropism
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 phototropism1
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.
transport in angiosperms
Transport in Angiosperms
  • Root System
  • Transpiration
    • Water uptake
    • Factors affecting Transpiration
  • Translocation
transport in angiosperms1
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
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 uptake1
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 uptake2
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 uptake3
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.

uptake of minerals
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
    • 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
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
mechanism of movement of water transpiration pull
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 pull1
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
factors that affect 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 transpiration1
Factors that affect Transpiration
  • Abiotic Factors
    • Temperature
    • Humidity
    • Wind
    • Light
    • All of these can be over ridden by abscisic acid
  • 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
  • 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
transpiration and adaptations of xerophytes
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
Reproduction in Flowering Plants
  • Parts of the flower
  • Pollination
  • Fertilization
  • Seed formation and dispersal
  • Seed germination
  • Control of flowering - Photoperiodism
typical dicotyledonous flower
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 flower1
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 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 fertilization1
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 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 dispersal1
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 dispersal2
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
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 germination1
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 germination2
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
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 photoperiodism1
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 photoperiodism2
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
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 photoperiodism1
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
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