VCE BIOLOGY UNIT ONE Chapter Four Plants Dr Adrian Mascia

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VCE BIOLOGY UNIT ONEChapter FourPlants Dr
Adrian Mascia
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Plant Structure

• Plants can be divided into 2 systems
• The Shoot system (above ground) stem, leaves,
  reproductive organs
• 2. The Root system (below the ground) roots
  and root hairs

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Inputs and outputs
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Plant Tissues

• There are 4 main types of plant tissues
• 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)

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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

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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

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Ground Tissue

• Consist of a variety of cells
• Functions include storage, support and
  photosynthesis
• Examples include fleshy portions of apples,
  pears, potatoes

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Vascular Tissues

• Transport tissues including xylem and phloem
• Xylem Water transport
• Phloem Nutrient transport
• Circulatory system of the plant

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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)

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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)

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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

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ROOTS

• 2 Types of roots
• 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
• Fibrous roots Many small roots of about equal
  size, do not grow deeply, rather spread out e.g.
  Grasses

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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)

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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

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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

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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)

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INTERNAL LEAF STRUCTURE

• 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

Xylem and phloem
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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.

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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

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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

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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)

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Single Cell Organisms

• Have the same requirements for life as
  multicellular organisms, their structure creates
  a difference in the method of obtaining these
  essentialsRequirements1. Nutrients for
  construction and structure 2. Energy to
  replenish and repair

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Obtaining essentials

• MINERALS / WATER
• Single cell organisms utilise diffusion and
  osmosis in order to in take essential substances
  such as Gases for respiration, and water.
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  ENERGYAutotrophs Take energy from the non
  living world
• (Photosynthesis, Chemosynthesis) e.g.
  DiatomsHeterotrophs Take energy from the
  living world (Ingestion through the cell
  membrane / Breaking down of other small
  organisms) e.g. Paramecium

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LOCOMOTION

• As single celled organisms do not have the
  ability to for tissues that work together to
  generate leverage, they have other ways of
  propelling themselves

Cilia small hairs
Flagella whip like tail
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Eating

• As mentioned, some single celled organisms rely
  on the diffusion of all energy and minerals to
  diffuse through their plasma membrane
• Other organisms such as the Paramecium use their
  cilia to sweep organisms into their oral groove,
  so it can then be digested in the gullet

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Organisation

• Some single celled organisms, particularly
  bacteria will form colonies. They are still
  individual organisms, however their close
  proximity allows them to share resources.