Plant Structure

1
Plant Structure Function
2
Root, Stem Leaf Structure Function

• A plant is organized into roots and shoots. The
  root system is below the ground and the shoot
  system is above the ground.
• Roots serve three functions they act as anchors
  to hold the plant in the soil, they absorb water
  and minerals, and they transport water and
  minerals to the stem for distribution to the rest
  of the plant.
• The leaves and the stem make up the shoot system.
  The primary role of the leaf is to serve as the
  main location of photosynthesis. The primary
  function of the stem is to support the leaves.
  Stems also transport water and minerals to the
  leaves and sugars from the leaves. Some stems
  store food as well.

3
The two parts of plantsThe root and shoot
systems
4
Monocots and Dicots

• Angiosperms can be further divided into two
  subclasses commonly called Monocots and Dicots.
• There are over 200,000 different species of
  dicots and more than 50,000 types of monocots.
• The names of the two subgroups are based on the
  structure of their seeds. Monocots have one seed
  leaf, or cotyledon and Dicots have two.

5
(No Transcript)
6
Roots

• There are two main types of roots found in
  plants taproots and fibrous roots.
• The primary root emerges from the germinating
  seed and develops into a long, thick root called
  a taproot. Branch roots emerge from the taproot
  as the plant grows.
• In fibrous root systems there are many main roots
  of the same size, and thousand of secondary and
  tertiary roots.

7
Tap and Fibrous Roots
8
Root tissues
9
Root tissues

• Epidermis- one cell layer thick and is the
  outermost layer of the root. Functions in
  protection and absorbing water and minerals from
  the soil. Specialized epidermal cells form root
  hairs.
• Cortex- a layer of cells found just below the
  epidermis and functions in storage of molecules
  such as starch. Also help transport water and
  minerals to the centre of the root by osmosis.
• Endodermis- inner wax-coated cell layer of the
  cortex. This layer controls the movement of water
  and minerals into the central area of the root
  known as the vascular cylinder.

10
Root tissues cont.

• Vascular cylinder- contains the plants
  conducting tissues, the xylem and phloem.
• Xylem conducts water and minerals to the leaves
  of the plant.
• Phloem transports sugars from the leaves to other
  parts of the plant.
• Phytoremediation is the use of plants to extract
  toxic substances (lead, arsenic, and uranium)
  from soil and water.

11
Stems

• There is a huge variety in shapes and sizes of
  stems in different plant species. Whatever the
  shape, its main functions are to hold leaves up
  to the sunlight and to conduct various substances
  between the roots and leaves.
• Two types of stems
• -Herbaceous stems are green and usually soft.
  These stems do not survive the winter and are
  regrown each year.
• -Woody stems contain tough, hard tissues
  called wood. These stems survive the winter.

12
Herbaceous Stems

• Vascular bundles are collections of xylem,
  phloem, and associated tissues. The xylem is
  always closer to the centre of the stem and the
  phloem is closer to the outside of the stem.

13
Woody Stems

• The most complex stem is a woody stem. They are
  able to grow thicker over time, (i.e. trees).
  This is due to the vascular cambium which makes
  new layers xylem and phloem each year.
• Sapwood is younger xylem, which conducts water
  and minerals. As new xylem is formed, the older
  xylem fills with resins, oils and becomes
  heartwood. Heartwood is no longer able to
  conduct fluids.
• Bark is the outer part of the woody stem. It is a
  protective tissue that consists of the phloem and
  the cork tissue. Outer cork cells are dead and
  contain fats, oils, and waxes which help prevent
  water loss.

14
Woody stem layers
15
Woody stem cross section
16
Specialized Stems

• Cacti stems are herbaceous but must be able to
  store the water they absorb during certain times
  of year.
• Stems can also be used to store food, to help the
  plant survive the winter and spring.
• There are different types of modified stems
• - Rhizomes are thick, fleshy stems that grow on
  or just below the soils surface. Rhizomes develop
  roots and can survive the winter. Ex. Irises,
  lilies and species of grass.
• Tubers stems that grow underground and become
  enlarged with stored food. Tubers have buds
  which grow into new shoots above the ground. Ex.
  Potatoes.
• Bulbs are underground stems. The stem is
  surrounded by layers of modified leaves. Ex.
  Tulips, onions and daffodils develop bulbs.

17
Specialized Stems
18
Leaves

• The leaf not only makes sugars for the plant but
  also supplies all living organisms with their
  source of food and oxygen.
• There are many types of leaves but most are
  designed to provide maximum exposure to the
  sunlight.
• Most leaves are covered by a waxy substance known
  as cuticle, which is produced by the epidermis.
  The epidermis forms the outer cell layer of the
  plant. Both of these structures waterproof and
  provide a protective barrier for the tissues
  inside the leaf.
• Water vapour, oxygen and carbon dioxide move into
  and out of the leaf through the stomata. In the
  day the stomata are open to except carbon dioxide
  and release water vapour. At night,
  photosynthesis doesnt occur so the stomata are
  closed to prevent excess water loss. The stomata
  may be closed during the day depending on
  environmental conditions.

19
Leaves cont.

• Each stoma is surrounded by two guard cells. The
  guard cells are specialized, kidney-shaped
  epidermal cells containing chloroplasts. Due to
  concentration gradients these guard cells swell
  during the day causing an opening at the stomata.
  These same cells shrink at night causing the
  closure of the stomata.
• The cells within the leaf are known as mesophyll
  cells. These thin walled cells contain numerous
  chloroplasts, the site of photosynthesis. These
  cells are also the site of gas exchange in the
  leaf.
• Over 90 of the water from the roots is lost
  through evaporation in leaves known as
  transpiration.
• The xylem and phloem continue from the stems into
  the leaves forming the veins. The veins in a
  leaf branch out extensively so the xylem and
  phloem are close to the mesophyll cells.
• Plants that live in dry environments have
  modified leaf structures to help retain water.
  The leaves have a thicker epidermis and cuticle
  to prevent water loss.

20
Leaf cross sections
21
Plant tissues and their functions

• A tissue is a group of cells that act together to
  carry out a specific function.
• Vascular tissue
• Xylem conducts water and dissolved minerals
  (sap) from the roots to all parts of the plant.
  There are two types of xylem cells vessel
  elements and tracheids.
• Vessel elements are only found in angiosperms.
  These elements are connected from end to end and
  side to side to permit the flow of xylem sap up
  and down and side to side.
• Tracheids are much narrower than the vessel
  elements. They are found in all vascular plants.
• The substances cellulose and lignin are deposited
  on the exterior surfaces of xylem cells to form
  rigid cell walls.

22
Plant tissues and their functions

• Phloem transports water and dissolved
  carbohydrates (sugars) from the leaves to other
  parts of the plant.
• Most phloem cells are called sieve tube cells
  because they have sieve plates at each end. They
  resemble vessel elements, but are much smaller.

23
Plant tissues and their functions

• Fundamental or Ground Tissue
• Most of the plant is made of this tissue and
  this tissue consists of parenchyma cells.
  Parenchyma is found in the roots, stems, leaves
  and fruit. The cell walls of these cells are
  quite thin and flexible. These provide support
  for the plant and they store food and water.
  Photosynthesis occurs in parenchyma cells that
  contain chloroplasts. (The flesh of an
  apple/watermelon is parenchyma).
• Collenchyma and Sclerenchyma are specialized
  types of parenchyma with thicker and more rigid
  cell walls. They provide support in plant stems.

24
(No Transcript)
25
Plant tissues and their functions

• Meristematic Tissue
• This is a type of tissue that produces new cells
  by mitosis. Mature cells cannot divide therefore
  plants can only grow where this tissue is found.
• These regions are referred to as meristems.
  Apical meristems are located at the ends of shoot
  and root tips. They are responsible for the
  primary growth of the stem and the root.
• Protective Tissue
• The epidermis (one cell layer thick) is the
  outer protective layer of leaves, stems and
  roots.
• Cork protects inner tissues from injury and is
  usually more than one cell layer thick.

26
Water and Food Transport
27
(No Transcript)