Chapter 35

Introduction to Plants

Kingdom Plantae

• We will primarily be discussing the angiosperms
  • Phylum Anthophyta
• Flowers and fruits
  • Only group that does/has these things
• Advanced traits
  • Seeds
  • Advanced vascular tissues

From seed to seed

The life of a flowering plant

• Seeds
  • reproductive structures produced by angiosperms and other seed plants
  • usually the result of sexual reproduction
  • contains embryos that develop into seedlings upon germination
  • has survival value

Alternation of Generations

• Exhibited by all plants (and plant-like organisms) that have sexual reproduction
• There is an alternation between a diploid (2N) form [sporophyte] and a haploid (1N) form [gametophyte]

Gametophyte (haploid)

• Gamete-producing plant fomr
• multicellular
• microscopic in flowering plants
  • female
    • embryo sac with egg
  • male
    • pollen grain
• grow and develop within flowers of angiosperms
• produces gametes by mitosis/cytokineses

Sporophyte (diploid)

• multicellular
• large "plant" in flowring plant
• produces haploid spores by meiosis (reduction)
  • called meiospores

The plant embryo

• Fertilization (syngamy) results in the formation of a diploid zygote, which undergoes mitosis to form an embryo (multicellular)
• the embryo is a sporophyte that lies dormant in the seed with a supply of stored food and a seed coat
• may lay dormant for long periods until conditions are favorable 

The plant body

Composed of three organ types

• stems
• leaves
• roots

Shoot system

• stem
  • produce leaves and branches and bear the reproductive structures
• leaves
  • flattened structure specialized for photosynthesis

Root system

• roots
  • Provide anchorage in the soil and foster efficient uptake of water and minerals
  • can store food

Growth

• Indeterminate growth
  • increasing in size as long as the plant is alive
• grows into a seedling and then a mature plant
• Plant growth occurs by 3 means
  • Increase in number of cells
    • cellular reproduction
      • (mitosis/cytokineses)
  • increase in cell size
    • elongation
  • increase in weight/mass

Development

• Mature plants produce reproductive structures
  • flowers
  • seeds
  • fruits
• flowers and floral buds are reproductive shoots that develop when shoot apical (tip) meristems produce flower parts instead of new tissues and leaves
• flowers are produced by determinate growth

Seed coats

• Flower tissues enclose and protect tiny male and female gametophytes
  • sperm in pollen fertilizes the egg, triggering ovules to develop into seed and flower parts to develop into fruit
• fruits enclose  seeds and function in seed dispersal
  • Angiosperms

 

Meristems

• Seedlings and mature plants produce new tissue from meristems
  • cell factories
• meristem is a region of undifferentiated cells that produce new tissue by cell division
• A dormant meristem occurs at the shoot and root of seed embryos
  • activate in seedlings
• mature plants have shoot apical meristems (SAM) and root apical meristems (RAM)

Mature sporophyte develop from seedlings

• photosynthesis powers the transformation of seedlings into mature plants
• provides the ability to produce organic food
• plants undergo both vegetative growth and reproductive development

Hierarchy of structures in a mature plant

• Specialized cells
• tissues
• organs
• organ systems
  • branches, buds, flowers, seeds, fruits
• root and shoot systems
• plant (the organism itself)

Primary Growth

• Elongation of plant organs
• roots, stems, and leaves
• Occurs in ALL plants
• Produces primary tissues from apical meristems (SAM  and RAM)

Primary Tissues

• Primary xylem
  • vascular/conducting tissue
  • water and minerals
• Primary  phloem
  • vascular/conducting tissue
  • food and solutes
• Epidermis
  • dermal
    • Outter-most tissue
  • protection
  • holds water in plant
• Support ground tissues
  • Parenchyma
    • most abundant type
    • storage
      • water and food
    • part of cortex/pith
  • Collenchyma
    • Protection/support of growing plant organs
    • cortex
  • Sclerenchyma
    • protection/support of non-elongating organs
    • cortex

Secondary Growth

• Expansion of plant organs
  • lateral meristems
• roots and stems only
  • does not occur in leaves
• noes not occur in all plants
• Produces secondary tissues
  • woody tissues

Major groups of Angiosperms

Eudicots

• >240,000 species
• all have primary growth
• most have secondary growth
  • for this class we are saying they all have secondary growth

Monocots

• >60,000 species
• all have primary growth
• very few have secondary growth
  • for this class we are saying that non have secondary growth
• grasses, corn, tulips, lilies

Root system adaptations

Major functions

• absorbing water and minerals
• anchoring the plant in the soil
• storing nutrients and water

Eudicots

Taproots

Monocots

fibrous roots

Three zones of root growth

1. Region of cell division
   • RAM and root cap
   • RAM contains cells that ar dividing
   • Quiescent center keeps nearby cells undifferentiated
   • Root cap embedded in mucigel
     • Mucigel is a slimy substance that covers the root cap of the roots of plants.
2. Region of elongation
   • cells extend by uptake of water
3. Region of maturation
   • root cell differentiation  and tissue specialization
   • identified by presence of root hair
     • water and mineral uptake

Root Internal Structure

• Epidermis of mature roots encloses a cylinder of parenchyma called the root cortex
  • One cell thick
  • often rich in starch
    • functions as food storage
  • many contain inter-cellular air spaces
• Endodermis
  • selective absorption of minerals
  • one cell thick
• Meristematic pericycle
  • encloses root in vascular tissues
  • provides lateral branches
• woody roots produce primary vascular tissues followed by secondary vascular tissues

Eudicot root

Monocot Root

The shoot system

Stem and leaf adaptations

Shoots are modular with 4 parts

1. Stem node
   • leaves or branches emerge
2. Internode
   • stem between adjacent nodes
   • elongation
3. Leaf
4. Axillary Meristem
   • generate axillary buds
   • can produce flowers or branches 
     • Lateral shoots
   • New branches bear SAM at their tips

Shoot Tip

• Terminal bud
  • at the end of each shoot
  • includes the SAM and other parts
  • scales

Leaf anatomy

Leaf adaptation

Leaf venation

Eudicot

• Pinate (feathery)
• Palmate (palm)
• Netted
  • provides more support for the leaves

Monocot

• Parallel 

Stem

Primary growth

• mostly above ground organs,but some modified stems are blow ground
  • Irish potato
    • underground stem

Eudicot Stem

• ALC
• Primary (elongation) and secondary (expansion) growth
• vascular bundles (xylem and phloem) form a ring pattern 
• exhibit both a pith and a cortex
• cambium ring produce cells
  • provide secondary growth

Lateral Meristems

• Produces secondary growth
• 2 lateral merstems
  • both are rings that retain cell division properties and produce secondary tissues to the inside and outside of the cambium ring
• Vascular cambium
  • produces ring of secondary xylem (wood) to the inside and a ring of secondary phloem (inner bark) to the outside
• Cork cambium
  • Produces ring of periderm (outter bark) that replaces the epidermis and cortex for external protection

• Secondary vascular tissue
  • woody plants begin life with only primary vascular systems
    • produces secondary tissues and bark as they mature
  • secondary xylem
    • wood
  • Secondary phloem
    • inner part
  • bark has both outer bark (mostly dead cork cells) and inner bark (secondary phloem)
• Secondary growth
  • begins late in first year of growth
  • eudicot stem after 3 years of growth

Monocot stem

• Primary growth (elongation)
• vascular bundles (xylem and phloem) are scattered
• lacks both pith and cortex

Comparison between Plant types

Leaves

Eudicot

• net venation

Monocot

• parallel venation

Roots

Eudicot

• primary and secondary growth (mostly)
• cortex
• no pith
• core of xylem in the root

Monocot

• Primary growth only
• both cortex and pith

Stems

Eudicot

• primary and secondary growth (mostly)
• vascular bundles in a ring pattern around cortex

Monocot

• Primary growth only
• vascular bundles scattered around
• no pith or cortex

Primary Growth

• Due to activities of Apical Meristems
  • RAM and SAM
• Results in production of primary growth

Secondary Growth

• Due to activities of lateral maristems
  • vascular and cork cambiums
• Results in production of secondary tissues