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

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.
Region of elongation
- cells extend by uptake of water
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

Stem node
- leaves or branches emerge
Internode
- stem between adjacent nodes
- elongation
Leaf
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

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