• Leaf anatomy
• Sporogenesis, Gametogenesis, Pollination, and Fertilization

Cells and tissues of plants, Chapters 20 and 22.

• Cell and Tissue Types
  Cell Types
  1. Parenchyma - most abundant cell type in plants (e.g. cells making up the fundamental ground tissues; usually unspecialized; characteristics include:
     1. living at maturity with a very thin cell wall
     2. large vacuole for storage and sequestering of materials
     3. large amount of intracellular space
     4. spherical
     5. relatively regular shape
     6. very elastic (can change shape and then return to original shape with little deformation)
     
     Functions of parenchyma cells include:
     1. photosynthesis
     2. storage
     3. secretion
  2. Collenchyma - found just below the epidermis in petiole (e.g. celery stalks), leaves, and young stems; usually specialized; characteristics include:
     1. living at maturity
     2. irregularly thichened cell walls
     3. prism shaped
     4. plastic (can change shape but do not usually return to the original shape; remain deformed)
     
     Functions of collenchyma cells include:
     1. support
     2. some involvement in transport of nutrients
  3. Sclerenchyma - in mature parts of the plant, especially in woody plants and herbaceous perennials; specialized; characteristics include:
     1. dead at maturity - protoplast is absent
     2. very thick, sclerified cell wall
     3. impermeable to water and other nutrients
     4. in cells specialized for transport of water and nutrients, the cell wall contains holes called pits.
     
     Functions include:
     1. support
     2. protection
     3. transport of water and nutrients
     
     Specific examples of sclerenchyma cells:
     1. fibers - long and slender
     2. sclerids (stone cells) - relatively spherical; the gritty texture of pears is due to the presence of stone cells.
  
  Tissue Types
  1. Simple tissues - all cells alike with the same structural and functional characteristics (e.g. parenchyma, collenchyma, and sclerenchyma).
  2. Complex - several different cell types with similar structure, each performing related functions (e.g. Xylem and Phloem).
• Simple tissue examples:
  1. Meristematic tissues - collection of a small number of undifferentiated cells that undergo specialization to give rise to both new meristematic cells and new differentiated, specialized cells that later mature into tissues making up leaves, flowers, etc..
  2. Fundamental (ground) tissue - makes up the bulk of the plant body; photosynthetic tissue; storage tissues; supportive tissues; mostly parenchyma cells of the cortex (outer ring) and pith (central core) of the stem.
• Complex tissue examples:
  1. Epidermis - surface, protective layer of cells which secrete cutin, waxes, and suberin which prevent water loss; mostly collenchyma cells; some parenchyma; specialized openings called stomata allow for gas exchange; stomata are surrounded by specialized type of collenchyma cells called guard cells.
  2. Xylem - water and some inorganic nutrient transport.
     Xylem tissue consists of 4 different cell types:
     1. Tracheids - thin, elongated sclerenchyma cells with oblique end walls; conduct water vertically; pits in side walls, perforations in end walls.
     2. Vessel elements - short, large diameter sclerenchyma cells with flat end walls; conduct water vertically; pits in side walls, perforations in end walls; collectively make up vessels.
     3. Undifferentiated sclerenchyma cells - mature into either tracheids or vessel elements.
     4. Parenchyma cells - Undifferentiated, living cells of the vascular meristematic region; develop into undifferentiated sclerenchyma cells.
  3. Phloem - organic and some inorganic nutrient transport.
     Phloem tissue consists of 5 different cell types:
     1. Sieve tube elements - similar in size and shape to vessel elements; dead at maturity; end walls look like a sieve (called a perforation plate); transport sugars (mostly) from source to sink; collectively make up sieve tubes.
     2. Companion cells - Living cells which are associated with sieve tube elements; actively transport sugars into the sieve tube elements (phloem loading).
     3. Sieve cell - similar in size and shape to tracheids except are living at maturity; function in sugar transports; usually not associated with companion cells.
     4. Undifferentiated sclerenchyma cells - mature into either sieve tube elements or sieve cells.
     5. Parenchyma cells - Undifferentiated (usually), living cells of the vascular meristematic region; develop into undifferentiated schlerenchyma cells or into companion cells.

• Leaf anatomy (Chapter 22, p. 424):
  Primary functions are:
  1. Photosynthesis
  2. Translocation
  3. Transpiration
  
  Secondary functions are:
  1. Storage
  2. Attraction (bracts)
  3. Support
  4. Protection
  
  Types of leaves:
  1. Foliage leaves - most common and familiar.
  2. Bracts - function in the attraction of insect pollinators (e.g. the red petal-like bracts of poinsettia)
  3. Cotyledons - not true leaves; embryonic leaf-like structures which function primarily in storage of nutrients for the developing seedling while true, photosynthetic leaves are being produced.
  4. Bud scales - distinguish axilary buds from stipules; protect axial and apical meristems.
  
  Key anatomical features:
  1. Upper (adaxial; ad - to or toward, axial - the leaf axis; some exceptions exist) epidermis - protection.
  2. Mesophyll (middle leaf; bulk of the leaf tissue in middle of blade between upper and lower epidermis) - ground tissue and vascular tissue; divided into:
     • Palisade parenchyma - adsorption of light; photosynthesis; not present in grass and other monocot leaves.
     • Spongy parenchyma - irregular shape; lots of intercellular spaces; gas exchange.
  
  Other anatomical features:
  1. Bundle sheath - cells surrounding vascular tissue (xylem and phloem).
  2. Vascular bundle - bundle sheath, xylem, and phloem collectively.
     Xylem oriented toward upper epidermis.
     Phloem oriented toward lower epidermis.
  
  Leaf Development and Abscission:
  1. Originates in apical meristem as a leaf primordium (first set of differentiated cells to be distinguished from meristematic tissue.
  2. Abscission (separation of leaf from plant) is caused by:
     1. Drought
     2. Change in temperature
     3. Injury
     4. Disease
     5. Change in day length
     6. Change in amount or intensity of light
  3. Species characteristics of leaf abscission:
     1. Deciduous - all leaves abscise roughly at once.
     2. Evergreen - few at a time or not at all.
  4. Pigmentation and leaf abscission:
     1. Before abscission, Chloroplasts are disrupted and chlorophyll is degraded (green color is lost).

Sporogenesis, Gametogenesis, Pollination, and Fertilization

Floral anatomy and terminology

Anther

pollen-producing portion of stamen.

Filament

supportive, stalk portion of stamen.

Stamen

male floral structure composed of anther and filament.

Pistil

female floral structure composed of stigma, style, and ovary.

ovary

ovule-producing portion of pistil

style

stalk-like structure linking ovary to stigma

stigma

pollen-receptive surface of pistil

carpel

ovule-producing portion of the ovary

ovule

the megasporangium located with in the ovary; produces the egg sac (megagametophyte) which contains the egg; the ovule, after fertilization of the egg, will become a seed.

locule

chamber in ovary formed by enclosure of ovule by one or more carpels and placental walls

Microsporogenesis

Microsporogenesis

production of microspores which eventually give rise to the pollen grains.

Microsporocyte

diploid cell which divides meiotically to produce a tetrad of haploid microspores, each of which will divide mitotically to produce a pollen grain.

Microgametogenesis

Microspore

haploid product of microsporogenesis which divides mitotically to produce, initially, an immature pollen grain.

Immature pollen grain

consists of two haploid cells, one a generative cell which divides to produce two sperm cells, and the other a vegetative cell which grows (does not necessarily divide) to produce the pollen tube.

Mature pollen grain

haploid, three-celled individual which consists of two sperm cells and one vegetative cell.

Microgametophyte

haploid, three-celled individual consisting of two sperm cells and the pollen tube which transfers the sperm to the female reproductive structures.

Megasporogenesis

In the ovule:

Megasporogenesis

production of megaspores which eventually give rise to the megagametophyte (egg or embryo sac).

Megasporocyte

diploid cell which divides meiotically to give rise to four megaspores, usually one of which gives rise to the megagametophye.