Biol.105

Plant Categories

• Annual plants complete their life cycle in a single growing season.
• Biennial plants complete their life cycle in two growing seasons.
• Perennial plants live for several or many growing seasons.

Flowering Plant Classes

• Magnoliopsida (dicots)
• Liliopsida (monocots)

Monocots and Dicots - Leaf Venation, Vascular Cambium/Cork Cambium, Vascular Bundles, and Pollen Grains

• Leaf venation:
  • Dicots: Network of veins
  • Monocots: Parallel primary veins
• Vascular Cambium and Cork Cambium:
  • Dicots: Present
  • Monocots: Absent
• Vascular bundles of stem:
  • Dicots: Bundles arranged in a ring
  • Monocots: Bundles scattered
• Pollen grains:
  • Dicots: Grains have three apertures
  • Monocots: Grains have one aperture

Sepals and Petals

• Sepals are the outermost whorl, collectively known as the calyx.
• Sepals protect the flower while it's in bud form.
• Petals are the next whorl inside the sepals, collectively known as the corolla.
• Showy corollas attract pollinators.
• Inconspicuous or missing corollas are found in trees, weeds, grasses, and wind-pollinated plants.
• Sepals and petals together form the perianth..

Ovaries

• Ovaries are derived from carpels with inward-rolled margins.
• Carpels are leaf-like structures containing ovules along their margins.
• Carpels can fuse into compound ovaries.
• Pistils can consist of one or more carpels..
• Superior Ovary: Calyx and corolla attached to receptacle at the base of the ovary.
• Inferior Ovary: Receptacle grows up and around the ovary; calyx and corolla appear attached at the top of the ovary.
• Ovules develop into seeds after fertilization.

Inflorescences

• Flowers are either produced singly or in groups called inflorescences.
• Inflorescence is a group of flowers.
• Examples of inflorescence types include panicle, spike, raceme, catkin, simple umbel, corymb, dichasium, head, composite umbel.

Exocarp, Endocarp, and Mesocarp

• Exocarp: The skin of the fruit.
• Endocarp: The inner boundary around the seed(s).
• Mesocarp: The tissue between the exocarp and endocarp.
• Pericarp: The collective name for exocarp, endocarp, and mesocarp

Berries

• Berries develop from compound ovaries, have more than one seed, and have fleshy pericarp.
• True berries have thin skin and relatively soft pericarp (e.g., tomatoes, grapes, peppers, blueberries, bananas)
• Pepo berries have a relatively thick rind (e.g., pumpkins, cucumbers), while Hesperidium berries have a leathery skin containing oils (e.g., citrus fruits).

Pomes

• Pomes have flesh derived from enlarged floral tubes or receptacles that grow around the ovary.
• The core and a little adjacent tissue come from the ovary, while the remainder is from the floral tube and receptacle.
• Apples and pears have a papery or leathery endocarp.

Aggregate Fruits

• Aggregate fruits develop from a single flower with several to many pistils.
• Individual pistils mature as a clustered unit on a single receptacle.
• Examples include raspberries, blackberries, and strawberries.

Fruit and Seed Dispersal (Wind)

• Fruits can be dispersed by wind, often through samaras (winged fruits), plumes, or hairs.
• Seeds can also be dispersed by wind, often being small and lightweight or bearing wings.

Seeds - Structure

• Ovules develop into seeds.
• Cotyledons store food and function like seed leaves.
• Embryo is the cotyledons and plantlet.
• Plumule is the embryo shoot.
• Epicotyl is stems above the cotyledon.
• Hypocotyl is stems below the cotyledon.
• Radicle develops into the root.

Germination

• Germination is the beginning or resumption of seed growth.
• Some seeds require a period of dormancy, which can be broken by mechanical abrasion, thawing, freezing, bacterial action, or soaking in rain.
• Scarification artificially breaks dormancy.
• After ripening, the embryo is composed of only a few cells, and seeds won't germinate until the embryo develops fully.

Epigeous and Hypogeous Germination

• Epigeous germination: The hypocotyl lengthens, bends, and becomes hook-shaped. Top of the hook emerges from the ground and pulls the cotyledons above the soil.
• Hypogeous germination: The hypocotyl remains short and the cotyledons do not emerge above the soil surface.

Seed Longevity

• Seed viability varies depending on species and storage conditions.
• Viability can be extended by low temperatures and dryness.
• Vivipary is when the embryo continues to grow while the fruit is still attached to the parent plant, and there is no period of dormancy.

Diffusion

• Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.
• Diffusion leads to a state of equilibrium where molecules are distributed throughout the available space.
• The rate of diffusion depends on pressure, temperature, and the density of the medium.

Osmosis

• Osmosis is the diffusion of a solvent (typically water) through a semipermeable membrane from a region of higher water concentration to a region of lower water concentration.
• It can be measured using an osmometer..

Osmotic Pressure and Osmotic Potential

• Osmotic pressure is the pressure required to prevent osmosis.
• Osmotic potential is balanced by the resistance of the cell wall.
• Pressure potential (turgor pressure) develops against the cell wall from water entering the cell.
• A turgid cell is firm due to water gained through osmosis.
• Water potential = osmotic pressure + pressure potential.

Pathway of Water Through a Plant

• Osmosis is the primary method of water entry into plant cells.
• Water moves through cell walls and intercellular spaces of the epidermis and root hairs to reach the endodermis.
• Water then crosses the endodermal cells to reach the xylem, travelling throughout the plant.
• It diffuses out through stomata.

Plasmolysis

• Plasmolysis is the loss of water through osmosis in plant cells, accompanied by shrinkage of the cytoplasm away from the cell wall.

Imbibition

• Imbibition is the initial step in seed germination. Large molecules like cellulose and starch develop electrical charges when wet, attracting water molecules.
• Water molecules adhering to large molecules causes tissue swelling.

Active Transport

• Active transport absorbs or retains solutes against a diffusion or electrical gradient, using energy.
• Proton pumps in the plasma membrane (energized by ATP) are involved.
• Transport proteins facilitate solute movement into or out of cells.

The Cohesion-Tension Theory

• The cohesion-tension theory explains water transport in plants.
• Transpiration generates tension that pulls water columns through the plant from roots to leaves.
• Water molecules adhere to and cohere with each other within tracheids and vessels of the xylem.

When Stomata Open

• Stomata open during photosynthesis.
• Guard cells expend energy to take up potassium ions from adjacent epidermal cells, leading to a lower water potential in guard cells.
• Water moves into guard cells via osmosis, causing them to become turgid and the stomata to open.

When Stomata Close

• Stomata close during periods when photosynthesis does not occur.
• Potassium ions leave guard cells.
• Water leaves guard cells via osmosis, causing them to become less turgid and the stomata to close.

Guttation

• Guttation is the loss of liquid water.
• It occurs if a cool night follows a warm, humid day, with water droplets forming on the tips of veins.
• In the absence of transpiration, pressure in xylem elements forces water out.

Transport of Food (Organic Solutes)

• Water plays a vital role in transporting food (organic solutes) through the phloem.
• The pressure-flow hypothesis describes the movement of organic solutes from sources (where they are made) to sinks (where they are used).
• Organic solutes move along concentration gradients between sources and sinks.

Macronutrients and Micronutrients

• Macronutrients are needed in larger amounts by plants (e.g., nitrogen, potassium, calcium, phosphorus, magnesium, and sulfur).
• Micronutrients are needed in smaller amounts (e.g., iron, sodium, chlorine, copper, manganese, cobalt, zinc, molybdenum, and boron).
• Deficiencies in any required element can cause characteristic symptoms in plants..