•Soil particles are classified by size; from largest to smallest.
-sand, silt, and clay
A soil's composition refers to its inorganic (mineral) and organic chemical components
•Cations (for example K+, Ca2+, Mg2+) adhere to negatively charged soil particles; this prevents them from leaching out of the soil through percolating groundwater
•Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching.
•Humus builds a crumbly soil that retains water but is still porous.
-Increases the soil's capacity to exchange cations
-Serves as a reservoir of mineral nutrients
•Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots.
-These organisms help to decompose organic material and mix the soil.
•plants require them in relatively large amounts
•macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium
•plants need them in very small amounts
•micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum
•the layer of soil bound to the plant's roots
•has high microbial activity because of sugars, amino acids, and organic acids secreted by roots
•Free-living organisms thrive in the rhizosphere, and some can enter roots
•Rhizobacteria can play several roles:
-Produce hormones that stimulate plant growth
-Produce antibiotics that protect roots from disease
-Absorb toxic metals or make nutrients more available to roots
•transforms nitrogen and nitrogen-containing compounds
•Most soil nitrogen comes from actions of soil bacteria
•Plants absorb nitrogen as either NO3- or NH4+.
•Bacteria break down organic compounds or use N2 to produce NH3, which is converted to NH4+.
•mutualistic associations of fungi and roots
•The fungus benefits from a steady supply of sugar from the host plant.
•The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption.
•Mycorrizal relationships are common and might have helped plants to first colonize land.
•the mycelium of the fungus forms a dense sheath over the surface of the root
-The hyphae form a network in the apoplast, but do not penetrate the root cells.
•microscopic fungal hyphae extend into the root
- These mycorrhizae penetrate the cell wall but not the plasma membrane to form branched arbuscules within root cells.
•are photosynthetic but obtain nitrogen by killing and digesting mostly insects
•Ex: venus flytrap, pitcher plants, and sundews
angiosperm life cycle
•Diploid (2n) sporophytes produce spores by meiosis; these grow into haploid (n) gametophytes
•Gametophytes produce haploid (n) gametes by mitosis; fertilization of gametes produces a sporophyte
•In angiosperms, the sporophyte is the dominant generation.
•The gametophytes are reduced in size and depend on the sporophyte for nutrients.
•are the reproductive shoots of the angiosperm sporophyte
•consist of four floral organs:
•has a long style with a stigma on which pollen may land
•At the base of the style is an ovary containing one or more ovules
Development of Male Gametophytes
•Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers.
•If pollination succeeds, a pollen grain produces a pollen tube that grows down into the ovary and discharges sperm near the embryo sac.
•The pollen grain consists of the two-celled male gametophyte and the spore wall.
Development of Female Gametophytes
Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes.
•results from the discharge of two sperm from the pollen tube into the embryo sac
•After double fertilization, each ovule develops into a seed
•The ovary develops into a fruit enclosing the seed(s)
food-storing part of the seed where one sperm fertilizes the egg, and the other combines with the nuclei
usually precedes embryo development
Most monocots and some eudicots, endosperm stores nutrients that can be used by the seedling
Other eudicots, the food reserves of the endosperm are exported to the cotyledons
The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell and a terminal cell.
•Some eudicots the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves)
•Some eudicots have thin cotyledons.
•develops from the ovary.
•protects the enclosed seeds and aids in seed dispersal by wind or animals
•may be classified as dry, if the ovary dries out at maturity, or fleshy, if the ovary becomes thick, soft, and sweet at maturity
•also classified by their development:
•results in offspring that are genetically different from their parents
•generates genetic variation.
•Only a fraction of seedlings survive.
•a plant's ability to reject its own pollen
•Some plants reject pollen that has an S-gene matching an allele in the stigma cells.
•Recognition of self pollen triggers a signal transduction pathway leading to a block in growth of a pollen tube which blocks reproduction.
a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots
•Mutations can arise spontaneously or can be induced by breeders.
•Plants with beneficial mutations are used in breeding experiments.
•Desirable traits can be introduced from different species or genera.
•Refers to innovations in the use of plants to make useful products
•Refers to use of GM organisms in agriculture and industry
•crops have been developed that:
-Produce proteins to defend them against insect pests
-Resist specific diseases