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•improves plant growth
•food substances that plants obtains

Soil Texture

•Soil particles are classified by size; from largest to smallest.
-sand, silt, and clay

soil horizons

layers where soil is stratified


consists of mineral particles, living organisms, and humus


decaying organic material

Topsoil Composition

A soil's composition refers to its inorganic (mineral) and organic chemical components

Inorganic 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.

cation exchange

cations are displaced from soil particles by other cations

Organic Components

•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.

essential element

A chemical element required for a plant to complete its life cycle

hydroponic culture

used by researchers to determine which chemical elements are essential


•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

nitrogen cycle

•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+.


carried out by bacteria that convert NH3 into NO3-


•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.

Two Main Types of Mycorrhizae

1. Ectomycorrhizae
2. arbuscular mycorrhizae


•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.

arbuscular mycorrhizae

•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.


•grows on another plant and obtains water and minerals from rain
•Ex: Staghorn fern

Parasitic plants

absorb sugars and minerals from their living host plant


a photosynthetic parasite plant


a nonphotosynthetic parasite plant

Indian pipe

a nonphotosynthetic parasite plant

Carnivorous plants

•are photosynthetic but obtain nitrogen by killing and digesting mostly insects
•Ex: venus flytrap, pitcher plants, and sundews

The angiosperm life cycle

characterized by "three Fs": flowers, double fertilization, and fruits

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.


a part of the stem where flowers are attached


•are the reproductive shoots of the angiosperm sporophyte
•consist of four floral organs:


consists of a filament topped by an anther with pollen sacs that produce pollen


•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


a single carpel or group of fused carpels

Complete flowers

contain all four floral organs

Incomplete flowers

lack one or more floral organs, for example stamens or carpels


• Clusters of flowers
• Ex: sunflower

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.


•the transfer of pollen from an anther to a stigma
•can be by wind, water, and animals

Double fertilization

•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

Endosperm development

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

Embryo Development

The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell and a terminal cell.

seed coat

a hard and protective coating where the embryo and its food supply are enclosed


when the seed enters this state, it stops growing and metabolic processes cease


the embryonic axis below the cotyledons and terminates in the radicle


embryonic root


above the cotyledons


•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:
-Accessory fruit


a single or several fused carpels


a single flower with multiple separate carpels


a group of flowers called an inflorescence

Accessory fruit

contains other floral parts in addition to ovaries

Sexual reproduction

•results in offspring that are genetically different from their parents
•generates genetic variation.
•Only a fraction of seedlings survive.

Asexual reproduction

results in a clone of genetically identical organisms


separation of a parent plant into parts that develop into whole plants


the asexual production of seeds from a diploid cell

Dioecious species

have staminate and carpellate flowers on separate plants


•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.


plant fragments where many kinds of plants are asexually reproduced


a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots


A twig or bud can be grafted onto a plant of a closely related species or variety.


provides the root system


grafted onto the stock

Transgenic plants

are genetically modified (GM) to express a gene from another organism

Plant Breeding

•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.

Plant biotechnology

•Refers to innovations in the use of plants to make useful products
•Refers to use of GM organisms in agriculture and industry

Transgenic crops

•crops have been developed that:
-Produce proteins to defend them against insect pests
-Tolerate herbicides
-Resist specific diseases


•are made by the fermentation & distillation of plant materials such as cellulose
•can be produced by rapidly growing crops.

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