Photosynthetic Light Reactions

Photosynthetic Light Reactions

Photosynthetic light reactions involve the absorption of light energy by plant pigments and the conversion of light energy into adenosine triphosphate (ATP).

Photosynthesis is the process by which plants, algae, and certain types of bacteria use the energy of sunlight to manufacture organic molecules from carbon dioxide and water.

The process may be divided into two parts: the light reactions and the dark reactions. In the light reactions of photosynthesis, light energy coming from the sun or from an artificial light source is absorbed by pigments and used to boost electrons into higher energy levels so they can be used to do cellular work.

Phytoplankton

The term “plankton,” from Greek planktos for “wandering,” is applied to any organism that floats or drifts with the movement of the ocean water.

Most plankton are microscopic and are usually single-celled, a chain of cells, or a loose group of cells. Algal and cyanobacterial plankton are referred to as phytoplankton. The heterotrophic crustaceans and larvae of animals are referred to as zooplankton.

The group of organisms known as phytoplankton (literally, “plant” plankton) do not constitute a taxonomic group but rather refer to a collection of diverse, largely algal and cyanobacterial, microorganisms that live in water and are at the base of the food chain.

Pigments in Plants

Pigments in plants

Photosynthetic pigments color plants and participate in photosynthesis. Other plant pigments are important in flowers and fruits to attract pollinators and seed dispersers. Humans use plant pigments in vitamins and dyes.

Plant pigments can be classified as either nitrogenous or non-nitrogenous, that is, either nitrogen-containing or non-nitrogen-containing.

Non-nitrogenous pigments

Non-nitrogenous forms are widely distributed and include the carotenoids and the quinones. Carotenoids are yellow, orange, or red pigments often involved as accessory pigments in photosynthesis. They are insoluble in water but soluble in a variety of nonpolar solvents. They are easily bleached by light or oxygen.

Plant Biotechnology

Plant Biotechnology

Plant biotechnology may be defined as the application of knowledge obtained from study of the life sciences to create technological improvements in plant species. By this very broad definition, plant biotechnology has been conducted for more than ten thousand years.

The roots of plant biotechnology can be traced back to the time when humans started collecting seeds from their favorite wild plants and began cultivating them in tended fields. It appears that when the plants were harvested, the seeds of the most desirable plants were retained and replanted the next growing season.

While these primitive agriculturists did not have extensive knowledge of the life sciences, they evidently did understand the basic principles of collecting and replanting the seeds of any naturally occurring variant plants with improved qualities, such as those with the largest fruits or the highest yield, in a process that we call artificial selection. This domestication and controlled improvement of plant species was the beginning of plant biotechnology.

Plant Cells, Molecular Level

Plant cells

Water, ions, salts, and gases all are types of inorganic molecules that are essential to cellular function. The chemical properties of water make it an ideal solvent and buffer for the chemistry that occurs inside cells.

The capillary action that helps water travel up plant tissues from the roots is a direct consequence of the polarity of the water molecule.

The chemistry of life on earth is carbon and water chemistry. Water is the most abundant compound in living cells and makes up as much as 90 percent of the weight of most plant tissues. Many of the molecules that are part of larger macro molecules in cells are linked together chemically by dehydration synthesis, or the loss of water.

Plant Domestication and Breeding

Plant Domestication and Breeding

Plant domestication and breeding are the processes by which wild plants are intentionally raised to meet human food, fiber, shelter, medicinal, or aesthetic needs.

No one knows exactly when the first crop was cultivated, but most authorities believe that it occurred at some time between eight and ten thousand years ago. For centuries prior to that time, humans had known that some wild plants and plant parts (such as fruits, leaves, and roots) were edible. These plants appeared periodically (usually annually) and randomly throughout a given region.

Eventually humans discovered that these wild plants grew from seeds and that the seeds from certain wild plants could be collected, planted, and later gathered for food. This most likely occurred at about the same time in both the Sumerian region between the Tigris and Euphrates Rivers and in Mexico and Central America.

Plant Fibers

Cotton plant

Plants are the natural sources of many raw materials used to produce textiles, ropes, twine, and similar products.

The major fiber crops are cotton, flax, and hemp, although less important plants, such as ramie, jute, and sisal, are grown in small amounts. With a total annual production of more than 13 million tons, cotton is by far the most important fiber crop in the world. Because humans heavily rely on cotton for clothing and other textiles, it enters the daily lives of more people than any other product except salt.

Cotton

Cotton (Gossypium) fiber has been known and highly valued by people throughout the world for more than three thousand years. The early history of cotton is obscure. Avigorous cotton industry was present in India as early as 1500 b.c.e. From India, the cultivation of cotton spread to Egypt and then to Spain and Italy.

Plant Life Spans

Plant life span

The cycle of a plant’s life, from seed germination to death, is referred to as its life span. Some plants have short life spans (less than one year), whereas others have life spans that are measured in centuries.

The longest-lived organisms are plants. For example, one bristlecone pine tree in eastern California is forty-nine hundred years old, and some creosote bushes, also in California, are estimated to be about twelve thousand years old. People have long recognized this variation in plant longevity, but the understanding of plant life spans improved greatly after research during the 1960’s.

Types of Life Spans

The life span of an individual plant depends upon two factors. The first is the innate, genetically determined potential for longevity. The second is the effects of the environment, including soil and weather conditions, competing plants, disease-causing microbes, and herbivores.

Plant Tissues

Plant Tissues

Plant tissues are the distinctive structural and functional units of a plant that carry out all its basic life functions, including growth, reproduction, support, metabolism, circulation, and protection from the environment.

The body plan of a plant is very different from that of most animals. Terrestrial plant bodies are anchored in a growing medium, which has an enormous influence over the form and behavior of plant tissues.

Growth and Protective Tissue

Meristematic tissues in plant bodies are responsible for the growth that results from an increase in cell number. In the meristems, individual cells divide to produce pairs of daughter cells which have the ability to divide further or to enlarge and differentiate.

Plantae

Plantae

Life on earth is dependent on the ability of plants to capture the sun’s energy. Directly or indirectly, members of the green kingdom, Plantae, provide food and shelter for nearly all other organisms, including humans. Plants also generate much of the earth’s oxygen. The biosphere would not exist without plants.

Most plants are multicellular, autotrophic organisms, that is, able to produce their own food from inorganic elements by converting water and carbon dioxide to sugar. Plants are sessile, stationed in one spot throughout their lives.

Most plants have a complex life cycle called alternation of generations between diploid and haploid forms. The diploid generation, in which the plant body is made up of diploid cells, is called the sporophyte. The sporophyte produces haploid spores by meiosis.

Plants with Potential

Guayule (Parthenium argentatum)

One of the primary reasons humans cultivate plants is to satisfy an economic need for natural resources. In order for a plant to realize its full economic potential, it must not only fill an economic need but also do so in a cost-efficient manner.

There are several examples of plants which, because of their unique products, appear to fulfill an economic need. However, these plants may not do so in a cost-effective manner.

With development of improved agronomic practices and plant-processing methods, which lower the cost of production, some plants may eventually realize their full economic potential.

Plasma Membranes

Plasma Membranes

The plasma membrane is a structure of the plant cell that forms a semipermeable, or selective, barrier between the interior of the cell and the external environment; they also function in transport of molecules into and out of the cell.

In addition to forming the structural barrier between the internal contents of a cell and the external environment, plasma membranes contain proteins involved in the transport of molecules and other substances into and out of the cell, and they contain proteins and other molecules that are essential for receiving signals from the environment and from plant hormones that direct growth and division.

Carbohydrates associated with the plasma membrane are markers of cell type. In plants, the plasma membrane is the site of cellulose synthesis.

Plasmodial Slime Molds

Plasmodial Slime Molds

The plasmodial slimemolds, or myxomycetes, phylum Myxomycota, are a group of fungus-like organisms usually present and sometimes abundant in terrestrial ecosystems. However, this group comprises about eight hundred species, related neither to cellular slime molds nor to fungi.

The plasmodial slime molds have no cell walls and exist as thin masses of protoplasm, which appear to be streaming in a fan like shape, under favorable conditions.

As these masses, called plasmodia, travel, they absorb small particles of decaying plant and animal matter as well as bacteria, fungi, and yeasts. When mature, a plasmodium may weigh 20-30 grams and take up an area of 1 meter or more.

Poisonous and Noxious Plants

Poisonous plants

Poisonous plants have evolved toxic substances that function to defend them against herbivores and thereby better adapt them for survival.

After evolving adaptations that facilitated colonization of terrestrial habitats, plants were confronted with a different type of problem.

This was the problem of herbivory, or the inclination of many different types of organisms, from bacteria to insects to four-legged herbivores, to eat plants. Pressures from herbivory drove many different types of plants, from many different families, to evolve defenses.

Pollination

Pollination

Pollination involves the transfer of pollen from anther to stigma in flowering plants, or from male cone to ovules in gymnosperms. There are two different types of pollination: self-pollination and cross-pollination.

Pollination is the process, in sexually reproducing plants (both angiosperms and gymnosperms), whereby the male sperm and female egg are joined via transfer of pollen (malemicrospore).

If the anthers and stigmas of the plants involved have the same genetic makeup or they are produced on the same plant, the type of pollination is called self-pollination. If anthers and stigmas are from plants with different geneticmakeups, the type of pollination is called cross-pollination.

Polyploidy and aneuploidy

Polyploidy and aneuploidy

In aneuploidy, one or more whole chromosomes has been lost or gained from the diploid state. In polyploidy, one or more complete sets of chromosomes has been gained from the usual state (generally diploid), as in triploidy and tetraploidy.

For each species of higher plants and animals, the base number of nuclear chromosomes is called the haploid number, denoted as n. Individuals of most species are diploid, having double the haploid number of chromosomes (2n) in each somatic cell. Aneuploid and polyploid organisms have abnormal numbers of whole chromosomes.

Aneuploidy

Strictly speaking, aneuploidy refers to any number of chromosomes in a cell or organism that is not an exact multiple of the haploid number. However, in common practice the termis used to refer specifically to situations in which an organism or cell has only one chromosome or a few chromosomes added or missing.

Population Genetics

Population Genetics

Population genetics is concerned with analyzing the frequencies of the alleles, or forms, of genes in a population of individuals within a species. It examines how gene frequencies change across generations in response to external forces, such as mutation, natural selection, migration, or genetic drift.

The natural process that eliminates individuals of low fitness and advances those of high fitness is termed natural selection. Natural selection causes changes in allele frequency in a population, which is a process called evolution.

Thus, population genetics combines Charles Darwin’s ideas of natural selection and evolution with the basic principles of genetics set forth by Gregor Mendel.

Prokaryotes

Prokaryotes

Prokaryotes are one of two types of cell that form living organisms. Prokaryotic cells lack a nucleus and other organelles found in eukaryotic cells.

Prokaryotes include the unicellular life-forms found in two of the three domains of life, Archaea and Bacteria, whereas all protists, algae, fungi, plants, and animals are eukaryotic organisms, together forming the domain Eukarya.

There are architecturally two distinct types of cells of living organisms: prokaryotic cells and eukaryotic cells. The defining difference between these two types of cells is that prokaryotic cells lack any of the internal membrane-bound structures (organelles) found in eukaryotic cells, such as a nucleus, mitochondria, chloroplasts, endoplasmic reticulum, and Golgi apparatus.