Characteristics of living things and the processes of photosynthesis

Biology

Living and Non-Living Things. Biology is the study of living things. Biologists are scientists who specialize in the study. They discovered more than a million life forms on earth, some of them living and some are not (Buckley 2003). They distinguish living things from non-living according to certain characteristics. These are nutrition, respiration, excretion, reproduction, growth, sensation, movement, transport, secretion, metabolism and regulation (Buckley). Other scientists recognize a living thing when it is composed of cells, requires energy to function and survive, display a hereditary pattern, responds to the environment, maintains homeostasis, and evolves and adapts (ThinkQuest Team 2000).

Nutrition means that living things eat to stay alive (Buckley 2003). Plants use energy from light to produce their food, while animals feed on plants or other animals. Respiration means that living things must breathe in oxygen to produce energy and function. Plants breathe in carbon dioxide and breathe out oxygen for use by animals. Excretion means that they eliminate matter, which they do not need. Examples are sweat, urine and feces. Reproduction means that living things reproduce their own kind or offspring like themselves. Growth means that they become bigger as they grow older. Sensation means that they perceive and react to stimuli in the environment, such as sound and light. Movement means that most living thinks change location or position. Most animals can move easily. Plants move in the direction of light. Transport means that living things must move things inside the cell or organism. Secretion means living things release specialized substances, like oils, hormones and enzymes. Metabolism refers to energy processes within a living thing or organism, which sustain its life. And regulation refers to internal balance within the organism in spite of internal and external changes (Buckley).

Other scientists believe that living things possess seven characteristics, which distinguish them from non-living things (ThinkQuest Team 2000). Living things or organisms are made up of cells, need energy to survive, reproduce their own kind, display hereditary patterns, respond to stimuli in the environment, maintain homeostasis or balance, and evolve and adapt to the demands of survival (ThinkQuest Team).

Non-living things do not possess these characteristics.

Photosynthesis and Cellular Respiration.

Some animals feed on other animals but other animals feed on plants (Alberts, et al.

2002). Plants trap energy directly from the sun to produce its food through photosynthesis. They use that energy to build atoms, which convert into proteins, nucleic acids, polysaccharides and lipids. These substances are later taken in by animals that eat these plants. Photosynthesis occurs in two stages. In the first, plants capture the sun's energy and store it as chemical bond energy in small molecules. These molecules act as carriers of energy. As a result, they give off molecular oxygen as a waste product. In the second stage, these carriers help produce sugars from carbon dioxide and water as a useful source of energy for both the plants and the animals, which later eat them (Alberts, et al.).

Energy is stored in all animals and plants in whatever form it is ingested (Alberts, et al. 2002). This energy is extracted in a usable form by living organisms through gradual oxidation or controlled burning. A vast amount of oxygen is present in the earth's atmosphere. The most energetically stable form of carbon is CO_2, while hydrogen's is as H_2O. A living cell gets energy from sugars or other organic molecules through cellular respiration. This process occurs when the cell allows its carbon and hydrogen atoms to combine with oxygen to produce CO_2 and H_2O (Alberts, et al.).

Photosynthesis and cellular respiration complement each other (Alberts, et al. 2002). Almost all living things or organisms breathe in the oxygen released by plants by photosynthesis. Animals, in turn, release carbon dioxide, which plants need to make their food by photosynthesis. This pattern shows the symbiosis among living organisms in the biosphere (Alberts, et al.).

White Blood Cells, Red Blood Cells and Platelets

Red blood cells or RBC account for almost 45% of the total volume of blood (Smith 2009). Their main function is to bring oxygen from the lungs to every cell in the body RBCs consist mainly of hemoglobin, which takes oxygen molecules from the lungs. Hemoglobin gives the blood its red color (Smith).

White blood cells or WBC comprise only about 1% of the blood volume (Smith 2009). Despite their diminutive number, they play a very important role. They are the immune system's primary defense against harmful microorganisms, such as bacteria, viruses, fungi and parasites. WBCs do this by directly attacking a perceived invader. They first identify it as foreign, attach themselves to it and then destroy it. The process is called phagocytosis.

WBCs perform this prime function by producing antibodies and releasing these into the blood (Smith 2009). An antibody attaches itself to the invader and destroy it or secure help from other cells in the immune system. The many types of WBCs include neutrophils, monocytes and lymphocytes. They interact among themselves and with plasma proteins or merge to make up a complex but very efficient immune system (Smith).

Platelets are the tiniest cells in the blood (Smith 2009). Their major function is to form clot whenever a blood vessel is broken. This process is called coagulation. Right after an injury, platelets in the area cleave and stick to the edges of the injury. They also activate a mechanism in response to the damage. This consists of constricting the blood vessels to reduce bleeding, bring in more platelets to the damage area, and trigger the plasma-based clotting components, such as fibrinogen. Fibrinogen turns into long, sticky threats of fibrin. Platelets and the fibrin join to create a mesh and a stable clot. This function of the blood is all-important to the body's survival (Smith).

The processes of transcription and translation decode DNA information in a gene

(Ridley 2009). A protein molecule evolves from these processes through which DNA produces its effects on every cell of every living organism. Information moves from DNA to RNA to protein on a one-way direction. This is referred to as the central dogma, which explains why acquired characters are not inherited (Ridley).

The process of transcription produces the three forms of RNA, namely messenger RNA or mRNA; ribosomal RNA or rRNA; and transfer RNA or tRNA (Ridley 2009).

Virus -- This is an infectious agent, which affects all life forms, such as humans, animals, plants, fungi and bacteria (Hardwick 2009). It consists of either DNA or RNA and surrounded by a protein, called capsid. It is 20 to 100 times smaller than bacteria so that it is visible only under light microscopy. A virus is not considered a living organism, as it cannot reproduce outside a living host. It can only replicate, that is, transmit its genetic information from one cell to another (Hardwick).

At first contact, an outer viral structure connects with and binds to a specific molecule on the host's cell surface (Hardwick 2009). The virus crosses the cell membrane often by fusing its lipid envelope that cell membrane. In the process, it releases nucleocapsid into the cytoplasm of the host's cell. When it gains entry, viral genes replicate. It produces proteins by the host's cellular machinery. The first proteins are often the enzymes used to copy the viral genome up to thousands of times. Later, the proteins in the capsid are synthesized to form new nucleocapsids. The virus completes the replication process by leaving the cell. It does this by budding out of the cell's plasma membrane, releasing new viral particles to infect other cells or move from one cell to an adjacent cell. A small virus can replicate in a few hours while a large virus can replicate for several days (Hardwick).

Examples of human illnesses caused by infective viruses are influenza, hepatitis B

and herpes simplex. #