The Ecosystem And Organism And The Cell Biolgy Essay


Definition: An ecosystem can be defined as a biologic environment where the living organisms, as well as the abiotic factors (the physical environment) interact. Animals, vegetables, as well as micro-organisms in a particular area form an ecosystem.

Features of the ecosystem:

The habitat: comprises the natural conditions of the ecosystem where the different species live and adapt to the living conditions

The ecological niche: relates to the ways an organism can be connected to both the biotic and abiotic existent factors in the living environment

Dynamic: there are constant changes that occur in an ecosystem that can be either temporary or cyclical. The biotic elements react to the changes in the ecosystem: fires or deforestation can affect the fertility of the soil and the food chain

Ecological succession: in the curse of time, some elements get replaced by others in an ecosystem. The primary succession refers to life that evolves from a land where there has never been life before, while the secondary succession refers to the revival of a pre-existent ecosystem after a disturbance, such as a fire, for example. In the case of secondary succession, the environment already contains the needed nutrients that facilitate the growth of different species of plants

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The food web: in ecosystems, nothing gets wasted; all the organisms (alive or dead) can be potential food source for other more evolved species. For example: a caterpillar feeds itself on a leaf, a sparrow eats the insect, but the bird is eaten by a bigger predator as well (an eagle). When these organisms die, decomposers transform them into inorganic substances. These relations between the biotic and abiotic factors in an ecosystem form the food web.

Energy transfer: in ecosystems, transfers of energy are organized in food chains. Food chains interconnecting form a food web. There are two types of organisms in an ecosystem: producers and consumers. Producers have the capacity to make their own organic food, while consumers are unable to synthesize organic compounds and as a result they feed on other living beings.

The producers: are plants that are able to make their own foods by using the energy that comes from the sunlight. Green plants containing chlorophyll, algae and several species of bacteria can be defined as producers. The process of using the sunlight in the process of converting carbon dioxide into organic compound is called Photosynthesis. The chemical energy that is obtained in this way is converted again into a form that cells are able to use in the processes of Cellular Respiration.

The Cell

What is the Cell? The cell is one of the most fundamental forms of life. They are structural units that make up the human body, animals, as well as plants. In the composition of a cell, fluids are the most important elements (90% of the cell are fluids called cytoplasm). Cells are very important aspects of inheritance because the cell environment affects the gene regulation and expression due to the fact that both the cytoplasm and the nucleus are DNA packed.

Molecules: contain 50% of proteins, 30% of nucleic acid and carbohydrates, 10% lipids and the rest of 10% of the molecules are composed of other elements.

The cytoplasm: Components


Made of: molecules (except organelles) + water


Made of: Nucleus and Endoplasmic Reticulum


DNA location, RNA transcription


Reticulum (ER)

The transport network for molecules, plays an important role in protein synthesis

Rough ER

Contains ribosomes

Smooth ER

Tabular- shaped network


50%- in the ER, 50%- free in the cytosol

Golgi Apparatus

Proteins are prepared to be shipped out of the cell


Food is converted into energy

Organelles in cells

Chloroplasts, Leucoplasts and Chromoplasts

Cell types: - Prokaryotes and Eukaryotes


Do not have the nucleus as a distinct organelle or any membrane (in most of the cases)

DNA is located in the cytoplasm

Have a cell wall


Have a nucleus surrounded by membrane, relatively similar to the outer cell membrane

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Found in multi-cellular organisms

Genetic material forms chromosomes in the nucleus

Plant Cells: - are different from the animal cells because they have Vacuoles, Chloroplasts and Cell walls, but do not have centrioles.


self- reproducing

the "energy factory" of the cell

capture light energy and convert it into the necessary nutrients for sustaining their life


Store water and food

Wastes are stored here as well

The structural support of the cell

Cell walls

Rigid and made out of cellulose and fibrils

Responsible for cell protection

Cell division: - Mitosis and Meiosis


Produces gametes and has two cell divisions resulting in four cells.

I division: the genetic crossover occurs and the cell will perform the prophase, metaphase (the crossover takes place) and finally anaphase and telophase.

After the first division, the process is not complete so that another division will take place, a second prophase.

Result: 4 haploid gamete cells

Crossover: - when two chromosomes connect and break to each other's ends.


Normal cell division

Prophase: chromosomes migrate to the middle of the cell

Metaphase: chromosomes form pairs

Anaphase: chromatids forming the chromosomes separate and form new chromosomes

Telophase: nuclei reforms

Cytokinesis: the membrane separates the cell into 2 daughter cells

The Organism

Definition: - any living system that has the capability to give a response to stimuli, reproduce, grow, develop and maintain homoeostasis as a stable whole. There are two types of organism: unicellular and multi-cellular organisms. Any organism composed out of more than one cell is a multi-cellular organism. Viruses are not considered to be organisms because of their incapability to have an autonomous metabolism and/or reproduce.

Unicellular organisms: - can be both eukaryotes and prokaryotes.

Bacteria: - are unicellular prokaryotes, ranging in shape from spheres to rods and spirals. They can sustain life in every habitat on Earth, from radioactive waste to soil, water or deep in the Earth's crust. Bacteria play a vital role in recycling nutrients in the food chain and form mostly the world's biomass.

Known as parasites, bacterial cells live in the human body as well: there are ten times more bacteria in the human flora than there are in the entire body. However, due to the protection of the immune system, most of them are harmless.

Infectious diseases that are caused by different species of bacteria are: cholera, bubonic plague, anthrax, but one common and fatal bacterial disease is tuberculosis, being common in underdeveloped countries of the Sub- Saharan Africa. The bacterial cells are classified as prokaryotes due to the fact that they do not contain a nucleus and organelles that are bound to the membrane.

Cellular structure of bacteria

Compared to the eukaryotes, bacteria have a relatively simple organism lacking the membrane-bound organelles found in more advanced forms of lives (they lack chloroplasts, mitochondria, etc). Simply put, bacteria can be defined as "bags of cytoplasm" having only a lipid membrane with protective role (holds the life- essential components of the cytoplasm within the cell)

The carboxyome are compartments within the bacteria providing a higher level of organization, surrounded generally by polyhedral protein shells and not lipid membranes. The function of these organelles is the localization and compartmentalization of the bacterial metabolism.

Due to the fact that bacteria have no membrane-bound nucleus, with their genetic material being one circular chromosome in the cytoplasm, the nucleoid contains the chromosome with the RNA material and the proteins. Even if bacteria contain ribosomes for protein production, their structure is different from the ribosomes in eukaryotes or Archaea.

Extracellular structure of bacteria

The cell membrane is surrounded by a cell wand made out of peptidoglycan, usually cross linked by peptides with D-amino acids content. There is a slight difference between bacterial cell walls and the cell walls of the plants, because the cell walls contain cellulose and chitin, but no peptidoglycan. The cell wall is very important in the lives of many bacteria due to its protective role. Penicillin can be effective in the killing of the bacteria because it destroys the synthesis of peptidoglycan. The cell walls can be divided in two categories in bacteria: Gram- positive and/or negative. Most of the bacteria have a Gram-negative cell wall with a relatively thin cell wall with few layers of peptidoglycan.

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Extracellular structures are mainly dependent on the bacterial secretion system which transfers proteins from the cytoplasm into the periplasm and/or in the environment of the cell. Because of the fact that many secretion systems play an essential role for the virulence of pathogens, they are intensively studied in bacteria.

Archaea: are also single-celled microorganisms with no nucleus or membrane- bound organelles like the bacteria. Due to the fact that they have an independent evolutionary history, they are now classified as a separate domain within the Bacteria and Eukaryote. Archaea are also similar in shape and size to bacteria. Despite this visual similarity, archaea are more evolved than bacteria due to the fact that they posses genes and also metabolic pathways that can be related to eukaryotes (for example, they rely on ether lipids in their cell membranes). Archaea are categorized as extremophiles that lived in extreme environments, such as arctic habitats, salt lakes or hot springs. However, they can also be found in oceans, soils or marshlands. Their occurrence is most present in oceans and may be one of the most abundant groups of organisms on Earth.

Multicellular organisms: - are all the organisms consisting of more than one cell. In multicellular organisms, each cell is specialized to complete a certain task. Basically, all organisms that can be seen with the naked eye are multicellular organisms.