The Earth went through a period of catastrophic and intense formation during its earliest beginnings roughly 4.5 to 4.4 billion years ago. Roughly about 3.8 to 4.1 billion years ago, Earth had become a planet with an atmosphere and an ocean, the atmosphere back then was far too toxic for humans and other life forms that we know today. It had no free oxygen. This stage of the Earth's formation is commonly referred to as the pre-Cambrian Period, and is divided into three sections: the Hadean, Archean and Proterozoic Periods (Eric Mclamb 2008).
In the Hadean period (4.5 to 3.8 billion years ago) the primitive Earth was nothing but a molten rock where it was continuously bombarded by asteroids, meteors and comets until it formed into a solid sphere, fell into an orbit around the sun, and began to cool down. It was so hot that the water droplets in its atmosphere evaporated. The atmosphere was so poisonous that nothing would be able to survive. The atmosphere consisted of volatile compounds like water vapour, carbon monoxide, methane, ammonia, nitrogen, carbon dioxide, nitrogen, hydrochloric acid and sulphur which were produced by the constant volcanic eruptions that plagued the primitive Earth (Eric Mclamb 2008).
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Throughout the Archean (3.8 to 2.5 billion years ago) period the Earth's crust began to cool and stabilize, when the Earth had cooled down sufficiently clouds began to form produce large amount of water that formed the oceans. This is where we begin to see the first sign of life to appear according to the fossil record, also this is when we see our primitive Earth's land masses began to form. At this time the only initial life forms were bacteria (cyanobacteria) as they can survive in the highly toxic atmosphere that existed during this time. There was little to no free oxygen in the atmosphere. What was produced by the cyanobacteria was probably consumed by the weathering process. Once the primitive Earth's crust was sufficiently oxidized, more oxygen could remain free in the atmosphere (Eric Mclamb 2008).
During the Proterozoic period (2.5 billion years ago) the amount of free oxygen in the atmosphere rose to 10 % (Origin of the Earth's atmosphere 2010). According to the 2.5 billion year old fossilised blue-green algae this is the first main sign of oxygen forming life.1.8 billion years ago oxygen began to build up and made way for the emergence of life as we know it today. This created conditions that would not allow most of the existing life to survive and therefore made way for the more oxygen dependent life forms (Eric Mclamb 2008).
1By the end of this period, our planet was well along in its evolutionary processes leading to our current period, the Holocene Period, which is commonly known as the Age of Man. The Cambrian (550 million years ago), this is where we see life on Earth ''explode'' into action by developing almost all of the major groups of plants and animals in a relatively short time. Of course it ended with the massive extinction of most of the existing species roughly 500 million years ago, making room for the new evolution of new plant and animal species. About 2.2 million years ago the modern human species emerged (Eric Mclamb 2008).
The levels of oxygen (21% free oxygen) we see in today's atmosphere were roughly achieved 400 Million years ago (Origin of the Earth's atmosphere 2010). Today's atmosphere contains 78% Nitrogen, 21% Oxygen, 0.9% Argon and 0.03% Carbon dioxide. The oxygen we have present in today's atmosphere has all been produced by plants (history of the universe 2010). Other gasses that we have on Earth are Methane 17% (Earth's observatory 2010), Hydrogen 0.05%, krypton 0.0114%, Neon 0.00182% and Helium 0.000524% (Lutgens and Tarbuck 2000).
Name two different sources of energy that could have powered the synthesis of the first organic molecules?
The two energy sources that might have powered the synthesis of the first organic molecules were the primordial soup and the deep sea vent theory.
2.1a Primordial soup theory
In 1924 Alexander Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for the evolution of life. In his origin of life, he thought that the spontaneous generation of life did in fact occur once, but was now impossible because the conditions found in the early earth had changed, and the presence of living organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in oxygen-less atmosphere through the action of sunlight. These would combine in ever-more complex fashions until they formed coacervate droplets. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote "cell integrity" survive, those that do not become extinct (Albrecht Moritz).
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Haldane suggested that the Earth's pre-biotic oceans which are very different from the modern ocean would have formed a "hot dilute soup" in which organic compounds could have formed. This idea was called biopoiesis, the process of living matter evolving from self-replicating but nonliving molecules (Albrecht Moritz).
2.2b The deep sea vent theory
The hydrothermal vent theory suggests that life may have begun at underwater in the hydrothermal vents, where hydrogen-rich fluids emerge from below the sea floor and interface with the carbon dioxide-rich ocean water. Sustained chemical energy in such systems is derived from redox reactions, in which electron donors, such as molecular hydrogen, react with electron acceptors, such as carbon dioxide (Albrecht Montriz).
State 2 ways in which a eukaryotic cell differs from a prokaryotic cell?
There are two main types of cells and they are the billion year old Prokaryotic Cell and the recent Eukaryotic Cell. The Pictures below show you the difference between the two cells; one of the big differences is that prokaryotic cells have a membrane wall but have no nucleus, while the eukaryotic cells have a nucleus.
The purpose of the nucleus is to sequester the DNA-related functions of the big eukaryotic cell into a smaller chamber, for the purpose of increased efficiency. This function is unnecessary for the prokaryotic cell, because it's much smaller size means that all materials within the cell are relatively close together. Of course, prokaryotic cells do have DNA and DNA functions. Biologists describe the central region of the cell as its "nucleoid", because it's pretty much where the DNA is located. There is no physical boundary enclosing the nucleoid (Prokaryotic and Eukaryotic cells 2004).
As can been seen from the pictures above the second major visual difference is the cytoplasm of eukaryotic cell is filled with a large collection of complex organelles which quite a few are enclosed within their own membranes. The organelles in the prokaryotic cell are not protected by a membrane (Julie Brega 2005). There is also a lot more space within a eukaryotic cell than what there is in the prokaryotic cell, the majority of the structures, like for an example the nucleus, increase the efficiency of their functions by confining them within a small space within the cell, or with communication and movement within the cell (Prokaryotic and Eukaryotic cells 2004).
What is Phagocytosis?
A phagocyte cell specializes in phagocytosis. Phagocytosis is a process which where cells engulf and ingest particles. This process is an important part of cell function, allowing cells to collect nutrients while allowing the body to protect itself from harmful pathogens. This process is referred to endocytosis. The opposite, of this process is exocytosis the expulsion of unwanted material from a cell (Wise Geek 2010).
Why is ATP and why is it important?
3Every cell in the body requires energy to carry out its tasks. This is done by chemical reactions from the breakdown of glucose in the blood or glycogen from muscle cells. Internal respiration describes the process by which sugars are oxidized to provide energy for the synthesis of Adenosine Triphosphate (ATP), the energy carrier molecules. So ATP is important to the cell because it provides the energy it needs for all its functions (Julie Brega 2005).
What is meant by 'free energy'?
To describe the energy changes, which occur during a chemical reaction, the concept of free energy is used. This is the energy in a system that is available for doing work. The majority of reactions in cells release free energy and are therefore described as exergonic. In contrast many reactions in cells require the addition of free energy to occur. These are referred to as endergonic and they end up with more energy than they started off with (Robert Burns and Donald Cave 2002).
Part 2 (approx 350 words).
Describe the structure and function of cell membranes?
The cell membrane surrounds the protoplasm of a cell and, that separates the components inside from the outside environment. The cell membrane also helps to keep the cells shape, and help to group cells together to form tissues. This barrier is permeable, so therefore allows the transfer of materials needed for the cells survival. The membrane also maintains the cell potential (Wikipedia 2010).
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There are proteins (receptors) within the membrane that acts as signals which enables the cell to communicate with each other. These receptors are found all over and their main function is to receive signals from its environment and other cells. Other proteins (markers) which are found also on the surface of the cell, the markers allow other cells to identify each other (Seorf 2010).
4The membrane as can be seen below is double layered and is made up of phospholipids, which look like sphere shaped molecules on the end of two tails. The spheres are made of phosphate, which are attracted to water. This means that they tend to move towards the water which is present inside and outside of the cell. The tails that are attached to the phosphate are made of lipids, and they are hydrophobic fat molecules which don't like water, so they move away from water and move towards each other to avoid contact with water. Due to their natural tendency to orient themselves, these molecules are able to repair any damage that is done to the membrane, making it flexible and strong (Telstar 2010).
Plate 1: Cell structure (odec 2006)
The membrane as can be seen above is lined with proteins which allow certain molecules to enter and to leave the cell as well as provide a structure which operates as markers which help to identify it to other cells. Some of these proteins only appear on one side of the membrane or are embedded entirely within it (Buzzle 2010).
The protein molecules that control transport into and out of the cell membrane operate primarily in two different ways, through passive and active transport. Passive transport is used for small molecules, which diffuse through small protein channels from an area of high concentration to an area of lower concentration. Sometimes two molecules move through a channel simultaneously, either together or in opposite directions, balancing out the concentrations on either side of the membrane. Active transport proteins use ATP energy to move molecules across the membrane that are too large for passive transport or that need to cross a gradient in the opposite direction of concentration. These proteins recognize and pull the desired molecules across the membrane (Biology suite 2010).
Another type of protein found on the cell membrane surface is the receptor. These molecules sit on the plasma membrane and convey important information about the cell to other cells, including neighbouring cells of similar type and immune system cells. This is important because it lets the cell coordinate its growth and activity with other cells as well as allowing the cell to let the immune system know when it has been attacked or infected(Biology suite 2010).
Part 3 (approx 400 words)
Describe the process of Mitosis?
Mitosis is the division of cells which at the end of the process produces identical daughter cells containing exactly the same genetic information and the same number of chromosomes. This division of cells only happens during growth stages (Juile Braga 2005).
5There are five stages to mitosis. To explain the process of mitosis more easily only two chromosomes will be used to represent thirty two pair of chromosomes that we see in horses (Julie Brega).
The first stage of this process is known as interphase, this is where the chromosomes look like a piece of long thread and they just visible under a microscope. All the genetic material and the cytoplasmic organelles replicate to ensure that there is enough material for all daughter cells. This stage is also in some texts referred to as the resting stage, even though organelle synthesis and cell division can still occur (Julie Brega 2005).
The second stage is referred to as the prophase, this is where the chromosomes start to shorten and thicken and the nucleolus shrinks. The chromosomes are now known as a pair of chromatids which attaches at the centromeres. The centrioles move to opposite sides of the cell known as the poles. Spindle like fibres start to form from the centrioles. The nucleolus disappears and the nuclear membrane breaks down (Julie Brega 2005).
The third stage is called metaphase, in this stage the spindle fibres are fully formed and now form across the cell from pole to pole. The chromatids attach by spindle fibers to the spindle at the centromeres. The chromatids move towards the centre of the spindle so the centromeres line up across the centre (Julie Brega 2005).
The fourth stage is known as anaphase and this is where the chromosomes separate and move towards the poles opposite side of the cell (Julie Brega 2005).
The fifth and final stage is called telophase, in this stage the membrane of the cell starts to constrict across the middle. The nucleus will re-form around the chromosomes on both sides of the constricting membrane. The nucleoli will reappear and a nuclear membrane forms around the nuclear material at both ends of the cell. The constricting of the cell continues, the spindle fibres degenerate and the interphase stage will start over again to prepare for the next division (Julie Brega 2005).
At the end of this process the result will be two daughter cells.
Part 4 (approx 500 words)
Describe 3 characteristics of living organisms?
All living things no matter what they are all have the ability to gain and respond to different stimuli within their environment, there are so many different kinds of characteristic to living organisms, but in order for them to survive they must be able to:
The ability and means to acquire material and energy. This means that they must be able to find food, covert that into energy, then into chemicals that our cells can use efficiently. For example plants use photosynthesis to make their food, bacteria uses chemosynthesis for their energy source and animals capture their food in a variety of ways. This intake of food is very important because without a constant supply of usable energy plants and animals will die (Cruz Lectures 2010).
In order to survive organism must be able to regulate their own body temperature (homeostasis). They must be able to balance their inside environment to the one outside, so if you're outside temperature is cold then you need to be slightly on the warmer side and opposite if you outside temperature is hot. For example a paramecium has a vacuole that pumps excess water out of its cell in order to survive in a fresh water environment and warm blooded mammals have an internal thermostat that help to regulate our body temperature at 98.6 degrees Fahrenheit (Cruz Lectures 2010).
All living things must have the ability to reproduce for the survival of the species. Every living thing has chromosomes that contain DNA. Bacteria have circular chromosomes called plasmid. Multicellular organisms like plants and humans have a species specific number of chromosomes. Humans have 46 chromosomes (23 pairs), Horse have 32 chromosomes (16 pairs), gorillas, chimpanzee have 48 chromosomes (24 pairs) and mice have 40 chromosomes (20 pairs). DNA (genes) is important as they contain instructions for the function and structure of an organism (Essortment 2010).
There is a huge range of diversity of living creatures on Earth due to the fact that most organisms reproduce sexually. For example earthworms are hermaphrodites; however other species have separate sex like male and female like for example humans, cows, fish, birds and some plants.
For the survival of the species they must be able to combine the genetic information without doubling the number of their chromosomes that is given to the next generation. So organisms have come up with a way that will reduce the number of chromosomes given to the offspring. The halving (haploid) of the chromosome number is completed by a process called meiosis. So in the female her ovaries will produce haploid eggs (gametes) and in the male he will produces haploid sperm (gamete). The gametes only carry one chromosome from each of the pairs of chromosomes (docstoc 2010).
In fertilization, the sperm and the egg merge together to form a zygote which hold the diploid number of chromosomes. The new generation will be different from either parent even though it contains characteristics from both. This is what gives us the great diversity of live. This diversity is known as biodiversity.
All living things must be able to adapt to the ever changing environment. Plants and animals must be able to modify itself in order for it to survive within its environment. This would be done through the means of natural selection which allow individuals to make better adaptations in order to survive and to reproduce. Therefore their modified characteristics will be passed down to the future offspring which will make the species as a whole better to survive. However, it is important to remember that it is only individuals that can adapt to their environment, but species don't adapt, they evolve, and this can only be done if individuals themselves successfully adapt (docstoc 2010).