Nature, biology and life science

The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. The principle predicts that both genotype and allele frequencies will remain constant. The Hardy-Weinberg principle describes an idealized state of a population. For a population to be in this kind of state, there can’t be any gene mutations, migrations of individuals, genetic drift and natural selection. Also, random mating must occur. When all these conditions are met, it’s said that the population is in equilibrium. But because all of these things commonly occur in nature, the Hardy-Weinberg equilibrium rarely applies in reality. However, The Hardy-Weinberg equations can still be used for any population, even if it is not in equilibrium. There are two equations: 𝑝 + 𝑞 = 1 and 𝑝² + 2𝑝𝑞 + 𝑞² = 1, where 𝑝 is the frequency of the dominant allele, 𝑞 is the frequency of the recessive allele, 𝑝² is the frequency of individuals with the homozygous dominant genotype, 2𝑝𝑞 is the frequency of individuals with the heterozygous genotype and𝑞² is the frequency of individuals with the homozygous recessive genotype. The first equation tells us that the sum of the frequencies of all alleles of one gene locus in one generation is 100%, while the second one tells us that the sum of the frequencies of all genotypes for one gene locus in one population is also100%.

Aluminium is a silvery-white metal. It’s the thirteenth element in the periodic table. It was discovered in the 19. century by the Danish physicist Christian Oersted who used electrolysis to obtain aluminium. Aluminium is the third most common element in the Earth’s crust, after oxygen and silicon. Because aluminium binds very easily with other elements, it does not occur in nature in its pure form, but in its compounds. The most common way of finding aluminium in nature is in aluminium sulfate. Aluminium has a lot of useful properties. It is a very light metal, but also very strong, extremely flexible and corrosion resistant (because its surface is always covered in a thin oxide layer). It doesn't magnetise, it can conduct electricity and form alloys with a large number of other metals.  It can be rolled, pulled and stamped. Aluminium doesn't catch fire, it doesn't need special paint and it's not toxic. Because of these properties, aluminium has a very important role in different industries. Some of them are: construction, automotive, aviation, energy and food industry.

The molecule of deoxyribonucleic acid is a very long chain which consists of a regular alternation of sugar and phosphate groups. To each sugar is attached a nitrogenous base. The bases can be purines (adenine or guanine) or pyrimidines (thymine or cytosine). The sequence of bases along the chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is called nucleotide. The first feature of our structure consists of two attached chains. The chains are held together by hydrogen bonds between the bases. The bases are joined together in pairs and only certain pairs of bases will fit into the structure. The only possible pairs are: adenine with thymine, and guanine with cytosine. Since the sequence of pars in the chain is irregular, there are a myriad of possible combinations. Ergo, it is believed that the precise sequence of bases in the code carries the genetic information. Also because of the specific pairing of the bases one is complement to another which suggests how the deoxyribonucleic acid molecule might duplicate itself.

Deoxyribonucleic acid or DNA represents very long chain of molecules. The monomers of DNA are called nucleotides. Nucleotide consists of phosphate group, nitrogenous base and sugar. There are four types of nitrogenous bases and they are separated into two groups called pyrimidine and purines. Pyrimidines include thiamine and cytosine, while purines include guanine and adenine. Scientists have evidence that DNA consists of two chains that are both coiled around common fiber axis. These two chains are held together by hydrogen bonds between bases. Pairs of bases are always same and these are thiamine and adenine or guanine and cytosine. Thus, one chain is complement of another. So if we know chemical formula of one chain we can also write formula of the second chain. Also, DNA is long chain which provides many possible permutations.

Plants are multicellular organisms and they have tissue systems that are made of various cell types that carry out specific functions. There are two types of plant tissue systems: meristematic and permanent tissue. Meristematic tissue cells are either undifferentiated or incompletely differentiated, and they continue to divide so the plant can grow. Permanent tissue consists of plant cells that have specific roles and are not dividing actively. Permanent tissue can be divided into: dermal, vascular, and ground tissue. Dermal tissue covers the plant and protects it from mechanical injuries, sudden temperature changes, strong light, parasites, and loss of water. Vascular tissue transports water, minerals, and sugars to different parts of the plant. It is made of two specialized tissues: xylem and phloem. Xylem tissue transports water and nutrients from the roots to different parts of the plant. Phloem tissue transports organic compounds from the site of photosynthesis to other parts of the plant. Ground tissue serves as a site for photosynthesis, provides a supporting matrix for the vascular tissue, and helps to store water and sugars.

Respiration is a chemical reaction that happens in all living cells. It is the process in which energy is released from glucose so that all the other chemical processes needed for life can happen. Respiration can be aerobic and anaerobic. For aerobic respiration, we need oxygen from the air. During aerobic respiration glucose and oxygen react together in cells to produce carbon dioxide and water and release energy. Aerobic respiration consists of three steps: glycolysis, Kreb’s cycle, and electron transport chain. The major part of the respiration happens in mitochondria (organelles found in the cell cytoplasm). Anaerobic respiration doesn’t need oxygen to happen. We use this process when not enough oxygen can reach our cells. Anaerobic respiration produces much less energy than aerobic respiration. The waste product of this kind of respiration is lactic acid. Yeast can carry out an anaerobic process called fermentation. The waste products of fermentation are ethanol and carbon dioxide. There are organisms that can use only anaerobic respiration, like some anaerobic bacteria. The energy that we get from respiration is in the form of ATP (adenosine triphosphate) molecules. ATP contains high-energy bonds and is able to power cellular processes by transferring a phosphate group to another molecule.

Types of Mixtures  

A mixture is composed of two or more types of matter that can be present in varying amounts and can be separated by physical changes, such as evaporation (you will learn more about this later).
A mixture with a composition that varies from point to point is called a heterogeneous mixture. Italian dressing is an example of a heterogeneous mixture. Its composition can vary because we can make it from varying amounts of oil, vinegar, and herbs. It is not the same from point to point throughout the mixture—one drop may be mostly vinegar, whereas a different drop may be mostly oil or herbs because the oil and vinegar separate and the herbs settle. Other examples of heterogeneous mixtures are chocolate chip cookies (we can see the separate bits of chocolate, nuts, and cookie dough) and granite (we can see the quartz, mica, feldspar, and more).
A homogeneous mixture, also called a solution, exhibits a uniform composition and appears visually the same throughout. An example of a solution is a sports drink, consisting of water, sugar, coloring, flavoring, and electrolytes mixed together uniformly. Each drop of a sports drink tastes the same because each drop contains the same amounts of water, sugar, and other components. Note that the composition of a sports drink can vary—it could be made with somewhat more or less sugar, flavoring, or other components, and still be a sports drink. Other examples of homogeneous mixtures include air, maple syrup, gasoline, and a solution of salt in water.

 Omega - 3 fatty acids, especially DHA, facilitate transmission of signals through the brain.  DHA makes it easier for electro signals to travel across synapses between two different neurons. With low concentrations of DHA, brain communications could collapse. To avoid this outcome, we consummate omega - 3 fatty acids through nutrition. We can find them in tofu, egg yolks and walnuts. But the richest nutrition source of those acids is cold water fish - especially salmon, cod and herring. Some scientists hypothesise that our brains developed as a result of our ancestors’ fish based nutrition. Fossil records show that brain capacity doubled with the emergence of homo sapiens. Furthermore, this development was reserved to those who lived in coastal and marine environments.

Perfect flowers consist of both female and male parts. Male component (stamen) includes an anther. Anther contains pollen grains, each containing two sperm cells. Female component (pistol) includes an ovary. The ovary is a protective covering of the egg cells (ovules). In cross pollination, insects, usually bees, attracted by scent and colour of the flower, land on it while foraging nectar. During that time, pollen attaches to their legs. Then, as bees move on to other flowers, pollen attaches to the sticky surface of the stigma on top of the pistol. Then, pollen grains migrate down the style of the pistol to the ovary. There, the sperm cell fertilises the egg. Later, egg grows into seed, which is dispersed by animals, wind or water. Then, this new seed begins to germinate (sprout). When the plant reaches full maturity, the cycle repeats.

Pheromones are chemical messages transferred from one organism to another. First discovered pheromones were like chemical love letters, used by female silkworm moths. Females disperse signals that they are ready to mate. Scientists discovered that signals can be surprisingly strong. In fact, some butterfly and moth male species can detect signals in 10km radius. Signals are scented by the VNO, an organ that is part of the olfactory system. VNO sends the chemical message to receptor neurons in the brain. This triggers some reaction in animals. Scientists discovered that a situation similar to this can be found in human behavior. It seems that females through pheromone detection pick their future mates. In order to produce stronger offspring, it is important to choose a male with different genetic makeup - a newborn with a greater variety of genes has greater chances in fighting numerous diseases. Women, somehow, through pheromone communication can sense which male will provide them with stronger offspring.

Chromium is a chemical element with the symbol Cr.  Its atomic number is 24. It is the first element in the sixth group of the periodic table, and a transition metal. It’s steely-grey, lustrous, hard and brittle. Chromium was discovered by the French chemist Nicholas Louis Vauquelin in Paris in 1798. He was intrigued by a bright red mineral that had been discovered in a Siberian gold mine. It is now called crocoite and is a form of lead chromate. Vauquelin scrutinized it and confirmed that it was a lead mineral. He then succeeded in isolating chromium. He was fascinated by the range of colours that this element could produce in a solution. He then discovered that the green colouration of emeralds was also due to chromium. That’s why chromium was named after the Greek word chroma, meaning colour. Chromium is used to harden steel, make stainless steel and produce several alloys. Chromium plating is also widely used. It can be used for plating steel, giving it a mirror polish. It is also possible to chromium plate plastics. Because of the extent of variations of colours that chromium can produce in its solutions, chromium compounds are used as pigments. Chromium solutions can also be used as industrial catalysts. Chromium is also an essential element for humans because it helps us to use glucose. We take in about 1 milligram of chromium a day through food. However, it is poisonous in excess.

Human embryogenesis refers to the development of the embryo after fertilization. The first step of embryogenesis that happens after fertilization is cleavage. It’s a very rapid mitotic cell division of a zygote that takes place in the first 12 to 24 hours. The next step is blastulation, when the mass of cells forms a hollow ball. Then, around day 4, they begin to differentiate and form cavities. Two layers develop: an outer shell layer called the trophoblast and an inner collection of cells called the inner cell mass. The trophoblast will develop into structures that help the growing embryo implant in the mother’s uterus. The inner cell mass will continue to differentiate and parts of it will become the embryo. Eventually, gastrulation will occur. That’s a phase during which cells differentiate into 3 layers: the ectoderm, the mesoderm, and the endoderm. The ectoderm is an outer layer that goes on to form the outer layer of skin, hair, nails, brain, spinal cord and peripheral nervous system. The mesoderm is a middle layer from which muscle, bone, connective tissue, kidney, gonads and circulatory system are going to form. And the endoderm is an inner layer that gives rise to the epithelial lining of the digestive tract, stomach, colon, liver, pancreas, bladder and lungs.

Photosynthesis is the process in which light energy is converted to chemical energy (in the form of sugars). Plants are the most common organisms that carry out photosynthesis in terrestrial ecosystems. All green plant tissues can photosynthesize, but the majority of photosynthesis usually takes place in the leaves. The cells in a middle layer of leaf tissue called the mesophyll are the primary site of photosynthesis. Each mesophyll cell contains organelles called chloroplasts, which are specialized to carry out the reactions of photosynthesis. Chloroplasts contain the pigment chlorophyll, which has an important role in absorbing light energy. Photosynthesis can be divided into two stages based on the requirement of the light supply: the light-dependent reactions and the Calvin cycle (the light-independent reactions). The light-dependent reactions require a continuous supply of light energy. Chlorophyll absorbs this light energy, which is converted into chemical energy through the formation of two compounds ATP (an energy storage molecule) and NADPH (reduced electron carrier). The Calvin cycle does not directly require light. Instead, it uses the energy stored by the light-dependent reactions to form glucose and other carbohydrate molecules.  The cycle repeats continuously. Because it takes six carbon molecules to make glucose, this cycle must be repeated six times to make a single molecule of glucose.

White blood cells are the cells of the immune system that are involved in protecting the body against infectious diseases and foreign invaders. White blood cells are also called leukocytes. They are made in the bone marrow and stored in our blood and lymph tissues. There are three main categories of white blood cells: granulocytes, lymphocytes and monocytes. Granulocytes are white blood cells that have small granules containing proteins. There are three types of granulocyte cells: basophils, eosinophils and neutrophils. Basophils have a role of an alarm when infectious agents invade your blood. They secrete chemicals such as histamine that help control the body's immune response. Eosinophils attack and kill parasites and cancer cells, and help with allergic responses. Neutrophils kill and digest bacteria and fungi. They are the first line of defense when infection occurs. Lymphocytes create antibodies to fight against bacteria, viruses, and other harmful invaders. There are three types of lymphocytes: B cells, T cells and natural killer cells. B cells produce antibodies to help the immune system build up a response to infection. T cells help recognize and remove cells that are causing the infection. Natural killer cells are responsible for attacking and killing viral and cancer cells. Monocytes are present when the body fights chronic infections. They target and destroy cells that cause infections and help to break down bacteria. They have a longer lifespan than other white blood cells and are also the largest.


Acid rain can best be curtailed by reducing the amount of sulfur dioxide and nitrogen oxides released by power plants, motorized vehicles, and factories. The simplest way to cut these emissions is to use less energy from fossil fuels. Individuals can help. Every time a consumer buys an energy-efficient appliance, adds insulation to a house, or takes a bus to work, he or she conserves energy and, as a result, fights acid rain. Another way to cut emissions of sulfur dioxide and nitrogen oxides is by switching to cleaner-burning fuels. For instance, coal can be high or low in sulfur, and some coal contains sulfur in a form that can be washed out easily before burning. By using more of the low-sulfur or cleanable types of coal, electric utility companies and other industries can pollute less. The gasoline and diesel oil that run most motor vehicles can also be formulated to burn more cleanly, producing less nitrogen oxide pollution. Clean-burning fuels such as natural gas are being used increasingly in vehicles. Natural gas contains almost no sulfur and produces very low nitrogen oxides. Pollution can also be reduced at the moment the fuel is burned. Several new kinds of burners and boilers alter the burning process to produce less nitrogen oxides and more free nitrogen, which is harmless. Limestone or sandstone added to the combustion chamber can capture some of the sulfur released by burning coal. Once sulfur dioxide and oxides of nitrogen have been formed, there is one more chance to keep them out of the atmosphere. In smokestacks, devices called scrubbers spray a mixture of water and powdered limestone into the waste gases (also called flue gases), recapturing the sulfur. Pollutants can also be removed by catalytic converters. In a converter, waste gases pass over small beads which are coated with metals. These metals promote chemical reactions that change harmful substances to noticeably less harmful ones. Once acid rain has occurred, a few techniques can limit environmental damage. In a process known as liming, powdered limestone can be added to water or soil to neutralize the acid dropping from the sky. In cities, exposed surfaces vulnerable to acid rain destruction can be coated with acid-resistant paints. Delicate objects like statues can be sheltered indoors in climate-controlled rooms.