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Biology

What is the bond that holds amino acids together?

The bond that holds amino acids together is called a peptide bond, or peptide link. A peptide bond forms during a condensation reaction, where one amino acid's carboxyl group (-COOH) reacts with another amino acid's amino group (-NH₂). This chemical reaction results in the release of a water molecule (H₂O) and creates a covalent bond between the carbon from the carboxyl group and the nitrogen from the amino group. This peptide bond links the amino acids together into a chain. These chains of amino acids are known as polypeptides, which then fold into specific three-dimensional structures to become functional proteins. The sequence of amino acids, held together by peptide bonds, determines how the polypeptide folds, and ultimately, what role the protein plays in biological systems. Peptide bonds are therefore fundamental to protein structure and function, as they allow amino acids to be assembled in precise sequences that dictate everything from muscle contraction to enzyme activity.

Economics

What is the difference between movement along the supply curve and a movement of the supply curve?

To understand the difference between movements along the supply curve and shifts of the supply curve, let’s start by understanding the law of supply. The law of supply states that if the price of a good or service increases, then the quantity supplied will also increase. To understand this fully, you have to think like a producer. Let’s assume that producers want to make as much money as possible. Also, remember that producers—like everyone else—make choices. For example, a T-shirt maker can choose to make T-shirts of various colours and styles, print different things on their T-shirts, or even make a different kind of clothing altogether. Putting these ideas together, we can better understand that the law of supply says that producers will allocate their productive resources towards whatever makes them the most money. So if the price of green T-shirts goes up—this doesn’t change the cost of making it—producers will be more interested in making (and selling) green T-shirts, because they can earn greater profits. The law of supply directly refers to the supply curve: the supply curve is upward-sloping because, based on the selling price, producers will produce more (or less) of a good. The supply schedule shows this relationship: |Price |Quantity supplied| |:-:|:-:| |$0|0| |$10|50| |$20|100| |$30|150| |$40|200| The supply schedule shows a movement **along** the supply curve. If this is true, then why don’t producers simply raise the price of a good and produce more? This is because, in the demand and supply model, price is determined by the interaction of the demand curve and the supply curve: consumers are less likely to buy a good at higher prices. Lastly, let’s look at a *shift* of the supply curve. As described above, the supply curve shows the relationship between price and quantity supplied, but it doesn’t give much insight into the production of the good itself. For a producer to make a given good or service, they will incur production costs. Among these are opportunity costs: the value of other goods or services the producer could make, and the best time to supply a product to the market. Along with the selling price, these factors influence how much of a product the producer will make. If one of these other factors changes, for example, the cost of raw materials increases, the relationship between price and quantity supplied changes. This is because the profit has decreased for every price, and the producers are less interested in producing the product. Together, these other factors are known as non-price determinants of supply. Changes to these determinants decrease supply (the supply curve shifts left) and increase supply (the supply curve shifts right). |Non-price determinant of supply |Supply shifts right if…|Supply shifts left if…| |:-:|:-:|:-:| |Cost of raw materials/labour|costs decrease|costs increase| |Price of related goods (joint supply)|price of other goods increases|price of other goods decreases| |Price of related goods (competitive supply)|price of other goods decreases|price of other goods increases| |Taxes and subsidies|indirect taxes decrease/subsidies increase|indirect taxes increase/subsidies decrease| |Future expectations of price|prices are expected to fall|prices are expected to rise| |Technology|technology increases|technology decreases| |Number of firms|firms join market|firms leave market|

Psychology

What is standard deviation in psychology?

The standard deviation is a measure of dispersion that shows how spread out the values in a data set are around the mean. It indicates the extent to which individual data points differ from the average. A smaller standard deviation means the data are closely clustered around the mean, while a larger one suggests greater variability. Because it is based on the original data, the standard deviation uses the same unit of measurement. For example, in a psychology study recording participants' reaction times in seconds, the standard deviation would also be in seconds. A low standard deviation would indicate that most participants responded at similar speeds, whereas a high standard deviation would reflect more varied reaction times.

Physics

Why is specific heat important?

Specific heat is defined as the amount of thermal energy required to raise the temperature of a unit mass of a substance by one degree of temperature. It is important because it determines the amount of energy that needs to be added or removed to heat up or cool down a substance or an object. The IB Physics data booklet formula involving specific heat is $\hspace{2em}$ $Q = mc\Delta T$ Where $\hspace{2em}$ $Q$ is the heat required in J\ $\hspace{2em}$ $m$ is the mass of the sample in kg\ $\hspace{2em}$ $c$ is the specific heat capacity of the substance \ $\hspace{2em}$ $\Delta T$ is the change in temperature in k. This formula can be rearranged to solve for specific heat capacity to get $\hspace{2em}$ $c = \dfrac{Q}{m\Delta T}$ We can see from the formula that the units on $c$ will be J kg$^{-1}\ ^o$C$^{-1}$. Substances with high values of specific heat require more energy for a given change in temperature than substances with a lower value for specific heat. Water is an example of a substance with a high specific heat, with $c$ equal to 4186 J kg$^{-1}\ ^o$C$^{-1}$. This relatively high value means that a significant amount of energy is required to raise water to its boiling point. It also means that a lot of energy is released when water cools down again. Some older heating systems in houses circulate hot water to deliver heat to the rooms. Water’s high carrying capacity for thermal energy makes it ideal for this use. Another example of where water’s high specific heat plays an important role is in weather. Although the land may heat up and cool down relatively quickly as the air temperature changes, bodies of water will take much more time for their temperature to change. In summer, the water will stay cooler than the air and help moderate extreme heat. Similarly, in winter bodies of water can help moderate very cold air temperatures. Because of our understanding of specific heat, we can calculate the heat capacity of objects. This is the amount of energy required to raise an object's temperature by one degree kelvin. Once this is known, we can predict the rate at which objects will change temperature and the amount of heat energy involved. Understanding specific heat is extremely valuable for designing systems where heat transfer is fundamental to their operation.

Chemistry

Can chlorine have an expanded octet?

Yes, chlorine can have an expanded octet because it has empty $3d$ orbitals available that can accommodate more than eight electrons. As a Period 3 element, chlorine has access to $3s,$ $3p,$ and $3d$ orbitals, which allows it to form compounds where it is surrounded by more than eight electrons. Common examples include $\ce{ClF3}$ (chlorine trifluoride) where chlorine has 10 electrons around it, and $\ce{ClF5}$ (chlorine pentafluoride) where chlorine has 12 electrons. This ability to expand the octet is only possible for elements in Period 3 and beyond because they have $d$ orbitals available in their valence shell.

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