Answers toStudent Questions

All IB Mathematics IB Sciences IB Individuals & Societies

Environmental Systems and Societies

What is a primary consumer in an ecosystem?

Primary consumers are organisms that eat producers. They occupy the second trophic level in a food chain. Examples are **zooplankton**, which eat phytoplankton, **mountain gorillas**, which eat various parts of about 142 different plant species, and **grasshoppers**, which eat the leaves of grasses like wheat and rice. $\hspace{2em}$ **producer $\rightarrow$ primary consumer $\rightarrow$ secondary consumer $\rightarrow$ tertiary consumer** As you can see in the food chain above, producers are the first trophic level in a food chain, using photosynthesis to make carbon compounds that provide matter and energy for growth and survival. Consumers cannot photosynthesise, and so must obtain carbon compounds from other organisms. Primary consumers eat producers, and are eaten by secondary consumers. They, in turn, are eaten by tertiary consumers. Primary consumers play an important role in regulating the population sizes of both the primary producers they eat and the secondary consumers that eat them. Because consumers feed in such different ways, we have specific terms to describe them. The following terms are most relevant in IB ESS: - Herbivores are primary consumers that eat plants, e.g. koalas eat eucalyptus leaves. The trophic level of the consumers below is determined by the trophic level of the organisms they eat. - Predators eat prey; a predator such as an owl is a secondary consumer if its prey is a primary consumer, such as a mouse that eats corn, but a tertiary consumer if its prey is a secondary consumer, such as a frog that eats grasshoppers that eat grass. - Parasites such as mistletoe and tapeworms live in or on another organism and harm it as they feed on it, but do not usually kill it. - Scavengers like vultures eat dead organisms that were killed by other organisms or died of natural causes. - Decomposers such as soil bacteria, fungi and earthworms break down dead organisms or their parts as they feed on them. - Detritivores, such as earthworms, are decomposers that eat decomposing parts of organisms from all trophic levels, as well as their faeces. - Saprotrophs such as fungi are decomposers that break down decomposing parts of organisms by excreting enzymes onto them and then absorbing the products.

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|

Mathematics

What is the tangent graph?

The tangent graph is the graph of a trigonometric function. $\tan x$ is a trigonometric ratio. If we substitute $x$ values into the function $y=\tan x$ then we generate a $\textbf{tangent graph}$. Like many graphs, the tangent graph has distinct characteristics. First we note that the trigonometric ratios, including tangent, have periodicity (i.e. they repeat a pattern over a certain period). For the standard tangent graph, the period is $\pi$ which means every $\pi$ units along the $x$-axis the pattern repeats itself. Another characteristic of the tangent graph is that there are vertical asymptotes. Tangent is the ratio of the sine function to the cosine function $$ \begin{align*} \tan x=\frac{\sin x}{\cos x} \end{align*} $$ so whenever the cosine function equals zero $(\cos x=0)$ then the tangent curve has a vertical asymptote, because we are not able to divide by $0$. Due to this, we cannot substitute every $x$ value. The domain of tangent is $\{x\in\mathbb{R}, x\neq\frac{\pi}{2},\frac{3\pi}{2}, \frac{5\pi}{2}...\}$. Between the asymptotes, the tangent graph starts from negative infinity, passes through the $x$-axis halfway between the asymptotes, and then rapidly increases to positive infinity as it approaches the next asymptote. Hence the range of values of tangent is $\{y\in\mathbb{R}\}$. It is not a straight diagonal line but increases rapidly near the asymptotes and has a more shallow gradient as it passes through the $x$-axis.

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.

Explore More IB Math Resources

Over 80% of IB students globally are experiencing the power of Revision Village

Questionbank

Practice Exams

Key Concepts