Answers toStudent Questions

All IB Mathematics IB Sciences IB Individuals & Societies IB English IB Language B

Psychology

Economics

Business Management

ESS

History

Environmental Systems and Societies

What factors contribute to different biomes around the globe?

Insolation (sunlight), temperature, and precipitation are the main abiotic factors that influence the distribution of biomes on land. These factors together determine an area's climate. For example, a climate that is consistently sunny, hot, and wet will support a different ecosystem compared to one with seasonal changes in daylight, temperature fluctuations, and little rain. Similar ecosystems form in similar climatic conditions, and these groups are called biomes. Higher **insolation** boosts photosynthesis, which converts more sunlight energy into chemical energy. This leads to more growth of plants, increasing primary productivity and supporting a more diverse ecosystem. Warmer **temperatures** also raise productivity. Chemical reactions in organisms, such as photosynthesis and respiration, happen faster in higher temperatures. This results in more plant food for herbivores, more energy for herbivores to escape predators, and faster decomposition, which speeds up the cycling of important nutrients like carbon, nitrogen, and phosphorus. More **precipitation** provides a steady water supply for ecosystems. Water’s unique properties, like its ability to dissolve chemicals for reactions and its high heat capacity, which allows it to absorb and transport heat, are essential for life. Each of these abiotic factors has an optimal range, known as the "Goldilocks zone" which is just right for life to thrive. This is named after a girl in a story. She wants her porridge to be ‘not too hot, not too cold, but just right.’

Environmental Systems and Societies

What is one major cause of species extinction?

Extinctions occur due to changes in a species’ habitat, natural disasters, or direct human actions aimed at the species. Humans are currently driving the **sixth mass extinction** through various factors: - Habitat destruction - Climate change - Introduction of non-native species - Hunting and overharvesting of wild species - Pollution The scale of environmental change and species loss we have caused over the past few centuries has led some scientists to propose naming a new geological epoch: the **Anthropocene**. The **first five mass extinctions** were triggered by natural events such as: - Meteorite impacts - Changes in sea level - Super-volcanic eruptions - Climate change - Tectonic plate movements A key difference between these events and the current mass extinction is the speed. While past extinctions occurred over thousands to millions of years, the current one is unfolding at an accelerated pace due to human activity. It’s important to recognize that extinctions are a natural part of life. As species evolve, they may shift into new niches or change their habitat, leading to the extinction of other species. This, in turn, creates opportunities for new species to evolve and fill the vacated niches. This roughly steady rate of extinction is known as the **background extinction rate**. However, the current extinction rate, driven by human actions, is estimated to be 100 to 10,000 times higher than the natural background rate.

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.

Environmental Systems and Societies

How does latitude affect climate?

In general, the farther you move from the Equator, the colder the climate becomes. At 0° latitude (the Equator), the climate is warm, while at 90° latitude (the Poles), it is cold. However, climate is actually shaped by insolation (sunlight received), temperature, and precipitation, which show distinct trends as latitude increases. Let’s examine how these three factors vary at different latitudes. At the Equator, the Sun’s rays strike the Earth almost directly throughout the year. As a result, insolation and temperatures remain high all year. The strong solar energy heats the air, increasing evaporation. The resulting water vapour leads to a humid climate with heavy rainfall. Water vapour also acts as a greenhouse gas, trapping heat and further raising temperatures. Countries such as **Ecuador, Brazil, Uganda**, and **Indonesia** all have warm tropical climates with high rainfall. At about 30° latitude, the Sun’s rays hit directly at the height of summer but at an angle of roughly 30° in the middle of winter. This creates hot summers and cooler winters, with insolation and temperature varying by season. Due to the Hadley circulation, air descending at this latitude is dry and causes low rainfall. As a result, these regions are dominated by **deserts**, with low precipitation, dry air, and extreme day–night temperature swings. At around 40° latitude, the Sun’s rays always strike at an angle, with the steepest angle in summer and the shallowest in winter. This creates warm summers and cold winters. Here, the Ferrell cells move heat and moisture poleward, producing moderate to high rainfall. Cities such as **Beijing, Istanbul, Madrid**, and **New York** sit at about 40° North, while **Argentina, Chile, Wellington (New Zealand)**, and **Tasmania (Australia)** lie near 40° South. These areas experience seasonal climates with significant precipitation, but local features such as proximity to oceans or mountains strongly influence the exact climate. At around 66° latitude, we reach the Arctic Circle (North) and the Antarctic Circle (South). From here until the Poles, the tilt of the Earth creates polar days (24 hours of sunlight) at the height of summer and polar nights (24 hours of darkness) at the height of winter. The extremely low insolation results in very cold temperatures. Precipitation is also minimal because evaporation is weak, and most moisture is already released around 60° latitude by the Polar cells, effectively creating polar deserts in the Arctic and Antarctic.

Explore More IB ESS Resources

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

Questionbank

Practice Exams

Key Concepts

Past Papers

Explore More IB ESS Resources

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

Questionbank

Practice Exams

Key Concepts

Past Papers