How Nature Works in Harmony | CBSE Class 8 Science Notes

This note covers habitats, living and non-living components, populations, communities, ecosystems, feeding relationships, nutrient recycling, interactions among organisms, ecological balance, ecosystem benefits, conservation, and sustainable farming.

What is a habitat, and how does it support life?

An organism is a living being. Its habitat is the place where it lives and finds conditions needed to live and grow. A habitat can be a pond, a forest, an agricultural farm, a large tree, or even the bark of a tree.

The living parts of a habitat are its biotic components. Plants, animals and microorganisms, or living beings too small to see with the naked eye, belong to this group. Its non-living parts are abiotic components, such as air, water, soil, sunlight and temperature.

How does a pond meet the needs of fish?

A pond supplies food, oxygen, shelter and space for growth. Fish obtain food from small plants and animals. They obtain oxygen from the water. Thus, their survival depends on both the living beings and the non-living conditions around them.

Ponds also support snakes, dragonflies, mosquitoes and ducks, together with plants such as duckweeds and lotus. These organisms interact with one another and with their surroundings. Listing organisms alone therefore gives an incomplete account of the conditions supporting pond life.

Different habitats offer different living conditions. Even within one habitat, organisms may use resources differently. A forest might be warm during the day and cool at night. A snake active at night and a rodent active during the day face different conditions in the same place.

The two illustrations show a pond with water, plants and animals, and a forest scene with trees, birds and other animals. Both scenes combine living beings with non-living surroundings.

See Fig. 12.1 in your NCERT textbook

How do populations and communities differ?

A population is a group of organisms of the same type living in a habitat at a given time. Several fish of the same kind living together in a pond form a population. The place and time are part of the description.

A community consists of different populations sharing the same habitat. Plants, animals and microorganisms together form its living community. Its members interact and depend on one another for survival. A community therefore includes more than one kind of organism.

How can a population be recorded?

1. Choose a particular area of a habitat to observe.
2. Identify the kinds of organisms present in that area.
3. Count the individual organisms of each kind separately.
4. Record the count for each kind at that place and time.

The count of one kind gives its population in the observed area. Combining several different kinds does not turn them into one population. Instead, their different populations contribute to the community. Keeping the categories separate helps explain how organisms interact.

If all organisms in a habitat were of the same type, they would have the same requirements for food, water and space. This would lead to competition, an interaction in which organisms seeking the same resources limit one another's access to them, and possible scarcity of those resources.

Note: Water and sunlight are parts of the surroundings, but they are not members of a community. A community consists of living populations.

How can pond fish influence flowers growing nearby?

Pollination is the movement of pollen from the stamens, the male reproductive parts of flowers, to the carpels, the female reproductive parts, of the same and/or different flowers. Pollen is the yellow dust-like material released by stamens. Pollination is essential for fruit and seed formation.

Wind, water, insects, bats and birds help carry pollen. Animals that help in this transfer are pollinators. Their activity connects flowers with other organisms. A change in an animal population can therefore influence plants even without that animal directly visiting the flowers.

What happened in the two-pond comparison?

Researchers compared Pond A, which had fish and many flowering plants around it, with Pond B, which lacked fish and had fewer flowering plants nearby. Pond A had fewer dragonflies than Pond B. The feeding relationships explained this difference.

1. Fish eat dragonfly larvae, the young stage of dragonflies, so ponds with fish had fewer dragonflies.
2. Dragonflies usually eat flies, bees and butterflies.
3. With fewer dragonflies, more bees, flies and butterflies were found.
4. These insects transfer pollen between flowers, helping plants produce seeds.
5. Flowers near ponds with fish may therefore produce more seeds than flowers near ponds without fish.

The connection between fish and seed production is indirect: it operates through dragonflies and pollinating insects. Fish do not have to pollinate flowers themselves to affect seed production. Water, temperature and nutrients, substances needed for growth, also form part of the interacting surroundings.

Pond A is illustrated with fish and more flowering plants around its margins. Pond B is illustrated without fish and with fewer flowering plants around it.

See Fig. 12.3 in your NCERT textbook

Note: Keep the conclusion as “may produce more seeds”. The relationship does not establish an unavoidable increase in every pond containing fish.

How do living and non-living components form an ecosystem?

Definition: An ecosystem consists of the biotic and abiotic components of an area interacting with one another. It includes living communities and the non-living surroundings on which they depend.

Interactions occur among living components, between living and non-living components, and between non-living components. These relationships influence life processes and the physical conditions of a habitat. Identifying both participants helps distinguish the different kinds of interaction.

How do the two kinds of components affect each other?

Plants make food through photosynthesis, using sunlight, carbon dioxide and water. Soil provides a medium for growth and essential nutrients. Air supplies oxygen for respiration, the life process that releases energy from food, in plants and animals.

Living things also influence non-living conditions. Plants release oxygen during photosynthesis. Their roots hold soil in place and prevent erosion, the removal of soil. Plants retain soil moisture and help cool the atmosphere. Dependence therefore works in both directions.

Aquatic ecosystems occur in water and include ponds, rivers and lakes. Terrestrial ecosystems occur on land and include forests, farms and large trees. An ecosystem need not be a vast area. A large banyan, mango or pilkhan tree can also be studied as one.

These ecosystems can overlap and interact. A river can occur alongside mountains, forest, grassland and farmland. The river is aquatic, while the surrounding examples are terrestrial. Farmland is also a human-made ecosystem because people create and manage it.

How are producers and consumers linked by food?

Producers make their own food. Plants produce food through photosynthesis and are also called autotrophs. The parts of this word mean self and food. Their ability to make food distinguishes them from organisms that depend on other organisms for food.

Consumers cannot produce their own food and depend on other organisms for it. They are also called heterotrophs, meaning other and food. Consumers differ in the kinds of food they eat, so they can be grouped by their feeding habits.

What distinguishes the three consumer groups?

A herbivore, such as a deer, obtains food only from plants. A carnivore, such as a leopard, feeds only on animals. An omnivore has both plants and animals in its diet. These terms describe feeding habits rather than the place where an organism lives.

A tree and a deer in the same forest have different feeding roles. The tree performs photosynthesis, whereas the deer feeds on grass and leaves. Sharing a habitat does not mean that organisms obtain food in the same way.

These feeding roles connect members of a community. Plants supply food to plant-eating consumers, which can become food for animal-eating consumers. Understanding each organism's food helps us connect organisms into a sequence rather than merely listing the kinds of organisms present.

Note: Producers still depend on abiotic components. Making their own food does not mean that plants are independent of sunlight, water, carbon dioxide or soil nutrients.

What do food chains, trophic levels and food webs show?

A food chain is a simple sequence showing who eats whom in an ecosystem. In the notation used here, the arrow → means “is eaten by” and points from food to its consumer. Read the sequence in the arrow's direction.

Grass → Hare → Leopard

The hare eats the grass, and the leopard eats the hare. A longer grassland example is Grass → Grasshopper → Frog → Snake → Eagle. Each link describes a feeding relationship, and each organism occupies a position within that particular chain.

What is a trophic level?

A trophic level is the position occupied by an organism in a food chain. Producers occupy the first level. Herbivores, such as hares and deer, occupy the second. Small carnivores, such as frogs, occupy the third, followed by further animal-eating consumers.

The illustration places grass at the bottom, followed upwards by grasshopper, frog, snake and eagle. Arrows join successive organisms. The Sun is drawn above the chain.

See Fig. 12.9 in your NCERT textbook

A food web is a network of interconnected food chains. An organism may be eaten by two or more types of organisms, linking different chains. A food web therefore shows several feeding connections rather than one linear sequence.

A crop-field example links millet, mouse and eagle. Their numbers can be represented as a pyramid by putting the largest number at the base and the smallest at the top. This is a way to represent that example; no universal numerical ratio follows from the drawing.

How do decomposers return nutrients to the environment?

Organisms grow, perform life processes, develop and die. Dead matter, food waste and animal droppings become part of their surroundings. Decomposition is the breakdown of complex substances in dead matter into simpler substances, returning nutrients to the environment.

Decomposers, also called saprotrophs, carry out this process. Fungi and bacteria break down dead plants and animals. Mushrooms are fungi that grow on dead matter. Their familiar umbrella-like structures can be seen on dead plants or trees during the rainy season.

How does decomposition connect back to plant growth?

1. Dead plants, dead animals and other organic waste enter the surroundings.
2. Fungi and bacteria break complex substances into simpler substances.
3. The process returns important nutrients to the soil.
4. Plants grow in this soil, using nutrients returned through decomposition.

Tiny insects, including beetles and flies, can be found on animal droppings such as elephant dung. They help break the material down and return nutrients to the environment. Recycling therefore involves organisms whose work might be less noticeable than that of larger animals.

Many nutrients in soil come from decomposition. This makes decomposers part of the connections sustaining other organisms, rather than an isolated group concerned only with waste. Their role links the remains of living things with the conditions supporting new plant growth.

If decomposition were removed from the explanation of an ecosystem, the return of nutrients from dead matter would be missing. Producers, consumers and decomposers should therefore be studied together when tracing the movement and reuse of materials in nature.

How can one disturbance cause several further changes?

Ecological balance exists when interactions among organisms and their surroundings keep populations and resources stable. The balance is dynamic, meaning it is not fixed. Natural changes and human-made changes can disrupt it and cause further effects elsewhere in an ecosystem.

How can pond pollution affect nearby farms?

1. Pollution causes many pond plants to die.
2. With fewer plants, less oxygen is produced in the water.
3. The fish population drops, reducing the number of consumers in the pond.
4. Insects increase in number and spread to nearby farmland.
5. Farmers use pesticides, substances used to control pests, to protect crops; this may again adversely affect the environment.

Pests are organisms that damage crops in this example. The effects do not stop at the pond boundary. A change in plants affects fish and insects, and those changes affect farming. Further environmental consequences may emerge from the response to the original disturbance.

What happened when frogs were heavily harvested?

In the 1980s, India was a significant exporter of frog legs, especially those of the Indian bullfrog. Large-scale harvesting reduced frog populations. Because frogs eat insects, fewer frogs resulted in more agricultural pests and increased use of synthetic, or human-manufactured, pesticides.

These pesticides harmed the environment, soil and water quality, and environmental and human health. The Government of India banned frog-leg exports to prevent further ecological damage. The example shows how removing an insect-eating animal can affect agriculture as well as wildlife.

Downward arrows connect boxes labelled “Plants die”, “Less oxygen”, “Fish die”, “More insects” and “Plants get damaged by pests”. The drawing presents the changes as a connected sequence.

See Fig. 12.13 in your NCERT textbook

How do competition and other relationships affect organisms?

Organisms interact through more than feeding alone. They compete for common resources, including food, water, space and sunlight. Competition helps control population size and maintain ecosystem balance. Without it, one type of organism could multiply too much and cause an imbalance.

Other relationships differ according to whether each participant benefits, is harmed or remains unaffected. Mutualism benefits both organisms. Commensalism benefits one while the other is unaffected. Parasitism benefits one while harming the other.

How do the examples distinguish these relationships?

Nectar is the food obtained by the bee from the flower in this example. The flower also benefits through pollination. Both benefits matter when identifying mutualism; describing only the bee's food would leave out the other side of the relationship.

The orchid uses the tree for support without harming it in this example. The tick benefits at the dog's expense. Thus, the fact that one organism lives on another is insufficient for classification: the effect on both organisms must be identified.

A predator feeds on another animal, its prey. Wildlife biologist Asir Jawahar Thomas Johnsingh studied forest relationships in Bandipur National Park, Karnataka. His research showed that predators such as tigers and leopards depend on prey such as deer and wild boar.

A healthy prey population is key to predator survival. This dependence connects the condition of one animal population with another, reinforcing why a community must be understood through its relationships as well as its individual members.

What benefits do ecosystems provide to people and wildlife?

Ecosystems support human survival and well-being. Forests provide fresh air, fertile soil, food, fibres, timber and medicines. Aquatic ecosystems supply water and food. Ecosystems also have aesthetic value, the enjoyment of their beauty, and recreational value, opportunities for leisure.

These benefits depend on interacting living and non-living components. Humans are connected to these systems through the materials and conditions they provide. Overusing or misusing natural resources disturbs the balance that supports those benefits.

Why do connected habitats matter?

In several Indian states, elephants often enter farms and villages. When vegetation is scarce and waterholes dry up, they may enter farms or plantations looking for food such as bananas and sugarcane. This can damage crops and, at times, harm people and domestic animals.

Rainfall and temperature changes affect vegetation. Cutting trees for roads and buildings worsens the drying and shrinking of forests. With habitat loss, animals tend to move into human habitats. Sudden changes make survival difficult even for animals adapted to forest life.

Wildlife corridors connect forest habitats and allow animals to move safely between large forest areas. Wildlife ecologists have identified and marked these routes to help animals such as elephants travel when needed without conflict with human settlements.

Migratory birds move between habitats to avoid harsh climates and find food. They also link habitats through pollination and seed dispersal, the movement of seeds. By eating insect pests, they help farmers control pest populations and indirectly support healthy crop growth.

Demoiselle cranes visit the water body of Khichan village in Jodhpur district during winter. This example connects seasonal movement with the value of particular habitats. Protecting places used by wildlife helps maintain the relationships that extend beyond any one locality.

Why do the Sundarbans and other ecosystems need protection?

The Sundarbans contain the world's largest mangrove forests, coastal forests formed by mangrove trees. They lie where the Ganges and Brahmaputra Rivers meet between India and Bangladesh. These forests and rivers support many kinds of plants and animals, including many that are endangered, meaning threatened with extinction.

Mangroves are the trees forming these coastal forests. The Sundarbans slow strong winds and waves during storms and floods. Their trees also absorb carbon dioxide and release oxygen. The forests therefore help protect people while supporting wildlife.

What threatens these forests?

Mangrove trees are cut for fuelwood and farming. Illegal hunting and excessive use of forest resources threaten wildlife. Industrial waste and untreated sewage pollute rivers, damaging water and habitats. These activities disrupt the way the ecosystem works.

Other Indian ecosystems face deforestation, or forest clearance, overuse of resources, pollution and unsustainable land use. The spread of invasive species, non-native organisms that spread after introduction and harm native species or ecosystems, is another threat. Forests, rivers, grasslands, wetlands and coastal areas are affected.

How do protected areas help?

Protected areas are parts of land or water set aside to conserve wildlife and habitats. National parks, wildlife sanctuaries, biosphere reserves and community conserved areas help protect whole habitats, including endangered animals, birds and rare plants.

Conservation protects the surroundings as well as the organisms living there. Protecting an animal while losing its food sources or habitat would leave essential relationships damaged. Preserving habitats helps keep the interacting components together for future generations.

How can farming work with healthy ecosystems?

Human-made ecosystems, such as fish ponds, farms and parks, are created to meet human needs. Unlike natural ecosystems, they require human care and management. When well designed, they can reduce pollution, support biodiversity, the variety of living organisms, and provide recreation.

Farming supplies food and is a major livelihood in India. Between 1950 and 1965, low crop production contributed to a food crisis. Tractors, machines, synthetic fertilisers and pesticides helped increase production in the mid-twentieth century, during the Green Revolution.

Why can intensive farming become unsustainable?

Fertilisers supply nutrients for crop growth. Synthetic fertilisers and pesticides have improved production and helped India become food secure, meaning able to meet food needs. However, their long-term use can affect the environment and soil health.

Overuse of synthetic fertilisers may reduce soil fertility, its ability to support plant growth, by decreasing friendly microorganisms and lowering organic matter called humus. Humus helps bind soil particles. Without enough humus, soil becomes prone to erosion. Reduced natural predator populations also allow pests to increase.

Heavy irrigation and repeated ploughing can disturb soil organisms such as earthworms and snails. Some pests may develop resistance to pesticides, making them difficult to control. These effects show why protecting soil organisms and feeding relationships matters to agriculture.

Monoculture means growing the same crop repeatedly. It can reduce biodiversity and affect pollinators. Many scientists believe that overusing pesticides and repeatedly growing the same type of crop on the same land leads to soil degradation, or deterioration of soil condition.

What approaches aim to make farming more sustainable?

Some farmers are exploring organic and natural farming methods. These aim to reduce synthetic fertiliser use and support farming with minimal interference in natural ecosystems. Sustainable farming seeks to protect soil, the environment and future food security while meeting food needs.

The ancient text Vrikshayurveda emphasises soil health and nourishment through organic manure and composted materials. It describes Kunapa Jala, a liquid fertiliser made from animal and plant waste through fermentation, a process that breaks complex substances into simpler ones.

A farm survey can ask how practices have changed, what effects farmers notice from synthetic inputs, and whether soil health has changed. Recording these observations links farming choices with the condition of the ecosystem on which production depends.

Glossary

• Habitat — The place where an organism lives and finds conditions needed for survival and growth.
• Biotic components — The living parts of a habitat, including plants, animals and microorganisms.
• Abiotic components — The non-living parts of a habitat, including water, air, soil, sunlight and temperature.
• Population — A group of organisms of the same type in a habitat at a given time.
• Community — Different populations sharing the same habitat and interacting with one another.
• Ecosystem — The interacting living communities and non-living components present in an area.
• Pollination — Transfer of pollen from stamens to carpels of the same and/or different flowers.
• Producer — An organism that makes its own food, as plants do through photosynthesis.
• Consumer — An organism unable to produce its own food and dependent on other organisms for food.
• Trophic level — The specific position an organism occupies within a food chain.
• Food web — A network formed when food chains in an ecosystem are interconnected.
• Decomposer — An organism that breaks down dead matter into simpler substances and helps recycle nutrients.
• Mutualism — A relationship in which both participating organisms benefit from their interaction.
• Commensalism — A relationship in which one organism benefits while the other remains unaffected.
• Parasitism — A relationship in which one organism benefits while the other is harmed.

Common errors and misconceptions

• Misconception: All organisms in a pond form one population. Correct: A population contains organisms of the same type; different populations together form a community.
• Misconception: A community includes water and sunlight. Correct: A community contains living populations. An ecosystem includes their interactions with non-living components.
• Misconception: Fish directly pollinate flowers beside ponds. Correct: Fish eat dragonfly larvae, indirectly influencing pollinating insects. Nearby flowers may consequently produce more seeds.
• Misconception: Food-chain arrows point from the eater towards its food. Correct: In these chains, arrows point from the food organism towards the organism eating it.
• Misconception: Decomposers merely remove waste. Correct: Their breakdown of dead matter also returns nutrients to soil and supports recycling within ecosystems.
• Misconception: Every relationship benefits both organisms. Correct: Mutualism benefits both; commensalism leaves one unaffected; parasitism harms one while benefiting the other.
• Misconception: A balanced ecosystem never changes. Correct: Ecological balance is dynamic and can be disrupted by natural or human-made changes.
• Misconception: Synthetic farm inputs have no benefits, or their increased use has no drawbacks. Correct: They have improved production, but long-term use can affect soil and environmental health.

Exam-style questions with model answers

Q1. A pond contains a group of fish of the same kind, together with frogs and plants. Identify the fish group and the combined living groups using ecological terms. [2 marks]

1. The fish of the same kind form a population in the pond at that time.
2. The different living populations, including fish, frogs and plants, together form the pond community.

Q2. Classify these interactions and explain each choice: an earthworm lives in moist soil; sunlight raises daytime temperature; a frog eats insects. [3 marks]

1. The earthworm and moist soil illustrate a biotic-abiotic interaction. The earthworm is living, while soil and its moisture are non-living surroundings.
2. Sunlight raising daytime temperature illustrates an abiotic-abiotic interaction. Both sunlight and temperature belong to the non-living conditions of the habitat.
3. A frog eating insects illustrates a biotic-biotic interaction. Both participants are living organisms, and the relationship involves one obtaining food from the other.

Q3. A food chain is Grass → Grasshopper → Frog → Snake, where → means “is eaten by”. Frogs disappear. Assuming other conditions remain the same and using only the feeding links shown, identify the frog's trophic level and predict changes in grasshopper numbers, grass abundance and snake numbers. [4 marks]

1. The frog occupies the third trophic level in this chain. Grass is the producer at the first level, and the grasshopper occupies the second.
2. Grasshopper numbers would be expected to increase because frogs, the animals shown eating grasshoppers in this chain, have disappeared.
3. Grass abundance would be expected to decrease because more grasshoppers would feed on it, assuming that other conditions remain unchanged.
4. Snake numbers would be expected to decrease because frogs provide their food in the supplied chain. The prediction uses only the feeding relationships given.

Q4. Pond A has fish; Pond B lacks fish. Fish eat dragonfly larvae. Dragonflies usually eat flies, bees and butterflies, which pollinate nearby flowers. Explain in five linked points why flowers near Pond A may produce more seeds. [5 marks]

1. Fish in Pond A eat dragonfly larvae. Their feeding removes young dragonflies from the pond and begins the connection between fish and nearby flowering plants.
2. With larvae being eaten, Pond A has fewer dragonflies than the pond without fish. The first change concerns the dragonfly population rather than direct contact with flowers.
3. Dragonflies usually eat flies, bees and butterflies. Fewer dragonflies therefore allow more of these flower-visiting insects to be present around the pond.
4. These insects help pollinate flowers by moving pollen between flowers. Their activity supports the process needed for fruit and seed formation.
5. Consequently, flowers near Pond A may produce more seeds. The effect of fish is indirect, operating through dragonflies and pollinators; it is not a guaranteed result for every pond.

Q5. Classify each relationship and justify it: a bee gets nectar while a flower is pollinated; an orchid gains support while its tree is unaffected; a tick feeds on a dog's blood while the dog suffers skin irritation. [3 marks]

1. The bee-flower relationship is mutualism because both organisms benefit: the bee obtains nectar and the flower receives help with pollination.
2. The orchid-tree relationship is commensalism because the orchid benefits from physical support while the tree remains unaffected by the stated interaction.
3. The tick-dog relationship is parasitism because the tick benefits by obtaining blood while the dog is harmed through skin irritation.

Q6. Fungi and bacteria break complex substances in dead plants and animals into simpler substances, returning nutrients to soil where plants grow. Explain this recycling process in three points. [3 marks]

1. Fungi and bacteria act as decomposers by breaking down the complex substances present in dead plants and animals into simpler substances.
2. This process, called decomposition, returns important nutrients from dead matter to the soil rather than leaving them within the remains of organisms.
3. Plants grow in this soil, and many soil nutrients come from decomposition. Decomposers therefore connect the breakdown of dead matter with nutrient availability for plant growth.

Q7. Overuse of synthetic fertilisers may decrease friendly soil microorganisms and humus. Humus binds soil particles. Heavy irrigation and repeated ploughing can disturb earthworms and snails. Some pests may develop pesticide resistance. Monoculture can reduce biodiversity and affect pollinators. Explain five concerns for farming. [5 marks]

1. Fertiliser overuse may reduce friendly microorganisms in the soil. This affects the living component of the farm and can contribute to reduced soil fertility.
2. Lower humus means less organic matter helping to bind soil particles. Without enough humus, soil becomes prone to erosion, threatening the soil on which crops depend.
3. Heavy irrigation and repeated ploughing can disturb earthworms and snails. These soil organisms are important for maintaining ecological balance within the agricultural ecosystem.
4. Some pests may develop resistance to pesticides and become difficult to control. Pesticide use therefore does not guarantee that pest control will remain equally effective.
5. Monoculture can reduce biodiversity and affect pollinators, which are crucial for food production. Repeatedly growing the same crop can therefore affect important biological relationships on farms.

Q8. Mangrove forests slow strong winds and waves during storms and floods, but trees are being cleared for fuelwood and farming. State one protective benefit and one threat described here. [2 marks]

1. Mangrove forests help protect people by slowing strong winds and waves during storms and floods.
2. Cutting mangrove trees for fuelwood and farming threatens these forests and disrupts their ecosystem.

Key takeaways

• Habitats support organisms through both biotic components, such as plants and animals, and abiotic conditions, such as water and temperature.
• A population contains one type of organism; a community contains different populations; an ecosystem includes interactions with non-living surroundings.
• Fish can influence nearby flowers indirectly through dragonflies and pollinators, so changes in one population can affect another.
• Producers make food, consumers depend on other organisms, and decomposers return nutrients from dead matter to the environment.
• Food chains describe feeding sequences, while food webs connect several chains through the feeding relationships of their organisms.
• Mutualism benefits both partners, commensalism leaves one unaffected, and parasitism benefits one organism while harming another.
• Ecological balance is dynamic, and disturbances such as pollution or heavy frog harvesting can produce further connected changes.
• Protecting habitats and managing farms sustainably helps preserve the relationships supporting soil health, wildlife and human well-being.

Test yourself

Why is water not part of a pond's community?

Water is non-living. A community consists of living populations, while the ecosystem includes their interactions with water and other abiotic components.

How can plants change abiotic conditions?

Plants release oxygen during photosynthesis, hold soil with their roots, retain soil moisture and help cool the atmosphere.

What does the arrow in Grass → Hare mean?

It means grass is eaten by the hare. The arrow points from the food towards its consumer.

Why are food webs more interconnected than single food chains?

An organism may be eaten by two or more types of organisms, linking different food chains into a network.

What is the difference between commensalism and parasitism?

In commensalism, one organism benefits and the other is unaffected. In parasitism, one benefits while the other is harmed.

Why are wildlife corridors useful to elephants?

They connect forest habitats, allowing elephants to move between large forest areas when needed without conflict with human settlements.

How does humus help protect soil?

Humus helps bind soil particles together. Without enough humus, the soil becomes prone to erosion.

What qualification should accompany the claim about pesticide resistance?

Some pests may develop resistance to pesticides. Do not replace this with a claim that every pest inevitably becomes resistant.