🌱 Interactions — Environment

• The environment covers everything around an organism — all the living and non-living things that affect it.
• Environments differ greatly, from baking-hot deserts to the frozen Arctic.
• The natural place an organism lives in is called its habitat.
• Which organisms can live in a habitat depends on its conditions. Only plants and animals that are adapted to those conditions survive there.

Environmental conditions are sorted into two groups of factors.

• Living factors — every living thing in the environment: producers, consumers and decomposers.
• Non-living factors — the physical conditions that affect organisms: temperature, water, air, light and the type of soil.

• Nearly all living things need oxygen for respiration.
• Green plants need carbon dioxide to make food during photosynthesis.
• In water habitats, plants and animals take their gases from the dissolved air in the water.
• Wind is moving air — very strong winds can wreck a habitat and kill many organisms at once.

• The Sun is Earth's main source of energy and keeps almost all life going.
• Plants trap light energy to make food through photosynthesis.
• Animals then get their energy by eating plants, or by eating animals that fed on plants.

• Temperature tells us how hot or cold an environment is.
• Warm-blooded organisms must keep their body temperature within a certain range.

• Living things need water for essential life processes such as digestion and photosynthesis.
• Fish must stay in water to take in dissolved oxygen through their gills.
• Amphibians need water to keep their skin moist for breathing, but they can also use their lungs when water is hard to find.
• Temperature and water go together: when it is hot, water evaporates and conditions turn dry; when it is very cold, water sources freeze into ice and little water is available.

• Soil is the material plants grow in, and it is made up of particles of different sizes.
• The type of soil decides how much air and water the roots receive, so some plants grow better in certain soils than others.

There are three common types of soil: sandy soil, loamy (or garden) soil and clayey soil.

• Made up of the largest particles, so it has the biggest air spaces.
• Water flows through it the most easily and it holds on to the least water — water drains through sandy soil the fastest.
• It is too dry for most plants, but cactus plants and coconut trees grow well in it.

• Made up of both small and large particles, so it has a moderate amount of air between them.
• Water flows through it at a moderate rate, and it holds an adequate amount of water — between that of sandy and clayey soil.
• Most plants grow well in loamy soil because the remains of dead organisms in it add nutrients.

• Made up of the smallest particles, so it has the smallest air spaces.
• Water flows through it the least easily and it holds on to the most water — water drains through clayey soil the slowest.
• It is too wet for most plants, but the rice plant grows well in it.

What happens to the other organisms when the number of floating plants increases?

• More floating plants such as duckweed mean more light is blocked from reaching fully-submerged plants such as hydrilla.
• With less light, the submerged plants photosynthesise at a slower rate, make less food and grow less healthily — or die.
• Other organisms are affected too: the submerged plants are a food source and they release oxygen into the water as they photosynthesise.
• So animals that rely on them for food and/or dissolved oxygen are negatively affected as well.

Living factors are all the living things in the environment. Food supplies them with the energy they need for repair, growth and reproduction.

• Green plants trap light energy from the Sun and turn it into food.
• They therefore feed all living things, whether directly or indirectly.

• Animals cannot make their own food — they feed on plants or on other animals.
• Animals that hunt and eat other animals are predators; animals that are hunted and eaten are prey.

• Bacteria and fungi break animal waste and dead matter down into simpler substances.
• This returns nutrients to the soil, so plants can grow more healthily.

• The number of predators lags behind the number of prey — it changes only after the prey population changes.
• When prey is plentiful, predators find plenty of food, so their reproduction rate is higher than their death rate and their numbers rise.
• When prey becomes scarce, predators go short of food, die out and their numbers fall.

Other organisms can help a population survive.

Organisms can also harm other populations and lower their chances of survival.

• Organism — a single living thing: a plant, animal, fungus or bacterium. Living things interact with their own kind, with other living things and with the environment, forming an ecosystem.
• Population — all the organisms of the same species living and reproducing together at a given place and time. A lone organism is not a population.
• Habitat — the place organisms live in. It can be man-made or natural, such as forests, fields, gardens, ponds, seashores, mangrove swamps, leaf litter, trees and rotting logs.
• Community — different populations living together in one place and depending on one another for survival, which means they are interdependent.
• Food is the main link: herbivores eat plants, carnivores eat other animals, and omnivores eat both.

Animals also depend on plants for oxygen, shelter and protection:

• Aquatic animals rely on submerged plants for dissolved oxygen, since those plants release oxygen as they photosynthesise.
• Many fruit-bearing plants rely on animals to pollinate their flowers and to disperse their fruits and seeds.
• Animal waste enriches the soil so plants grow healthier.
• Animals release carbon dioxide when respiring, and plants take it in for photosynthesis.

1. The graph shows the number of organisms in a garden community.
2. There are three populations of organisms — butterflies, ladybirds and aphids.
3. The caterpillar is the young of the butterfly, so all the caterpillars and butterflies together form one population.
4. The garden is the habitat of the organisms shown.