Unit 9: Natural ecosystems and human activity
9.1 The ecosystem
An ecosystem is all the biotic and non-biotic components in an area.
Ecosystem structure
Populations are all the individuals of one species living in an area.
Communities are groups of populations of different species that live together in an area and
interact with each other.
Living things are found in habitats, the place where the population of an organism lives,
finds food and reproduces.
In the habitat, each species has a role in terms of its interactions with other species and its
effect on the environment, this is called its niche.
(an ecosystem consists of communities that live in single-species populations in particular
habitats where they perform particular functions within their niche)
Abiotic factors
Temperature: Living things have a range of temperatures within which they can survive.
Humidity: Measure of how damp the air is, how much water vapour it can hold. Expressed
in relative humidity (RH), expresses humidity as a percentage of how much water vapour the
air could hold if fully saturated.
Water: Essential for all life. It’s a raw material for photosynthesis and a medium for chemical
reactions. Living things can survive without water in liquid form. Plants obtain water from the
soil, and the water content of soil is an important factor in determining where a plant species
lives. The plants that live in soil saturated with water have roots that are adapted to function
in low oxygen conditions.
Oxygen: Oxygen level is nearly always 20% of the gas in the air, the amount of oxygen is
expressed as parts per million (ppm). It decreases as altitude increases. Oxygen is not
soluble in water so all aquatic organisms have special adaptations to get enough. Plants with
their roots in waterlogged soil have adaptations to get oxygen to the roots.
Salinity: How salty something is, measured as parts per million (ppm) or thousand (ppt), or
as a concentration (milligrams per litre). Affects mainly aquatic animals, all marine species
live in water that has 34 ppt. Water with a salinity that is less than 35 ppt, but more than
zero, is referred to as brackish water. In some cases, the water in the soil is saline, plants
that live in saline water are adapted. Salty soil can arise as a result of proof irrigation
practices, this can be a problem for farmers trying to grow crops.
Light: Expressed as lumens. Essential for photosynthesis, nearly all living species depend
on it. With no light, there’s no food. Some plants are adapted to live in low light levels and
can support a community of animals.
pH: Measure of how acid or alkaline an aqueous solution is. Expressed as a number without
units on the pH scale. The pH of soil water is an important factor for plants, some plants
require soil with an acidic water content. Others cannot survive in the acidic soils at all.
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, Ecosystem processes
Organisms interact with each other, you can see this in a food chain
producers → primary consumers → secondary consumers → tertiary consumers
plants → herbivores → 1st carnivores → 2nd carnivores
If an organism consumes dead bodies, it's called a decomposer.
A more accurate picture of the interactions between organisms is shown in a food web
The number of organisms in an ecosystem can be represented in a pyramid of numbers
Plants trap energy in the form of light in a process called photosynthesis
carbon dioxide + water → glucose + oxygen
CO₂ + H₂O → C₆H₁₂O₆ + O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose is sugar used by plants in the process of respiration to release energy (opposite to
photosynthesis), it's also converted by the plant to make other substances such as starch.
Plants obtain CO₂ from the atmosphere through pores in their leaves, they obtain water from
the soil through their roots, and absorb light through the chlorophyll in their leaves. The light
energy is used to split the water into hydrogen and oxygen, the hydrogen is added to carbon
dioxide to make glucose. The oxygen not used in respiration is given off to the atmosphere.
Interactions between living things (biotic interactions)
● Competition: Living things need a range of resources from the environment. More
young are produced than will survive, so there’s competition for those resources. The
ones that couldn’t adapt well to the current conditions will die earlier or fail to
reproduce.
● Predation: When one animal eats another it’s called a predator. (lions, beetles, etc)
● Pollination: The male sex cells are found in a pollen grain, made in the anther. It’s
either blown away by the wind or carried by insects. The anther is in the flower which
attracts animals with bright colours, scent and nectar. The pollen grain lands on the
stigma of another flower and sends out a tube that grows down to where the female
egg is. The egg is fertilised and an embryo in a seed develops into a new plant.
Energy flows and nutrient cycles
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9.1 The ecosystem
An ecosystem is all the biotic and non-biotic components in an area.
Ecosystem structure
Populations are all the individuals of one species living in an area.
Communities are groups of populations of different species that live together in an area and
interact with each other.
Living things are found in habitats, the place where the population of an organism lives,
finds food and reproduces.
In the habitat, each species has a role in terms of its interactions with other species and its
effect on the environment, this is called its niche.
(an ecosystem consists of communities that live in single-species populations in particular
habitats where they perform particular functions within their niche)
Abiotic factors
Temperature: Living things have a range of temperatures within which they can survive.
Humidity: Measure of how damp the air is, how much water vapour it can hold. Expressed
in relative humidity (RH), expresses humidity as a percentage of how much water vapour the
air could hold if fully saturated.
Water: Essential for all life. It’s a raw material for photosynthesis and a medium for chemical
reactions. Living things can survive without water in liquid form. Plants obtain water from the
soil, and the water content of soil is an important factor in determining where a plant species
lives. The plants that live in soil saturated with water have roots that are adapted to function
in low oxygen conditions.
Oxygen: Oxygen level is nearly always 20% of the gas in the air, the amount of oxygen is
expressed as parts per million (ppm). It decreases as altitude increases. Oxygen is not
soluble in water so all aquatic organisms have special adaptations to get enough. Plants with
their roots in waterlogged soil have adaptations to get oxygen to the roots.
Salinity: How salty something is, measured as parts per million (ppm) or thousand (ppt), or
as a concentration (milligrams per litre). Affects mainly aquatic animals, all marine species
live in water that has 34 ppt. Water with a salinity that is less than 35 ppt, but more than
zero, is referred to as brackish water. In some cases, the water in the soil is saline, plants
that live in saline water are adapted. Salty soil can arise as a result of proof irrigation
practices, this can be a problem for farmers trying to grow crops.
Light: Expressed as lumens. Essential for photosynthesis, nearly all living species depend
on it. With no light, there’s no food. Some plants are adapted to live in low light levels and
can support a community of animals.
pH: Measure of how acid or alkaline an aqueous solution is. Expressed as a number without
units on the pH scale. The pH of soil water is an important factor for plants, some plants
require soil with an acidic water content. Others cannot survive in the acidic soils at all.
Página 1 | 9
, Ecosystem processes
Organisms interact with each other, you can see this in a food chain
producers → primary consumers → secondary consumers → tertiary consumers
plants → herbivores → 1st carnivores → 2nd carnivores
If an organism consumes dead bodies, it's called a decomposer.
A more accurate picture of the interactions between organisms is shown in a food web
The number of organisms in an ecosystem can be represented in a pyramid of numbers
Plants trap energy in the form of light in a process called photosynthesis
carbon dioxide + water → glucose + oxygen
CO₂ + H₂O → C₆H₁₂O₆ + O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose is sugar used by plants in the process of respiration to release energy (opposite to
photosynthesis), it's also converted by the plant to make other substances such as starch.
Plants obtain CO₂ from the atmosphere through pores in their leaves, they obtain water from
the soil through their roots, and absorb light through the chlorophyll in their leaves. The light
energy is used to split the water into hydrogen and oxygen, the hydrogen is added to carbon
dioxide to make glucose. The oxygen not used in respiration is given off to the atmosphere.
Interactions between living things (biotic interactions)
● Competition: Living things need a range of resources from the environment. More
young are produced than will survive, so there’s competition for those resources. The
ones that couldn’t adapt well to the current conditions will die earlier or fail to
reproduce.
● Predation: When one animal eats another it’s called a predator. (lions, beetles, etc)
● Pollination: The male sex cells are found in a pollen grain, made in the anther. It’s
either blown away by the wind or carried by insects. The anther is in the flower which
attracts animals with bright colours, scent and nectar. The pollen grain lands on the
stigma of another flower and sends out a tube that grows down to where the female
egg is. The egg is fertilised and an embryo in a seed develops into a new plant.
Energy flows and nutrient cycles
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