Our Environment Class 7 Science Notes and Questions

Please refer to Our Environment Class 7 Science notes and questions with solutions below. These revision notes and important examination questions have been prepared based on the latest Science books for Class 7. You can go through the questions and solutions below which will help you to get better marks in your examinations.

Class 7 Science Our Environment Notes and Questions

Ecology:- Ecology is the scientific study of the interaction of living organisms and their environment. These interactions are studied with a view to discover the principles which govern them.

Ecosystem: Ecological system or ecosystem is an open space built by physical and biological components of an environment. Ecosystem is result of an active interaction between living and non- living components. Ecosystem is where community of plants, animals and their environment function as a whole, and relationship between organism and environment thrives blissfully.
Ecosystems have no particular size. An ecosystem can be as large as a desert or lake or as small as a tree or a puddle. If you have a terrarium, gardens or crop field that is an artificial ecosystem.

Structure of Ecosystem:- Ecosystem is composed of two components –

1. Abiotic components: It includes inorganic, organic and climatic factors like air, water, soil
and sunlight etc.
(i) Inorganic substances:
These include nutrient elements and compounds like- carbon, nitrogen, Sulphur, phosphorus,
carbon dioxide and water. All these substances undergo cycling in ecosystem.
(ii) Organic compounds:
These include proteins, fats, carbohydrates and humic substances. They usually belong to the
living body of organisms and link compounds of abiotic (non- living) and biotic (living) origin.
(iii) Climatic factors: These are of two types:-
(a) Atmospheric factors: For examples- light, temperature, humidity, precipitation etc.
(b) Edaphic factors: For example- topography, soil texture etc. These factors influence the
distribution of number, metabolic processes and behavior of organisms.

2. Biotic components: They are divided in following parts:
(i) Producers:
They are chlorophyll containing plants which include algae, grasses and plants. They convert
solar energy into chemical energy by photosynthesis. Photosynthesis is the source of food for majority of animals.
Green plants are also called autotrophs since they synthesize their own food.
(ii) Consumers:
Those organisms which cannot synthesize their own food but depend on others for the
same are called Heterotrophs. They are mostly animals. Those animals which are directly
dependent on plants for food are called herbivores e.g. locust, goat, sheep, rabbit. Those
animals which depend on herbivores for food are called carnivores e.g. lion, cat. The carnivores
can be predators or parasites. Those organisms which depend on both plants as well as
animals for food are called omnivores e.g. cockroach, man.
(i) Decomposers:
They include mostly bacteria and fungi. In ecosystem generally bacteria attack or act on
animal tissues and fungi on plant tissues. They digest dead tissues by the secretion of
enzymes liberating their basic elements of protoplasm in enviro nment. The liberating
elements are utilised by producer s.

Types of Ecosystem:-

There are two main types of ecosystems:

1. Natural ecosystem: They are self controlled in natural conditions. The
interference of human being is minimum; These can be further classified as follows on
the basis of specific type of habitats.
(a) Terrestrial ecosystem: For example- forests, grasslands, deserts etc.
(b) Aquatic ecosystem: It is of two types- fresh water ecosystem and marine water
ecosystem. Fresh water is again of two types- Lotic e.g. river, water fall etc.and Lentic e.g.
pond, lake etc.

2. Artificial ecosystem: They are completely controlled by man, e.g. cropland which includes
fields of wheat, bajra, rice etc. In this type man controls the biotic community and physicochemical
atmosphere of the ecosystem.
In addition to the above two main types a third type ‘space ecosystem’ has also been
recognized.

There are four main cycles that occur in ecosystem:

1. The water cycle: Liquid water from the ocean evaporates, condenses to form clouds, falls
to the Earth as precipitation, and returns to the ocean as runoff.

2. The carbon cycle: Plants convert the carbon dioxide in the atmosphere into carbon
compounds, which are used by animals that consume the plants.

3. The nitrogen cycle: Nitrogen from the atmosphere is fixed by bacteria and made available to plants.

4. The phosphorus cycle: Phosphate dissolves in water, making phosphate ions available to
plants. Plants convert the phosphorus into biological molecules, which are then passed
through the ecosystem’s food chain.

Productivity in Ecosystem:-
The flow of energy through an ecosystem is not an efficient process. Only around 1
percent of the solar energy that reaches a plant is used to produce food. From there, at
each level that organisms consume each other for food, energy is lost as heat.
Scientists use three calculations for measuring plant productivity in an ecosystem:
Primary productivity measures how much energy is produced by the

photosynthetic organisms in an ecosystem. Gross primary productivity measures the total
amount of organic matter produced by the photosynthetic organisms in the ecosystem.
Plants also use some of the matter they produce for respiration. The remainder is available
for heterotrophs.

Net primary productivity (NPP) measures the amount of matter produced that is available for heterotrophs. NPP for an ecosystem is generally measured in grams per square meter (g/ m ₂).

• Biomass is the total weight of all an ecosystem’s organisms. Biomass increases
as net primary productivity increases. Secondary productivity is a measure of the rate of
biomass production by an ecosystem’s heterotrophs. Only around 10 percent of the
energy available at one trophic level is available to the next. Energy may be lost as feacal
matter or converted to heat. As energy passes from consumer to consumer down the
food chain, the amount of available energy is continuously diminished, limiting the
number of steps a given ecosystem’s food chain can sustain the energy.

• Biomes are ecosystems that have similar climates and organisms. There are eight major
biomes: trophic rainforest, savanna, desert, temperate grassland, temperate deciduous
forest, temperate evergreen forest, taiga , and tundra.

Marine Ecosystem:-
Marine ecosystems are characterized based on water depth and light levels.
The neritic zone is the relatively shallow region along the edges of continents and islands.
It stretches to a depth of 300 meters.
The pelagic zone is the area of water above the ocean floor, stretching from the surface to
depth approaching 1,000 meters.
The benthic zone is the ocean floor.

Food chain and Food web:-
A food chain shows how each living thing gets its food. Some animal eat plants and
some animals eat other animals. For example, a simple food chain links the trees &
shrubs, the giraffes (that eat trees & shrubs), and the lions (that eat the giraffes). Each
link in this chain is food for the next link. A food chain always starts with plant life and
ends with an animal.

Following are some more examples of food chain.
(i) grains sparrows cats
(ii) Algae, moss and food crumbs in the drains → cockroach → lizard → birds
(iii) grass → rabbit → hawks (garden and parks)
(iv) bark of a tree → wood house → spider → shrew → fox (woodland)
(v) cacti → ants / locusts → spiders → lizards → snakes (desert)
Food chains can be long or short depending upon the number of trophic level involved.

There are several different kinds of food chains, including
• predator chain : plant herbivore, carnivore, larger carnivore.
• parasite chain: various organisms sequentially parasitize one another
• saprophyte chain: decomposers, especially fungi, which feed an dead organic matter,
including the body of other decomposers.

Food web:-
A food web consists of many food chains. A food chain only follows just one path as animals
find food. e.g: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper,
which has eaten grass. A food web shows the many different paths plants and animals are
connected. E.g. : A hawk might also eat
a mouse, a frog or some other animal. The snake may eat a beetle, a caterpillar, or
some other animal. And so on for all the other animals in the food chain.
A food web is several food chains connected together.

Trophic Levels and Food Chains:-
The trophic level of an organism is its position in a food chain, the sequence of consumption and
energy transfer through the environment.
For example, a simple grazing food chain is comprised of Plant → herbivore
→ carnivore
At the base of the food chain lies the primary producers.

Primary producers:-
Autotrophs (usually photosynthetic) are the organisms that support all other trophic levels either
directly or indirectly by synthesizing sugars and other organic molecules using light energy.
Some examples of these include terrestrial plants, aquatic photosynthetic protists, and
cyanobacteria. An exception is communities of organisms living around hot water, deep sea
vents where producers are cheomosynthetic bacteria that oxidize H 2S (driven by geothermal energy).

Primary consumers:-
These are herbivores that consume primary producers. Some examples are terrestrial
insects, snails, grazing mammals, seed- eating birds, aquatic zoo- plankton, and some fish.

Secondary consumers:-
These are the carnivores that eat herbivores. This group include terrestrial spiders, frogs,
insects- eating birds, lions, many fish, and sea- stars.

Tertiary consumers:-
These are the carnivores that eat other carnivores. eg. Eagle, etc.

Detritivores:-
These are the consumers that derive energy from organic wastes and dead organisms
some examples include the bacteria and fungi. Also include scavengers such as
cockroaches and bald eagles. This level often forms a major link between primary
producers and higher- level consumers, and is important components of the recycling process.
Fungi are important components of the decomposers

Ecological efficiency:-
Ecological efficiency is the ratio of net productivity at one trophic level compared to net
productivity at the level below. It can vary greatly depending on the organisms involved, but
is roughly 10%. This means that 90% of the energy available at one trophic level never
transfers to the next.

Habitat Destruction and the Biodiversity Crisis:-

The destruction of natural systems due to human encroachment has resulted in only a small
proportion of natural, undisturbed habitat remaining in existence. Over 75% of the Earth’s
original forests have been cleared or severely disrupted.
One result of the destruction of natural habitat will be the exitinction of many species as
their ecosystem disappear. This biodiversity crisis has many aspects that must be
considered in order to protect endangered species. Not only is localized protection
necessary, but many migratory species are facing habitat destruction in both their
northern breeding grounds and their tropical wintering grounds.

Ecological pyramids:
• Ecological pyramids are diagrammatic are representation that show the relationships between
the trophic levels of an ecosystem. The pyramid shape reflects the loss of energy that occurs
from one trophic level to the next. There will generally be many individuals at the lowest
trophic level, where energy levels are more abundant. Since only 10 percent of the energy is
passed on to the next level, there will be fewer individuals at the second level, and even
fewer at the third.

Ecological pyramids can be represented in three ways:
1. A pyramid of numbers shows the number of individuals at each level.
2. A pyramid of biomass shows the amount of biomass produced at each level.
3. A pyramid of energy shows the amount of energy available at each level.

• A population is a group of individuals of the same species occupying a given area. It has a
characteristic size, density, distribution, and age structure as well as characteristic ranges
of heritable traits.

MCQs for NCERT Class 7 Science Our Environment

Question: Term ‘ecology’ was proposed by-
(A) William
(B) Odum
(C) Reiter
(D) Daubenmier

Question: Habitat together with functions of species constitute is –
(A) Trophic level
(B) Boundary
(C) Topography
(D) Niche

Question: The best source of energy in the environment is –
(A) Water
(B) Soil
(C) Trees
(D) Ponds

Question: Which one of the following factors is biotic
(A) Photoperiod
(B) CO2 extent to the soil
(C) Texture and porosity
(D) Rainfall

Question: As a biologist, if you become very interested in the study of the interaction of organisms
with each other and the environment your subspeciality would be –
(A) Zoology
(B) Ecology
(C) Botany
(D) Herpetology

Question: As energy is passed from one trophic level to another, the amount of usable energy –
(A) Increases
(B)Decreases
(C) Remain the same
(D) Energy is not passed from one trophic level to another

Question: An example of a producer in the aquatic food web would be –
(A) Duckweed
(B) Ducks
(C) Fish
(D) Insects

Question: When you were a child, you may have heard the old poem, “Fishy, fishy in the brook, daddy catch it with a hook, mamma fries it in pan, baby eats it like a man.” This poem illustrates the biological concept of –
(A) Trophic levels in a food web
(B) Primary productivity
(C) The decomposition of organic matter
(D) A poem that would be considered politically incorrect today

Question: In the biosphere, which of the following is the ultimate source of energy –
(A) Carbon
(B) Water
(C) Sunlight
(D) Nitrogen

Question: Free services provided to humans by ecosystems include –
(A) control of atmospheric carbon dioxide concentration.
(B) prevention of soil erosion.
(C) filtering of pollutants from water and air.
(D) all of the above

Question: Each step in a food chain is called a
(A) trophic level.
(B) consumer level
(C) food web
(D) producer

Question: As a black widow spider consumes her mate, what is the lowest trophic level she could be
occupying-
(A) third
(B) first
(C) second
(D) fourth

Question: How do mountain ranges create deserts –
(A) by lifting land up into colder, driver air
(B) by completely blocking the flow of air into desert areas, thus preventing clouds from getting there
(C) by forcing air to first rise and then fall, thus causing rain on one side of the mountains
and desert on the other
(D) by causing the global wind patterns that make certain latitudes very dry

Question: Individuals of any species at a place form-
(A) biotic community
(B) ecosystem
(C) population
(D) biome

Question: The part of earth comprising water is called an –
(A) atmosphere
(B) hydrosphere
(C) lithosphere
(D) none of these

Question: The last chain of food is –
(A) producers
(B) decomposers
(C) parasites
(D) none

Question: Trophic levels are formed by –
(A) only plants
(B) only animals
(C) only carnivores
(D) organism linked in food chain

Question: Which of the following is the most important climatic factor
(A) precipitation
(B) soil
(C) gradient of slope
( D ) atmosphere

Question: In an ecosystem green plants are known as
(A) primary consumers
(B) secondary consumers
(C) producers
(D) tertiary consumers

Question: Sun gives radiations in the form of –
(A) Infra- red radiation
(B) Visible light
(C) Ultra- violet
(D) All of the above

Question: For corrosion of metals, there should be-
(A) Exposed surface of metal
(B) Moisture
(C) Air
(D) All of the above

Question: Which of the following constitute a food- chain ?
(A) Grass, wheat and mango
(B) Grass, goat and human
(C) Goat, cow and elephant
(D) Grass, fish and goat

Question: Which of the following are environment- friendly practices?
(A) Carrying cloth- bags to put purchases in while shopping
(B) Switching off unnecessary lights and fans
(C) Walking to school instead of getting your mother to drop you on her scooter
(D) All of the above

Question: Pyramids of energy are-
(A) always upright
(B) always inverted
(C) mostly upright
(D) mostly inverted

Question: The maximum energy is stored at following tropical level in any ecosystem-
(A) Producers
(B) Herbivores
(C) Carnivores
(D) Top carnivores

Question: In an ecosystem the function of the producers is to
(A) Convert organic compounds into inorganic compounds
(B) Trap solar energy and convert it into chemical energy
(C) Utilize chemical energy
(D) Release energy

Question: Pyramid of energy in a forest ecosystem is
(A) Always inverted
(B) Always upright
(C) Both upright and inverted depending on ecosystem
(D) First upright then inverted

Question: The study of the relationship between living things and the environment is called
(A) evolution
(B) paleontology
(C) ecology
(D) cytology

Question: Which of the following would be considered a population?
(A) all the insects in the world
(B) all the birds in North America
(C) all the bullfrogs in a pond
(D) all the trees in a state park

Question: All the living organisms and the nonliving environment in a particular, location make up
what is called a(n)
(A) population
(B) species
(C) biotic factors
(D) community

Question: The physical location an organism lives is sometimes referred to as its
(A) gene pool
(B) biosphere
(C) habitat
(D) population

Question: The portion of the earth’s surface that supports life is known as
(A) the biome
(B) the atmosphere
(C) the biosphere
(D) the strata

Question: An organism that cannot synthesize its own organic molecules is called a
(A) producer
(B) autotroph
(C) heterotroph
(D) A and B

Question: Which of the following would not be considered an autotroph ?
(A) plant
(B) algae
(C) photosynthetic bacteria
(D)mushroom

Question: Organisms that feed on producers in the ecosystem are called
(A) first level consumers
(B) second level consumers
(C) autotrophs
(D) none of these

Question: In energy pyramids, which of the following trophic levels contains the largest amounts of
us able energy ?
(A) producers
(B) first level consumers
(C) second level consumers
(D) third level consumers

Question: Which of the following organisms feeds on animal and plant material?
(A) carnivores
(B) herbivores
(C) omnivores
(D) autotrophs

Question: Which of the following is not correct concerning the nitrogen cycle ?
(A) nitrogen is an element needed to produce amino acids
(B) atmosphere nitrogen is converted to ammonia by certain bacteria
(C) denitrification is when atmospheric nitrogen is changed into ammonia
(D) plants use nitrates in the soil to make proteins

Question; The burning of fossil fuels releases large amounts of
(A) iron into the soil
(B) carbon into the atmosphere
(C) oxygen into the atmosphere
(D) sulfur into the soil

Question; Which organisms are responsible for removing carbon from the atmosphere and fixing
this carbon into organic molecules
(A) autotrophs
(B) plants
(C) producers
(D) all of these

Question: Transpiration is when
(A) atmospheric nitrogen is chemically fixed as ammonia
(B) ice is changed directly into water vapor
(C) liquid water that has entered a plant leaves as water vapor
(D) water vapor is changed into liquid water

Question: Which of the following would best describe the niche of a rabbit?
(A) its fur color
(B) how many offspring it produces
(C) the grass it eats in the environment
(D) the enzymes present in its blood

Question: Which of the following conditions would probably result in the most competition for food?
(A) a lion and a zebra in a savannah
(B) an elephant and an ant colony in a forest
(C) a spider and a plant in someone’s backyard
(D) a deer and a rabbit in a grass field

Question: Commensalism is
(A) an interaction among two species where both species benefit from the relationship
(B) an interaction among two species where one species benefits and the other species is unaffected
(C) an interaction among two species where one species benefits and the other species is harmed
(D) when two organisms do not interact at all in an environment

Question: In the process of ecological succession, the final community or group of organisms that
will exist in the ecosystem are called
(A) pioneer organisms
(B) climax community
(C) secondary consumers
(D) none of these

Question: Which of the following statements are true about secondary succession ?
(A) Secondary succession will begin in an area that has no soil.
(B) Secondary succession occurs on a site where no previous community existed.
(C) Secondary succession will begin in an area that has been disturbed by a condition,
such as fire, that destroys the vegetation, but leaves the soil.
(D) Secondary succession will cause all plant life in the area to die.

Question: The first organism that will appear in an area experiencing primary succession is called a(n)
(A) pioneer organisms
(B) secondary consumer
(C) parasites
(D) heterotroph

Question: What characteristic is usually used as the major identifying factor of a particular biome ?
(A) latitude
(B) longitude
(C) rock formations
(D) climax plant life

Question: Which of the following biomes receives the highest annual rainfall?
(A) taigas
(B) deserts
(C) grasslands
(D) tropical rainforests

Question: Which of the following biomes contains many trees that lose their leaves in the colder
months of the year ?
(A) tropical rainforest
(B) grasslands
(C) temperate deciduous forest
(D) tundra

We hope the above Our Environment Class 7 Science are useful for you. If you have any questions then post them in the comments section below. Our teachers will provide you an answer. Also refer to MCQ Questions for Class 7 Science