CBSE CLASS 10 CHAPTER 15 NOTES

 

CHAPTER 15

CBSE SCIENCE
CLASS 10

CHAPTER 15

OUR ENVIRONMENT

 

INTRODUCTION

·        Our environment – composed of various biotic & abiotic factors – interact with each other

·        Human activities have  a great impact on the functioning of the environment

 

ENVIRONMENT

·        Ecosystem – structural & functional unit of biosphere – comprising of all the interacting organisms in an area together with non-living constituents of the environment

·        The size of the ecosystem – ranges from as small as a pond or a backyard garden to as large as an entire rain forest

 

COMPONENTS OF AN ECOSYSTEM

·        Ecosystem – biotic & abiotic components

·        Biotic components – living things like plants, animals, humans, microbes, etc.,

·        Biotic factors may be classified as – producers, consumers & decomposers – depending on the mode of nutrition

·        Abiotic components – non-living parts of the environment – i.e., air, water, soil & minerals, climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure, wind, etc., 

 

TYPES OF ECOSYSTEM

·        Ecosystem – two types – Natural & Man-made or Artificial ecosystem

 

NATURAL ECOSYSTEM

·        They are terrestrial land as well as aquatic

·        Examples of land ecosystem – forests, grassland, deserts, etc.,

·        Examples of aquatic ecosystem – ponds, lakes, rivers, oceans, etc.,

 

MAN – MADE ECOSYSTEM

·        These are made by human beings

·        Example: crop field, gardens, parks, aquarium, etc.,

 

We don’t clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why?

·        Aquarium – is an artificial & incomplete ecosystem – compared to ponds or lakes – natural, self – sustained & complete ecosystem – where there is a perfect recycling of materials

·        Cleaning of aquarium is necessary due to

·        Absence of natural decomposers

·        Stagnancy of water

 

BIOTIC FACTORS

PRODUCERS

·        Also called autotrophs – as they prepare their own food

·        They fix up the solar energy – makes it available for other organisms

 

CONSUMERS

·        The food manufactured by the producers – from simple inorganic substances – used by other consumers

·        Consumers – organisms which depend upon the producers for their food – either directly or indirectly by feeding on other consumers

·        Types of consumers – Herbivores, carnivores, omnivores and parasites

·        They are called heterotroph

 

PARASITES

·        Parasites – organisms that live on or inside the body of another organism – host – from which it obtains nutrients

·        Example: parasites of man – lice

 

DECOMPOSERS

·        Micro organisms – that obtain energy from the break down of dead organisms or plants & animals waste

·        Decomposers – break down – complex organic substances into simple organic substance – go into the soil – are used up once more by the plants

 

FOOD CHAIN

·        A sequence of organisms – through which energy – transferred in the form of food – by the process of one organism consuming the other

·        Example:   

·        grass (Producer) à grasshopper (Herbivore) à frog (Carnivore) à snake (Omnivore) à    eagle (Top Carnivore)

 

TROPHIC LEVEL

·        Trophic levels – various steps or levels in the food chain – transfer of food or energy take place

·        Producers – first trophic level

·        Herbivores – second trophic level

·        Carnivores or secondary consumers – third trophic level

·        Large carnivores or tertiary consumers – fourth trophic level

 

DIFFERENCE BETWEEN FIRST & SECOND TROPHIC LEVEL

 

 FOOD WEB

·        Food web – network of various food chains – interconnected at various trophic level

·        An organism – can occupy position in more than one food chain – so it occupies more than one trophic level

DIFFERENCE BETWEEN FOOD CHAIN & FOOD WEB

FLOW OF ENERGY IN TROPHIC LEVELS

·        The flow of energy in food chain – unidirectional

·        Energy trapped by autotrophs – donot revert back to solar – only passes to herbivores

·        About 1% of solar energy falling on leaves – utilized by plants – photosynthesis – to produce food

·        A large amount of energy loss occur – when organism of higher trophic level feeds on lower trophic level organisms

·        There is only 10% flow of energy from one trophic level to the next trophic level

 

FLOW OF ENERGY IN TROPHIC LEVELS

·        Due to energy loss – only 4 or 5 trophic levels are present in each chain

·        This is known as ‘Ten Percent Law’

·        Large amount of energy loss – in the form of heat, maintaining metabolic activities – at different trophic levels

·        Amount of heat loss – 90% ; amount of energy retained – 10% at every trophic level

 

What happens if we kill all the organisms in one trophic level?

·        The population of organisms in the previous trophic level increase

 

BIOLOGICAL MAGNIFICATION

·        Pesticides – chemicals used to kill pest organisms

·        Includes – Insecticides, weedicides, fungicides, nematicides & rodenticide

·        Harmful or poisonous substance such as DDT – sprinkled to kill pest on plants – enter the food chain & gets accumulated within organisms of different trophic levels

·        BIOLOGICAL MAGNIFICATION – process of increase in the concentration of a toxic chemical – with increasing trophic level in a food chain

 

OZONE

·        Ozone (O3) – an isotope of oxygen i.e., a molecule formed by 3 atoms of oxygen

·        Ozone – function – shielding the surface of the earth from UV radiations of the sun (harmful radiations)

·        Ozone layer – layer of the earth’s atmosphere – where atmosphere’s ozone is concentrated

 

HOW & WHEN IS OZONE FORMED?

·        UV radiation split some molecular oxygen O2 apart to free oxygen atoms (O + O)

·        These atoms combine with molecular oxygen (O2) to form ozone

HOW IS OZONE DEPLETED?

·        The use of CFCs (Chloro Fluoro Carbon) – responsible for depletion of ozone layer

·        Other factor – Nitrogen Monoxide (pollution)

·        When harmful chemicals (CFCs) – released into air – accumulate in the upper atmosphere – reacts with ozone – reduce the thickness of the ozone layer

·        Ozone layer – becomes thinner – allows more UV rays to pass through

·        UV rays – reaches the earth – may cause severe damage

·        For example: They cause skin cancer in humans

 

EFFECTS OF OZONE DEPLETION ON HEALTH

·         Skin Cancer

·         Damage eyes

·         Effects immunity

·         Can change the structure of DNA

 

ENVIRONMENTAL FRIENDLY PRACTICES

·        Gardening & planting trees

·        Use of gunny bags / paper bags in place of polythene

·        Use of compost & vermicompost in place of fertilizers

·        Separation of biodegradable & non-biodegradable substances

 

DIFFERENCE BETWEEN BIODEGRADABLE & NON-BIODEGRADABLE SUBSTANCES

 

 

Why should bio-degradable & non-biodegradable waste be discarded in two separate dustbin?

·        Biodegradable materials – broken down by micro organisms in nature into simple harmless substances

·        Non- biodegradable materials need a different treatment like heat & temperature & hence should be discarded in a different bin