CBSE Class 9 Biology Diversity In Living Organisms Worksheet Set 01

Question. What are autotrophic bacteria? Give an example for autotrophic bacteria.
Ans : The bacteria which synthesize their own food from inorganic substances are called autotrophic bacteria.
Example : Nostoc, Anabaena.

Question. What are heterocysts?
Ans : The colourless specialized cells of nostoc filament meant for fixing atmospheric nitrogen are called heterocysts.

Question. What are chemosynthetic autotrophic bacteria?
Ans : The bacteria which oxidize inorganic substances like nitrate, nitrities and ammonia to release energy in the form of ATP are called chemosynthetic bacteria.

Question. What are mycoplasmas?
Ans : The smallest living organisms without cell walls and survive without oxygen are called mycoplasmas.

Question. What are planktons?
Ans : The microscopic organisms which floats on water are called planktons.

Question. Name the chemical component of cell wall of Diatoms.
Ans : Chitin.

Question. What are euglenoids?
Ans : The fresh water organisms found in stagnant water with protein rich particle in their cell wall are called euglenoids.

Question. What are plasmodium?
Ans : Aggregation of slime moulds under suitable conditions are called plasmodium, which may grow and spread over several feet. During unfavorable conditions they differentiate and follows fruiting bodies.

Question. Name parasitic protozoa.
Ans : Entamoeba, Plasmodium (Malarial parasite).

Question. Name the disease caused by Trypanosoma.
Ans : Sleeping sickness.

Question. What are the characteristic features of mammals?
Ans : Characteristic features of mammals :
(a) Body is covered with hair.
(b) Skin is provided with sweat and sebaceous glands.
(c) Heart is four-chambered.
(d) Fertilization is internal.
(e) Females have mammary glands to produce milk to nourish their young ones.
(f) External ear–pinna present.
(g) Eyes have eye lids.
(h) Warm-blooded.
(i) Respiration through lungs.

Question. What is the importance of heterotrophic bacteria?
Ans :
(1) Conversion of milk to curd.
(2) Antibiotic productions.
(3) N2 fixation in leguminous roots.
(4) Act as pathogen, causing diseases like cholera, typhoid, tetanus.
(5) Damage corps (citrus canker disease)
(6) Act as ‘Scavengers of nature’ by decomposing dead and decaying organic matter.

Question. Name the 2 methods of protistan’s reproduction.
Ans : (1) Asexual reproduction (cell fusion),
(2) Sexual reproduction (zygote formation).

Question. What are prokaryotes? Give one example for prokaryote.
Ans : The organisms which do not have well organized nucleus in their cell are called prokaryotes. Organisms containing incipient nucleus (Nucleoid) in their cells are called prokaryotes. Example : Bacteria, Nostoc (cyano bacteria/ B.G. Algae)

Question. Give one example for ciliated protozoans.
Ans : Paramecium.

Question. Which one is called malarial parasite?
Ans : Plasmodium.

Question. Name the disease caused by plasmodium.
Ans : Malaria.

Question. Which fungi act as a source of antibiotics?
Ans : Penicillium.

Question. What are saprophytic fungi?
Ans : The heterotrophic fungi which absorb soluble organic matter from dead substrates are called saprophytes.

Question. How are pores or holes all over the body of Porifera important?
Ans : The pores present all over the body of the organisms lead to a canal system that helps in circulating water throughout the body to bring in food and oxygen.

Question. If you are provided seeds of gram, wheat, rice, pumpkin, maize and pea. Classify these as Monocots/ Dicots.
Ans : Monocots : Wheat, Rice, Maize. Dicots : Gram, Pumpkin, Pea.

Question. What are hermaphrodites? Give two examples.
Ans : Hermaphrodites are the organisms that have both the sexes. Thus, it can produce both sperms and eggs and called hermaphrodites. Example : Sponges, earthworms.

Question. Give general characteristics of Porifera.
Ans :
(a) Animals with pores all over the body.
(b) Body is not well differentiated.
(c) Non-motile animals remain attached to solid support.
(d) Body is covered with hard outer skeleton. Example : Sponges.

Question. Give the characteristics of Arthropoda with 2 examples.
Ans :
(a) Arthropoda means jointed legs.
(b) Animals are bilaterally symmetrical and segmented.
(c) It has an open circulatory system.
(d) This is the largest group of animals.
Examples : Spider, scorpions, crabs, house flies.

Question. Give the characteristics of Ayes.
Ans : (a) Aves/birds can fly.
(b) Streamlined body.
(c) Hollow and light bones.
(d) Forelimbs are modified into wings.
(e) Warm-blooded animals, heart with four chambers.
(f) Egg laying animals.
(g) Beak present, teeth are absent.

Question. Write briefly about lichens.
Ans :
(1) Lichens are symbiotic close association of two different organisms such as algae and fungi.
(2) Algal component of lichen known as phycobiont which is photosynthetic in nature.
(3) Fungal component of living form is known as mycobiont which is non-photosynthetic, but helps in absorption of minerals, nutrients and water.
(4) Lichens are very good pollution indicator as they do not grow in polluted areas.
Question. Define species.
Ans : Species are organisms within genus with slight difference from other and capable of breeding and perpetuate.

Question. What is symbiotic relationship?
Ans : It is a relationship between two organisms in which both of them are benefitted, e.g., fungi gets food from blue-green algae and in return blue-green gets shelter (lichens).

Question. What is saprophytic nutrition?
Ans : The organisms that use dead and decaying organic matter as mode of nutrition is known as saprophytic nutrition.

Question. Name the plant amphibian.
Ans : Bryophyta, e.g. funaria.

Question. What are cryptogamae?
Ans : The plants with hidden reproductive organs are called cryptogamae, e.g., fern.

Question. Which divisions of the plant kingdom are called cryptogams? Why are they called so?
Ans : Thallophyta, Bryophyta and Pteridophyta divisions of plant kingdom are called cryptogamae. All these divisions have hidden reproductive organs.

Question. What are angiosperms?
Ans : Angiosperms are the group of plants with covered seeds. These are flowering plants.

Question. What is the meaning of triploblastic?
Ans : Animals which have three layers of cells : ectoderm, mesoderm and endoderm from which differentiated tissues can be made, e.g. tapeworm.

Question. What is bilateral symmetry?
Ans : Anything is said to have bilateral symmetry if its body have same design in left and right halves of the body.

Question. What do you mean by “cold-blooded animals”?
Ans : Cold-blooded animals are the animals that show the variation in their body temperature according to the surroundings, e.g., fish, amphibians, reptiles.

Question. Name a fish with skeleton made up of cartilage.
Ans : Shark.

Question. What is taxonomy?
Ans : The systematic study of identification, classification and naming of oraganisms is called taxonomy.

Question. Name the 2 kingdoms of classification?
Ans : (1) Plantae or Metaphyta
(2) Animalia or Metazoa

Question. What are Eukaryotes? Give an example of Eukaryotes?
Ans : Organisms which have well organized nuclei (True nucleus) are called Eukaryotes.
Example : Amoeba, mango, Man.

Question. What are multicellular organisms? Give an example for multi cellular organisms.
Ans : Organisms whose body is made up of many numbers of cells are called multicellular organisms.
Example : Spirogyra, Mango, Man.

Question. Who proposed five kingdom classification?
Ans : R.H. Whittaker (1969).

Question. What are Monerans?
Ans : Prokaryotic celled, unicellular and Autotrophic organisms.

Question. Name the kingdom which includes Bacteria.
Ans : Kingdom Monera.

Question. What is diatomaceous earth?
Answer : Accumulation of cell wall deposition of dead diatoms.

Diversity in living organisms

Question 1. Who proposed binomial nomenclature of classification and is considered as father of Taxonomy?
Answer: Carolus Linnaeus proposed the system of binomial nomenclature and is considered the father of modern taxonomy.
In simple words: Carolus Linnaeus gave the two-word naming system for organisms and started modern classification.

Exam Tip: Always remember Carolus Linnaeus for binomial nomenclature (Genus and species format, e.g., Homo sapiens).

Question 2. What are phanerogams?
Answer: Phanerogams are seed-bearing plants that have well-differentiated reproductive organs that produce seeds containing embryos along with stored food for the initial growth of the embryo.
In simple words: Phanerogams are plants that bear visible flowers and seeds.

Exam Tip: Phanerogams are divided into gymnosperms (naked seeds) and angiosperms (covered seeds).

Question 3. To which division of Cryptogamae do algae belong?
Answer: Algae belong to the division Thallophyta of Cryptogamae.
In simple words: Algae belong to Thallophyta, where plant bodies are not differentiated into roots, stems, and leaves.

Exam Tip: Thallophyta is the simplest group of plant kingdom.

Question 4. Name the group which (a) seeds are naked (b) Reproductive organs are flowers.
Answer: (a) Gymnosperms
(b) Angiosperms
In simple words: Plants with uncovered seeds are gymnosperms, and plants with flowers are angiosperms.

Exam Tip: Gymno means naked and sperma means seed; angio means covered.

Question 5. What is the most important feature of Arthropoda?
Answer: The most important features of Arthropoda are the presence of jointed appendages and a chitinous exoskeleton.
In simple words: Arthropods have jointed legs and a hard outer covering.

Exam Tip: Arthropoda is the largest phylum in the animal kingdom.

Question 6. Why are bats not placed in birds? Differentiate them.
Answer: Bats are not placed in birds because, despite having wings and the ability to fly, they possess mammary glands, external ears (pinnae), give birth to live young ones, and have body hair, which are characteristic features of mammals.
Differences:
1. Birds have feathers, beaks, and lay eggs; bats have hair/fur, teeth in jaws, and give birth to young ones.
2. Birds have pneumatic (hollow) bones to aid flight; bats have solid bones.
In simple words: Bats give birth to babies and feed them milk, making them mammals despite flying like birds.

Exam Tip: Focus on mammary glands and pinnae as definitive mammalian characters.

Question 7. Name the phylum to which the following belong: (i) Silver fish (ii) Jelly fish (iii) Sea horse (iv) Liver fluke (v) Sea cucumber (vi) Tape worm
Answer: (i) Silver fish - Arthropoda
(ii) Jelly fish - Cnidaria (Coelenterata)
(iii) Sea horse - Chordata (Vertebrata)
(iv) Liver fluke - Platyhelminthes
(v) Sea cucumber - Echinodermata
(vi) Tape worm - Platyhelminthes
In simple words: Each animal is categorized based on its body symmetry, cavity, and tissue organization.

Exam Tip: Be careful with common names like 'Silver fish' (insect/arthropod) and 'Jelly fish' (cnidarian), which are not true fishes.

Question 8. List any two bases of five kingdom classification proposed by Robert Whittaker. Mention in brief the basis of classification between (a) bacteria and fungi (b) plants and animals.
Answer: Two bases of Robert Whittaker's five kingdom classification are:
1. Complexity of cell structure (prokaryotic vs. eukaryotic)
2. Mode of nutrition (autotrophic vs. heterotrophic)
(a) Bacteria are prokaryotic (lack a well-defined nucleus and membrane-bound organelles), whereas fungi are eukaryotic (possess a true nucleus and membrane-bound organelles with a cell wall made of chitin).
(b) Plants are multicellular, eukaryotic autotrophs that prepare their own food via photosynthesis; animals are multicellular, eukaryotic heterotrophs that ingest food and lack cell walls.
In simple words: Whittaker classified organisms based on cell type, body organization, and how they get their food.

Question 9. Write three distinguishing features between the animals belonging to Aves group and Mammalia.
Answer:

In simple words: Birds have feathers and lay eggs, while mammals have hair, external ears, and feed milk to their young.

Exam Tip: Use a comparative table for differentiation questions to secure full marks.

Question 10. Distinguish between gymnosperms and angiosperms in respect of the following characters: (a) Nature of seeds (b) Reproductive organs (c) Xylem (d) Phloem
Answer:
(a) Nature of seeds: Gymnosperms have naked seeds not enclosed within fruit walls; angiosperms have seeds enclosed within fruits.
(b) Reproductive organs: Gymnosperms bear reproductive organs in cones (strobili) without true flowers; angiosperms bear flowers as reproductive organs.
(c) Xylem: In gymnosperms, xylem lacks true vessels (contains tracheids); in angiosperms, xylem typically contains true vessels.
(d) Phloem: In gymnosperms, phloem lacks companion cells (contains sieve cells); in angiosperms, phloem contains companion cells along with sieve tubes.
In simple words: Gymnosperms have naked seeds and cones, while angiosperms have covered seeds inside fruits and true flowers.

Exam Tip: Mention both vascular tissue differences (vessels and companion cells) clearly.

Question 11. A person enters a museum and observes the animal specimen. He looks at the one marked "Salamander" and calls it a "Lizard". How will you explain to him that Salamanders and Lizards belong to two different classes? List four distinguishing features and also give one example each of the other members of the above two classes.
Answer: Salamanders belong to class Amphibia, while lizards belong to class Reptilia. Explanation and differences:
1. Skin: Salamanders have smooth, moist, glandular skin without scales; lizards have dry, cornified skin covered with epidermal scales or scutes.
2. Respiratory organs: Salamanders respire through gills (in larvae), lungs, and moist skin; lizards respire exclusively through lungs.
3. Fertilization: Salamanders usually undergo external fertilization in water; lizards exhibit internal fertilization on land.
4. Eggs: Salamanders lay jelly-coated eggs in water; lizards lay amniotic eggs with leathery shells on land.
Other examples: Toad (Amphibia), Snake or Turtle (Reptilia).
In simple words: Salamanders are amphibians needing water and moist skin, while lizards are reptiles with dry scales and land-adapted eggs.

Exam Tip: Emphasize skin texture and egg type as key class markers.

Question 12. Describe the characteristics of the division Bryophyta, Pteridophyta and Thallophyta.
Answer:
1. Thallophyta: Plant body is a thallus (not differentiated into true roots, stems, and leaves). Vascular tissues are absent. Mostly aquatic (e.g., Spirogyra, Ulothrix).
2. Bryophyta: Plant body is differentiated to form stem and leaf-like structures, but true roots are absent (rhizoids present). Vascular tissue (xylem and phloem) is absent. Known as amphibians of the plant kingdom (e.g., Funaria, Marchantia).
3. Pteridophyta: Plant body is well-differentiated into true roots, stem, and leaves. Specialized vascular tissues (xylem and phloem) are present for conduction. Produce spores in structures called sporangia (e.g., Ferns, Marsilea).
In simple words: Thallophytes have simple thallus bodies, bryophytes have stems and leaves without vascular tissue, and pteridophytes have true roots, stems, leaves, and vascular tissue.

Exam Tip: Remember the evolutionary progression: Thallophyta (no roots/stems) -> Bryophyta (no vascular tissue) -> Pteridophyta (first vascular plants).

Chapter-13 Why do we fall ill?

Question 1. Define (a) Antibiotics (b) Vaccine (c) Immunisation (d) Inflammation
Answer:
(a) Antibiotics: Chemical substances produced by microorganisms that can kill or inhibit the growth of bacteria.
(b) Vaccine: A preparation of weakened or dead pathogens (or their parts) introduced into the body to stimulate an immune response and develop immunity against specific diseases.
(c) Immunisation: The process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine.
(d) Inflammation: A localized physical condition in which part of the body becomes reddened, swollen, hot, and often painful, as a reaction to injury or infection.
In simple words: Antibiotics kill bacteria, vaccines prevent diseases, immunisation builds long-term defense, and inflammation is the body's local reaction to infection or injury.

Exam Tip: Note that antibiotics target bacteria, not viruses.

Question 2. Expand AIDS.
Answer: Acquired Immuno Deficiency Syndrome.
In simple words: AIDS stands for Acquired Immuno Deficiency Syndrome.

Exam Tip: Spell every word correctly in expansions; minor spelling errors result in loss of marks.

Question 3. Name the groups of organisms which commonly cause infectious diseases.
Answer: Viruses, bacteria, fungi, protozoans, and parasitic worms (helminths).
In simple words: Infectious diseases are commonly caused by microbes like viruses, bacteria, fungi, and protozoa.

Exam Tip: Group them clearly under infectious agents.

Question 4. What are the different means by which infectious diseases are spread?
Answer: Infectious diseases spread through:
1. Air (droplets from coughing or sneezing, e.g., common cold, tuberculosis)
2. Water and food (contaminated water or food, e.g., cholera, typhoid)
3. Sexual contact (e.g., AIDS, syphilis)
4. Vectors (animals/insects carrying pathogens, e.g., mosquitoes spreading malaria, dogs spreading rabies)
5. Direct physical contact with an infected person (e.g., fungal skin infections)
In simple words: Diseases spread via air, water, food, physical contact, sexual contact, and vector animals like mosquitoes.

Exam Tip: Categorize transmission into direct and indirect methods for clarity.

Question 5. How does Personal health related to community health?
Answer: Personal health depends heavily on the surrounding community environment and social conditions. If garbage is uncollected, drains are stagnant, or safe drinking water is not available in the community, individuals cannot remain healthy. Conversely, healthy individuals contribute to a productive, clean, and disease-free community.
In simple words: An individual cannot stay healthy if their community environment is dirty and prone to disease outbreaks.

Exam Tip: Mention public hygiene, sanitation, and social well-being.

Question 6. What is the meaning of the term Disease?
Answer: Disease literally means disturbed ease. It is a condition of abnormal functioning of the body or a part of it, characterized by specific signs and symptoms, causing physical, mental, or social discomfort.
In simple words: Disease is a condition where body functions are impaired, causing discomfort and poor health.

Question 7. Why female anopheles mosquito feeds on human blood?
Answer: Female Anopheles mosquitoes feed on human blood because they require the proteins and nutrients found in blood for the maturation and development of their eggs.
In simple words: Female mosquitoes need nutrients from human blood to produce eggs.

Exam Tip: Remember that male mosquitoes feed exclusively on plant nectar and plant juices.

Question 8. How are diseases spread through water?
Answer: When drinking water gets contaminated with the excreta of a person suffering from an infectious gut disease (such as cholera or hepatitis), the disease-causing microbes enter the water supply. When healthy people drink this contaminated water, the pathogens enter their digestive system, causing infection.
In simple words: Waterborne diseases spread when sewage or infected waste contaminates drinking water sources.

Exam Tip: Examples include cholera, typhoid, and hepatitis A.

Question 9. What is the most common method to prevent infection?
Answer: The most common general method to prevent infection is maintaining personal and public hygiene, ensuring access to clean drinking water, proper waste disposal, and avoiding overcrowding. Specific prevention includes vaccination.
In simple words: Maintaining hygiene, clean water supply, and vaccination are the best ways to prevent infections.

Question 10. Explain why antibiotic do not work against viruses but work against many group of bacteria.
Answer: Antibiotics work by blocking biochemical pathways essential for bacteria, such as inhibiting cell wall synthesis or bacterial protein synthesis. Viruses do not possess their own metabolic machinery or cell walls; instead, they hijack the host cell's machinery to replicate. Therefore, antibiotics find no bacterial pathways to target in viruses, rendering them ineffective.
In simple words: Antibiotics block bacterial processes like cell wall formation, but viruses use host cells and lack these bacterial structures.

Exam Tip: This is a classic board exam question; emphasize the lack of metabolic pathways and cell walls in viruses.

Question 11. Write the symptoms and disease associated with the following: (a) when the microbe attacks the lungs. (b) when the virus enters the liver.
Answer:
(a) When microbes attack the lungs: Disease is Tuberculosis (or pneumonia). Symptoms include breathlessness, persistent cough, chest pain, and blood-stained sputum.
(b) When virus enters the liver: Disease is Jaundice (Viral Hepatitis). Symptoms include yellowing of eyes and skin, dark urine, loss of appetite, and nausea.
In simple words: Lung infections cause coughing and breathlessness (Tuberculosis), while liver infections cause yellowing of eyes and skin (Jaundice).

Question 12. What making anti-viral medicine is harder than making anti-bacterial medicines?
Answer: Making antiviral drugs is much harder than making antibacterial drugs because viruses have very few biochemical mechanisms of their own. They use the host cell's metabolic machinery to multiply. Consequently, finding a drug target that harms the virus without harming the host's own cells is extremely difficult.
In simple words: Viruses use our own body cells to multiply, so medicines that kill viruses often end up harming human cells as well.

Question 13. How is the disease AIDS caused? State any two modes of transmission of this disease from a patient to other persons. What symptom is found in the body of a person suffering from AIDS?
Answer: AIDS is caused by the Human Immunodeficiency Virus (HIV).
Two modes of transmission:
1. Sexual contact with an infected person.
2. Transfusion of blood contaminated with HIV or sharing infected needles.
Symptom found in the body: The immune system of the person becomes severely damaged and weak (immunodeficiency), making the body unable to fight off minor infections, leading to a cluster of diseases.
In simple words: AIDS is caused by HIV and spreads via infected blood or sexual contact, destroying the body's immune system.

Question 14. Why does a person suffered once from small pox cannot suffer with it again?
Answer: When the immune system first encounters the smallpox pathogen, it responds and remembers it specifically. When the same pathogen enters the body a second time, the immune system mounts a much faster and stronger response (memory response) using pre-existing memory cells, destroying the pathogen before it can cause the disease.
In simple words: Our immune system remembers past infections and destroys the same germs instantly if they attack again.

Question 15. State differences between acute and chronic diseases.
Answer:

In simple words: Acute diseases last a short time and cure completely (like the common cold), while chronic diseases last long and cause lasting damage (like diabetes).

Exam Tip: Give examples: Acute (common cold, typhoid) and Chronic (tuberculosis, elephantiasis, diabetes).

Chapter-14 Natural Resources

Question 1. What is the green house effect?
Answer: The greenhouse effect is a natural process where certain gases (like carbon dioxide, methane, and water vapor) in the Earth's atmosphere trap heat radiated from the Earth's surface, preventing it from escaping into space and keeping the planet warm enough to sustain life.
In simple words: Greenhouse gases trap heat from the sun in the atmosphere, keeping the Earth warm.

Exam Tip: Mention the role of greenhouse gases like \(\text{CO}_2\) and methane in trapping infrared radiation.

Question 2. How is ozone layer formed?
Answer: Ozone (\(\text{O}_3\)) is formed in the upper atmosphere (stratosphere) when high-energy ultraviolet (UV) radiations split molecular oxygen (\(\text{O}_2\)) into free oxygen atoms (\(\text{O}\)). These free oxygen atoms react with molecular oxygen (\(\text{O}_2\)) to form ozone (\(\text{O}_3\)).
Step 1: \(\text{O}_2 \xrightarrow{\text{UV light}} \text{O} + \text{O}\)
Step 2: \(\text{O} + \text{O}_2 \rightarrow \text{O}_3\)
In simple words: UV rays break oxygen molecules into atoms, which then combine with other oxygen molecules to form ozone.

Exam Tip: State both steps clearly with equations for full credit.

Question 3. Arrange the following steps in order of their sequence of occurrence in nitrogen cycle starting from Nitrogen gas: Ammonification, Nitrification, Denitrification, Nitrogen fixation.
Answer:
1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification
In simple words: Nitrogen is fixed into compounds, converted to ammonia, oxidized to nitrates, and finally released back as nitrogen gas.

Exam Tip: Memorize the cyclic flow: Atmosphere -> Fixation -> Ammonification -> Nitrification -> Denitrification -> Atmosphere.

Question 4. How does ozone layer protect us from harmful effects of the environment?
Answer: The ozone layer absorbs harmful ultraviolet (UV) radiations coming from the sun, preventing them from reaching the Earth's surface. This protects living organisms from severe damage such as skin cancer, damage to eyes (cataracts), and destruction of the immune system.
In simple words: Ozone acts as a shield blocking harmful UV rays from the sun.

Exam Tip: Mention ultraviolet (UV) rays and skin cancer.

Question 5. What is biogeochemical cycle?
Answer: A biogeochemical cycle is the cyclic pathway through which essential chemical elements (such as nitrogen, carbon, oxygen, and water) circulate between the biotic (living organisms) and abiotic (air, water, soil) components of the biosphere.
In simple words: It is the continuous recycling of nutrients between living organisms and their environment.

Exam Tip: 'Bio' refers to living organisms, 'geo' to rocks/soil/air, and 'chemical' to elements.

Question 6. What is the role of Nitrogen fixing bacteria in the biosphere?
Answer: Nitrogen-fixing bacteria (such as Rhizobium in legume root nodules and free-living bacteria like Azotobacter) convert inert atmospheric nitrogen gas into usable nitrogen compounds (like nitrates and ammonia) that plants can absorb and utilize to synthesize proteins and nucleic acids.
In simple words: Nitrogen-fixing bacteria turn unusable nitrogen gas from the air into forms that plants can absorb.

Exam Tip: Mention Rhizobium and root nodules of leguminous plants.

Question 7. Illustrate Nitrogen cycle in biosphere. Name two non-leguminous plants which can fix free Nitrogen.
Answer:
Nitrogen cycle illustration flow:
Atmospheric Nitrogen \(\rightarrow\) Biological & Physical Nitrogen Fixation \(\rightarrow\) Soil Nitrates/Ammonia \(\rightarrow\) Plant Proteins \(\rightarrow\) Animal Proteins \(\rightarrow\) Excretion/Death (Ammonification) \(\rightarrow\) Nitrification \(\rightarrow\) Denitrification \(\rightarrow\) Atmospheric Nitrogen.
Two non-leguminous plants that fix free nitrogen: Alnus and Casuarina (or Cycas).
In simple words: Nitrogen moves from air to soil, into plants and animals, and returns back to the air through microbial action.

Exam Tip: Name Alnus or Cycas when asked for non-leguminous nitrogen fixers.

Question 8. With the help of labelled diagram explain in brief the carbon cycle in nature.
Answer: Carbon is cycled in nature through photosynthesis and respiration. Green plants take up carbon dioxide from the atmosphere to perform photosynthesis and produce organic compounds. These compounds are passed to animals through food chains. Both plants and animals release carbon dioxide back into the atmosphere through cellular respiration and combustion of fossil fuels.
In simple words: Plants absorb carbon dioxide for food, animals eat plants, and both release carbon dioxide back through respiration and burning.

Exam Tip: Draw arrows showing uptake by photosynthesis and release by respiration and combustion.

Question 9. State two forms in which elemental oxygen is found in the earth's atmosphere. Mention in brief the essential function performed by each at the place they are found.
Answer: Two forms of elemental oxygen in the atmosphere:
1. Diatomic Oxygen (\(\text{O}_2\)): Found in the lower atmosphere (troposphere). Essential function: Required by all aerobic living organisms for cellular respiration to generate energy.
2. Triatomic Oxygen or Ozone (\(\text{O}_3\)): Found in the upper atmosphere (stratosphere). Essential function: Acts as a protective shield absorbing harmful ultraviolet (UV) radiation from the sun.
In simple words: Oxygen gas (\(\text{O}_2\)) is used for breathing, and ozone (\(\text{O}_3\)) protects us from UV rays.

Exam Tip: Clearly differentiate between tropospheric oxygen and stratospheric ozone.

Question 10. What are CFCs and why are these considered harmful for the life on earth?
Answer: CFCs stand for Chlorofluorocarbons. They are synthetic chemical compounds used in refrigerators, air conditioners, and aerosol sprays. They are harmful because when they reach the stratosphere, UV rays break them down to release chlorine atoms, which catalytically destroy ozone molecules (\(\text{O}_3\)), leading to the depletion of the ozone layer and allowing harmful UV radiation to reach the Earth.
In simple words: CFCs destroy the ozone layer, letting harmful UV rays reach the Earth and cause health hazards.

Exam Tip: Mention the catalytic destruction of ozone by chlorine atoms released from CFCs.