Chapter 12 : NUTRITION AND RESPIRATION

1. Answer the following questions in short.
   1. Which inorganic substances are used as food by autotrophic organisms?
   2. What is the mode of nutrition in fungi?
   3. Name one organism each having saprophytic, parasitic and holozoic mode of nutrition.
   4. Name the process by which plants prepare food.
   5. In addition to carbon dioxide and water, state two other conditions necessary for the process of photosynthesis.
   6. Name the pigment which can absorb solar energy.
   7. Where is chlorophyll mainly present in a plant?
   8. Which structure of food vacuole in amoeba breaks down the food?
   9. From which part of the body is undigested food egested in amoeba?
   10. Name one organism which can live without oxygen.
   11. In which type of respiration is more energy released?
   12. Which part of the root is involved in the exchange of respiratory gases?
   13. Name the respiratory organ of fish.
   14. What are various type of heterotrophic nutrition?
   15. What is the role of hydrochloric acid in our stomach?
   16. Mention the function of enzymes in human digestive system.
   17. Mention the type of respiration taking place in (i) yeast (ii) humans.
   
   ANS
   1. Carbon dioxide and water.
   2. Saprophytic and parasitic.
   3. • Saprophytic : Mushroom (fungi)
      • Parasitic : Tapeworm, ascaris
      • Holozoic : Amoeba, human being
   4. Photosynthesis
   5. Chlorophyll and presence of sunlight.
   6. Chlorophyll
   7. In chloroplast present on leaves of green plants.
   8. Lysosome
   9. Cell membrane
   10. Yeast
   11. Aerobic respiration
   12. Root hair
   13. Gills
   14. Parasitic nutrition, saprophytic nutrition and holozoic nutrition.
   15. Hydrochloric acid makes the food in stomach acidic so that the enzyme pepsin can digest proteins present in food into simpler molecules. It also kills harmful bacteria present in food.
   16. Enzymes break down complex organic molecules present in food into simpler molecules which can be absorbed by the cells of the body easily.
   17. (i)In yeast : anaerobic respiration (ii) In humans : aerobic respiration
   
   
2. Define Nutrition. Name four important nutrients present in food.
   ANS
   • Nutrition is the process of intake of food (nutrients) from which the organism can derive energy.
   • Important nutrients present in food are : carbohydrates, proteins, fats (lipids), vitamins and minerals.
   
   
3. What is autotrophic nutrition? Give one example of autotroph. What are necessary conditions for autotrophic nutrition?
   ANS
   • Autotrophic nutrition is the mode of nutrition by which an organism synthesizes its own food from water and carbon dioxide by the process of photosynthesis.
   • Green plants, Euglena, volvox are examples of autotrophs.
   • Availability of natural inorganic substances like carbon dioxide and water and presence of sunlight and chlorophyll are the necessary conditions for autotrophic nutrition.
   
   
4. What is heterotrophic nutrition? Give one example of heterotroph.
   ANS
   • Heterotrophic nutrition is the mode of nutrition in which an organism cannot synthesize food on its own using carbon dioxide and water but derives energy by digesting organic substances obtained from other organisms (plants and animals).
   • Human being is an example of heterotroph.
   
   
5. Define : (i)Saprophytic nutrition (ii) Parasitic nutrition (iii)Holozoic nutrition. Give one example of each type.
   ANS
   • SAPROPHYTIC NUTRITION: The process of obtaining nutrition from the dead and decaying organic matter is called saprophytic nutrition. Example: nutrition in some bacteria and fungi (mushroom).
   • PARASITIC NUTRITION: The process of obtaining nutrition from the body of other organisms called 'host' in which the host is not benefitted but harmed is known as parasitic nutrition. Example : tapeworm, ascaris, cuscuta.
   • HOLOZOIC NUTRITION: The process of obtaining nutrition by consuming plants or animals in part or whole, digesting them into simpler molecules and then absorbing the nutrients into body cells is called holozoic nutrition. Example : Amoeba, human being.
   
   
6. Describe exchange of gases in leaves of a plant (i) during daytime (ii) at night.
   ANS
   • Exchange of gases in leaves of a plant occurs through tiny pores called stomata present on the surface of the leaves.
   • During daytime photosynthesis occurs in leaves. Therefore, oxygen diffuses out and carbon dioxide diffuses in.
   • At night, in absence of photosynthesis, oxygen diffuses in and carbon dioxide diffuses out.
   
   
7. Describe the process of nutrition in amoeba with labelled diagram of various steps involved.
   ANS
   
   • The mode of nutrition in unicellular amoeba is holozoic and the process is called phagocytosis.
   • INGESTION: Amoeba captures food particles by forming temporary finger-like projections called pseudopodia around food particle. Food along with lysosome enters food vacuole.
   • DIGESTION: Food is digested by digestive enzymes within food vacuole.
   • ABSORPTION: The digested food is absorbed directly into cytoplasm from food vacuole by diffusion.
   • ASSIMILATION: The food absorbed in cell is used to obtain energy and for growth.
   • EGESTION: The undigested food is thrown out of the body by rupturing the cell membrane.
   
   
   
   
   
   
   
8. Draw a labelled diagram of human digestive system and describe the process of digestion.
   ANS
   
   • The human digestive system consists of the alimentary canal and associated glands.
   • The digestive organs are mouth, oesophagus (food pipe), stomach, small intestine and large intestine.
   • The associated glands are salivary glands, liver and pancreas.
   • The food is put in mouth with the help of hands (ingestion).
   • The mouth cavity has teeth, tongue and salivary glands.
   • Teeth are used to cut, chew and grind food particles. Salivary glands secrete saliva which wets the food and tongue mixes the foods with saliva.
   • Enzyme amylase secreted by salivary glands digests starch into maltose.
   • Partially digested food enters stomach through oesophagus.
   • Stomach is located on the left side of abdomen.
   • Food remains in stomach for about three hours.
   • The wall of stomach has three tubular glands which secrete gastric juice which contains dilute hydrochloric acid, enzyme pepsinogen and mucus.
   • Mucus protects stomach from its own secretion of hydrochloric acid and pepsin.
   • Hydrochloric acid makes medium in stomach acidic and kills bacteria.
   • Due to acidic medium, enzyme pepsin digests food proteins.
   • The partly digested food enters small intestine from stomach.
   • In an adult human the length of small intestine is about 6.5 m.
   • Complete digestion of carbohydrates, proteins and fats occurs in small intestine.
   • The small intestine receives alkaline bile (greenish yellow liquid) secreted by liver and stored in gall bladder.
   • Bile converts acidic food into alkaline so that pancreatic enzymes can act on it. Bile salts break fat in small globules making digestion easy.
   • Pancreatic juice secreted by pancreas contains enzymes amylase, trypsin and lipase.
   • Amylase digests starch, trypsin digests proteins and lipase digests fats.
   • The glands in the wall of small intestine secrete intestinal juice containing different enzymes which complete digestion of carbohydrates into glucose, proteins into amino acids and fats into fatty acids and glycerol.
   • The inner wall of small intestine possesses millions of small, finger-like projections called villi. Villi increase the surface area for rapid absorption of digested food by blood.
   • Blood carries digested food to all parts of the body where it is assimilated as part of the cells.
   • The assimilated food is used by the body for energy, growth and repairs.
   • The undigested food passes from small intestine to large intestine where most of the water from undigested food is absorbed.
   • The undigested food (now almost solid) is egested out of the body via anus.
   
   
9. Describe respiration occurring in following parts of a plant: (i) Root (ii) Stem (iii) Leaves
   ANS
   • Respiration (Exchange of Gases) in Root
     
     
     • Plant roots possess tiny root hair which are extension of epidermal cells of root.
     • Root hair are in contact with the air present between the soil particles.
     • Oxygen present in this air diffuses into root hair and reaches all the cells of root for respiration.
     • Carbon dioxide produced in the cells during respiration moves out through root hair by diffusion.
   • Respiration in Stem
     • Stems of herbs (soft plants) possess stomata on their surface.
     • Oxygen from air diffuses into stem through stomata and reaches cells of stem for respiration.
     • Carbon dioxide produced during respiration diffuses out through stomata.
     • Big plants have hard and woody stem without stomata.
     • The bark of such plants has tiny pores called lenticels through which gaseous exchange occurs.
   • Respiration in Leaves
     • The leaves of a plant have plenty of tiny pores called stomata.
     • During night time (in absence of photosynthesis) oxygen from air diffuses in through stomata amd carbon dioxide produced during respiration diffuses out.
   
   
10. What is the difference between autotrophic nutrition and heterotrophic nutrition?
    ANS
    • In autotrophic nutrition, the organism prepares its own food from carbon dioxide and water using sunlight in presence of chlorophyll.
    • In heterotrophic nutrition, the organism cannot prepare its own food and depends on other plants and animals for obtaining food from which it can derive energy.
    
    
11. Write in brief about aerobic respiration.
    ANS
    • The respiration which takes place in presence of oxygen is called aerobic respiration.
    • It occurs in cells, so it is also called cellular respiration.
    • Food (glucose) is broken down into carbon dioxide and water.
    • The energy released during the process is stored in ATP.
      
      
    
    
12. Write in brief about anaerobic respiration.
    ANS
    • Anaerobic respiration occurs without oxygen.
    • It occurs in some micro-organisms (bacteria, yeast, fungi), in endoparasites and in muscle cells.
    • In micro-organisms and plants, glucose is broken down and ethanol and carbon dioxide are produced as end products.
    • In muscle cells of animals, lactic acid is produced as end product.
      
      
    
    
13. Describe human respiratory system.
    ANS
    
    
    • Human respiratory system consists of nostrils, nasal passage, pharynx, laropharynx, trachea, bronchi, lungs and diaphragm.
    • Respiratory air enters nasal cavity through nostrils.
    • Nasal cavity is lined with fine hair and mucus in which dust particles and micro-organisms present in air get trapped.
    • Air passes to pharynx which leads to trachea through a slit called glottis.
    • A cartilaginous flap called epiglottis covers glottis so that food cannot enter trachea during swallowing.
    • Trachea is supported by 'C' shaped cartilaginous rings so that it would not collapse when there is no air in it.
    • Trachea has larynx (voice-box) at its upper end.
    • Trachea divides into two bronchi leading to lungs and each bronchus divides into many smaller bronchioles within lungs.
    • The bronchioles terminate into alveoli.
    • The walls of alveoli are thin and covered by blood capillaries.
    • Gaseous exchange takes place in alveoli.
    
    
14. Describe mechanism of breathing.
    ANS
    • Intake of air into lungs is called inspiration.
    • When the diaphragm and the muscles attached to the ribs contract, the volume inside the thoracic cavity increases, the air pressure within lungs decreases and the oxygen-rich air from atmosphere enters lungs through nostrils.
    • Alveoli are filled with oxygen-rich air and exchange of gases occurs.
    • When diaphragm relaxes the volume in the thoracic cavity decreases, the pressure within lungs increases and the air containing carbon dioxide is expelled out of lungs through nostrils.
    • This is called expiration.
    • The process of inspiration and expiration is collectively called breathing.
    
    
15. Distinguish between breathing and respiration.
    ANS
    
    
    
    
16. 
    ANS
    

Chapter 13 : TRANSPORTATION, CIRCULATION, EXCRETION

1. Answer in brief:
   1. Mention the colour of blood and lymph.
   2. Define Transpiration.
   3. What is transported through phloem?
   4. Define Ultrafiltration.
   5. Name the organs of excretory system in human being.
   6. Name the components of human circulatory system.
   7. Why is the wall of artery thick and elastic?
   8. What is the advantage of four-chambered heart?
   9. Define Excretion.
   10. Mention two components of xylem.
   11. Define Human circulatory system.
   12. What is lymph?
   
   ANS
   1. The colour of blood is red and lymph is colourless.
   2. The loss of water in the form of vapour from the aerial parts of the plant is called transpiration.
   3. Carbohydrates produced in leaves, amino acids and plant hormones synthesized at the shoot and root tips are transported through phloem.
   4. The filtration of blood carrying waste materials under pressure in glomerulus (Bowman's capsule) is called ultrafiltration.
   5. A pair of reddish brown bean-shaped kidneys, a pair of ureters (onr from each kidney), a urinary bladder, a muscular tube called urethra and urinary opening are organs of human excretory system.
   6. • Heart, blood vessels (arteries, veins, capillaries) and blood are components of blood circulatory system.
      • Lymph, lymph vessels, lymphatic capillaries and lymphatic nodes are components of lymph circulatory system.
   7. The wall of artery is thick and elastic because artery receives blood pumped by heart under high pressure.
   8. The advantage of four-chambered heart is that mixing of oxygen-rich blood with blood containing carbon dioxide is prevented.
   9. The process of removal of biochemical wastes generated within the body in liquid form is called excretion.
   10. Tracheids and Tracheae (vessels) are main components of xylem.
   11. The system associated with the transport of various substances like nutrients, hormones, enzymes, respiratory gases, excretory products, etc. is called circulatory system.
   12. The transparent (colourless) fluid which oozes out in the surrounding intercellular space from the blood flowing in the capillaries is called lymph.
   
   
2. Write a note on Lymphatic system.
   ANS
   Lymphatic system consists of lymph, lymph vessels, lymph capillaries and lymphatic nodes.
   • Lymph is colourless fluid involved in transportation.
   • Lymph is formed by plasma, some proteins and blood cells that escape from the walls of capillaries into the intercellular space.
   • From intercellular space lymph drains into lymphatic capillaries.
   • Lymphatic capillaries join to form lymph vessels.
   • Lymph vessels open into large veins.
   • FUNCTIONS OF LYMPHATIC SYSTEM
     • It collects intercellular fluid through lymph vessels and returns it to blood circulation.
     • Lymph vessels in the villi of small intestine absorb lipids and carry them to blood circulation.
     • It protects against diseases.
   
   
3. Distinguish between artery and vein.
   ANS
   
   
   
   
4. Describe excretory system in human being.
   ANS
   
   
   • Human excretory system consists of a pair of kidneys, a pair of ureters (one from each kidney), a urinary bladder, a muscular tube called urethra and urinary opening. The kidneys are reddish brown, bean-shaped and are located on dorsal side in abdomen.
   • From each kidney opens an excretory tube called ureter.
   • Ureter opens into urinary bladder and urinary bladder passes into a muscular tube called urethra.
   • Urethra opens out as small opening called urinary opening.
   • Each kidney is divided into cortex and medulla.
   • Each kidney has minute convoluted structures called uriniferous tubules (nephron).
   • Each kidney has about one million such tubules.
   
   
   
   
5. Explain structure and working of human heart.
   ANS
   
   
   • STRUCTURE
     • Human heart is located slightly on the left side in the space between two lungs.
     • It is conical and of the size of a closed fist.
     • It has four chambers. Two upper chambers are called atrium and the lower chambers are called ventricle.
     • Left atrium, right atrium, left ventricle and right ventricle are the four chambers based on their location in heart.
     • The walls of the atria are thin whereas the walls of ventricles are thick.
     • All four chambers are separated from one another by partition called septa.
     • There is a bicuspid valve between left atrium and left ventricle whereas there is a tricuspid valve between right atrium and right ventricle.
     • These valves allow blood to flow from atrium to ventricle but do not allow it to flow from ventricle to atrium.
     • Heart is made of cardiac muscles.
   • WORKING
     • When all four chambers of heart are in relaxed state (diastolic stage), deoxygenated blood from the organs enters the right atrium through superior and inferior vena cava.
     • At the same time oxygenated blood from lungs enters the left atrium through the pulmonary vein.
     • When both atria are filled with blood, they contract and deoxygenated blood from right atrium is poured into right ventricle through tricuspid valve. Similarly, the oxygenated blood from the left atrium is poured into left ventricle through bicuspid valve.
     • When both ventricles are filled with blood, they contract (systolic stage) and deoxygenated blood from right ventricle goes to lungs through pulmonary artery and oxygenated blood from left ventricle is distributed to all the parts of the body through aorta.
     • Since blood flows twice through the heart it is called double circulation.
   
   
6. Describe the structure of nephron and explain the process of formation of urine.
   ANS
   
   
   
   • STRUCTURE
     • A kidney has very minute tubular and convoluted structures known as uriniferous tubules(nephron).
     • A kidney has about one million (ten lac) such units.
     • Each nephron has a double-walled cup-shaped structure called Bowman's capsule at its beginning.
     • Bowman's capsule encloses a small group of capillaries called glomerulus.
     • The short region after Bowman's capsule is called the neck.
     • The tubule after the neck is narrow and coiled.
     • It consists of proximal convolution, Henle's loop and distal convolution.
     • The distal convolutions of many nephrons join to a common collecting duct which leads to the renal pelvis.
     • Renal pelvis opens into the ureter.
   • PROCESS OF FORMATION OF URINE
     • Renal arteries bring blood containing the waste material to the kidney.
     • By ultrafiltration the blood is filtered out from blood capillaries into Bowman's capsule under pressure.
     • During the passage of this filtrate through tubular parts of nephron, useful materials such as water, amino acids, minerals, ions, etc are re-absorbed by blood capillaries surrounding the nephron.
     • The remaining fluid contains excretory substance called urine which passes into urinary bladder through ureter. When the bladder is filled with urine, it contracts and urine passes out of the body.
   
   
7. 
   ANS
   

Chapter 14 : CONTROL AND CO-ORDINATION IN ORGANISMS

1. Answer the following in short:
   
   1. Name a plant which shows thigmonasty.
   2. Give example of the movement of a plant which is caused by the loss of water.
   3. Name the two systems of control and co-ordination in higher animals.
   4. Name the three components of a nerve cell.
   5. Name the most important part of the human brain.
   6. State one function each of cerebellum and pons.
   7. Name one hormone secreted by the pituitary gland.
   8. Where are hormones synthesized in human body?
   9. Which gland secretes the growth hormone?
   10. Name the disease caused by the deficiency of insulin.
   11. What does CNS stand for?
   12. What is a stimulus?
   13. Mention some factors (stimuli) to which plants respond.
   14. Mention some plant hormones.
   15. What is sensory neuron?
   16. What is motor neuron?
   17. What is the function of cerebrospinal fluid?
   18. What does the fore-brain consist of?
   19. What does hind-brain consist of?
   20. Which gland is called the master galnd?
   21. What does a root do in response to gravity? What is this phenomenon known as?
   22. What does a stem do in response to gravity? What is this phenomenon known as?
   23. What does a stem do in response to light? What is this phenomenon known as?
   24. What does a root do in response to light? What is this phenomenon known as?
   
   ANS
   1. Mimosa
   2. Thigmonasty observed in plants like mimosa.
   3. (i) Nervous system (ii) Endocrine system.
   4. (i) Cell body (ii) Dendrite (iii) Axon
   5. Cerebrum
   6. • Cerebellum maintains body balance and posture.
      • Pons regulates the process of respiration.
   7. TSH (Thyroid Stimulating Hormone).
   8. Hormones are synthesized in endocrine glands like thyroid, pituitary, testes, etc.
   9. Pituitary gland.
   10. Diabetes
   11. Central Nervous System.
   12. Any environmental factor that affects a living organism by showing changes is called a stimulus.
   13. Light, touch, water, gravity and some chemicals.
   14. Auxin, Gibberellin, Cytokinin, Abscisic acid, Ethylene.
   15. Sensory neuron is a nerve cell which receives the stimuli from receptor and passes the message to the brain.
   16. Motor neuron is a nerve cell which receives information from brain, transmits it to the effector organ and stimulates it to respond.
   17. Cerebrospinal fluid acts as a cushion and protects brain from mechanical shock.
   18. Fore-brain consists of cerebrum (with olfactory lobes), thalamus and hypothalamus.
   19. Hind-brain consists of cerebellum, pons and medulla oblongata.
   20. Pituitary gland is called the master gland.
   21. Root grows in the direction of gravity. This phenomenon is known as positive geotropism.
   22. Stem grows in the direction opposite to gravity. This phenomenon is known as negative geotropism.
   23. Stem grows in the direction of light. This phenomenon is known as positive phototropism.
   24. Root grows in the direction opposite to light. This phenomenon is known as negative phototropism.
   
   
2. Give the scientific terms used to represent the following.
   1. Bending of a shoot towards light
   2. Growing of roots towards earth
   3. Growing of pollen tube towards ovule
   4. Bending of roots towards water
   5. Winding of tendril around a support
   
   ANS
   1. Phototropism
   2. Geotropism
   3. Chemotropism
   4. Hydrotropism
   5. Thigmotropism
   
   
3. What is spinal cord? What is its main function?
   ANS
   • Spinal cord is a cylindrical structure consisting of 31 pairs of nerves and it is the posterior extension of medulla oblongata.
   • Its main function is to conduct sensory information from organ to brain and motor information from brain to organ.
   • It also plays an important role in reflex action.
   
   
4. Write the functions of medulla oblongata.
   ANS
   • Medulla oblongata controls various involuntary activities like breathing, heart-beats, blood pressure. peristaltic movement of alimentary canal, etc.
   • Medulla oblongata also controls the centre of reflexes like coughing, sneezing, swallowing, vomiting and secretion of saliva.
   
   
5. Write a note on Tropism.
   ANS
   • TROPISM
     • The movement of curvature of plant organs in response to some external stimuli is known as tropism.
     • If the plant organ grows in the direction of the stimulus, then it is called positive tropism.
     • If the plant organ grows in the direction away from the stimulus, then it is called negative tropism.
     • The most common stimuli are: light, gravity, chemicals, water and touch.
   • TYPES OF TROPISM
     Depending upon the type of the stimulus, the types of tropism are: (i) phototropism (ii) geotropism (iii) chemotropism (iv) hydrotropism (v) thigmotropism.
   • PHOTOTROPISM
     • The movement of growth of a plant part in response to light is called phototropism.
     • Stem shows positive phototropism whereas roots show negative phototropism.
     
   • GEOTROPISM
     • The movement of growth of a plant part in response to gravity is called geotropism.
     • Roots show positive geotropism as they grow in the direction of gravity.
     • Stem shows negative geotropism as it grows in the direction opposite to gravity.
   • CHEMOTROPISM
     The movement of growth of a plant part in response to a chemical is called chemotropism. The growth of pollen tube towards ovule in a flower is an example of chemotropism.
   • HYDROTROPISM
     • The movement of growth of a plant part in response to water is called hydrotropism.
     • Roots of a plant grow towards water
     
   • THIGMOTROPISM
     The movement of growth of a plant part in response to touch is called thigmotropism. For example, tendrils of a plant.
   
   
   
   
   
6. Write a note on human brain with neat diagram.
   ANS
   • Human brain is a part of the central nervous system(CNS).
   • It is the main coordinating centre for all activities of the human body.
   • It is protected by a box called cranium in the skull and three membranes called meninges.
   • The space between meninges is filled with cerebrospinal fluid which acts as a cushion and protects the brain from mechanical shock.
   • The brain of an adult human weighs about 1350 gram.
   • The brain is divided into three regions: (i) Fore-brain (ii) Mid-brain (iii) Hind-brain.
     
     
     
     
   • FORE-BRAIN
     • Fore-brain consists of cerebrum (with olfactory lobe), thalamus and hypothalamus.
     • Cerebrum is the most complex and specialized part of the brain.
     • It consists of two cerebral hemispheres joined together by a band called corpus callosum.
     • It has sensory area to receive impulse from the sense organs and motor area to send impulse to muscles and effector organs.
     • The outer region of cerebral hemispheres is densely packed with nerve cells and is called cerebral cortex. It is highly convoluted so that its surface area gets increased.
     • Each cerebral hemisphere is divided into four lobes.
       
       
     • Frontal lobe controls both voluntary and involuntary activities including thought, speech and memory.
     • Parietal lobe possesses centres for sensation like smell, touch and temperature.
     • Occipital lobe has centre for visual reception.
     • Temporal lobe controls activities of auditory recepation.
     • Thalamus is located at the centre of the fore-brain. All sensory information reaching cerebrum passes through thalamus.
     • Hypothalamus lies below thalamus and it controls and regulates blood pressure, hunger, body temperature and thirst.
   • MID-BRAIN
     Mid-brain possesses the regions for controlling functions of eyes (visual reception) and ears (auditory reception). Corpora quadrigemina is a part of mid-brain. Mid-brain connects fore-brain and hind-brain.
   • HIND-BRAIN
     • Hind-brain consists of three regions: Cerebellumon the dorsal side and pons and medulla oblongata on the ventral side.
     • Cerebellum maintains balance and posture of the body. It coordinates movements like dancing, walking and riding a bicycle.
     • Pons regulates the process of respiration.
     • Medulla oblongata controls involuntary activities like breathing, heartbeats, blood pressure, peristaltic movement of alimentary canal, etc.
     • Medulla oblongata also controls the centres of reflexes like coughing, sneezing, vomiting, secretion of saliva, etc.
   
   
7. Write a brief note on spinal cord.
   ANS
   • Spinal cord is a cylindrical structure and it is the posterior extension of medulla oblongata.
   • It is protected by three membranes called meninges.
   • Its central part consists of grey matter in 'H' shape. The grey matter contains non-medullated nerve fibres and neurons possessing short processes.
   • White matter forms the periphery of spinal cord. White matter contains medullated nerve fibres and neurons possessing long processes.
   • Cerebrospinal fluid is present in the central canal of spinal cord.
   • 31 pairs of nerves arise from spinal cord.
   • Bundles of nerves run ascending and descending in tracts and link the spinal cord with brain.
   • Ascending tracts conduct sensory information from spinal cord to brain and descending tracts conduct motor information from brain to spinal cord.
   • Spinal cord plays an important role in reflex action.
   
   
8. What is autonomous nervous system? What is its function?
   ANS
   • Autonomous nervous system means 'self-governing' nervous system.
   • It controls the activity of body organs like heart, blood vessels, glands, uterus, etc., automatically (i.e. without our thinking and without the awareness of brain).
   • Autonomous nervous system is of two types: (i) Sympathetic (ii) Parasympathetic.
   • The involuntary actions of the body are controlled and regulated by the coordination of these two systems.
   • The effects of sympathetic and parasympathetic nervous systems are complementary and contradictory to each other.
   • For example, if the sympathetic system increases the heart-beats abnormally, the parasympathetic system decreases it and brings it back to normal.
   
   
9. Mention properties (characteristics) of hormones.
   ANS
   • Each hormone is produced by a specific kind of cells.
   • Generally, the hormones are not effective at the site of their synthesis (i.e. the target area is different than origin).
   • They are directly poured into the blood and carried by blood to the specific organ.
   • Their influence may be stimulatory or regulatory. Thus, they are 'regulatory chemicals'.
   • Hormones are used up in producing their regulatory effect.
   • They are chemical messengers in the form of peptides, steroids and biogenic amines.
   
   
10. What is voluntary nervous system? Explain its working with an example.
    ANS
    • Actions which need thinking and which we perform knowingly are called voluntary actions.For example, speaking to a friend, putting on shoes, reading a book, drawing a picture, etc. are called voluntary actions.
    • The system which helps us do voluntary actions consciously under the control of brain is called voluntary nervous system.
    • Suppose we have to go somewhere by plane. We first choose a flight, book out seat, and then at the time of journey we leave for airport some time before departure of plane and after reaching airport we follow certain procedure and then board the flight. Voluntary nervous system is directly in this sequence of actions. When we leave for airport we frequently see our watch and if need be we speed up our vehicle so that we do not miss the plane.
    • Our eyes see the time in watch and that information is sent to brain through sensory nerves. The brain on analysis realizes the risk of missing the flight so it decides that we should speed up.
    • The brain gives instructions to muscles of our legs through motor nerves and the muscles accordingly press accelerator to uncrease the speed of our vehicle.
    • This is an example of how the voluntary nervous system works.
    
    
11. Write a detailed note on endocrine glands of human body.
    ANS
    • GENERAL
      • Endocrine glands situated in different parts of the body form the endocrine system and play an important role in coordination.
      • These are ductless glands which secrete specific hormones into the blood stream.
      • The main endocrine glands are hypothalamus, pituitary, thyroid, parathyroid, pancreas, adrenal, testis and ovary.
    • HYPOTHALAMUS
      • Hypothalamus is located in brain below the thalamus and above the pituitary gland.
      • Its neurosecretory cells produce releasing hormones (RH) that stimulate the anterior pituitary gland to secrete specific hormones.
      • TSH releasing hormone activates pituitary gland to release TSH (Thyroid Stimulating Hormone).
      • GH releasing hormone activates pituitary gland to release growth hormone (GH).
      • ACTH releasing hormone activates pituitary gland to release Adrino Cortico Trophic Hormone (ACTH).
      • Gonadotrophic releasing hormone activates pituitary gland to release FSH (Follicle Stimulating Hormone) and LH (Leutenizing hormone).
      • Hypothalamus also releases two inhibitory hormones: (i) GH inhibitory factor inhibits the release of GH. (ii) PIF (Prolactin Inhibitor Factor) inhibits the release of prolactin from pituitary gland.
    • PITUITARY
      • Pituitary gland is located just below the hypothalamus.
      • It is divided into three lobes: (i) anterior lobe (ii) intermediate lobe (iii) posterior lobe.
      • Anterior pituitary lobe releases TSH, ACTH, FSH, LH, GH and prolactin. Secretion of all these hormones is controlled by hypothalamus.
      • Intermediate pituitary lobe secretes MSH (Melanocyte Stimulating Hormone).
      • Posterior pituitary lobe secretes vasopressin and oxytocin.
      • Vasopressin is anti-diuretic hormone (ADH) and it stimulates re-absorption of water and thus controls the loss of water through urine. It also acts as vasoconstrictor and increases arterial blood pressure.
      • Oxytocin (in female) causes contraction of uterine muscles during child birth and ejection of milk from mammary glands.
      • Since pituitary gland controls the secretion of hormones from other glands it is called the master gland.
    • PANCREAS
      • Pancreas lies just below stomach.
      • It secretes hormone insulin which lowers the sugar level in blood.
      • Deficiency of insulin results in large amount of sugar in blood and urine. This disorder is called diabetes.
      • Diabetes, if not controlled, causes many harmful effects.
      • A diabetic person should consume less amount of sugar.
      • To control diabetes, one should control diet, do physical exercise, reduce body weight and take necessary medicines and insulin regularly.
    • THYROID
      Thyroid gland is attached to the wind pipe and it secretes hormone thyroxine which contains iodine.
      • Thyroxine controls the metabolic rate of carbohydrates, proteins and fat.
      • Deficiency of iodine in our diet results in hypothyroidism (deficiency of thyroxine) and enlargement of thyroid gland. This disorder is called goitre.
      • Hyperthyroidism (over-secretion of thyroxine) is called exophthalmic goitre which results in bulging of the eyeball.
      • Deficiency of iodine can be set off by consuming iodized salt (salt containing small amount of iodine).
    • PARATHYROID
      Parathyroid glands are four small glands embedded in the thyroid gland. These glands secrete parahormone which regulates calcium and phosphate level in blood.
    • ADRENAL
      • There are two adrenal glands.
      • Adrenal gland is small, conical in shape and composed of two distinct regions: (i) outer cortex (ii) inner medulla.
      • Adrenal cortex secretes three types of steroid hormones.
      • Mineral corticoids regulate balance of water and ions like Na⁺, K⁺ and Cl^- in our body.
      • Glucocorticoids stimulate metabolism of carbohydrates, proteins and fats.
      • Sex corticoids induce secondary sexual characters.
      • Adrenal medulla secretes adrenaline and non-adrenaline.
      • Adrenaline is called 'fight or flight' hormone.
      • Adrenal glands are also called glands of 'emergency'.
    • TESTIS
      • Testes are in pair and they produce male sex hormone testosterone and sperms.
      • Testosterone controls the development of sex organs in male.
      • The secondary sexual characters like deeper voice, beard and moustache are induced by testosterone.
    • OVARY
      • Ovaries produce female sex hormones estrogen and progesterone.
      • Estrogen controls development of female sex organs and secondary sexual characters like feminine voice, soft skin and mammary glands.
      • Progesterone controls changes in uterus during menstrual cycle and regulates the production of ova in ovaries.
    
    
12. Explain: Reflex Action.
    ANS
    • Reflex action is a rapid automatic response without thinking like pulling our hand away on pricking a pin or unknowingly touching a very hot object.
    • A knee-jerk, coughing, yawning, blinking of eyes, sneezing and movement of diaphragm, etc. are examples of reflex action.
    • Reflex action is an automatic process and is an unconscious and involuntary response of the effectors to a stimulus.
      
    • REFLEX ARC: The nerve impulse pathway in a reflex action is called reflex arc.
    • Suppose we touch a hot plate. We immediately pull our hand away without thinking. This happens because the thermoreceptors in our hand sense the heat. An impulse triggered by the receptor in sensory neuron transmits to the spinal cord. Spinal cord transmits the impulse to motor neuron which sends it to the muscle which contracts and pulls the hand away from the hot plate. The pathway of transmission of impulse ia called reflex arc.
    • Reflex action is performed by the spinal cord without the knowledge of brain.
    
    
13. Describe disorders of growth hormone (GH).
    ANS
    • Dwarfism, gigantism and acromegaly are disorders of growth hormone.
    • Hypo or under-secretion of growth hormone during childhood leads to dwarfism.
    • Hyper or over-secretion of growth hormone during childhood leads to gigantism (giant height).
    • Too much secretion of growth hormone during adolescence causes enlargement of certain body parts like hands, feet and jaws and gives appearance like a gorilla.
    
    
14. Distinguish between tropism and nastism (or tropic movement and nastic movement).
    ANS
    
    
    
15. How does our body respond when adrenaline is secreted in large amounts into blood?
    ANS
    • Adrenaline is secreted by adrenal gland in small amounts all the time but in large amount if a person is in critical (or frightening) situation.
    • Secretion of adrenaline in large amounts increases the energy level of the body suddenly and the person either fights the situation or runs away from it (flight).
    • Thus, adrenal is 'fight or flight' gland or 'gland of emergency'.
    
    
16. Explain structure of a nerve cell (neuron) with diagram.
    ANS
    • Nerve cell is the structural and functional unit of the nervous system.
    • Cell body, dendrites and axon are the three components of a nerve cell.
    • The cell body contains cytoplasm and nucleus.
    • The short fibres extending from the cell body are called dendrites.
    • The long fibre extending from the cell body is called axon.
    • An insulating sheath of myelin around axon is made of fat and protein and it protects axon.
      
      
    • The dendrite receives message from receptors, sets off a chemical reaction and creates an electrical impulse called nerve impulse.
    • The message is passed to the cell body and then to axon. Axon passes the message to another nerve cell through a junction.
    • At the junction, there is a small gap between two nerve cells. This gap is called synapse.
    • The nerve cell acquires a message which travels as an electric impulse. This impulse is converted into a chemical signal for onward transmission.
    
    
17. 
    ANS
    

Chapter 15 : REPRODUCTION IN ORGANISMS

1. What is reproduction? What is the aim (purpose) of reproduction?
   ANS
   
   • Reproduction is the process by which new organisms of the same species are produced by existing living organisms.
   • The aim of reproduction is the continuation of life on earth. It ensures survival of the existing species of organisms and formation of new species from existing ones by the process of evolution.
2. How do organisms create exact copies of themselves?
   ANS
   
   • Organisms of the same species have similar characteristics as regards body design and body function.
   • In the nucleus of the cells of an organism, the information controlling the common characteristics of the species is stored in DNA.
   • This information leads to the synthesis of proteins controlling the characteristics of the species.
   • During reproduction, duplication of DNA takes place and the information is exactly copied. This leads to the formation of new cells with similar characteristics.
   • If the information is changed due to some reason, the characteristics transferred to the progeny change and the body design changes in the progeny.
   • If these changes are compatible, then the cells survive and a progeny with differing characteristics comes into existence.
   • This is called variation and is the essence of evolutionary process.
3. Describe the importance of variation.
   ANS
   
   • Reproduction gives stability of populations of species in an ecosystem by the maintenance of overall body features.
   • This is achieved by consistency of DNA copying during reproduction.
   • However, the niches (ecosystems) keep on changing because the factors affecting the change are not controlled by the organisms.
   • Alteration in temperature, humidity, water level and phenomena like meteorite hits are examples of factors affecting the change.
   • Suppose the population of reproducing organisms is suited to a particular niche and if there is a drastic change in the niche, the population may be wiped out.
   • But if there were some variations present in a few individuals of this population, there would be some chance for them to survive.
   • For example, if there was a population of bacteria living in water with moderate temperature and if the water temperatures were to rise due to global warming, many bacteria would die but a few temperature resistant bacteria would survive and grow further.
   • Thus, variation is useful for the survival of the species.
4. What is the basic difference between asexual reproduction and sexual reproduction?
   ANS
   The basic difference between asexual reproduction and sexual reproduction is that only one parent is required for asexual reproduction, i.e. there is no distinction like male and female whereas sexual reproduction requires two parents, one male and one female.
5. Describe different methods (types) of asexual reproduction.
   ANS
   
   • Fission:
     • This is the simplest method of asexual reproduction in which a unicellular organism (like protozoa, bacteria) divides to form two new organisms.
     • There are two types of fission: (i) Binary fission (ii) Multiple fission.
     • Binary Fission:In binary fission, the nucleus lengthens and divides into teo parts. Then the cytoplasm divides into two parts, one part around each nucleus. This results into two daughter cells which then grow as individual organisms.
       Example: Amoeba, Paramoecium.
       
       
     • Multiple Fission: Under certain circumstances, the nucleus of the cell divides several times within the cell forming many nuclei. Particularly when a unicellular organism forms cyst around the cell during unfavourable conditions, the nucleus divides several times within the cyst forming many smaller daughter nuclei. Each nucleus is then surrounded by a small amount of cytoplasm and a thin membrane. When favourable conditions arrive, the cyst breaks and all those daughter cells are released.Each cell then forms a new organism.
       Example: Plasmodium, Amoeba.
       
       
   • Fragmentation: Fragmentation is the breaking up of the body of a multicellular organism into two or more pieces. On maturing each piece grows to form a completely new organism.
     Example: Spirogyra.
     
     
   • Regeneration:
     • Regeneration is the ability of an organism to reproduce the lost parts of its body.
     • When some body part of an organism breaks suddenly, a new part similar to the lost (broken) part is created at the point of breaking after some time.
     • All broken parts thus develop into completely new organisms.
       
       
   • Budding:
     • A small part of the body of the parent organism grows out as a bud.
     • On maturing the bud gets detached from the parent and becomes a new organism.
       Example: Hydra, Yeast
       
       
   • Spore Formation:
     • Spores are microscopic reproductive units of plants.
     • Spores are covered by a protective coat.
     • When the spore coat bursts, the spores spread into air.
     • These air-borne spores germinate to produce new plants under favourable conditions if they settle on food.
       Example: Rhizopus, Mucor
       
       
6. Write a brief note on Vegetative propagation.
   ANS
   
   • Vegetative propagation is an asexual method of reproduction occurring only in plants.
   • New plants are obtained from old plants using their parts like roots, stem or leaves. Thus, reproductive organs are not involved in this method.
   • It involves development and growth of dormant buds present in the parts of old plants.
   • These dormant buds grow into a new plant under suitable conditions of temperature and moisture.
   • For example, buds present on bryophyllum leaves develop into a new plant.
   • There are several buds on a potato tuber. When these buds are planted in the ground, a new plant develops.
     
     
     
     
     
7. Describe various methods of Artificial Propagation.
   ANS
   
   • Artificial propagation involves development of a new plant from an old plant using artificial method.
   • The commonly used methods of artificial propagation are: (i) Cutting (ii) Layering (iii) Grafting.
   • CUTTING: A cutting of stem or shoot or leaf having buds on it is taken and its lower part is buried in the moist soil. After some days the cutting develops roots and grows into a similar plant. The advantage of this method is that many new plants can be grown from one plant in short time without seeds.
     Example: Rose, Bougainvillae.
     
     
   • Layering: In this method a part of stem is pulled towards the ground and covered by the soil. The covered part develops roots after some time and behaves as an independent plant. It is then separated from the parent plant and grows into a mature plant.
     Example: Lemon, Bougainvillae, Crysenthemum.
     
     
   • Grafting:
     • In this method two parts (stems) of different plants are joined together in such a way that they unite to grow as one plant.
     • The portion of the plant having roots is called 'stock'.
     • The portion of the plant without roots is called 'scion'.
     • By this method desirable characteristics of different plants can be combined.
     • This method is useful for plants whose seeds have long dormancy period and poor germination capacity.
     • Example: On the stock of lemon, a scion of lemon or orange can be grafted.
       
       
8. What is sexual reproduction? Describe its importance.
   ANS
   
   • Sexual reproduction is the process in which a male gamete and a female gamete unite to produce a zygote which develops into a new organism after some time.
   • IMPORTANCE:
     • Sexual reproduction introduces genetic variations which lead to a greater variety in offspring.
     • Genetic variations bring diversity of characters.
     • It gives different species of plants and animals to adapt to the changing environment. Organisms which adapt quickly to these changes survive and reproduce sexually.
     • Sexual reproduction plays an important role in the origin of new species through evolution.
9. Describe sexual reproduction in flowering plants.
   ANS
   
   • Flower is the reproductive part in higher plants.
   • The reproductive organs are located within the flower.
   • If the same flower contains both the male and female reproductive organs, the plant is known as bisexual.
   • The function of the flower is to produce male and female gametes and to ensure fertilization.
   • The male organ is called stamen and it produces male gametes.
   • The female organ is called carpel and it produces female gametes.
   • Female gametes are called ova or egg cells and they are present in ovules.
   • Male gametes are present in pollen grains and they fertilize the egg cells in ovules.
   • The fertilized egg cell develops within ovule which produces embryo and then entire ovule is converted into a seed.
   • Seeds germinate to produce new plants under favourable conditions.
     
     
10. Write a brief note on puberty.
    ANS
    
    • Puberty is the stage in the life of a human being when the reproductive organs show gradual changes in structure and they become functional.
    • A boy attains puberty at the age of 13-14 years whereas a girl attains puberty at the age of 12 years.
    • During puberty, testes in male start producing male gametes (sperms) and the sex hormone testosterone.
    • Similarly, ovaries in female start producing female gametes (ova) and sex hormones estrogen and progesterone.
    • During puberty hair grow in armpits and around genital organs between the thighs. This is common to both boys and girls.
    • In addition, in boys the body becomes more muscular, the voice deepens and shoulders and chest broaden. The penis grows and becomes capable to be erect.
    • In girls, the breasts show development and the reproductive system changes. These changes are necessary to accommodate developing child within mother's body and to breast-feed the child after birth.
    • This stage between childhood and adulthood is called 'adolescence'.
11. Describe reproductive system in human male with diagram.
    ANS
    
    • A pair of testes is the main reproductive organ in human male.
    • Testes produce male gametes,i.e., sperms and the male sex hormone testosterone.
    • Epididymis, vas deferens and penis are the accessory reproductive organs which facilitate the transfer of gametes to the site of fertilization.
    • Seminal vesicle and prostate gland are accessory reproductive glands.
    • The two oval shaped testes lie in a muscular sac called scrotum outside the abdominal cavity.
    • The temperature in the scrotum is 2 to 3° C lower than the body temperature. This temperature is suitable for the formation of sperms.
    • The sperms produced in testes are transported to penis through epididymis and vas deferens.
    • Vas deferens connects to the urinary duct coming from urinary bladder.
    • Seminal vesicle and prostate gland secrete fluids which mix with sperms and increase their mobility.
    • Urethra transfers sperms to penis and sperms pass into vagina through genital pore during mating.
      
      
12. Describe reproductive system in human female with diagram.
    ANS
    
    • Female reproductive system in humans is more complicated than that in male as fertilization and development of embryo takes place in it.
    • It consists of ovaries, oviduct, uterus and vagina.
    • Two ovaries are oval in shape and lie within the abdominal cavity.
    • Ovaries produce ova or eggs and secrete female sex hormones estrogen and progesterone.
    • There are two fallopian tubes (oviducts) which are funnel shaped and which receive the mature ova released by the ovary.
    • Oviducts carry the ova from ovary to the uterus, if it is fertilized by a sperm.
    • Uterus is a muscular bag where the fertilized egg further develops into embryo.
    • The lower tip of the uterus is called cervix.
    • The ovaries contain thousands of immature ovarian follicles which start maturing when a girl reaches puberty stage.
    • One of the ovaries produces one ovum every month which is carried to the fallopian tube.
    • During sexual intercourse, if the ovum is fertilized by a sperm, then the fertilized ovum gets implanted in the lining (wall) of the uterus and develops into a hollow ball of cells called embryo.
    • The embryo obtains nutrition from the mother's blood through a tissue called placenta.
    • The development of child within uterus takes about nine months before it is born.
      
      
13. Write an explanatory note on menstrual cycle (or menstruation) in human female.
    ANS
    
    • When a girl reaches puberty stage at the age of 10-12 years, the sex hormones cause ova to become mature.
    • Every 28 days one mature ovum is released by ovary into the oviduct.
    • The process of release of ovum is called ovulation.
    • Before ovulation, the inner wall of the uterus becomes thick and full of blood capillaries.
    • Thus, it becomes prepared to receive fertilized ovum.
    • If fertilization does not take place during certain time, the wall of the uterus disintegrates and blood vessels break.
    • The disintegrated tissue and the dead ovum come out of the vagina along with blood.
    • This is known as menstruation which lasts for 3 to 5 days.
    • When menstruation is over, the inner wall of the uterus starts becoming thick again so that it may receive the next fertilized ovum.
    • If the ovum is not fertilized, the menstruation takes place again.
    • This menstruation cycle is repeated every 28 days.
    • If fertilization occurs and the woman becomes pregnant, then menstruation stops temporarily.
    • At the age of about 50 years, menstruation stops permanently.
    • This is called menopause and the woman loses the capability to reproduce.
      
      
14. Write a note on Reproductive Health.
    ANS
    
    • The diseases which are transmitted by sexual contact with an infected person are called Sexually Transmitted Diseases (STD).
    • Syphilis is caused by bacterial infection by bacteria Treponema palidium.
    • Lesions in mucus membrane of urinogenital tract and ulcers are symptoms of syphilis.
    • Gonorrhoea is caused by bacteria Neissena gonorrhoea. It results in inflammation of urinogenital tract.
    • Both syphilis and gonorrhoea are curable diseases.
    • AIDS (Acquired Immuno Deficiency Syndrome) is caused by HIV (Human Immuno-deficiency Virus).
    • AIDS damages the immune system of the body and weakens body's protection against infections.
    • AIDS is a fatal disease.
    • Research work is in progress to find out medicines to cure AIDS.
    • In India, NACO (National AIDS Control Organization) creates awareness regarding AIDS and provides information about reproductive health.
    • Multiple pregnancies adversely affect a woman's health.
    • Different methods have been devised to avoid unwanted pregnancy. These methods are called contraceptive methods.
15. Describe different methods of contraception (Birth control or Prevention of pregnancy)
    ANS
    
    • Contraceptive methods used for the birth control are of three types: (i) Mechanical method (ii) Chemical method (iii) Surgical method.
    • Mechanical method:
      In this method, the entry of sperms in the genital tract is prevented by creating a mechanical barrier. Due to this the fertilization of egg cannot occur. Condom worn on penis or diaphragm worn in vagina by female work as mechanical barriers. IUCDs (Intrauterine Contraceptive Devices) like copper-T placed in uterus prevent pregnancy.
      
      
    • Chemical method:
      Pills are used by female in this method. The oral pills contain hormones which stop the production of ova and prevent fertilization. Vaginal pills contain chemicals called spermicide which kill the sperms.
    • Surgical method:
      In male, a small portion of vas deferens is surgically removed and both the cut ends are tied properly. This prevents the entry of sperms to urethra. The process is called Vasectomy.
      In female, a small portion of oviduct is removed and tied up. This prevents ovum from entering the oviduct. The process is called Tubectomy.
      
      
16. 
    ANS
    

Chapter 16 : HEREDITY AND EVOLUTION

1. Define Sex Determination. What are the methods (mechanisms) of sex determination in different organisms?
   ANS
   
   • The mechanism to determine the sex of an individual is known as sex determination.
   • Different species use different mechanisms for sex determination.
     • In some species, the temperature at which fertilized eggs are kept determines whether the organism developing in the egg would be male or female.
     • In human beings the sex is determined genetically.
     • In animals like snail, the individual can change the sex, indicating that their sex is not determined genetically.
2. Answer in short.
   1. Name the ancestor of Broccoli, Kohlarabi, Kale, Cauliflower and Cabbage.
   2. Name at least two organisms which are now extinct and are studied from their fossils.
   3. Name five varieties of vegetables which have been produced from 'Wild cabbage' by the process of artificial selection.
   4. Choose the one term from the following which includes the other three: Broccoli, Wild cabbage, Cauliflower, Cabbage
   
   ANS
   
   1. Wild cabbage
   2. Ammonite, Trilobite, Dinosaur
   3. Broccoli, Kohlrabi, Kale, Cauliflower and Cabbage
   4. Wild cabbage
3. Explain : Variation.
   ANS
   
   • The occurrence of differences among the individuals of same species is known as variation.
   • Organisms which reproduce asexually or vegetatively show very little variation.
   • Organisms which reproduce sexually show distinct variations.
   • In sexual reproduction, crossing over of genes during meiosis gives rise to new combinations of characteristics. This results in variation among the individuals of species.
   • All these variations, however, do not have equal chance of survival in the environment in which they find themselves.
   • Different individuals get different advantages of these variations.
   • Selection of variants by environmental factors forms the basis of evolutionary process.
4. Write a note on Heredity.
   ANS
   
   • Heredity means continuity of features from one generation to another.
   • Heredity can be defined as "the transmission of characters from parents to the offspring" or "the tendency of every individual to resemble his/her parents".
   • Due to heredity, eggs laid by a sparrow hatch into sparrows only and a dog gives birth to pups only.
   • Hereditary information is present in the fertilized egg (zygote) which develops into an organism of a particular type only.
5. Write a note on Sex Determination.
   ANS
   
   • In humans, the sex is determined by the genes located on chromosomes.
   • Genes are inherited from parents.
   • Out of 23 pairs of chromosomes, 22 pairs are autosomes which are similar in male and female.
   • In female, the 23rd pair has two similar chromosomes called X-chromosome.
   • In male, one chromosome in 23rd pair is X chromosome and the other is Y chromosome which is smaller in size.
     
     
   • All eggs (ova) of female are similar. Each egg contains 22 autosomes and one X chromosome.
   • 50% sperms in male have X chromosome and 50% have the Y chromosome (along with 22 autosomes).
   • If a sperm carrying X chromosome fertilizes an egg, the zygote develops into a female.
   • If a sperm carrying Y chromosome fertilizes an egg, the zygote develops into a male.
6. Explain the following as Evidence of Evolution: (i) Homologous organs (ii) Analogous organs (iii) Fossils
   ANS
   
   1. HOMOLOGOUS ORGANS
      • The organs having the same internal structure but different functions are called homologous organs.
      • The basic design of the bones of forelimbs of a frog, a lizard, a bird, a bat and a man is similar in in their internal structure but they perform different functions.
      • This is an evidence that the forelimbs of all these organisms have evolved from a common ancestor with same basic internal structure.
   2. ANALOGOUS ORGANS
      • The organs with different basic design but similar appearance and similar function in different organisms are called analogous organs.
      • The wings of insects and the wings of birds have different structure but they perform similar function.
      • The presence of analogous organs in different animals give the evidence that they may not have evolved from a common ancestor but they perform similar function to survive in prevailing environment.
   3. FOSSILS
      • The impressions of dead organisms that lived in the past are known as fossils.
      • The dead bodies of organisms are decomposed by micro-organisms. Sometimes, due to environmental conditions, these bodies do not decompose completely and are preserved in the earth.
      • For example, a dead leaf trapped in mud is not decomposed completely and the mud forms impression of the leaf by setting around it as a mould. It then hardens to form a rock and retains the impression of the leaf. Thus, fossil of a leaf is formed.
      • The age of the fossils can be estimated by carbon dating method. The age is determined by the radioactive isotope of carbon (C-14).
      • Ammonite, Trilobite and Dinosaur are the examples of fossils. The age of their fossils is determined by carbon dating method.
7. Define 'Speciation'. Explain how speciation occurs.
   ANS
   
   • The process by which new species develop from the existing species is known as speciation.
   • When the population of a species splits into two groups separated geographically, new species are formed.
   • The geographical isolation leads to reproductive isolation and there is no gene flow between two separated groups of the population.
   • Some variation arises in individuals due to natural selection.
   • Due to the process of random change in gene frequency (genetic drift), the individuals (of two groups) become so different that they cannot reproduce with each other. This may take thousands of years.
   • There can be more ways like DNA changes, the change in the number of chromosomes, the inability of the germ cells of two isolated groups to fuse with each other, etc. which can lead to speciation.
   • Thus, new species come into existence.
8. Write a note on 'Expression of inherited characters' OR Explain how genes control characteristics.
   ANS
   
   • Gene is a unit of heredity.
   • Genes are located on DNA in a linear order.
   • Each gene synthesizes a specific protein responsible for the expression of a characteristic.
   • Consider the height of a plant as a characteristic. The height of a plant depends upon the amount of a particular growth hormone.
   • The synthesis of hormones is catalyzed by specific enzymes and the synthesis of enzymes is regulated by genes located on DNA.
   • If the enzyme is synthesized in large amount, a lot of hormone will be produced and the plant will be tall.
   • If the gene has an alteration that makes the enzyme less efficient, less hormone will be produced and the plant will be dwarf.
   • Thus, characteristics (traits) are controlled by genes.
9. Write a brief note on Evolution.
   ANS
   
   • Evolution is gradual formation of new species from pre-existing primitive organisms by constant and relatively long time changes.
   • Evolution is the sequence of gradual changes in primitive organisms from which new species have been formed.
   • It is a constant process that started since the origin of life and took millions of years. It is continuous and will occur in future, too.
   • The great variety of living organisms on earth is the result of evolution.
10. Explain : Acquired characteristics (traits).
    ANS
    
    • Acquired trait means a trait developed by an organism in response to the environment.
    • It is not inherited from parents.
    • For example, if the weight of an organism is reduced due to starvation, it would not change the DNA of germ cells. Thus, reduced weight is not a trait inherited by the future generation of starving organism.
    • Other examples of acquired traits are: (i) Cut tail of a mouse (ii) a man knowing how to swim (iii) a man speaking German language (iv) a scar on the body of a man due to accident.
    • These all are traits which cannot be passed on to the next generation as these are changes in non-reproductive cells of the body.
11. Explain : Inherited Characteristics (Traits).
    ANS
    
    • A trait of an organism caused by some change in its DNA is known as inherited trait.
    • Inherited traits can be passed on to the progeny of the organism.
    • Example: Suppose there is a population of red beetles in green bushes. If a colour variation arises during reproduction and a beetle green in colour is produced. Since this change is the result of a change in the DNA of reproductive cells, it is an inherited trait which can be passed on to the next generations.
    • This is the essence of the concept of evolution.
12. Write a brief note on Evolution of eyes.
    ANS
    
    • The eye is an important organ for animals.
    • It is a so complicated organ that it cannot have been generated by a single DNA change.
    • The eyes of animals have been created in stages over many generations.
    • First of all, eyes were formed in planaria (flat worm). These eyes were very simple just like 'eye spots' which could detect light.
    • These eyes provide a survival advantage to planaria.
    • The development of eyes seems to be a very popular adaptation.
    • The eyes in animals like insects, octopus, invertebrates and vertebrates have quite different structures suggesting that the evolution of eyes has occurred in stages.
13. Write a brief note on Evolution of Feathers.
    ANS
    
    • An evolutionary change produced in an organism for one purpose may later on become more useful for an entirely different function. Evolution of feathers is an example of this fact.
    • In some dinosaurs feathers provided insulation in cold weather but they could not be used for flying. Later, they might have become useful for flying.
    • Birds, however, adapted to flight. Thus, presence of feathers in birds indicates that birds are closely related to reptiles (like dinosaurs).
14. Explain : Evolution by Artificial Selection.
    ANS
    
    • The evidences for evolution suggest that very dissimilar looking structures can evolve from a common ancestor.
    • Different looking organisms can in fact be created from the same ancestor by artificial selection in place of natural selection.
    • The farmers have produced entirely different looking vegetables like cabbage, broccoli, cauliflower, kohlrabi and kale from the plant of wild cabbage by artificial selection.
    • Some farmers, in an attempt to have very short distance between the leaves of wild cabbage, produced the commonly used 'cabbage'.
    • Some farmers opted for the arrested flower development of wild cabbage and produced 'broccoli'.
    • Some farmers opted for sterile flowers of wild cabbage and developed 'cauliflower'.
    • When farmers opted for swollen parts of wild cabbage, it resulted in the evolution of 'kohlrabi'.
    • Those farmers who wanted to grow large leaves of wild cabbage produced a leafy vegetable called/kale'.
    • Thus, wild cabbage is the common ancestor and cabbage, broccoli, cauliflower, kohlrabi and kale are the varieties of wild cabbage which have been obtained by artificial selection.
15. Write a note on Human Evolution.
    ANS
    
    • To study human evolution tools like digging of earth, time-dating, study of fossils and DNA sequencing have been used.
    • There is a great variety of human forms and features across the earth.
    • This diversity of features was the basis of different human races. The human races were identified commonly on the basis of the colour of their skin. They were named as white, black, yellow and brown.
    • It is now a well-known fact that the sop called human races have not evolved differently. All human beings are a single species called 'Homo sapiens'.
    • It has been established scientifically that we lived for past few thousand years and our genetic footprint can be traced back to our African roots,i.e. we all came from Africa.
    • A couple of thousand years ago, some of our ancestors left Africa while others stayed back. Those who left Africa spread over the planet from Africa to different parts of Asia, Australia and America.
    • They went in groups, sometimes separating from one another and mixing with one another. Some of them even moved in and out of Africa.
    • This led to evolutionary changes like in all other species.
16. Explain Mendel's contribution.
    ANS
    
    • Mendel performed experiments for explaining the transmission of characteristics (traits) from parents to their offspring.
    • He performed experiments on Pisum Sativum (Garden Pea) and worked out the main rules of inheritance.
    • He studied the inheritance of some of the pairs of contrasting characters like tall and short plants, white and violet flowers, round and wrinkled seeds, axial and terminal flower positions, etc.
    • When Mendel crossed a tall plant (with TT traits on DNA) with a dwarf plant (with tt trait on DNA), the F₁ generation was found to be tall. There were no dwarf or medium height plants in F₁ generation. Thus, only one of the two parental characters was seen in F₁ generation.
    • When the plants of F₁ generation were used to obtain F₂ generation, 25% of the plants were dwarf and 75% were tall.
    • Thus, in F₁ generation both the characters of tallness and dwarfness were inherited from the parents but only the character of tallness was expressed because tallness was dominant trait and dwarfness was recessive trait. [Dominant trait is denoted by capital letter (T) and recessive trait bt small letter (t)].
    • The plants having TT or Tt traits for height were tall and those with tt trait were dwarf. A single trait T is enough for making a plant tall but for dwarfness tt traits are required.
      
      
    • In other experiment, Mendel selected two different traits in a plant. He crossed a plant having yellow and round seed with a plant having green and wrinkled seeds.
    • In F₁ generation, all the plants were with yellow and round seeds indicating that yellow and round are dominating traits.
    • When the plants of F₁ generation are self-pollinated, the plants along with parental combinations (yellow and round seeds, green and wrinkled seeds) new combinations (yellow and wrinkled seeds, grren and round seeds) are also formed in F₂ generation.
    • This indicates that yellow seeds/green seeds traits and round seeds/wrinkled seeds traits are independently inherited.
      
      
      
      
      
17. 
    ANS
    

Chapter 17: OUR ENVIRONMENT

1. Explain : Environment.
   ANS
   
   • DEFINITION: All organisms including plants, animals, micro-organisms and human beings and their physical surroundings with which they interact is called environment.
   • All biotic and abiotic components of the environment are interlinked and interdependent for maintaining environmental balance.
   • Environment varies from place to place due to variation in climate, soil type and topography.
   • All organisms adjust to their environment for survival and any change in any component of the environment may cause discomfort and affect the normal life of the organism.
2. Explain : Ecosystem.
   ANS
   
   • DEFINITION: An interacting system formed by the biotic community together with its physical environment is called ecosystem.
   • An ecosystem may be of small size or large size.
   • There are mainly two types of ecosystem based on the kind of habitat: (i) Aquatic (ii) Terrestrial.
   • Aquatic ecosystems include fresh water ecosystems like rivers, springs, ponds and lakes as well as marine ecosystem formed by oceans.
   • Terrestrial ecosystems include forests, grasslands and deserts.
   • Every ecosystem possesses a specific structure and performs definite functions.
   • Every ecosystem gradually merges into another one.
3. Explain : Components of ecosystem.
   ANS
   
   • An ecosystem consists of mainly two types of components: (A) Biotic components (B) Abiotic components.
   • Biotic components include all living organisms like producers, consumers and decomposers.
   • Abiotic components include non-living factors such as soil, water, light, temperature, wind, humidity, rain, inorganic nutrients and dead organic matter.
   • BIOTIC COMPONENTS:
     (i)Producers:
     • Producers are autotrophic organisms.
     • They possess chlorophyll and produce food througfh the process of photosynthesis.
     • Green plants in terrestrial ecosystem and various algae in aquatic ecosystem act as producers.
     
     (ii)Consumers:
     • Consumers are heterotrophic organisms.
     • They cannot synthesize their food.
     • They consume other organisms and their products as food.
     • They are divided into following four categories.
       1. HERBIVORES (First order consumers): These organisms obtain their food from plants.
       2. CARNIVORES(Secondary/Tertiary level consumers): They predate upon herbivores and other carnivores. If they consume herbivores, they are second order consumers.If they consume other carnivores, they are third (and higher) order consumers.
       3. OMNIVORES: They consume food from both plants and animals.
       4. DECOMPOSERS: They obtain food by decomposing dead bodies of plants and animals. They convert complex organic matter into simple organic molecules and then transform them into inorganic molecules.
   • ABIOTIC COMPONENTS: All nonliving components of an ecosystem are included in abiotic components and divided into two categories.
     1. CLIMATIC factors which include temperature, water, light, wind, mineral elements, and topography of habitat.
     2. EDAPHIC factors which include soil structure and composition.
4. Explain food chain giving suitable example.
   ANS
   
   • DEFINITION: A sequence of living organisms in a community in which one organism consumes another organism is called food chain.
   • Each link of a food chain forms a trophic level.
   • Producers form first trophic level, herbivores form the second level and carnivores form the third level. Thus , a food chain usually starts with producers and ends with carnivores.
   • Food chains are of two types (i) Grazing food chain (ii) Detritus food chain.
   • A grazing food chain begins with chlorophyllous producers and extends through herbivores, carnivores and decomposers.
   • A detritus food chain begins with decomposers and passes through detritus feeding organisms in soil to organisms feeding on detriytus feeders.
   • EXAMPLE : Terrestrial food chain
     
     
   • EXAMPLE : Marine food chain
     
     
   • ENERGY TRANSFER (FLOW) IN A FOOD CHAIN
     • A food chain describes how energy and nutrients move through an ecosystem.
     • Producers (autotrophs) are at the first trophic level. They produce energy.
     • Herbivores (primary consumers) are at the second trophic level. They obtain energy from the producers.
     • Carnivores (secondary and higher level consumers) are at next higher trophic levels. They obtain energy from herbivores or previous level carnivores.
     • Thus, chemical energy produced by autotrophs from sunlight is transferred progressively to next trophic levels.
     • Flow of energy in a food chain is unidirectional and does not revert back to the previous trophic level.
     • For example, energy captured by producers does not go back to sun, energy captured by herbivores does not go back to producers and so on.
5. Explain Food Web with example.
   ANS
   
   • A large number of food chains exist in an ecosystem and many organisms act as a link in more than one food chain.
   • The network formed by the interconnected food chains in an ecosystem is called a food web.
   • This means that the various food chains in an ecosystem do not operate in isolation but they operate in the form of a network of food chains called food web.
   • EXAMPLE:
     
     
6. Write a note on Biological Magnification.
   ANS
   
   • Pesticides like DDT and other chemicals are widely used to protect crops from diseases and pests. Most of these chemicals are non-biodegradable.
   • Due to uncontrolled use of such chemicals, their level increases in the soil and water bodies.
   • These chemicals enter the body of plants and aquatic animals and then they get accumulated progressively at each trophic level.
   • This phenomenon is called Biological Magnification.
7. Mention some global problems.
   ANS
   
   • Global problems are faced not only by individual but by the whole planet and potentially all the people.
   • Some of the major global problems are:
     

     (i) Climate change (ii) Global warming (iii) Deforestation (iv) Depletion of ozone layer
     (v) Loss of biodiversity (vi) Scarcity of water (vii) Problems of waste disposal 
     (viii) Maritime safety (ix) Pollution

8. Write a note on Ozone layer and its depletion.
   ANS
   
   • Ozone layer is located in the stratosphere which is about 50 km high in atmosphere from earth's surface.
   • This layer absorbs UV-radiation from sunlight and prevents it from reaching earth's surface> Ultraviolet rays have harmful effect on living organisms.
   • FORMATION OF OZONE
     
     • Oxygen molecules absorb ultraviolet photons and break down into two oxygen atoms by the process of photo-dissociation or photolysis.
       O₂ ----> O + O
     • The free oxygen atom combines with oxygen molecule to form a molecule of ozone.
       O + O₂ ----> O₃
   • DEPLETION OF OZONE LAYER
     • The phenomenon of depletion of ozone layer was first noticed in the year 1980.
     • It was observed that about 40-50% depletion of ozone layer had occurred over South polar region. Such a large depletion is called 'Ozone Hole'.
     • Later, such ozone holes were also noticed in North polar region.
     • It is probable that ozone holes may develop in other regions with human population.
     • Development of ozone holes depends on the prevalent wind, climatic conditions and suspended particulate matter in the atmosphere.
     • The main factor responsible for the depletion of ozone layer is the addition of chloride ions (Cl^-) in the atmosphere.
     • Chlorine reacts with ozone and removes atoms of oxygen(O) one by one. One chlorine atom can decompose 100,000 molecules of ozone in this manner.
     • Almost 80% of total depletion of ozone layer in the stratosphere is done by chlorofluorocarbons (CFCs). Freon is a CFC used in refrigerators and air-conditioners.
9. Explain : Biodegradable waste and non-biodegradable waste.
   ANS
   
   • BIODEGRADABLE WASTE:
     The waste materials which are broken down by biological processes are called biodegradable. Vegetables, fruits, torn clothes, paper, etc., are examples of biodegradable substances.
   • NON-BIODEGRADABLE WASTE:
     The waste materials which cannot be decomposed by biological processes are called non-biodegradable. Plastic bags, plastic bottles, glass, polythene, etc., are examples of non-biodegradable substances.
10. How the amount of house-hold waste can be reduced?
    ANS
    We can reduce house-hold waste by the following practice:
    • Buy loose fruits and vegetables in order to avoid packaging.
    • Avoid buying disposable items such as razors and pens.
    • Use reusable nappies.
    • Uae reusable carry-bags.
    • Use rechargable batteries.
    • Donate old clothes and shoes to the needy.
    • Reuse the back of papers and envelops.
    • Collect kitchen waste in bags or containers and as soon as they are filled dispose off them properly.
    • Some waste materials can be used to generate extra income if managed properly.