Science [3 Mark Questions]

(1) Several factors such as infections, injury or restricted blood flow to kidney reduce the activity of kidneys. This leads to accumulation of toxic nitrogenous substances, gradually may lead to kidney failure.
(2) An artificial kidney is a device to remove nitrogenous waste products from the blood through dialysis.
(3) Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialysing fluid. This fluid has same osmotic pressure as blood but nitrogenous nitrogenous wastes are absent.
As shown in diagram, patient's blood is passed through tubes. During this, nitrogenous waste products from blood pass into dialysing fluid by diffusion. The purified blood is pumped back into the patient's vein.

(1) The upper part of respiratory tract is provided with small hair-like structures called cilia, which help to remove germs, dust and other harmful particles from inhaled air.
(2) Smoking destroys hair like cilia due to which germs, dust, smoke and other harmful chemicals enter lungs and causes harm.
(3) Smoking reduces the breathing efficiency of lungs, may cause various infection and even lung cancer. So, called it is injurious to health. Cigarette contains nicotine which can cause cancer to the respiratory organs.

(1) Gall bladder stores bile juice.
(2) Emulsification (i.e., bile salts breakdown large oil globules into fine small droplets) process initiate the digestion of oils.
(3) After surgery, food with low fat content, i.e., less oil, ghee, butter, etc. is advisable.

(1) Sugar content is very high in chocolates, pastries and sweets. Bacteria act on sugars and produce acidic substances. Acids soften the enamel, i.e., cause dental caries or tooth decay.
Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. This is responsible for pain in teeth.
(2) Brushing the teeth after eating, will remove plaque.
(3) If this problem is untreated, microorganisms may invade the gums causing inflammation and infection.

Blood passes through the heart twice during each cycle in human beings. This is called double circulation.
[Deoxygenated blood from different organs is drained and finally through vena cava it is poured in right atrium. From here this blood is transported to lungs via right ventricle. In lungs, blood become oxygenated and is again transported to left atrium. From here it transports in left ventricle and then by aorta to different body parts.]
It is necessary because it allows a highly efficient supply of oxygen to the body cells, which fulfill the high energy need of body.

	Aerobic respiration		Anaerobic respiration
1.	O2 is used in this process.	1.	O2 is not used in this process.
2.	At the end of this process CO2 and H2O are produced.	2.	At the end of this process in medium of plant origin Ethanol and CO2 are produced and in medium of animal origin only lactic acid is produced and no CO2.
3.	In aerobic respiration complete oxidation of glucose molecules occurs, in which one mole of glucose on oxidation releases much greater energy.	3.	In anaerobic respiration glucose molecules are incompletely oxidized, so one mole of glucose releases less energy along with the organic by - products.
4.	There are two phases in aerobic respiration, the first phase occurs in the cytoplasm and does not utilize O2. The second phase occurs in the mitochondria and utilizes O2.	4.	There is only one phase in anaerobic respiration. It occurs in the cytoplasm. It occurs entirely in the absence of O2.

Name of organisms that use the anaerobic mode of respiration : Yeast and some other fungi, certain bacteria, endoparasites.

Unlike animals, the plants do not possess any special organs or system for excretion. However, the plants excrete their wastes in different ways :
(1) O₂ produced during photosynthesis by the green plants is set free directly in the atmosphere.
(2) Plants remove surplus water by the process of transpiration through the stomata.
(3) Sometimes plants store certain wastes in the cells of their leaves which are ultimately shed off.
(4) Certain plants store wastes in the cellular vacuoles of their cells.
(5) Other waste products such as resin and gum are stored especially in old xylem.
(6) Plants excrete some waste substances into the soil around them.

Lymph is a colourless fluid involved in transportation. It is also called tissue fluid.
Through the pores present in the wall of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the lymph or tissue fluid.
Lymph is similar to the plasma of blood but contains less protein.
Lymph drains into lymphatic capillaries from the intercellular spaces, which join to form large lymph vessels that finally open into larger veins.
Functions : (1) Lymph carries digested and absorbed fat from intestine.
(2) It drains excess fluid from intercellular space back into the blood.

When the body size of animals is large, the diffusion pressure alone cannot be sufficient to deliver oxygen to all parts of the body in short time.
If diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a molecule of oxygen to get to our toes from our lungs.
Instead, respiratory pigment haemoglobin present in the red blood corpuscles, take up oxygen from the air in the lungs and carry it to tissues and cells of body through blood circulation. Oxygen is released to oxygen deficient tissue. Haemoglobin has a high affinity for oxygen, so it carries oxygen to all the cells of the body.
So, respiratory pigment is essential in human beings.

Role or Functions of the acid :
(1) Acid destroys the bacteria and other microorganisms that enter the stomach, along with the food.
(2) It converts the inactive enzyme pepsinogen into active enzyme pepsin.
(3)It provides acidic medium required for the action of pepsin.
Pepsin can digest proteins present in food only in acidic medium.
(4) Insoluble mineral salts get dissolved in acid.

Small intestine is the longest part of the alimentary canal which is fitted into a compact space because of extensive coiling in human beings.
The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.
Digestion in small intestine : Small intestine is the longest part of the alimentary canal. It is the site of the complete digestion of carbohydrates, proteins and fat.
From the stomach, the food enters the small Intestine. Small intestine receives bile juice from liver and pancreatic juice from pancreas.
(1) Action of bile juice : The food coming from stomach is acidic and bile makes it alkaline for the pancreatic enzymes to act.
Bile salts break large fat globules present in food down into smaller globules. This process is called emulsification. This process increases the efficiency of enzyme action.
(2) Action of pancreatic juice : The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins. pancreatic amylase for carbohydrates and lipase for breaking down emulsified fats.
(3) Action of intestinal juice : The wall of small intestine contain glands which secrete intestinal juice.
The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.
Absorption of digested food : Digested food is taken up by the walls of the intestine. The inner lining of the small intestine has numerous fingerlike projection called villi. Villi increase the surface area for absorption. The villi are richly supplied with blood vessels, which increase the efficiency of absorption of digested food.

Autotrophs meet their requirement of raw materials by following :
(1) CO₂ used in photosynthesis is taken from atmosphere through stomatal pores.
(2) Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants.
(3) Other materials like nitrogen, phosphorous, iron and magnesium are taken up from the soil.
Nitrogen is an essential element used in the synthesis of proteins and other nitrogenous compounds. Nitrogen is taken up in the form of inorganic nitrates or nitrites. If may be taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.

Autotrophic nutrition is shown by all photosynthetic organisms.
Photosynthesis is a process in which carbon dioxide and water are converted into carbohydrates in the presence of sunlight and chlorophyll.
All the green plants show autotrophic nutrition, by which they produce starch and some proteins.
Carbohydrates are utilised for providing energy to the plants. The excess carbohydrates are stored in form of starch, which is a complex carbohydrate. It serves as the internal reserve energy to be used as and when required.

The requirement for energy and materials is common in all organisms.
On the basis of the mode of nutrition, organisms are of two types:
(1) Autotrophs: These organisms use simple
food material obtained from inorganic sources in the form of carbon dioxide and water.
Green plants and some bacteria are autotrophs.
(2) Heterotrophs: These organisms utilise
complex substances from other organisms and broken down into simpler ones. To achieve this, organisms use bio-catalysts called enzymes.
The heterotrophs survival depends directly or indirectly on autotrophs.
Animals and fungi are heterotrophs.

The living cells of the body need energy for performing various vital functions. The energy is obtained by the biological oxidation of organic nutrients in the cell.
The process of breakdown of food sources for cellular needs either using oxygen or without oxygen is called respiration. The energy, so released is for continuation of various functions and thereby maintaining the living state of the organism. Thus. respiration is essential for life.

Bile is a greenish yellow alkaline digestive juice secreted from the liver cells. Bile contains bile salts, certain bile pigments but does not contain any digestive enzymes.
The bile salts turn the acidic food from stomach, alkaline and thereby provide alkaline medium for further reactions in intestine. Pancreatic enzymes and intestinal enzymes need alkaline medium. Bile salts emulsify the large fat globules into a very large number of very minute fat droplets and thereby greatly increase the exposed surface area of fat for the rapid action of lipases. Hence bile is an important digestive juice though it does not contain any digestive enzymes.

The length of small intestine is different in different animals and that depends upon the nature of food taken by the animal.
The carnivorous eat flesh. The digestion of flesh as food is quite easy and rapid and there is very small amount of roughage. Hence these animals have short small intestine. The herbivorous eat grass and other vegetation. The cellulose of the plant cells is a complex substance and its complete digestion needs more space and time and hence longer small intestine and longer large intestine. Hence, the length of small intestine of herbivorous is relatively much longer than that of carnivorous.

For the chemical digestion of food in stomach, the stomach secretes gastric juice from its gastric glands. HCl is one of the constituents of gastric juice.
HCl destroys the bacteria and other micro-organisms entering along with the ingested food and thereby prevent the decay of food in stomach. HCl provides acidic medium for the action of gastric enzyme. HCl converts inactive enzyme pepsinogen into an active enzyme pepsin. Pepsin acts in acidic medium on proteins and starts their digestion and convert them into preoteoses and peptones. Thus, HCl is an important constituent of gastric juice.

In parasitic nutrition, one organism depends fully for obtaining its nutritional needs. directly on other living organism. The latter is called a host from whom the parasite directly obtains food. The parasitic organism keeps close contact with the host and sucks or absorbs. nutrients from its body. The host goes on becoming weaker physically and physiological. The health of host thus is affected. Thus, the parasitic mode of nutrition is harmful for the host organism.

On one or both the surfaces of the leaves of flowering plants, there are numerous stomata as minute pores. Each of these pores is guarded by a pair of guard cells. The opening and closing of the stomata is controlled by these guard cells, which contain chloroplasts. When water enters the guard cells, the latter swell and cause the opening of stomata and when the guard cells lose water, the guard cells contract and cause the closing of stomata. Thus, the stomata in leaves keep on opening and closing due to entry and exit of water in the guard cells.

The organisms, possessing chlorophyll, can trap and utilize the solar energy to synthesize their own food using CO₂ and water. This process of trapping the solar energy for synthesis of ones own food is called photosynthesis and the mode of nutrition of such organisms is called autotrophic. In photosynthesis, the food synthesized is the simplest hexose sugar-glucose, which is utilized for obtaining energy. The surplus glucose is stored as reserve food in the form of starch. Hence, the organisms possessing chlorophyll are autotrophs.

The arteries carry blood from the heart towards different organs. When the ventricles contract, the blood is pushed in the arteries under high pressure. In order to withstand this pressure, the arteries must have thick and elastic walls.
The veins receive blood from different organs and carry it to the heart. The blood in the veins flows at relatively low pressure. Hence, the wall of the veins is relatively thin and less elastic.

The lymph oozes out through the pores in thin walls of the blood capillaries, as a fluid from the blood flowing through the capillaries. It flows very slowly in the intercellular spaces between the tissue cells. The intercellular spaces have no walls of their own and are called lymph capillaries. These lymph capillaries meet and join with each other to form larger ones which finally open in a vein to pour its contents. Thus, lymph, as a colourless watery fluid collects in a large lymph vessels that finally open in particular veins in the body to pour its contents back in blood.

The four-chambered heart, in man, is formed of two atria and two ventricles. All the four chambers of the heart are separated from each other by septa.
Deoxygenated blood from different organs of the body (except lungs) is brought through superior and inferior vena cava and poured in the right atrium and then into the right ventricle. Similarly oxygenated blood from the two lungs is brought through pulmonary veins and poured in the left atrium and then into the left ventricle. The four-chambered heart prevents the mixing of oxygenated blood with deoxygenated blood. Hence, the right side chambers of the heart have deoxygenated blood and the left side chambers have oxygenated blood in them.

The phloem transports amino acids, various plant hormones and other organic substances in addition to the products of photosynthesis.
Carbohydrates are synthesized in the leaves due to photosynthesis. These carbohydrates are transported to the roots and stem through phloem. The plant hormones synthesized in shoot apex flow downwards through the phloem and the plant hormones synthesized in the root apex and the food reserve stored in roots are transported upwards through the phloem. Thus, the translocation in the phloem takes place in both, upward and downward directions.

The xylem tissue in all the organs of a plant remains connected to each other and forms a continuous path for the flow of water, etc. Thus, us a continuous water column is formed therein.
Mere root pressure, created in small herbs, is not sufficient to push water and minerals to the great height of very tall plants. The plants adopt another way to reach the target of fulfilling the water requirement. Evaporation of water molecules in the form of vapour occurs through stomata. Due to that a suction force arises in the cells. of leaves. This suction force comes into being from the cells of the leaves and is gradually experienced in the xylem of roots. As a result, the water column in the xylem rises up. Hence in very tall plants, the suction force created due to transpiration is the main conducting force for water and mineral ions through the xylem.

The green leaves of plants obtain CO₂ from the atmosphere and synthesize carbohydrates. The plants, through their roots, absorb water and other raw mineral elements essential for the constitution of the body, from the soil. In higher plants the distance between the roots and the leaves being more, the water, mineral elements and the products of photosynthesis cannot be sent to all the different parts of the plant body, merely by diffusion from cell to cell. Therefore, in order to distribute all these substances rapidly and timely, a proper transportation (conducting) system is necessary in higher plants.