[h]1. LIFE PROCESSES[/h]
Life processes:- The processes which together perform The maintenance functions of living organisms are life processes.
Movement is one of the important criteria we use to decide whether something is alive.
For life processes living organism’s need energy . Energy is taken inside body in the form of food.
The general requirement for energy and materials is common in all organisms, but it is fulfilled in different ways.
- Some organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water. These organisms, the autotrophs, include green plants and some bacteria.
- Other organisms utilise complex substances. These complex substances have to be broken down into simpler ones before they can be used for the upkeep and growth of the body.
- To achieve this, organisms use bio-catalysts called enzymes. Thus, the heterotrophs survival depends directly or indirectly on autotrophs.
- Heterotrophic organisms include animals and fungi.
2.1 Autotrophic Nutrition
Autotrophs are those organism’s which makes their own food . Like ,green plants.
Green Plants makes their own food by the process called photosynthesis.
Photosynthesis :- It is the process by which autotrophs makes their own food with the help of carbon dioxide and water in the presence of sunlight and chlorophyll.
- carbon dioxide and water are converted into carbohydrates
- Carbohydrates are utilised for providing energy to the plant.
- The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant.
The following events occur during this photosynthesis –
(i) Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to carbohydrates.
Cross-section of a leaf
Leaf of a green plant as seen under microscope.
Chloroplast: In above image Some cells contain green dots. These green dots are cell organelles called chloroplasts which contain chlorophyll.
Stomata : are tiny pores present on the surface of the leaves.
- Massive amounts of gaseous exchange takes place in the leaves through these stmata pores for the purpose of photosynthesis.
- But it is important to note here that exchange of gases occurs across the surface of stems, roots and leaves as well.
- The plant closes these pores when it does not need carbon dioxide for photosynthesis.
Guard cells:- The opening and closing of the pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink.
- Autotrophs also need other raw materials for building their body.
- Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants.
- Other materials like nitrogen, phosphorus, iron and magnesium are taken up from the soil.
- Nitrogen is an essential element used in the synthesis of proteins and other compounds. This is taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.
2.2 Heterotrophic Nutrition
Heterotrophs : An organism that cannot manufacture its own food and instead obtains its food and energy by taking in organic substances, usually plant or animal matter.
Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organism.
Nutrition in Amoeba
Amoeba is a single-celled organism.
- Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole.
- Inside the food-vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm.
- The remaining undigested material is moved to the surface of the cell and thrown out.
In Paramoecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell.
2.4 Nutrition in Human Beings
The alimentary canal is basically a long tube extending from the mouth to the anus.
The digestive system
The digestive system is all about the digestion of food we eat.
- When we take food in mouth , the teeth breaks them into small pieces. Then,
- The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give sugar. The food is mixed thoroughly with saliva and moved around the mouth while chewing by the muscular tongue. then,
- From the mouth, the food is taken to the stomach through the food-pipe or oesophagus. From food pipe the food enters our stomach .
- The stomach is a large organ which expands when food enters it. The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices.
- These digestion functions are taken care of by the gastric glands present in the wall of the stomach. These release hydrochloric acid, a protein digesting enzyme called pepsin, and mucus. The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin.
- The mucus protects the inner lining of the stomach from the action of the acid under normal conditions.
- From stomach with the help of sphincter muscle the food is released into small intestine in a small amount.
- Small intestine is the longest part of the alimentary canal which is fitted into a compact space because of extensive coiling.
- The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose.
- The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act. Bile juice from the liver accomplishes this in addition to acting on fats.
- Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules increasing the efficiency of enzyme action.
- The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.
- The walls of the 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.
- The digested food is taken up by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi which increase the surface area for absorption.
- The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body, where it is utilised for obtaining energy, building up new tissues and the repair of old tissues.
- The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is removed from the body via the anus. The exit of this waste material is regulated by the anal sphincter.
Break-down of glucose by various pathways:-
- The food material taken in during the process of nutrition is used in cells to provide energy for various life processes.
- Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen .
- In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm.
- Further, the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration.
- Break- down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration.
- The release of energy in this aerobic process is a lot greater than in the anaerobic process.
- Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.
ATP:- ATP is the energy currency for most cellular processes. The energy released during the process of respiration is used to make an ATP molecule from ADP and inorganic phosphate
Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water.
Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood.
[h]Human respiratory system[/h]
- In human beings air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage.
- The passage is also lined with mucus which helps in this process. From here, the air passes through the throat and into the lungs. Rings of cartilage are present in the throat. These ensure that the air-passage does not collapse.
- Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli. The alveoli provide a surface where the exchange of gases can take place.
- when we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result.
- Because of this, air is sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body.
Respiratory pigment :When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it.
- In human beings, the respiratory pigment is haemoglobin which has a very high affinity for oxygen. This pigment is present in the red blood corpuscles.
- Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.
4.1 Transportation in Human Beings
Blood transports food, oxygen and waste materials in our bodies.
Blood is a fluid connective tissue. Blood consists of a fluid medium called plasma in which the cells are suspended.
Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form.
Oxygen is carried by the red blood cells. Many other substances like salts, are also transported by the blood.
Our pump — the heart
The heart is a muscular organ which is as big as our fist . Because both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide.
- Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium. The left atrium relaxes when it is collecting this blood.
- It then contracts, while the next chamber, the left ventricle, expands, so that the blood is transferred to it. When the muscular left ventricle contracts in its turn, the blood is pumped out to the body.
- De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates.
- This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation.
- Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do.
- Valves ensure that blood does not flow backwards when the atria or ventricles contract.
Oxygen enters the blood in the lungs
The separation of the right side and the left side of the heart is useful to keep oxygenated and de-oxygenated blood from mixing. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature.
Animals, like amphibians or many reptiles have three-chambered hearts, and tolerate some mixing of the oxygenated and de-oxygenated blood streams.
Fishes, on the other hand, have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body.
Double circulation :- The majority of mammals (including humans) utilize a double circulatory system. This means we have two loops in our body in which blood circulates. One is oxygenated, meaningoxygen rich, and the other is deoxygenated, which means it has little to no oxygen, but a lot of carbon dioxide.
The tubes – blood vessels
- Arteries are the vessels which carry blood away from the heart to various organs of the body. Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls.
- Veins collect the blood from different organs and bring it back to the heart. They do not need thick walls because the blood is no longer under pressure, instead they have valves that ensure that the blood flows only in one direction.
Capillaries: On reaching an organ or tissue, the artery divides into smaller and smaller vessels to bring the blood in contact with all the individual cells. The smallest vessels have walls which are one-cell thick and are called capillaries. Exchange of material between the blood and surrounding cells takes place across this thin wall. The capillaries then join together to form veins that convey the blood away from the organ or tissue.
Maintenance by platelets
The blood has platelet cells which circulate around the body and plug these leaks(or bleeding when we are injured) by helping to clot the blood at these points of injury.
It is a colourless fluid which is also involved in the transportation .
How it is made ?
Through the pores present in the walls of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the tissue fluid or lymph.
Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood.
4.2 Transportation in Plants
In highly organised plants, there are two different types of conducting tissues – xylem and phloem. Xylem conducts water and minerals obtained from the soil (via roots) to the rest of the plant. Phloem transports food materials from the leaves to different parts of the plant body.
Xylem: the xylem moves water and minerals obtained from the soil.
Phloem: transports food from the leaves where they are sent to other parts of the plant.
Transport of water
- Water and minerals are transported through xylem cells from soil to the leaves. The xylem cells of roots stem and leaves are interconnected to form a conducting channel that reaches all parts of the plant.
- The root cells take ions from the soil. This creates a difference between the concentration of ions of roots and soil. Therefore, there is a steady movement of water into xylem. An osmotic pressure is formed and water and minerals are transported from one cell to the other cell due to osmosis.
- The continuous loss of water takes place due to transpiration. Because of transpiration, a suction pressure is created as a result of which water is forced into the xylem cells of roots. The effect of root pressure for transportation in plants is more important in night while during day time transpiration pull becomes the major driving force.
Transpiration: The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.
It helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation.
Transport of food and other substances
Phloem transports food materials from the leaves to different parts of the plant. The transportation of food in phloem is achieved by utilizing energy from ATP which helps in creating osmotic pressure that transport food from the area of high concentration to low concentration.
The transport of soluble products of photosynthesis is called translocation and it occurs in the part of the vascular tissue known as phloem.
Besides the products of photosynthesis, the phloem transports amino acids and other substances.
The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.
Excretion is the process by which metabolic waste is eliminated from an organism.
5.1 Excretion in Human Beings
- The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
- Kidneys are located in the abdomen, one on either side of the backbone.
- Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
Structure and function of nephrons
Nephrons are the basic filtering units of kidneys. Each kidney possesses large number of nephrons, approximately 1-1.5 million. The main components of the nephron are glomerulus, Bowman’s capsule, and a long renal tubule.
Functioning of a nephron:
→ The blood enters the kidney through the renal artery, which branches into many capillaries associated with glomerulus.
→ The water and solute are transferred to the nephron at Bowman’s capsule.
→ In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine.
→ The filtrate then moves down into the loop of Henle, where more water is absorbed.
→ From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct. Collecting duct collects urine from many nephrons.
→ The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.
5.2 Excretion in Plants
- Plants can get rid of excess of water by transpiration.
- Waste materials may be stored in the cell vacuoles or as gum and resin, especially in old xylem. It is also stored in the leaves that later fall off.
- Plants also excrete some waste substances into the soil around them.