Biology [Ch-1] -Life Processes

the processes which together perform the maintenance jobs of the body are called life processes. these processes are;

• nutrition

• respiration

• transportation

• excretion

we can tell if an organism is alive if there is movement; either it is visible to the eye or it is the movement of molecules, which is invisible to the eye

• to perform life processes, an organism needs energy

• the process by which a source of energy (food) is transferred from outside of the body to inside is called nutrition

• if the organism is growing, it needs larger amount of energy

• most of this energy is carbon-based as life depends on carbon molecules

• this energy cannot be found directly; the food has to be broken down into simpler substances by other processes

types of nutrition are divided based on mode of acquisition. they are as follows;

• autotrophic

• heterotrophic

  • saphrophytic

  • parasitic

  • holozoic

it is the mode of nutrition where organisms take substances from outside and convert them into energy through photosynthesis. in other words, these organisms prepare their own food

• absorption of light energy by chlorophyll

• conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen

• reduction of carbon dioxide into carbohydrates

carbon dioxide and water is converted into carbohydrates (glucose) in the presence of chlorophyll and sunlight

6CO2 + 12H2O → (chlorophyll & sunlight) C6H12O6 (glucose) + 6O2 + 6H2O

they take in carbon dioxide at night and store it in the form of an acid, which is then acted upon once sunlight is absorbed by chlorophyll during the day

• keep a potted plant with variegated leaves (money plant, crotons, etc) in a dark room for 3 days so that all starch gets used up

• keep the plant in sunlight for 6 hours

• pluck a leaf and mark the green areas in it and trace them on paper

• dip the leaf in boiling water

• after that, dip the leaf in a beaker with alcohol

• heat the beaker until the alcohol begins to boil

• a lot of the gaseous exchange takes place in the stomata. however, as a lot of water is lost through the stomata, its kept closed when the plant doesnt need CO2 for photosynthesis

• the opening and closing of stomata is done by guard cells; it swells when water flows into them, causing it to open. similarly, it closes when the guard cells shrink

• when its closed, exchange of gases happens across the surface of stems, roots and leaves

• nitrogen : synthesis of proteins etc. it is taken in the form of inorganic nitrates/nitrites OR as organic compounds prepared by bacteria from atmospheric nitrogen

• phosphorus, iron, magnesium etc. are some other raw materials taken up from the soil

• it is the type of nutrition in which the organism cannot prepare food and depends on other organisms for it

• the form of this nutrition depends on type, method of obtaining, availability of food etc.

• saprotrophic: feed on dead and decaying matter (eg: fungi like bread mould, yeast, mushroom)

• parasitic: derive nutrition from living organisms by living on the body of the host (eg: fleas, lice, tapeworms)

• holozoic: ingest solid material which is digested and absorbed into their bodies (eg: humans, animals, insectivorous plants)

• in amoeba: it takes in food by using temporary finger-like extensions which form a food vacuole and trap the food inside it

• in paramecium: unlike amoeba, the cell has a definite shape and food is taken in at a specific spot. the food is moved to the spot by cilia, which covers the entire cell surface

in both cases, the food is broken down into simpler substances and dissolved into the cytoplasm. the undigested matter is excreted through the cell surface

• mouth

• oesophagus (food pipe)

• stomach

• gallbladder

• small intestine

• large intestine

• liver

• pancreas

• the food is first taken in by the mouth

• the food particles have to be small and of same texture. thus, food is crushed with our teeth

• saliva, a fluid secreted by salivary glands, contains an enzyme called salivary amylase that breaks down starch into simple sugar. it also helps in wetting the food for smooth movement

the food has to be moved in a regulated manner along the digestive system so that it can be processed properly in each part. the lining of canal has muscles that contract rhythmically in order to push the food. this is called peristaltic movement

• the food is brought from the mouth to the stomach, a large organ which contains digestive juices and breaks down food, and stores it until digestion

• it expand when food enters it. its muscular walls help mix the food with digestive juices

• the food is digested with the help of gastric glands present in the walls of the stomach. these gastric glands release hydrochloric acid, pepsin (protein digesting enzyme) and mucus

• the hydrochloric acid creates an acidic medium to help the action of pepsin. the mucus protects the inner lining of the stomach from the acid

• the food comes from the stomach to the small intestine, which is the longest part of the alimentary canal

• its length depends on the type of animal; herbivores have longer small intestines in order for cellulose to be digested while carnivores have shorter ones as meat is easier to digest

• it completely digests fats, proteins and carbs with the help of liver and pancreatic secretions

• the bile juice from the liver makes the acidic food alkaline, so that the pancreatic enzymes can act on it

• the fat globules are very big and have to be broken down into small pieces in order to be digested. this is done by the bile salts

• the pancreatic enzymes trypsin and lipase digest proteins and fats respectively

• finally, the walls of the intestine contains glands that produce intestinal juice, which has enzymes that breaks down

  • proteins → amino acids

  • carbs → glucose

  • fats → fatty acids & glycerol

• the digested food is absorbed by the small intestine. it has finger-like projection called vili to increase the surface area for absorption

• the villi take absorbed food to each and every cell of the body

• the undigested food is sent to the large intestine where its wall absorbs the water from it and sends it for excretion

• respiration is the process by which the glucose obtained during nutrition is burnt in the cells with the help of oxygen to produce energy

• there are two types of respiratioin

  • aerobic respiration

  • anaerobic respiration

• it is the respiration that takes place in cells in the presence of oxygen

• the process is as follows;

  • breakdown of glucose (6-carbon molecule) to pyruvate (3-carbon molecule) + energy in cytoplasm

  • breakdown of pyruvate to CO2 + H2O + energy in mitochondria

• sometimes, there is not enough oxygen in our muscle cells. in that case, pyruvate breaks down into lactic acid and a little less energy instead

• it is the respiration that takes place in yeast etc. due to the absence of oxygen

• the process is as follows;

  • breakdown of glucose (6-carbon molecule) into pyruvate (3-carbon molecule) + energy in cytoplasm

  • breakdown of pyruvate into ethanol (2- carbon molecule) + CO2 + energy

• it is immediately used to synthesise a molecule called ATP (adenosine triphosphate)

• it is used to fuel all activities in the cell

since the amount of dissolved oxygen in water is low compared to air, the breathing rate in aquatic organisms is faster

• air is first taken through nostrils. it is filtered by the nostril hair. the passage is also lined with mucus to help with movement

• the air passes through the throat. there are rings of cartilage present so that the air passage is sturdy

• the air enters the lungs. within the lungs, the passage divides into smaller and smaller tubes which are called alveoli. both lungs are entirely made up of alveoli and it is where the exchange of gases occurs\

• when we inhale, our diaphragm flattens and thus the chest cavity becomes larger. due to this, the air is sucked into the lungs and fills the expanded alveoli

• the CO2 rich blood comes from the blood vessels into the alveoli and an exchange of gases takes place

lungs contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released

• in complex organisms like humans, simple diffusion of oxygen from one cell to another is difficult

• thus, a red pigment called haemoglobin, which is found in blood, carries the oxygen from the lungs to the tissues

• it is found in red blood corpuscles (RBCs)

• blood is a fluid connective tissue

• it has 3 components;

  • plasma: transports food, CO2 etc.

  • RBC: transports oxygen

  • WBC: defends body against diseases

• it is a muscular organ that pushes blood to all parts of the body

• it has 4 chambers; 2 atriums and 2 ventricles. this is to prevent O2 and CO2 blood from mixing

• the process of pumping of blood is as follows;

  • oxygen-rich blood comes from the lungs into the heart through left atrium. it relaxes while collecting the blood

  • then, the left atrium contracts while the left ventricle relaxes and the blood goes into it

  • the left ventricle then contracts and the blood is pumped out to the body

  • the blood then comes back deoxygenated and enters through the right atrium as it relaxes

  • the right atrium contracts, the right ventricle relaxes and the blood goes into it

  • the right ventricle pumps the blood out to the lungs where it gets oxygenation

• in animals like birds and mammals, the energy requirement is very high. thus, they cannot have oxygenated and deoxygenated blood mixing

• for this, they have 4 chambered hearts where the blood passes through twice in each circulation

• this is called double circulation

• the force that blood exerts on the walls of vessels is called blood pressure

• the pressure of artery during ventricular systole (contraction) is called systolic pressure

• the pressure of artery during ventricular diastole (relaxation) is called diastolic pressure

• blood pressure is measured by sphygmomanometer

• high blood pressure is called hypertension

• it is caused by the constriction of arterioles, which results in increased resistance to blood flow

• arteries are the vessels which carry blood away from the heart to various parts of the body

• they have thick walls due to high pressure

• veins are vessels which carry blood from various parts of the body back to heart

• they have thin valves as they have low pressure. instead, they have valves which ensure that blood flows only in one direction

• leakage would result in loss of blood and pressure, which would reduce the efficiency of the pumping system

• to avoid this, the blood has platelet cells which circulate around the body and plug the leaks by clotting the blood

• carries digested and absorbed fat from intestine

• drains excess fluid from intercellular space back into the blood

• when the plant is small, the raw material can be easily diffused to all parts of the organism

• however, when it grows and becomes taller, diffusion may take a lot of time

• thus, plants have a transportation system consisting of two pathways; xylem and phloem. as energy requirement for plants is low, the system is quite slow

• in xylem, vessels and tracheids of roots, stems and leaves connect to form a continuous system of water-conducting channels reaching all parts of the plant

• the roots actively take in ions from the soil. this creates a difference in the concentration of these ions between root and soil. therefore, water moves into the root to eliminate this difference. this creates a column of water that steadily moves upwards

• but this upward movement of water is not enough to reach all parts of the plant. thus, when plant loses water through transpiration, it creates a suction which pulls water from the xylem of roots

• in phloem, sieve tubes and companion cells connect to form a continuous system of food-conducting channels reaching all parts of the plant

• this transport of soluble products of photosynthesis is called translocation

• this translocation is achieved by using energy. material like sucrose is transferred into phloem using energy from ATP. this increases the osmotic pressure of the tissue causing water to move into it. this allows the phloem to move material according to the plant’s need

• the excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra

• the kidney is completely made up of structures called nephron which produce the urine

• urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra

• it is a cluster of very thin-walled blood capillaries

• each nephron has a cup-shaped structure called bowman’s capsule which collects the filterate

• some substances in the initial filtrate, such as glucose, amino acids, salts and water is selectively reabsorbed back by the body

• the amount of water reabsorbed depends on how much excess water there is in the body and how much dissolved waste there is to be excreted

• sometimes, when a person’s kidney stops working, they are unable to remove waste from their body

• thus, an artificial kidney, or dialysis is attached to the person

• it contains a number of tubes suspended in a tank filled with dialysing fluid. this fluid has the same osmotic pressure as blood, but it doesnt have any waste material. the patients blood passes through the tubes. the waste products diffuse into the dialysing fluid by diffusion

• the purified blood is then pumped back to the patient

• the only difference between this and normal excretion is that there is no selective reabsorption

• their excretion process is very simple

• excess water is removed through transpiration

• for other wastes, the waste products are stored in cellular vacuoles of dead cells or in leaves that fall off