Solution-Class 9-Science-Chapter-15-Life Processes in Living Organisms-Maharashtra Board

The milk was on the stove. Rasika was engrossed watching television. She smelled something burning. She ran towards the kitchen. The milk was boiling over. She held the vessel with her bare hands but, screaming, she let it go at once. This activity was controlled by nerve cells. Special ends of dendrites in these cells collected the information, from where it was transferred to the cell body and then towards the terminal end of the axon The chemicals produced at the terminal end passed through the minute space i.e. synapse. In this way, impulses were conducted in the body and the process of reflex action was completed by conducting the impulses from nerve to  muscle cell

The pressure created in the root cells is called a root pressure.

• Root cells are in contact with water and minerals in the soil. But the concentration inside the cells and the concentration in the surrounding soil is different from each other and thus there is concentration gradient created.
• Due to concentration gradient, the water and minerals from the surrounding areas enter in the root cells.
• Due to this, the root cells become turgid and exert pressure on the adjacent cells.
• Due to root pressure, the water and minerals enter the xylem present in the roots. To reduce this difference in concentration they are continuously pushed forward. This continuous movement creates a water column that is continuously pushed ahead.
• The pressure exerted by the root cells thus is sufficient to lift the water up in small shrubs and small trees.

There are stomata on the leaves of the plants. Through these opening the excess of water is thrown out in the form of water vapours. This process is called transpiration.

• There are two guard cells around the opening of stomata. They have an external membrane. They control the opening and closing of the stomata.
• Also some amount of water is lost due to evaporation from the leaves.
• As a result, water level in the epidermal layer of the leaf decreases.
• To compensate this loss, more water is brought to the leaves through the xylem.
• Transpiration thus helps in absorption of water and minerals and their distribution to all parts of the plant.
• Root pressure pushes the water up during the night time.
• Plants get rid of excess water by transpiration. It helps to keep the surface of the leaves cool.

Nerve cell-  Nerve cells are also known as neurons.

• Neurons or nerve cells are structural and functional units of the nervous system that carry impulses from one place to other.

• Neuron is the largest cell of the body which measures to about few metres in length.
• Neuron has the ability to generate and conduct electrochemical impulses.
• Every neuron has three main parts, viz. cyton or cell body, axon and dendrites. Dendrites pick up the electrochemical signals produced.
• These signals are transferred to cyton and from cyton they are sent to axons. From axon of one neuron, the impulse is then given to dendrites of next neuron.
• The cells called neuroglia support the nerve cells and help in their functioning. Nerve is formed of neurons and neuroglial cells together.

• Human brain is highly evolved organ. It is the main controlling centre of nervous system. It is the part of the central nervous system. It is very well protected inside the cranium or cranial cavity.
• The brain is enclosed by meninges which are protective coverings. There are hollow ventricles inside the brain which are filled up with cerebrospinal fluid. This fluid is protective and nourishing in function. The average weight of adult human brain is about 1300 — 1460 grams and there are approximately 100 billion neurons in the brain.

There are three main parts of the brain, viz. Cerebrum, cerebellum and medulla oblongata.

Cerebrum : It is the largest part of the brain occupying two-third area of brain. It consists of two cerebral hemispheres. The two hemispheres are joined with each other by tough nerve fibres.

Cerebral surface has deep, irregular ridges and grooves called convolutions due to which the surface area of the cerebrum is increased. Large number of neurons are accommodated in cerebrum due to convolution.

• Functions of cerebrum : Controlling all the voluntary movements. Mental faculties such as concentration, planning, decision making, intelligence and intellectual activities.

Cerebellum : This is the smaller part of the brain situated below the cerebrum at the back of the cranial cavity. Its surface shows shallow grooves instead of deep convolutions.

• Functions of cerebellum : Coordination of voluntary movements and maintaining the balance of the body.

Medulla oblongata : Hind-most part of brain consisting of two triangular swollen structures called pyramids on the upper side. The medulla oblongata extends downwards as the spinal cord.

• Functions of medulla oblongata : It controls all the vital and involuntary activities like beating of the heart, blood circulation, breathing, sneezing, coughing, salivation, etc.

• • Reflex action is an immediate and involuntary response given to a stimulus from the environment.
  • The reflex action is so spontaneous that it does not require thinking or control by our brain.
  • Reflex actions are not controlled by brain. But the control and coordination is maintained by the reflex actions by which the load on the brain is reduced. They are of survival value as a person is saved from a dangerous situations due to reflex actions.
  • The path of reflex action is as follows : This is also known as reflex arc. Sense organs->Sensory neurons->Towards the spinal cord -> Coordination neuron -> Motor neuron -> Muscle or gland.

Pituitary- The pituitary gland is known as the master gland because it secretes growth hormone and many other hormones which regulate the secretion of many other endocrine glands in the body. Some of the hormones produced by pituitary are:

• Growth hormone : This hormone brings about the growth of the body, especially growth of the bones. The transformation of child into adult is mainly due to this hormone.
• Prolactin- Growth of mammary glands and formation of milk in them.
• TSH- Synthesis and release of thyroid hormones.
• Follicle stimulating hormone (FSH) : FSH helps in the growth and control of gonads.
• Luteinizing hormone (LH) : The mature ovum is liberated from the ovary of a woman under the influence of LH. This process is called ovulation. The control of menstrual cycle is also done by LH along with other ovarian hormones.
• Adrenocorticotrophic hormone (ACTH)- Stimulates synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.

The next two hormones are actually secreted in hypothalamus but their secretions are stored in the pituitary. Whenever there is need these secretions are sent further.

• Vasopressin- Stimulates reabsorption of water from the distal tubules, and hence, prevents loss of water through urine (diuresis); therefore, also called anti-diuretic hormone (ADH).
• Oxytocin : Oxytocin helps the process of child birth or parturition.

Thyroid secretes two hormones, thyroxine and calcitonin.

Functions of thyroxine include:

• Control of BMR (Basal metabolism rate)
• Control of working of kidney and urine formation
• Regulation of physical, mental, and sexual growth
• Regulation of growth of CNS and bones
• Regulation of carbohydrate and fat metabolism

Adrenal : The cortex i.e. outer part of the adrenal gland produces corticosteroid. The inner part or medulla secrete adrenaline and noradrenaline.

• Corticosteroids bring about regulation and balance of levels of Na and K and stimulates metabolism. It also takes part in the glucose metabolism.
• Adrenaline and noradrenaline controls behaviour during crisis and emotional situations. They also stimulate heart and its conducting tissue and metabolic processes.

Thymus : Thymus secretes peptide hormone called thymosins. Thymosins play an important role in the differentiation of T-lymphocytes (Cell Mediated Immunity) and promotes production of antibodies (Humoral Immunity). Thymus is degenerated in old people, hence, their immune response becomes weak.

Testis : Testis are the male gonads and they secrete testosterone which is very important hormone in males. It brings about secondary sexual characters in males.

Functions of testosterone include:

• Development, maturation and functioning of the male accessory sex organs like vas deferens and seminal vesicles

• Stimulate muscular growth, growth of facial hair, low pitch voice, etc.
• Help in the formation of sperms.
• Act on the CNS and influence male sexual behaviour (libido)
• Anabolism of proteins and carbohydrates

Ovary- Ovaries are the female gonads that produce two hormones called oestrogen and progesterone.
Functions of oestrogen:

• Growth and functioning of the female secondary sex organs
• Development of growing follicles and mammary glands
• Regulates female secondary sex characters (Examples − high pitch voice)

Functions of progesterone:

• Acts on mammary glands and stimulates formation of alveoli-like structures storing milk
• Milk secretion

Coordination in humans occurs in two levels i.e. nervous coordination and chemical coordination.

• The chemical control and coordination in human body is brought about by neurotransmitters (chemical substances secreted at nerve endings) and also the hormones secreted by endocrine glands.
• The endocrine glands are ductless. Their secretions are directly poured into the blood circulation. Though they are located at a particular place, their secretions are sent throughout the body. The endocrine system works in association with nervous system to control and coordinate our bodies.
• Endocrine glands and nervous system together control and coordinate the physiological functions of the body. There is a special mechanism which controls the quantity and timing of hormone secretion.

Pituitary, thyroid, parathyroid, adrenal, some cells of the pancreas, thymus, gonads such as testes and ovaries are the important endocrine glands of our body.

Some of the hormones produced by pituitary are: Prolactin, Oxytocin, LH and FSH are all hormones essential for womanhood and reproduction.

• Prolactin- Growth of mammary glands and formation of milk in them.
• TSH- Synthesis and release of thyroid hormones.
• Adrenocorticotrophic hormone (ACTH)- Stimulates synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.
• Anti-diuretic hormone (ADH).- Stimulates reabsorption of water from the distal tubules, and hence, prevents loss of water through urine (diuresis).

• Thyroxine and calcitonin hormone is produced by thyroid gland and its functions are: Thyroxine maintains the metabolic rate of the body. Calcitonin of thyroid and parathormone of parathyroid both regulate the blood calcium level in the body.
• Oestrogen and Progesterone are hormones of ovary. Testosterone is the hormone of testis. These gonadal harmones are essential for sexual development and maturation respectively in female and male.

• The hormones secreted by the pancreatic cells i.e., insulin and glucagon are essential for maintaining the blood glucose level.
• The hormones of adrenal like corticosteroid and adrenaline and noradrenalin control behavior during crisis and emotional situations. They stimulate heart and its conducting tissue, speed up the metabolic processes and maintain balance of Na+ and K and glucose.

Chemical coordination is very slow but long lasting.

Since plants do not have nervous and muscular system like animals, coordination in plants occurs in response to particular stimuli. The two types of movements are growth relevant movements and growth irrelevant movements. Such movements bring about coordination in plants. They are also called tropic movements or tropism.
These tropic movements can be of various types like:

• Phototropism: The growth movement in plants in response to light stimulus is known as phototropism. For example, the flower head of a sunflower is positively phototropic as it moves from East to West, along with the movement of the Sun.
• Geotropism: The growth movement in plants in response to the force of gravity is known as geotropism. In geotropism, the roots of the plant always grow downwards, while the shoots always grow upwards, away from the earth.
• Chemotropism: The growth movement in plants in response to chemical stimuli is known as chemotropism. For example, the growth of pollen tube towards the ovule in the ovary (through the stigma and style) is an example of positive chemotropism.
• Hydrotropism: The growth movement in plants in response to water is known as hydrotropism. For example, the roots of some plants grow towards the water source, even when the water source is not present directly below it.
• Thigmotropism: The growth movement in plants in response to a touch stimulus or contact with a solid object is known as thigmotropism. For example, in some plants, the coiling of tendrils occurs when they come in contact with objects for support.

Since all the above movements are related with growth, they are called growth-relevant movements.

• The growth-irrelevant movements are not concerned With the growth of a plant. Plant hormones bring about various movements in plants as a response to changes in the surroundings.
• Plants like Mimosa or ‘touch-me-not’ use electro-chemical impulses for transfer of information from one place to another.
• Some plant cells can change their shapes by increasing or decreasing the water content present in them and hence show movements.

The different processes in the body always occur in the proper sequence which is called a coordination. In multicellular organisms several different organ systems function simultaneously.

• Life can function smoothly if there is coordination between all of these different organ systems or organs and the stimuli in the surrounding.
• The systematic regulation of different processes is in control. E.g. Beating of heart and respiration is always coordinated with each other.

Coordination in humans:

• In humans coordination is achieved by two systems
• Nervous system
• Endocrine system
• Chemical coordination in humans is achieved by hormones.

Coordination in plants:

• Since plants do not have nervous and muscular system like animals, coordination in plants occurs in response to particular stimuli.
• Tropism/tropic movement is the term used for the movement or growth of any plant part in response to an external stimulus.

The removal of waste products from the body is known as excretion. In the human body, kidneys, lungs and skin perform the function of excretion. Lungs remove carbon dioxide as waste. Skin helps in the removal of waste in the form of sweat. However, the major organ involved in excretion is the urinary system, which contains the kidneys to filter the blood and form urine.
In human beings, excretion is performed by the excretory system consisting of a pair of kidneys, a pair of ureters, a urinary bladder and urethra.

Process of Urine formation :

• The urine is formed in kidneys and passes on to the urinary bladder via the ureters. The urinary bladder stores the urine until it is excreted through the urethra.
• The kidney contains numerous filtration units called the nephrons. Nephron is the structural and functional unit of the kidney.
• The nephrons consist of a network of capillaries associated with a cup-shaped end of a tube in which the filtered urine is collected.
• When the blood passes through the tube, some substances such as glucose, amino acids, salts, and water are selectively reabsorbed.
• The final filtrate is collected in the collecting tubule and eventually enters the ureters.

The other organs which are involved in the excretory process include:

• Lungs:They remove CO₂ and water. About 18 L of carbon dioxide is eliminated per day with the help of lungs.
• Liver: It excretes bile pigments (such as bilirubin, biliverdin), vitamins, cholesterols and drugs along with digestive wastes.
• Skin: Sweat and sebaceous glands present on the skin eliminate substances such as sterols, hydrocarbons, wax sebum, etc.

Excretion in plants results in the production of various kinds of excreta which are waste for the plant but are equally important for human use.

The following are the examples of the waste products which are not useful for the tree can be very useful for the human beings,

• The latex of rubber gives various rubber products.
• Gum, resin are waste materials for plants but they have various uses for man.
• The waste substances of plants are also stored in vacuoles of leaf-cells and in various plant’s parts. When these leaves and other parts fall off, they act like manures.

The transportation in case of plants occurs due to two main processes, such as root pressure and transpiration. Similarly due to translocation, the phloem carries the food as per requirement of the plant. The conducting system of the plants such as xylem and phloem help in the transport of waterand food respectively . Transportation of water :

• The first step in transportation of water is absorption of water by roots of plants. As the water is absorbed by the roots from the soil and moved to the vascular system, it has to be transported to various parts of the plant. Two forces responsible for transporting the water up in a plant are root pressure and transpiration pull.
• Root Pressure is the positive pressure created inside the xylem when water follows the ions transported along the concentration gradients into the vascular system. However, majority of water is transported through transpiration pull.
• Transpiration pull is the pull of water as a result of tension created by transpiration is the major driving force of water movement upwards in a plants. It accounts for loss of 99% of water taken by the plant and this loss is mainly through stomata.
• As the water is released by leaves into the atmosphere, the water level in the epidermal layer decreases. To compensate this water loss, water is brought to the leaves through xylem. Transpiration helps in the absorption of water and minerals to all the parts of the plants.

Transportation of food

• The transportation of food from the leaves to other parts of the plant occurs in the vascular tissue, phloem and this process of transporting food is known as translocation.
• The phloem also transports amino acids and other substances to storage organs of the plant (along with the growing organs) such as roots, fruits, and seeds.
• The phloem consists of companion cells, sieve tubes, phloem parenchyma, and fibres.The translocation of food occurs in the sieve tubes with the help of companion cells.
• Translocation in the phloem, unlike the xylem, is achieved by utilizing energy from ATP. For example, a food material such as sucrose is transported into the phloem tissue using ATP energy. As a result, the osmotic pressure in the tissue increases, causing the water to move into it. This pressure moves the material in the phloem to the tissues, which have less pressure.
• This is helpful in moving materials according to the requirements of the plant.