Chapter 15 - Life Processes in Living Organisms
1. Match the pairs and explain.
| A | B |
|---|---|
1. Growth of pollen tube towards ovule | a. Gravitropic movement |
2. Growth of shoot system | b. Chemotropic movement |
3. Growth of root system | c. Phototropic movement |
4. Growth towards water | d. Growth-irrelevant movement |
e. Hydrotropic movement |
Ans:
| A | B |
|---|---|
1. Growth of pollen tube towards ovule | b. Chemotropic movement |
2. Growth of shoot system | c. Phototropic movement |
3. Growth of root system | a. Gravitropic movement |
4. Growth towards water | e. Hydrotropic movement |
2. Complete the paragraph.
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 ……………….. cells. Special ends of ……………….. in these cells collected the information, from where it was transferred to the ……………….. and then towards the terminal end of the ……………….. The chemicals produced at the terminal end passed through the minute space i.e. ………………. . In this way, ……………….. were conducted in the body and the process of ……………….. was completed by conducting the impulses from ……………….. to ………………
(Nerve, muscle cell, impulse, dendrite, synapse, axon, reflex action, cell body)
Ans:
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, the impulse was conducted in the body and the process of reflex action was completed by conducting the impulses from nerve to muscle cells.
3. Write notes on-
a. Root pressure
Ans:
(i) Root cells are in contact with water and minerals in the soil.
(ii) Water and minerals enter the cells of the root surface due to differences in concentration. As a result, these cells become turgid.
(iii) This is called root pressure.
(iv) Under the effect of this pressure, water and minerals reach the xylem of the roots, and to reduce this difference in concentration, they are continuously pushed forward.
(v) As a result of this continuous movement, a water column is formed, which is continuously pushed ahead.
(vi) This pressure is sufficient to lift the water up in shrubs, small plants, and small trees.
b. Transpiration
Ans:
(i) Plants give out water in the form of water vapour through the stomata on their leaves. This is known as transpiration.
(ii) Two cells called guard cells are present around the stomata. They control the opening and closing of stomata.
(iii) Water is released into the atmosphere by leaves through the process of evaporation.
(iv) As a result, water in the epidermal layer of the leaf decreases.
(v) Water is brought up to the leaves through the xylem to compensate for the lost water.
(vi) Transpiration helps in the absorption of water and minerals and their distribution to all parts of the plant.
c. Nerve cell
Ans:
(i) Nerve cells, also called neurons, are special types of cells that conduct impulses from one place in the body to another.
(ii) Neurons are the structural and functional units of the nervous system.
(iii) Nerve cells, the largest cell in the human body, may measure up to a few metres in length.
(iv) Nerve cells have the ability to generate and conduct electrochemical impulses.
(v) The cells that support the nerve cells and help in their functioning are called neuroglia. Nerve cells and neuroglial cells together form nerves.
d. Human brain
Ans:
(i) The brain is the main controlling part of the nervous system and is safely located in the cranial cavity.
(ii) The brain is covered by protective layers called the meninges.
(iii) Cavities present in various parts of the brain are called ventricles.
(iv) The ventricles are filled with cerebrospinal fluid. This fluid supplies nutrients to the brain and also protects it from shock.
(v) The brain of an adult human weighs about 1300–1400 grammes and consists of approximately 100 million neurons.
(vi) The left side of our brain controls the right side of our body, and the right side of our brain controls the left side of our body. In addition, the left side of the brain controls our speech and conversation, writing, logical thinking, etc., whereas the right side controls artistic abilities.
The human brain is made up of the following parts:
(a) Cerebrum:
(i) This is the largest part of the brain and consists of two cerebral hemispheres. These hemispheres are joined with each other with the help of tough fibres and nerve tracts.
(ii) The cerebrum occupies two-thirds of the brain. Hence, it is also called a “large brain.”
(iii) Its surface has deep, irregular ridges and grooves, which are called convolutions; convolution increases the surface area of the cerebrum, and therefore a large number of nerve cells can be accommodated.
(b) Cerebellum:
(i) This is the smaller part of the brain situated below the cerebrum at the back of the cranial cavity.
(ii) Its surface shows shallow grooves instead of deep convolutions.
(c) Medulla Oblongata:
(i) This is the hindmost part of the brain.
(ii) There are two triangular, swollen structures called pyramids on the upper side of the medulla oblongata.
(iii) The medulla oblongata continues downwards along the spinal cord.
e. Reflex action
Ans:
(i) An immediate and involuntary response given to a stimulus from the environment is called a reflex action.
(ii) Sometimes we react to an incident without any thought on our part or control over the reaction. (iii) This is a response given to a certain stimulus from the surroundings.
(iv) Even without brain intervention, proper control and coordination are achieved in such situations.
(v) For example, when our hand touches a hot object, the receptor in the skin detects the stimulus. The sensory neuron sends the impulse to a relay neuron in the spinal cord. The impulses are then sent to motor neurons, which cause the muscles of the hand to contract and move away from the hot object.
(vi) The spinal cord is the centre of coordination for reflex actions.
4. Name the hormones of the following endocrine glands and the function of each.
a. Pituitary
Ans:
| Hormone | Function |
|---|---|
(i) Growth hormone | Stimulates growth of bones. |
(ii) Adrenocorticotropic hormone | Stimulates adrenal gland. |
(iii) Thyroid stimulating hormone | Stimulates thyroid gland. |
(iv) Prolactin | Stimulates milk production. |
(v) Follicle stimulating hormone | Controls growth of gonads. |
(vi) Luteinizing hormone | Controls menstrual cycle and ovulation. |
(vii) Oxytocin | Contracts uterus during parturition. |
(viii) Antidiuretic hormone | Regulates water-level in the body. |
b. Thyroid
Ans:
| Hormone | Function |
|---|---|
(i) Thyroxine | Controls growth of body and metabolic activities. |
(ii) Calcitonin | Controls calcium metabolism and calcium level in blood. |
c. Adrenal
Ans:
| Hormone | Function |
|---|---|
(i) Adrenalin and nor-adrenalin | Controls behaviour during crisis and emotional situation. |
(ii) Corticosteroid | Maintains balance of Na and K and stimulates metabolism. |
d. Thymus
Ans:
| Hormone | Function |
|---|---|
Thymosin | Control the cells which give rise to immunity. |
e. Testis
Ans:
| Hormone | Function |
|---|---|
Testosterone | Stimulates growth of secondary sexual characteristics. like beard, mustache, hoarse voice etc. in men. |
f. Ovary
Ans:
| Hormone | Function |
|---|---|
(i) Oestrogen | Stimulates growth of endometrium. Stimulates growth of secondary sexual characteristics in women. |
(ii) Progesterone | Prepares the endometrium for conception and maintains pregnancy. |
5. Draw and label the diagrams.
a. Human endocrine glands
Ans:
b. Human brain
Ans:
c. Nephron
Ans:
d. Nerve cell,
Ans:
e. Human excretory system
Ans:
6. Answer the following.
a. Explain chemical co-ordination in humans and give the names and functions of some hormones.
Ans: Chemical coordination in humans:
(i) In humans, chemical coordination is brought about with the help of certain chemical substances called hormones.
(ii) Hormones are secreted by endocrine glands. These glands are also called ductless glands.
(iii) These glands do not have any arrangement of their own to either store or carry their secretions. So, the hormones are directly released into the blood circulation.
(iv) Though the endocrine glands are present at specific locations in our body, their secretions reach all parts of the body via the blood.
(v) Endocrine glands, along with the nervous system, are responsible for control and coordination in our body.
These two systems help each other to control and integrate the various activities of the body.
(vi) A noted difference between these two systems is that nerve impulses are fast but short-lived, whereas hormone actions are very slow but long-lasting.
(vii) It is very important that hormones are secreted only in the required quantity, and there is a special mechanism that controls the quantity and timing of hormone secretion.
(viii) For example, whenever there is an increase in blood glucose level, certain cells in the pancreas get stimulated, and as a response, they release a greater quantity of insulin, thus bringing down the sugar level to normal.
Names and functions of some hormones:
| Hormone | Function |
|---|---|
(1) Growth hormone | Stimulates growth of bones. |
(2) Luteinizing hormone | Controls menstrual cycle and ovulation. |
(3) Thyroxine | Controls growth of body and metabolic activities. |
(4) Insulin | Stimulates the liver to convert excess blood glucose to glycogen. |
(5) Testosterone | Stimulates growth of secondary sexual characters like beard, mustache, hoarse voice, etc. in men. |
b. Explain the difference between the excretory system of humans and plants.
Ans:
| Excretory system of humans | Excretory system of plants |
|---|---|
(i) In humans, the excretory system carries out the function of removal of waste from the body. | (i) In plants, there is no special system or organ for excretion. |
(ii) Waste substances are generally eliminated out of the body. | (ii) Most of the waste substances are stored in the leaves, flowers, fruits and bark of the stem. |
(iii) The excretory products are urea, uric acid, ammonia, etc. | (iii) The excretory products are gum, resin, latex of rubber, etc. |
c. Explain co-ordination in plants with the help of suitable examples.
Ans:
(i) Plants do not have systems like the nervous system or muscular system.
(ii) In plants, movements are mainly the result of responses given to stimuli.
(iii) Plants show two types of movements: growth-relevant movements and growth-irrelevant movements.
(iv) The movement or growth of any part of the plant in response to an external stimulus is called tropism or tropic movement.
(v) Examples of growth-relevant movements are: The shoot system of any plant responds to the light stimulus, i.e., it grows toward the source of light. This is called phototropic movement.
(vi) The root system of plants responds to stimuli like gravitation and water. These responses are called gravitropic movement and hydrotropic movement, respectively.
(vii) The movement shown by plants in response to specific chemicals is called chemotropic movement. For example, the growth of the pollen tube towards the ovule
(viii) Some specific movements of the plants do not lead to plant growth. Such movements are called growth-irrelevant movements. As a response to changes in the surroundings, plant hormones bring about various movements in plants.
(ix) Examples of growth-irrelevant movements are the closing of leaflets of the touch-me-not (Mimosa) plant on touch. In the plant called Venus fly trap, when an insect visits the flower-like trap, the trap closes up and the trapped insect is digested by the plant.
(x) The lotus flower opens during the day while that of the tuberose opens at night.
(xi) In plants like touch-me-not (Mimosa), movement also occurs at places other than where it has been touched. Hence, we can infer that the information about the touch must have been released within the plant from one place to another.
(xii) Plants use electrochemical impulses for the transfer of information from one place to another. Plant cells change their shape by increasing or decreasing the water content, which thereby brings about the movements of plants.
7. Explain in your own words with suitable examples.
a. What is meant by co-ordination?
Ans:
(i) Several different organ systems function in multicellular organisms.
(ii) Their lives go smoothly if there is coordination between different organ systems or organs and the stimuli in their surroundings.
(iii) Depending on this, we can say that systematic regulation of different processes can be called “control,” and bringing about the different processes in the proper sequence is called “coordination.”
(iv) If any activity in the body is to be completed successfully, proper coordination between different systems and organs participating at different steps of that activity is necessary.
(v) If, due to a lack of coordination, there is confusion at any step, the activity may not get completed. There should be no randomness at any step.
(vi) There should be proper coordination between internal activities of the body resulting from various factors like body temperature, water level, enzyme level, etc. or stimuli arising in the surrounding environment.
(vii) Proper coordination between various systems of an organism helps to maintain a state of equilibrium called homeostasis, which is necessary for the optimal efficiency of the body.
b. How does excretion occur in human beings?
Ans:
(i) The removal of wastes from the body is very important, and it is the excretory system that carries out this function.
(ii) The human excretory system consists of a pair of kidneys, a pair of ureters, and the urinary
bladder and the urethra. Urine is formed by the kidneys by separating the waste and unwanted substances from the blood.
(iii) The functional unit of the kidney that performs the basic function of filtration is called a nephron. The urea produced in the liver enters the blood.
(iv) When the urea-containing blood comes into the glomerulus, it is filtered through capillaries, and urea and other similar substances are separated from it.
(v) Water molecules and small molecules of some other substances can cross the semipermeable membrane of Bowman’s capsule.
(vi) The solution accumulated in the cavity of Bowman’s capsule passes into the tubular part of the nephron. Here, molecules of water and some other useful substances are reabsorbed into the blood.
(vii) Urine is formed from the remaining solution, which is full of waste materials. The urine is carried by the ureters and stored in the urinary bladder. Afterwards, urine is given out through the urethra.
c. How is excretion in plants useful to human beings?
Ans:
(i) Plants give out oxygen during photosynthesis by diffusion which is useful to human beings for respiration.
(ii) Some waste materials of plants for example, gum, resin, latex of rubber, etc. are useful to humans.
d. Describe the transportation system in plants.
Ans:
(i) Plants have two types of conducting tissues, i.e., xylem, which conducts water, and phloem, which conducts food.
(ii) During transpiration, water is released into the atmosphere.
(iii) As a result, the water level in the epidermal layer of the leaf decreases.
(iv) Water is brought up to the leaves through the xylem so as to compensate for the lost water.
(v) Transpiration helps in the absorption of water and minerals and their distribution to all parts of the plant, whereas root pressure performs the important role of pushing the water up at night.
(vi) The food produced by leaves is transported to each cell of the plant through phloem.
(vii) When the food material, like sucrose, is transported to a part of the plant through phloem using ATP, the water concentration in that part of the plant decreases.
(viii) As a result, water enters the cell by diffusion. The pressure on the cell wall increases due to an increase in the cellular contents.
(ix) Due to the increased pressure, food is pushed into the neighbouring cells where the pressure is low.
(x) This process helps the phloem transport materials as needed by the plant.