- Heat a few crystals of copper sulphate in a dry boiling tube.
- What is the colour of the copper sulphate after heating?
- Do you notice water droplets in the boiling tube? Where have these come from?
- Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
- What do you observe? Is the blue colour of copper sulphate restored?
Thursday, April 29, 2021
- Collect the following salt samples – sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogencarbonate (some other salts available can also be taken).
- Check their solubility in water (use distilled water only).
- Check the action of these solutions on litmus and find the pH using a pH paper.
- Which of the salts are acidic, basic or neutral?
- Identify the acid or base used to form the salt.
- Report your observations in Table 2.4.
- Write the chemical formulae of the salts given below.
- Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
- Identify the acids and bases from which the above salts may be obtained.
- Salts having the same positive or negative radicals are said to belong to a family. For example, NaCl and Na2SO4 belong to the family of sodium salts. Similarly, NaCl and KCl belong to the family of chloride salts. How many families can you identify among the salts given in this Activity?
- Put about 2 g soil in a test tube and add 5 mL water to it.
- Shake the contents of the test tube.
- Filter the contents and collect the filtrate in a test tube.
- Check the pH of this filtrate with the help of universal indicator paper.
- What can you conclude about the ideal soil pH for the growth of plants in your region?
- Test the pH values of solutions given in Table 2.2.
- Record your observations.
- What is the nature of each substance on the basis of your observations?
- Take 10 mL water in a beaker.
- Add a few drops of concentrated H2SO4 to it and swirl the beaker slowly.
- Touch the base of the beaker.
- Is there a change in temperature?
- Is this an exothermic or endothermic process?
- Repeat the above Activity with sodium hydroxide pellets and record your observations
- Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in Fig. 2.4.
- Add some concentrated sulphuric acid to the test tube.
- What do you observe? Is there a gas coming out of the delivery tube?
- Test the gas evolved successively with dry and wet blue litmus paper.
- In which case does the litmus paper change colour?
- On the basis of the above Activity, what do you infer about the acidic character of:
(ii) HCl solution?
- Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
- Fix two nails on a cork, and place the cork in a 100 mL beaker.
- Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch, as shown in Fig. 2.3.
- Now pour some dilute HCl in the beaker and switch on the current.
- Repeat with dilute sulphuric acid.
- What do you observe?
- Repeat the experiment separately with glucose and alcohol solutions. What do you observe now?
- Does the bulb glow in all cases?
- Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring.
- Note the colour of the solution. What has happened to the copper oxide?
- Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
- What is the colour of the solution?
- Add dilute HCl solution to the above solution drop by drop.
- Is there any colour change for the reaction mixture?
- Why did the colour of phenolphthalein change after the addition of an acid?
- Now add a few drops of NaOH to the above mixture.
- Does the pink colour of phenolphthalein reappear?
- Why do you think this has happened?
- Take two test tubes, label them as A and B.
- Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about 0.5 g of sodium hydrogencarbonate (NaHCO3) in test tube B.
- Add about 2 mL of dilute HCl to both the test tubes.
- What do you observe?
- Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. 2.2 and record your observations.
- Place a few pieces of granulated zinc metal in a test tube.
- Add 2 mL of sodium hydroxide solution and warm the contents of the test tube.
- Repeat the rest of the steps as in Activity 2.3 and record your observations.
CAUTION: This activity needs the teacher’s assistance.
- Set the apparatus as shown in Fig. 2.1.
- Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
- What do you observe on the surface of zinc granules?
- Pass the gas being evolved through the soap solution.
- Why are bubbles formed in the soap solution?
- Take a burning candle near a gas filled bubble.
- What do you observe?
- Repeat this Activity with some more acids like HCl, HNO3 and CH3COOH.
- Are the observations in all the cases the same or different?
- Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.
- Take two of these cloth strips and check their odour.
- Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other. Rinse both cloth strips with water and again check their odour.
- Note your observations.
- Now take some dilute vanilla essence and clove oil and check their odour.
- Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in odour, if any.
- Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations.
- Collect the following solutions from the science laboratory– hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2], potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)2], and ammonium hydroxide (NH4OH).
- Put a drop of each of the above solutions on a watch-glass one by one and test with a drop of the indicators shown in Table 2.1.
- What change in colour did you observe with red litmus, blue litmus, phenolphthalein and methyl orange solutions for each of the solutions taken?
- Tabulate your observations in Table 2.1
- Soak a few seeds of Bengal gram (chana) and keep them overnight.
- Drain the excess water and cover the seeds with a wet cloth and leave them for a day. Make sure that the seeds do not become dry.
- Cut open the seeds carefully and observe the different parts.
- Compare your observations with the Fig. 8.9 and see if you can identify all the parts.
Figure 8.9 Germination
Two cotyledons of the seed can be observed showing radicle and plumule.
These parts are similar as shown in the figure 8.9.
- Select a money-plant.
- Cut some pieces such that they contain at least one leaf.
- Cut out some other portions between two leaves.
- Dip one end of all the pieces in water and observe over the next few days.
- Which ones grow and give rise to fresh leaves?
- What can you conclude from your observations?
- Take a potato and observe its surface. Can notches be seen?
- Cut the potato into small pieces such that some pieces contain a notch or bud and some do not.
- Spread some cotton on a tray and wet it. Place the potato pieces on this cotton. Note where the pieces with the buds are placed.
- Observe changes taking place in these potato pieces over the next few days. Make sure that the cotton is kept moistened.
- Which are the potato pieces that give rise to fresh green shoots and roots?
- Collect water from a lake or pond that appears dark green and contains filamentous structures.
- Put one or two filaments on a slide.
- Put a drop of glycerin on these filaments and cover it with a coverslip.
- Observe the slide under a microscope.
- Can you identify different tissues in the Spirogyra filaments?
- Observe a permanent slide of Amoeba under a microscope.
- Similarly observe another permanent slide of Amoeba showing binary fission.
- Now, compare the observations of both the slides.
- Wet a slice of bread, and keep it in a cool, moist and dark place.
- Observe the surface of the slice with a magnifying glass.
- Record your observations for a week.
The thread-like structures that developed on the bread are the hyphae of the bread mould.
- Dissolve about 10 gm of sugar in 100 mL of water.
- Take 20 mL of this solution in a test tube and add a pinch of yeast granules to it.
- Put a cotton plug on the mouth of the test tube and keep it in a warm place.
- After 1 or 2 hours, put a small drop of yeast culture from the test tube on a slide and cover it with a cover slip.
- Observe the slide under a microscope.
Wednesday, April 28, 2021
16. SUSTAINABLE MANAGEMENT OF NATURAL RESOURCES
15. OUR ENVIRONMENT
14. SOURCES OF ENERGY
13. MAGNETIC EFFECTS OF ELECTRIC CURRENT
11. THE HUMAN EYE & COLOURFUL WORLD
10. LIGHT-REFLECTION & REFRACTION
9. HEREDITY AND EVOLUTION
7. CONTROL AND COORDINATION
In organisms, many movements are responses to changes in the environment or to use changes in environment. E.g.
- Plants grow out into the sunshine.
- Children get pleasure and fun out of swinging.
- Buffaloes chew cud for better digestion.
- Falling light on eyes or touching a hot object cause responses.
Such movements are carefully controlled and coordinated by specialised tissues. Also, they are connected to recognition of various events in the environment.
In animals, control and coordination are provided by nervous and muscular tissues.
Nervous tissue is made up of a network of nerve cells (neurons). It conducts information (electrical impulses) from one part of the body to another.
Some nerve cells have specialised tips called receptors. They are usually located in sense organs. They detect information from environment. E.g. gustatory receptors detect taste, olfactory receptors detect smell.
General perception of taste is jointly created by tongue (taste) and nose (smell). That’s why if nose is blocked or we have cold, there is a difference in taste of foods.
Transmission of nerve impulse
Information from receptors → dendritic tip of nerve cell → sets off a chemical reaction → generation of electrical impulse → impulse to cell body → axon → axonal end releases some chemicals → chemicals cross the gap (synapse) → generation of electrical impulse in dendrite of the next neuron → impulses deliver to muscles cells or gland.
Reflex actions are sudden unconscious actions of the body in response to a stimulus in the environment. E.g.
o Withdrawal of hand when we touch a flame.
o Blinking of eyes when light falls on them.
Here there is no thinking as it needs an immediate response.
Thinking needs complicated interaction of many nerve impulses from many neurons.
In brain, thinking tissue sits in the forward end of the skull. It receives signals from all over the body and thinks about before responding to them.
If thinking part is to instruct muscles to move, nerves must carry this signal back to different parts of the body. It takes much time and prevents quick response. E.g. when we touch a hot object, it would take much time to withdraw the hand if thinking tissue is involved.
The pathway of impulses in a reflex action is called reflex arc. It includes receptor, sensory neuron, CNS, motor neuron & effector (muscle or gland).
Nerves from all body parts meet in spinal cord on their way to the brain.
Reflex arcs evolved as efficient ways of functioning in the absence of true thought processes in animals. However, after complex neuron networks have evolved, reflex arcs continue to be more efficient for quick responses.
Sequence of events (reflex arc) of focussing bright light on eyes are given below:
Receptor → Sensory neuron → Brain → Motor neuron → Eye → Eye muscle contracts.
Brain & spinal cord constitute the central nervous system (CNS). They receive information from all parts of the body and integrate it.
Brain is protected in a fluid-filled balloon (shock absorber) inside the bony box (cranium).
Spinal cord is protected in vertebral column or backbone.
Brain is the main coordinating centre of the body. It involves more complex mechanisms & neural connections for complex processes such as thinking.
Spinal cord contains nerves which supply information to think about.
Brain sends messages to muscles to control voluntary actions such as writing, talking, moving, clapping etc.
Communication between CNS and other parts of the body is facilitated by the peripheral nervous system (PNS). It consists of cranial nerves (from brain) and spinal nerves (from spinal cord).
Brain has 3 regions: forebrain, midbrain & hindbrain.
Forebrain is the main thinking part of the brain. It has the following regions:
o Sensory regions: which receive sensory impulses of hearing, smell, sight etc.
o Association areas: They interpret sensory information by associating with information from other receptors and previously stored information. Thus, a decision is made to respond. This information is passed to the motor areas which control the movement of voluntary muscles.
o Centre of hunger: It gives sensations such as feeling full when food is eaten.
In our body, there are involuntary actions between simple reflex actions and thought-out actions. We do not have thinking control on them. E.g. salivation, heartbeat etc. They are controlled by mid-brain and hind-brain.
Medulla in hindbrain controls involuntary actions such as blood pressure, salivation, vomiting etc.
Cerebellum in hindbrain controls voluntary actions like walking, riding a bicycle, picking up a pencil etc. It also maintains the posture and balance of the body.
When a nerve impulse reaches the muscle, the muscle fibres (muscle cells) move by changing their shape so that they shorten.
Muscle cells have special proteins that change their shape and arrangement in response to nervous electrical impulses. This gives the muscle cells a shorter form.
Voluntary muscles: The muscles attached to skeleton. They can be moved as we decide.
Involuntary muscles: The muscles found in visceral organs. They are not under our control.
Plants have no nervous system or muscles. But they can respond to stimuli.
Like animals, plants show 2 types of movement:
o Dependent on growth: E.g. When a seed germinates, root goes down and stem comes up.
o Independent of growth: E.g. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ of Mimosa family), they quickly fold up and droop.
In sensitive plant, movement happens at a point different from the point of touch. It means information about touch is communicated. Plants use electrical-chemical means to conduct information from cell to cell.
In animals, some muscle proteins help to change the shape of cells. But plant cells change the shape (swelling or shrinking) by changing amount of water in them.
Some plants (e.g. pea) have tendrils to climb up or fence. They are sensitive to touch.
When tendrils contact with a support, the touching part does not grow as rapidly as the part away from object. So, tendril circles around and clings to the object.
Plants respond to stimuli slowly by growing in a direction. Because of the directional growth, it appears as if the plant is moving.
Environmental triggers such as light, gravity etc. change the directions of plant growth. They are called tropic (directional) movements. These can be towards the stimulus (positive), or away from it (negative).
Types of tropic movements
It is the tropic movement in response to light.
Shoots respond by bending towards light (positive).
Roots respond by bending away from light (negative).
It can be proved by the following activity.
- Fill a conical flask with water and cover its neck with a wire mesh having 2-3 freshly germinated bean seeds.
- Keep the flask in a cardboard such that its open side faces light coming from a window.
- After 2 or 3 days, it is noticed that the shoots bend towards light and roots away from light.
- Now turn the flask so that shoots are away from light and roots towards light. Leave it for a few days.
- The old parts of the shoot and root have no noticeable change in direction. But new growth parts show change in direction. i.e., shoot bends towards light and roots bend away from it.
Movement in response to the pull of earth or gravity.
Roots always grow downwards (positive).
Shoots grow upwards and away from earth (negative).
The movement of a plant toward or away from water.
E.g. Roots bend towards the moist soil.
The movement of plant towards or away from chemicals.
E.g. growth of pollen tubes towards ovules.
Controlled movements can be either slow or fast. E.g.
o Sensitive plant quickly moves in response to touch.
o Sunflowers slowly move in response to day or night.
o Growth-related movements of plants are slower.
In animal bodies also have controlled directions to growth. E.g. growth of arms & fingers.
For fast responses to stimuli, information must be transferred very quickly. Electrical impulses are an excellent means for this. But it has some limitations:
o They reach only the cells having connection with nervous tissue.
o Once an impulse is generated and transmitted, the cell will take some time to reset its mechanism to generate a new impulse. So, cells cannot continually create and transmit electrical impulses.
So most multicellular organisms use chemical (hormone) communication between cells.
In this, stimulated cells release a hormone and it diffuses around the original cell. Other cells detect hormone using special molecules on their surfaces. Then they recognise information and transmit it.
This is slower process but can reach all cells and can be done steadily and persistently.
Plant hormones can coordinate growth, development and responses to the environment. They are synthesised at some places and diffuse to the area of action.
Some Plant Hormones
o Auxin: Regulates growth in plants. When plants detect light, auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. As a result, the cells on the shady side grow longer. Thus, the plant bends towards light.
o Gibberellins: Help in the growth of the stem.
o Cytokinins: Promote cell division. They are present in greater amount in areas of rapid cell division, such as fruits and seeds.
The above hormones help in promoting growth.
o Abscisic acid: Inhibits growth. Causes wilting of leaves.
Electrical impulses can instruct only few tissues to prepare for an activity. So, in animals, there is another way of control & coordination called Endocrine system.
It includes endocrine glands and their secretions called hormones (chemical signals). They can reach all cells and provide wide-ranging changes. E.g. Adrenal glands secretes adrenaline.
Adrenaline prepares body to cope with emergency situations. E.g. E.g. a scary animal such as squirrels prepare to fight or run away. It needs more energy.
Though fighting & running are different, both have some common preparations.
Adrenaline is secreted into blood and carried to different body parts. As a result, the following events occur:
o Heart beats faster to supply more oxygen to muscles.
o Blood to the digestive system and skin is reduced by contracting muscles around small arteries in these organs. This diverts the blood to skeletal muscles.
o Breathing rate increases due to the contraction of diaphragm and rib muscles.
These responses prepare the body to deal with the situation (fighting and running).
The timing and amount of hormone released are regulated by feedback mechanisms. E.g. if the blood sugar level increases, it is detected by cells of pancreas and produce more insulin. As the blood sugar level falls, insulin secretion is reduced.
SOME IMPORTANT HORMONES AND THEIR FUNCTIONS
Functions & other info
Stimulates pituitary gland to release hormones. E.g. growth hormone releasing factor stimulates pituitary gland to release GH.
Growth hormone (GH)
Stimulates growth & development of the body.
Dwarfism: Deficiency of GH in childhood.
Gigantism: Overproduction of GH in childhood.
Regulates carbohydrate, protein & fat metabolism for balanced growth.
Iodine is essential for synthesis of thyroxin. Iodised salts provide iodine.
Deficiency of iodine causes goitre. Swollen neck is the main symptom.
Regulates blood sugar level.
Deficiency of insulin causes diabetes (sugar level increases).
Such patients are given insulin injections.
Prepares body to cope with emergency situations.
Testes (in male)
Changes during puberty. Development of male sex organs, behaviour etc.
Ovaries (in female)
Changes during puberty. Development of female sex organs, regulates menstrual cycle, etc.