#. IMPORTANT QUESTIONS FOR GRADE 10TH LAST MINUTE REVISION FOR SCIENCE .
CBSE 10th exams are going on and your Science paper is on 2nd March 2024. You have only a few hours left for the Science exam.
Therefore, we have introduced students to the best last minute revision tool – the important Topic-Wise Most Important Questions!
This article is for you for CBSE Class 10 Science (Multiple Choice, Assertion-Reason, Case-Based Question, Conceptual Question, Short/Long Question) 4 or 5 marks questions are long answer type questions where students have to answer in the final. A detailed answer with additional information is required to score correctly.
In this, every important question has been sorted and collected, which is very important for your paper, so that the student can score good marks in less time. Answers to all the questions are given together.
CBSE Class 10th Science Important Questions 2023-24
Multiple Choice Question
1. In which of the following equations, the mass is not same on both the sides?
(a) Word equation
(b) Skeletal equation
(c) Balanced equation
(d) Both (a) and (b)
Ans. (d) Both (a) and (b)
2. Some reactions require conditions like specific temperature, pressure, etc. While writing chemical equations for such reactions, where are these conditions usually mentioned?
(a) Above the arrow
(b) Along with products
(c) Below the plus signs
(d) Before the reactants
Ans. (a) Above the arrow
3. On adding dilute HCl to copper oxide in a beaker, the solution turns blue green due to formation of
(a) copper(II) hydroxide
(b) copper nitrate
(c) copper (II) chloride
(d) copper sulphate
Ans. (c) copper (II) chloride
4. Calcium carbonate is the chemical formula of
(a) limestone
(b) chalk
(c) marble
(d) all (a), (b) and (c)
Ans. (d) all (a), (b) and (c)
5. Which among the following statements is incorrect for magnesium metal?
(a) It burns in oxygen with a dazzling white flame.
(b) It reacts with cold water to form magnesium oxide and evolves hydrogen gas.
(c) It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas.
(d) It reacts with steam to form magnesium hydroxide and evolves hydrogen gas.
Ans. (b) It reacts with cold water to form magnesium oxide and evolves hydrogen gas.
6. Upon receiving a signal, the dendrite tip of a nerve cell sets off a chemical reaction that
(a) creates an electrical impulse in the dendrite.
(b) creates an electrical impulse in the next neuron.
(c) releases some chemicals in the cell body of the neuron.
(d) creates a stimulus.
Ans. (a) creates an electrical impulse in the dendrite.
7. Dwarfism in human beings is caused due to deficiency of
(a) thyroxin
(b) growth hormone
(c) adrenalin
(d) insulin
Ans. (b) growth hormone
8. Which of the following statements is correct about receptors?
(a) Gustatory receptors detect taste while olfactory receptors detect smell.
(b) Both gustatory and olfactory receptors detect smell.
(c) Auditory receptors detect smell and olfactory receptors detect test.
(d) Olfactory receptors detect taste and gustatory receptors smell.
Ans. (a) Gustatory receptors detect taste while olfactory receptors detect smell.
9. In a flower, the parts that produce male and female gametes (germ cells) are
(a) stamen and anther
(b) filament and stigma
(c) anther and ovary
(d) stamen and style
Ans. (c) anther and ovary
10. Which of the following is the correct sequence of events of sexual reproduction in a flower?
(a) pollination, fertilisation, seedling, embryo
(b) seedling, embryo, fertilisation, pollination
(c) pollination, fertilisation, embryo, seedling
(d) embryo, seedling, pollination, fertilisation.
Ans. (c) pollination, fertilisation, embryo, seedling
11. In Spirogyra, asexual reproduction takes place by
(a) breaking up of filaments into smaller bits
(b) division of a cell into two cells
(c) division of a cell into many cells
(d) formation of young cells from older cells
Ans. (a) breaking up of filaments into smaller bits
12. Exchange of genetic material takes place in
(a) vegetative reproduction
(b) asexual reproduction
(c) sexual reproduction
(d) budding
Ans. (c) sexual reproduction
13. Which of the following statement is incorrect?
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene.
Ans. (d) For every molecule of fat there is a gene.
14. The maleness of a child is determined by
(a) the X chromosome in the zygote.
(b) the Y chromosome in zygote.
(c) the cytoplasm of germ cell which determines the sex.
(d) sex is determined by chance.
Ans. (b) the Y chromosome in zygote.
15. Humans have two different sex chromosomes, X and Y. Based on the Mendel's laws, a male offspring will inherit which combination of chromosomes?
(a) both the X chromosomes from one of its parents
(b) both the Y chromosomes from one of its parents
(c) combination of X chromosomes from either of its parents
(d) combination of X and Y chromosome from either of its parents
Ans. (d) combination of X and Y chromosome from either of its parents
16. Two lenses of power +2.50 D and -3.75 D are combined to form a compound lens. Its focal length in cm will be
(a) 40
(b)-40
(c) 80
(d) -80
Ans. (d) -80
17. As a ray of light entered medium P from medium Q, its velocity increased. What can be said about the refractive index of medium P as compared to that of the medium Q?
(a) It is lower.
(b) It is higher.
(c) It is the same.
(d) Nothing can be said without knowing what medium P and medium Q are.
Ans. (a) It is lower.
18. The full length image of a distant tall building can definitely be seen by using
(a) a concave mirror
(b) a convex mirror
(c) a plane mirror
(d) both concave as well as plane mirrors
Ans. (b) a convex mirror
19. The most rapidly dwindling natural resource in the world is
(a) water
(b) forests
(c) wind
(d) sunlight
Ans. (b) forests
20. The pH range most conducive for life of fresh water plants and animals is
(a) 6.5-7.5
(b) 2.0-3.5
(c) 3.5-5.0
(d) 9.0-10.5
Ans. (a) 6.5-7.5
21. Select the wrong statement.
(a) Forests provide variety of products.
(b) Forests have greater plant diversity.
(c) Forests do not conserve soil.
(d) Forests conserve water.
Ans. (c) Forests do not conserve soil.
22. Arabari forests of Bengal is dominated by
(a) Tea
(b) Sal
(c) Bamboo
(d) Mangroove
Ans. (b) Sal
23. Opposition to the construction of large dams is due to
(a) social reasons
(b) economic reasons
(c) environmental reasons
(d) all the above
Ans. (d) all the above
24. Bandharas and Tals are age old water harvesting concepts/structures found in
(a) Bihar
(b) Maharashtra
(c) Tamil Nadu
(d) Rajasthan
Ans. (b) Maharashtra
25. The major ill effect of mono culture practice in forests is on the
(a) biodiversity which faces large destruction
(b) local people whose basic needs can no longer be met from such forests
(c) industries
(d) forest department
Ans. (a) biodiversity which faces large destruction
26. The Reni village of Garhwal is famous for
(a) monocultures of pine, teak and eucalyptus
(b) Chipko Movement
(c) extensive biodiversity
(d) participation of local people in efficient management of forests
Ans. (b) Chipko Movement
27. A student studies that we should switch off unnecessary lights and fans in order to save the environment. How does switching off unnecessary electrical appliances help the environment?
(a) It reduces the wastage of energy
(b) It generates electricity when switched off
(c) It recycles the amount of energy used
(d) It increases the efficiency of the electrical appliances
Ans. (a) It reduces the wastage of energy
28. Which of these is an example of sustainable development in order to conserve natural resources for the future generation?
(a) cleaning water resources
(b) finding alternate fuel reservoirs
(c) clearing forests to set up new industries
(d) planning for safe disposal of wastes after mining
Ans. (d) planning for safe disposal of wastes after mining
Assertion-Reason Question
The following questions consist of two statements — Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
1. Assertion (A) : Brown fumes are produced when lead nitrate is heated.
Reason (R) Nitrogen dioxide gas is produced as a by product due to the decomposition of lead nitrate.
Ans. (a) Both A and R are true and R is the correct explanation of A.
2. Assertion(A)The acid must always be added to water with constant stirring.
Reason (R) Mixing of an acid with water decreases the concentration of H+ ions per unit volume.
Ans. (b) Both A and R are true but R is not the correct explanation of A.
3. Assertion (A) Cyton region of nerve fibre collects information for the brain.
Reason (R) Nerve fibres can either have or lack myelin sheath.
Ans. (a) Both A and R are true and R is the correct explanation of A.
4. Assertion (A) Animals can react to stimuli in different ways.
Reason (R): All animals have a nervous system and an endocrine system involving hormones.
Ans. (a) Both A and R are true and R is the correct explanation of A.
5. Assertion(4) The effect of auxin hormone on the growth of root is exactly opposite to that on a stem.
Reason (R) Auxin hormone increases the rate of growth in root and decreases the rate of growth in stem.
Ans. (c) A is true but R is false.
6. Assertion(A) Asexual reproduction is a primitive type of reproduction.
Reason (R) Asexual reproduction involves only mitotic cell division.
Ans. (a) Both A and R are true and R is the correct explanation of A.
7. Assertion (4): Clones are offspring of an organism formed by asexual reproduction.
Reason (R): Clones have exact copies of DNA as their parent.
Ans. (b) Both A and R are true but R is not the correct explanation of A.
8. Assertion(4) Pollen grains from the carpel stick to the stigma of stamen.
Reason (R): The fertilised egg cells grow inside the ovules and become seeds.
Ans. (d) A is false but R is true.
9. Assertion(A) Testes lie in penis outside the body.
Reason (R) Sperms require temperature lower than the body temperature for development.
Ans. (d) A is false but R is true.
10. Assertion(A) Light does not travel in the same direction in all the media.
Reason (R): The speed of light does not change as it enters from one transparent medium to another.
Ans. (c) A is true but R is false.
11. Assertion(4) Mirror formula can be applied to a plane mirror.
Reason (R): A plane mirror is a spherical mirror of infinite focal length.
Ans. (a) Both A and R are true and R is the correct explanation of A.
12. Assertion (4): Refractive index has no units.
Reason (R) The refractive index is a ratio of two similar quantities.
Ans. (a) Both A and R are true and R is the correct explanation of A.
13. Assertion(A) Dams cause discontentment among people.
Reason (R) Local people are alienated from their land without adequate compensation.
Ans. (a) Both A and R are true and R is the correct explanation of A.
14. Assertion(A) : Natural resources need to be used carefully.
Reason (R) : Resources are finite in supply and human population is tremendously increasing.
Ans. (a) Both A and R are true and R is the correct explanation of A.
Case-Based Question
PASSAGE-1
Oxidation is the process of gaining of oxygen, or losing of hydrogen. Reduction is the process of losing of oxygen or gaining of hydrogen. The substance which undergoes oxidation is the reducing agent while the substance which undergoes reduction is known as the oxidising agent. Oxidation and reduction always take place together and these types of reactions are known as redox reactions. Some of the examples of redox reactions are given below:
(i) Which of the following is an oxidising agent?
(a) LiAlH4
(b) Alkaline KMnO4
(c) Acidified K2Cr2O7
(d) Both (b) and (c)
Ans. (i) (d); Alkaline KMnO4 and acidified K,Cr₂O7 both act as oxidizing agents.
(ii) The reducing agent in the reaction IV and V is
(a) Fe and V₂O5
(b) Ca and Fe
(c) H₂O and Ca
(d) V and H₂O
Ans. (b); Since Ca and Fe is gaining oxygen in the reaction IV and V respectively, i.e., they are undergoing oxidation and therefore they act as reducing agent.
(iii) If hydrogen gas is passed over CuO, then the colour of the product formed is
(a) brown
(b) yellow
(c) green
(d) blue
Ans. (a); If hydrogen gas is passed over CuO, the opposite reaction takes place. The black coating turns brown and copper is obtained.
(iv) Out of the examples shown in the table which of the redox reactions is also a combination reaction?
(a) I
(b) II
(c) III
(d) IV
Ans. (b); Since Mg is combining with O2 to form MgO so it is a combination reaction.
PASSAGE-2
The pH of a solution is a measure of its hydrogen ion (H*) concentration. It is measured generally using pH scale. The values on pH scale ranges from 0 to 14. A pH of 1 is very acidic and corresponds to a high concentration of H+ ions. A pH of 14 is very basic and corresponds to a low concentration of H+ ions. The pH of a neutral solution is 7. The table given below shows the pH and H+ ion concentration of some common aqueous solutions. The leftmost column shows the number of moles of H+ ions in 1 mole of liquid.
(i) How is the hydrogen ion concentration and pH related to each other?
Ans. (i) pH is inversely proportional to the hydrogen ion concentration.
(ii) On the basis of above table, arrange the following in the decreasing order of H* concentration. Pure water, tomato juice, milk of magnesia, sea water
Ans. The decreasing order of H+ concentration is Tomato juice > Pure water > Sea water > Milk of magnesia
(iii) A solution of pH 2 is filled in two separate beakers. A few drops of methyl orange and phenolphthalein are added into separate solutions. How will the colour of the indicators change?
PASSAGE-3
(i) Name two metals that react violently with cold water.
Ans. Metals like potassium and sodium react violently with cold water.
Ans. Since element X forms an oxide which is basic in nature and therefore 'X' is a metal.
(iii) What happens to the red litmus when it is treated with the solution of ash obtained after burning magnesium ribbon in air?
PASSAGE-4
When we touch the leaves of a chhui-mui ('touch-me-not' plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down and the stem comes up in the air. Plants show two different types of movements - one dependent on growth and the other independent of growth. The plants also use electrical-chemical means to convey information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information. In animals some cells must change shape in order for movement to happen. Instead of the specialised proteins found
in animal muscle cells, plant cells change shape by changing the amount of water in them resulting in swelling or shrinking and therefore changing shapes. More commonly, plants respond to stimuli slowly by growing in a particular direction. Because this growth is directional, it appears as if the plant is moving.
(i) The movement in a plant caused as a result of differential growth is called
(a) tactic movement
(b) tropic movement
(c) turgor movement
(d) growth movement
Ans. (d); Plant movement is of two types: growth movement and turgor movement. Growth movement occurs by differential growth of plants while turgor movement is caused by changes in turgidity of the cells.
(ii) The figure given below represents the types of plant movements.
Identify X, Y, Z and choose the correct option.
(a) X-Haptotropism, Y-Chemotropism and Z-Geotropism
(b) X-Chemotropism, Y-Hydrotropism and Z-Geotropism
(c) X-Geotropism, Y-Haptotropism and Z-Hydrotropism
(d) X-Phototropism, Y-Hydrotropism and Z-Geotropism
Ans. (b); In the given figure, X, Y and Z represents chemotropism, hydrotropism and geotropism respectively.
(iii) Choose the incorrect combination of information provided in the following table.
Ans. Ans. (b); The folding or drooping of leaves of 'touch-me-not' plants is growth independent movement.
(iv) Which of the following is a tropic movement?
(a) Response of plant to touch
(b) Movement due to change in temperature
(c) Movement induced by the change in the light intensity
(d) Response of plants to gravity
Ans. (d); Response to gravity is geotropism. Hence, it is a tropic movement.
PASSAGE-5
Reflex action is a rapid, automatic response to a stimulus which is not under the voluntary control of the brain. Thus, a reflex action is the one which we perform automatically. It is a comparatively simple form of behaviour in which the same stimulus produces the same response every time. If we unknowingly touch a hot plate, we immediately move our hand away from it. Moving our hand away on touching a hot plate is an example of reflex action. In a reflex action, we are unaware of what is going to happen to us and are done without thinking. How do we respond to it? We respond to it by the process of detecting the signal or the input and responding to it by an output action. Such a connection is commonly called a reflex arc. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain.
(i) Reflex arc consists of
(a) motor nerve
(b) sensory nerve
(c) both motor and sensory nerve
(d) mixed nerve
Ans. (c); Reflex arc is a neural pathway that controls the reflex. It includes sensory nerve and a motor nerve with a synapse in between.
(ii) The given figure represents the path of message from the receptor to the effector.
In the given figure, identify "X" and its function.
(a) It is a sensory neuron that carries the message from the receptor to the central nervous system.
(b) It is a motor neuron that carries the message from the central nervous system to the effector.
(c) It is a sensory neuron that carries the message from the central nervous system to the effector.
(d) It is a motor neuron that carries the message from the receptor to the central nervous system.
Ans. (a); In the given figure, "X" is a sensory neuron that carries the message from the receptor to the central nervous system (the spinal cord and brain).
(iii) The following stages occur in a reflex action:
1. Receptor detects a stimulus
2. Sensory neuron sends impulses to relay neuron
3. Effector produces a response
4. Motor neuron sends impulses to effector
The correct order of the stages is:
(a) 2, 3, 4, 1
(c) 1, 2, 4, 3
(b) 2,1,4,3
(d) 3, 4, 1, 2
Ans. (c)
(iv) Which of the given pair of activities doesn't come under reflex action?
(a) Salivation and blinking of eyes
(b) Salivation and sweating
(c) Sweating and breathing
(d) Salivation and coughing
Ans. (c); An automatic (involuntary) neuromuscular action excited by a defined stimulus is called reflex action. Sweating and breathing are not reflex actions.
PASSAGE-6
The sexual act is a very intimate connection of bodies so that may lead to transmission of many diseases. Is it possible to prevent the transmission of such disease? The sexual act always has the potential to lead to pregnancy. Is there any way to avoid pregnancy? It is possible via surgery but this method may be misused by people who do not want a particular child. As reproduction leads to increase in population size, the size of the human population is a cause of concern for many people.
(i) Vasectomy is
(a) also called tubectomy
(b) a method of preventing the passage of eggs
(c) a method of blocking the continuity of oviduct
(d) a method of sterilisation in human males
Ans. (i)—(d); Vasectomy is a surgical procedure for male sterilisation and is a permanent form of contraception.
(ii) The given graph indicates the percentage of widely used postpartum contraceptive methods among women of a country.
Out of the given methods, how many are the natural family planning method?
(a) 7
(b) 3
(c) 8
(d) 1
Ans. (b); Out of the given methods, there are three natural family planning methods and those are periodic abstinence (fertility awareness) method, use of breastfeeding or lactational amenorrhoea method (LAM), coitus interruptus (withdrawal or pulling out) method.
(iii) Which of the following statement(s) is (are) true about reproductive health of humans?
I. Condoms serve the role of mechanical barrier in pregnancies.
II. The copper-T are placed in the uterus to prevent ovulation.
III. If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus.
IV. Surgery cannot be used for removal of unwanted pregnancies.
(a) I and II only
(b) II and III only
(c) I and III only
(d) I, III and IV only
Ans. (c); Copper-T prevents pregnancy by disrupting the process of conception and unwanted pregnancies can be removed via surgery.
(iv) Study the table below and select the row that has the incorrect information.
Ans. (c); A condom acts as a physical barrier that prevents sperm from entering the uterus and reaching an egg.
PASSAGE-7
The atmosphere is a blanket of air and a precious natural resource for sustaining life on the Earth. Unfortunately, human activities based on national/personal interests are causing harm to this common resource, notably by depleting the fragile ozone layer, which acts as a protective shield for life on the Earth. Ozone molecules consist of three oxygen atoms. Ozone molecules are exceeding rare: fewer than ten in every million molecules of air. However, for nearly a billion years, their presence in the atmosphere has played a vital role in safeguarding life on Earth. The ozone in the troposphere (up to 110 kilometres above the Earth's surface) is 'bad' ozone which can damage lung tissues and plants. But about 90 per cent of ozone found in the stratosphere (between 10 and 40 kilometres above the Earth's surface) is "good" ozone which plays a beneficial role by absorbing dangerous ultraviolet (UV-B) radiations from the Sun. Without this beneficial ozone layer, humans would be more susceptible to certain diseases due to the increased incidence of ultraviolet rays from the Sun.
(i) Ozone is also formed during thunderstorms. It causes the typical smell after such a storm. Is the ozone formed during thunderstorm 'bad ozone' or 'good ozone?? Give reason.
Ans. (i) It is bad ozone' as it is formed in the troposphere.
(ii) How can increased incidence of ultra-violet rays harm humans?
Ans. (ii) It can cause skin cancer and snow-blindness.
(iii) What destructive effect do chlorofluorocarbons bring about in the atmosphere? Name any two sources of chemicals that are said to deplete ozone.
Ans. (iii) CFCs deplete ozone from ozone shield, resulting in increasing the passage of harmful ultraviolet radiation to the Earth. Nuclear weapons; fertilisers releasing nitrous oxides (N2O).
PASSAGE-8
Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in extinction of a species in some cases. The foundation of the food chain consists of primary producers. Primary producers, or autotrophs, can use either solar energy or chemical energy to create complex organic compounds, whereas species at higher trophic levels cannot and so must consume producers or other life that itself consumes producers. Because the sun's light is necessary for photosynthesis, most life could not exist if the sun disappeared. Even so, it has recently been discovered that there are some forms of life, chemotrophs, that appear to gain all their metabolic energy from chemosythesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive.
(i) If 10,000 J solar energy falls on green plants in a terrestrial ecosystem, what percentage of solar energy will be converted into food energy?
(a) 10,000 J
(b) 100 J
(c) 1000 J
(d) It will depend on the type of the terrestrial plant.
Ans. (b); 100 J
(ii) Mr. X is eating curd/yogurt. For this food intake in a food chain he should be considered as occupying
(a) First trophic level
(b) Second trophic level
(c) Third trophic level
(d) Fourth trophic level
Ans. (c); Third trophic level
(iii) The decomposers are not included in the food chain. The correct reason for the same is because decomposers:
(a) Act at every trophic level of the food chain.
(b) Do not breakdown organic compounds.
(c) Convert organic material to inorganic forms.
(d) Release enzymes outside their body to convert organic material to inorganic forms.
Ans. (a); Act at every trophic level of the food chain
(iv) Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy in higher trophic levels
(b) Less availability of food
(c) Polluted air
(d) Water
Ans. (a); Decrease in energy at higher trophic levels
PASSAGE-9
Wherever we look, we find plastics-be it a food packet, a toy, storage packing, any furniture or an electronic item. According to UN estimates, every year the world uses 500 billion plastic bags and half of this plastic is single-use plastic such as plastic bags, straws, cups, plates and bottles. Plastic is currently the biggest environmental concern. Plastic waste takes a lot of time to decompose naturally. It is harmful for animals who might eat it and can cause severe air pollution on burning. In oceans, pollution is mainly caused due to plastic wastes. Each year, at least eight million tonnes of plastic wastes are released into the oceans which means a full garbage truck every minute. This is damaging the marine life and also threatening human health.
(i) Why has there been huge hue and cry against the use of single-use plastics?
Ans. Single-use plastic is non-biodegradable in nature and thus, harmful to the environment.
(ii) The pH of ocean water as measured using pH paper is found to be 5. What does this pH tell us about the ocean water?
Ans. The pH 5 tells us that ocean water has become highly acidic.
(iii) Based on the data shown in the graph that follows, which industrial sector produces the most plastic waste? Suggest the alternative that can be used in place of plastic in this sector? 2
Ans. Packaging sector produces the maximum plastic waste. Paper and cardboard can be used in place of plastic in this sector as these are reusable, recyclable and biodegradable.
PASSAGE-10
Disposal of solid waste materials has become one of the key environmental challenges in almost all major cities of the world. Changes in lifestyles and attitude of humans have resulted in greater amount of waste material particularly in urban areas. Municipal corporations and other local authorities have adopted different mechanisms to meet the emerging challenges.
(i) Recycling of paper is a good practice but recycled paper should not be used as food packaging because
(a) recycled papers take lots of space
(b) recycled papers can't cover food properly
(c) recycled papers can cause infection
(d) recycled papers are costly
Ans. (c) Recycle papers can cause infection due to release of methane.
(ii) According to the 'Solid Waste Management Rule 2016', the waste should be segregated into three
Ans. 
(iii) The given graph shows the amount of waste generated, dumped and treated in percentage. Identify the reason of low success rate of waste management process.
(a) only 15% of urban India's waste is processed
(b) less than 60% of waste is collected from households
(c) more than 60% of waste is collected from households
(d) both (a) and (b)
Ans. (d)
Very Short Answer Question
Q. 1. What does the word aqueous (aq) represent in a chemical reaction?
Ans. It represents that the compound is present as a solution in water.
Q. 2. Two solutions X and Y have pH values of 3.0 and 9.5 respectively. Which of these will turn litmus solution from blue to red and which will turn phenolphthalein from colourless to pink?
Ans. X will turn blue litmus to red because it is acidic in nature having pH value less than 7. Y will turn phenolphthalein from colourless to pink because it is basic in nature having pH value greater than 7.
Q.3. Which hormone regulates the concentration of sugar in the blood?
Ans. Insulin secreted by islets of Langerhans of pancreas.
Q. 4. What is the function of pollen grains in flowers?
Ans. Pollen grains are the male gametes which fertilise the egg cell present in the ovule of a flower.
Q. 5. Explain the role of cotyledon and plumule in germination.
Ans. Cotyledon stores food and the plumule acts as future shoot.
Q. 6. What is menopause?
Ans. The period of permanent cessation of menstruation in females, usually occurring between the age of 45 and 50 is called as menopause.
Q. 7. What is syngamy?
Ans. One male gamete fuses with one female gamete or egg. This process of fusion of male and female nuclei is called syngamy.
Q. 8. Define alleles.
Ans. Genes which code for a pair of contrasting traits are known as alleles, i.e., they are the different forms of the same gene.
Q.9. Which of the following traits are recessive in pea plant? Dwarfness, violet flower, wrinkled seed.
Ans. Dwarfness and wrinkled seeds are the recessive characters.
Q. 10. Give reasons for the appearance of new combinations of characters in the F₂ progeny.
Ans. The tall/short and round/wrinkled seed trait are independently inherited.
Q. 11. What is light?
Ans. Light is a form of energy which gives us the sensation of sight or vision.
Q. 12. We often use the word environment. What does it mean?
Ans. Environment is the physical, chemical and biological conditions of the region.
Q. 13. Name the award given in the memory of Amrita Devi Bishnoi.
Ans. Amrita Devi Bishnoi award for wildlife conservation
Q. 14. What are biodiversity hotspots?
Ans. Biodiversity hotspots: are regions rich in biodiversity.
Long Answer Question
Q.1. (i) Crystals of copper sulphate are heated in a test tube for some time.
(a) What is the colour of copper sulphate crystals before heating, and after heating?
(b) What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process?
(ii) A metal 'X' when dipped in aqueous solution of aluminium sulphate, no reaction is observed whereas when it is dipped in an aqueous solution of ferrous sulphate, the pale green solution turns colourless. Identify metal 'X' with reason.
Ans. (i) (a) The colour of copper sulphate crystals before heating is blue and turns white after heating.
(b) The liquid droplets are actually the water droplets. The source of water droplets is the water of crystallisation of hydrated copper sulphate crystals (CuSO4.5H2O).
(ii) When metal 'X' is dipped in aqueous solution of aluminium sulphate no reaction is observed, it means it is less reactive than aluminium. But when it is dipped in ferrous sulphate solution, the solution turns from pale green to colourless, so 'X' is more reactive than iron and thus displaces it from its solution. Therefore, 'X' must be zinc. It reacts with ferrous sulphate to form colourless zinc sulphate solution by displacing iron.
Zn(s) + FeSO4(aq) → ZnSO4(aq) + Fe(s)
Q. 2. Which two metals do not corrode easily? Give an example in each case to support that
(i) corrosion of some metals is an advantage.
(ii) corrosion of some metals is a serious problem.
Ans. Gold and platinum.
(i) A thin impervious layer of aluminium oxide forms a protective layer which protects the aluminium metal underneath from further damage.
(ii) Corrosion of iron is a serious problem. Every year enormous amount of money is spent to replace damaged iron and steel structures.
Q. 3. Differentiate between tropic and nastic movements in plants.
Ans. 
Q. 4. Which hormone is released into the blood when its sugar level rises? Name the organ which produces the hormone and describe its effect on blood sugar level. Also name one digestive enzyme that this organ secretes and the function of this enzyme.
Ans. Ans. Insulin hormone is released into the blood when its sugar level rises. Pancreas secretes the insulin hormone. The function of insulin hormone is to lower the blood sugar level. Deficiency of insulin hormone in the body causes a disease known as diabetes. Diabetes is characterised by large quantities of sugar in the blood. The insulin hormone controls the metabolism of sugar. If due to some reason pancreas does not produce and secrete sufficient amount of insulin into blood, then the sugar level in the blood rises. The high sugar level in the blood can cause many harmful effects to the body of person. The person having severe diabetes are treated by giving injection of insulin. The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins, lipase for breakdown of emulsified fats and amylase for breakdown of starch.
Q. 5. Name various plant hormones. Also give their physiological effects on plant growth and development.
Ans. The various functions performed by the plant hormones are:
(i) Auxins promote cell enlargement and cell differentiation. They also promote growth.
(ii) Gibberellins promote cell enlargement and cell differentiation in the presence of auxin. It also help in breaking the dormancy in seeds and buds. It promote the growth in fruits.
(iii) Cytokinins promote cell division and help in breaking the dormancy of seeds and buds. It delays the ageing in leaves. It promotes the opening of stomata and also fruit growth.
(iv) Abscisic acid promotes the dormancy in seeds and buds. It promotes the closing of stomata and falling of leaves. It also inhibits growth, reverses the growth promoting effects of auxins and gibberellins. Its effects include wilting of leaves.
(v) Ethylene promotes the falling of leaves, ripening of fruits and helps in breaking bud dormancy.
Q.6. What are reflex actions? Give two examples. Explain a reflex arc.
Ans. A reflex action is defined as a spontaneous, automatic and mechanical response to a stimuli without the will of an individual. In such actions there i no involvement of the brain. All reflex actions are conveyed through the spinal cord by a path called reflex arc. The reflex action travels in the following sequence:
The reflex arc constitutes the following components:
(1) A receptor to perceive the stimulus.
(ii) A sensory or afferent nerve which carries the message from the receptor to the spinal cord.
(iii) The neurons of spinal cord transmit the impulse from afferent neurons to efferent neurons.
(iv) The motor or efferent nerve carries messages from spinal cord to the muscles (effectors) that show the response.
Some examples of reflex actions are:
(i) Blinking of eyes when a foreign particle gets in them.
(ii) Sneezing if an unwanted particle enters the nose.
(iii) Watering of mouth at the sight or smell of good food.
(iv) Withdrawal of foot if a nail comes in the way while walking and pricks the foot.
(v) Immediate withdrawal of hand on touching some hot thing.
Q. 7. Give the basic features of the mechanism of inheritance.
Ans. (i) Characters are controlled by genes.
(ii) Each gene controls one character.
(iii) There may be two or more forms of gene.
(iv) One form may be dominant over the other.
(v) Genes are present on chromosomes.
(vi) An individual has two forms of gene whether similar or dissimilar.
(vii) The two forms separate from each other at the time of gamete formation.
(viii) The two forms are brought together in the zygote.
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