10        Living Creatures: Exploring
Chapter
                                          their Characteristics
                       Avadhi and Aayush go for a morning walk with their parents.
                       Avadhi notices some shells and tries to pick them up. Her
                       mother advises her not to do so and explains that the shell
                       could be home to a living snail and is actually a part of its
                       body. Avadhi and Aayush wonder how the shell that is not
                       even moving could have a living being inside! Later that
                       day in school, Avadhi and Aayush share this incident with
                       their friends. They approach the teacher to understand how
                       a shell which is not even moving could be a body part of a
                       living snail. The teacher initiates a discussion in the class on
                       living and non-living.
Chapter 10.indd 183                                                                       10-07-2024 18:21:03
                                                       Activity 10.1: Let us record
                                                       We are surrounded by numerous things. Just look around
                                                       in your classroom and you may find many examples—the
                                                       pencil that you are holding, the book that you are reading or
                                                       the pigeon near the window.
                                                        List them in Table 10.1 and identify each of them as
                                                           living or non-living on the basis of your understanding
                                                           in column II.
                                                           Write a reason for grouping them as living or non living
                                                             in column III.
                                                              Table 10.1: Living beings and non-living things in our
                                                                                   surroundings
                                                             (I)         (II)         (III)      (IV)         (V)
                                                                      My guess                              Reason/
                                                                      (Living/     Reason/     Correct    Remarks for
                                                            Name
                                                                        Non-       Remarks     answer     the correct
                                                                       living)                              answer
                                                            Pencil    Non-living
                                                            Book
                                                            Pigeon      Living
                                                             Car
                                                            Plant
                                                        Any other
                                                       10.1 What Sets the Living Apart from the
              Curiosity | Science Textbook | Grade 6
                                                            Non-living?
                                                       Look at Table 10.1. Why do you think a pencil is non-living
                                                       but a pigeon is living? What do you think are the differences
                                                       between living beings and non-living things according to
                                                       you? What similarities do the identified living beings share
                                                       with each other?
                                                          You may have identified movement as one of the
                                                       similarities among living beings. You have also seen cars
                                                       moving on a road. Does it mean that a car is living? List the
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                      tasks that you can do but a car cannot. You are a wonderful
                      example of a living being. Whenever you attempt to group
                      things around you as living or non-living, you can compare
                      them with yourself. Which characteristics help you in
                      differentiating yourself from a car? For instance, a car
                      does not grow. Does it mean it is non-living? Now, which
                      characteristics have you used to classify a car as non-living?
                      Continue your discussion in a similar way to identify the
                      essential characteristics of living beings.
                          What are some common characteristics that make living
                      beings very different from the non-living things? Let us
                      learn about them.
                          Can we consider movement as one of the characteristics to
                      differentiate between the living and the non-living? List five
                      things around you that can move on their own. Do you think
                      that all five things that you have listed can be considered as
                      living just because they can move on their
                      own? However, unlike animals, plants do
                      not move from one place to another. Do
                      you consider them as living?
                          Even though plants do not move from
                      one place to another, they do show certain
                      types of movements. Opening of flowers is
                      one of the examples of movement in plants.
                      Another example of movement in plants is
                      seen in insectivorous plants. Insectivorous                Drosera
                      plants are dependent on insects for their nutrition. Drosera
                      is one of the examples of an insectivore. Drosera is
                      featured with saucer-shaped leaves having many hair-like
                      projections of unequal length with sticky ends. Whenever
                      an insect enters the saucer, hairs move inward and
                                                                                           Living Creatures: Exploring their
                      trap the insect with their sticky ends. Try to observe
                      the mechanism of movement in other insectivorous
                      plants. Climbers also wind themselves around
                      any object placed close to them. That means,
                                                                                           Characteristics
                      even though plants do not move from
                      one place to another, they do show
                      some movements.
                          Compare yourself with the
                      picture of your childhood. Can you              Growth of a child
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                                                                  wear the dress that you used to wear four years ago? No,
                                                                  because you have become larger in size. This is due to growth
                                                                  in your body. Plants and other living beings also grow. Can
                                                                  we consider growth as a characteristic of living beings?
                                                                      Living beings need food (nutrition) for their growth
                                                                  and development. List five living beings that require food
                                                                  to grow.
                                                                      Now, think of a process without which we cannot live.
                                                                  Count the number of breaths you take per minute after
                                                                  a normal walk, after a run, and after a few dance steps.
                                                                  Record the data and observe. Do you notice any difference
                                                                  in the number of breaths after each situation? Do you notice
                                                                  the process of breathing in other animals like dogs, cats,
                                                                  cows and buffaloes? Notice the movement of their abdomen
                                                                  while they are taking rest.
                                                                      In the process of breathing, when we inhale, the air
                                                                  moves from outside to inside our body. When we breathe
                                                                  out, the air moves from inside our body to outside.
                                                                  Breathing is part of a process called respiration. Do
                                                                  plants also respire? There are tiny pores called stomata
                                                                  on the surface of leaves. These pores help plants in taking
                                                                  air in and out. Interact with senior class students in your
                                                                  school and request if they can demonstrate stomata using
                                                                  a microscope in your class. All living beings respire.
                                                                      Have you noticed white patches forming on shirts around
                                                                                    the armpits during summers? These
                                                                                    patches are formed due to sweat. The
                                                                                    sweat consists of water and salts removed
                                                                                    by the body as waste products. Removal
              Curiosity | Textbook of Science | Grade 6
                                                                                    of waste products from the body is called
                                                                                    excretion. Urine is also formed as a
                                                                                    product of excretion in animals. Do you
                                                                                    know that plants also excrete? You may
                                                                                    notice plants excrete excess water and
                                                                                    minerals in the form of small droplets on
                                                                                    leaves. For example, grasses and roses. All
                                                                                    living beings excrete.
                                                                                        Let us look at another characteristic.
                                                                                    What is your reaction if you unexpectedly
                                                          Water droplets on grass   step on a sharp object, such as a thorn,
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                      while walking without shoes, or you accidentally touch a hot
                      cup of tea? Stepping on a thorn and touching a hot object are
                      stimuli. Any thing or any event that prompts living beings
                      to respond is called a stimulus. List three stimuli (plural
                      of stimulus) and your body’s
                      instant response to them.
                          Do plants also respond to
                      stimuli? Yes, plants also respond
                      to stimuli. For example, touch-
                      me-not (mimosa, chhui-mui,
                      lajjalu) plants fold their leaves
                      when we touch them. Have you
                      also observed that certain plants
                      fold their leaves after sunset?
                      Specifically, the leaves of certain
                      plants facing each other tend
                      to come together. This can be
                      observed in the sleeping leaves          Touch-me-not (chhui-mui) plant
                      of amla (Indian gooseberry)
                      tree. All living beings respond to stimuli. Find a few more
                      plants in your neighbourhood which fold their leaves after
                      sunset.
                          Why do the leaves of chhui-mui and amla plants respond
                      in this way? Which stimulus could be responsible for their
                      behaviour?
                          Have you seen young ones of cats, dogs or other animals?
                      List young ones of five different animals. Have you seen
                      young ones of any non-living things such as a pencil, a chair
                      or an electric bulb?
                          All living beings reproduce. Reproduction is the
                      process of producing new ones of one’s own kind. Why is
                                                                                                Living Creatures: Exploring their
                      reproduction necessary? It is necessary for the continuity
                      of life.
                          When a living being is not able to exhibit all of the above
                      mentioned characteristics, despite the availability of all
                                                                                                Characteristics
                      resources (like food, air and water) needed for being alive,
                      it is said to be dead.
                          From the above discussion, we can understand that
                      all living beings share some common characteristics. For
                      example, all living beings show movement, they need
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                                                            food, and they grow. They also respire, reproduce, excrete,
                                                            respond to stimuli, and eventually, die. Absence of any of
                                                            these features indicates that they are non-living things.
                                                                Now that you know how to identify a living being, fill
                                                            up the remaining two columns (IV and V) of Table 10.1 and
                                                            complete the activity.
                                                                In which category would you place a seed—living or non-
                                                            living? Why?
                                                                Let us explore how a seed germinates to observe some
                                                            of these essential characteristics in plants.
                                                            10.2 Essential Conditions for Germination
                                                                 of a Seed
                                                            Have you observed a seed germinating? You might have
                                                            wondered what conditions are required for germination
                                                            of a seed. What conditions do you think are required for
                                                            seed germination? How will you investigate whether these
                                                            conditions have an effect on the germination of a seed?
                                                            Let us find out by performing Activity 10.2.
                                                            Activity 10.2: Let us experiment
                                                               Take four identical pots filled with garden soil. Sow
                                                                 four bean seeds in each pot. Now, keep these pots in the
                                                                 following conditions for 15 days.
                                                                    Pot A: Do not water the soil. Place this pot in direct
                                                                      sunlight.
              Curiosity | Textbook of Science | Grade 6
                                                           (a) Pot A kept in    (b) Pot B kept in     (c) Pot C with     (d) Pot D with moist
                                                          direct sunlight, no    direct sunlight,     moist soil, kept    soil, kept in direct
                                                                 water            excess water         in the dark              sunlight
             188                                                          Fig 10.1: Bean seeds exposed to different conditions
Chapter 10.indd 188                                                                                                                              10-07-2024 18:21:13
                                Pot B: Add excess water to the soil such that water
                                  is always present above the soil. Keep adding water
                                  on a regular basis if water reduces. Place this pot in
                                  direct sunlight.
                                Pot C: Keep the soil in this pot slightly moist by adding
                                  a moderate amount of water on a regular basis. Place
                                  this pot in a dark location.
                             Pot D: Maintain the soil in this pot slightly moist by
                               adding a moderate amount of water on a regular
                               basis. Place this pot in direct sunlight.
                           Indicate the availability of air, sunlight and water for
                             the seeds in each of these cases in Table 10.2.
                           When a seed turns into a sprout, it is said to have
                             germinated. Predict whether the seeds in each pot will
                             germinate. Record your predictions for each pot kept
                             under different conditions in Table 10.2.
                                   Table 10.2: Effect of certain conditions on seed germination
                                                                                                   Possible
                           Pot with
                                                                              Seed                  reason
                            bean               Availability of
                                                                           germination              for the
                            seeds
                                                                                                 observation
                                         Air     Sunlight    Water    Prediction   Observation
                      A: In direct                               No
                      sunlight
                      and without
                      water
                      B: In direct
                      sunlight
                                                                                                               Living Creatures: Exploring their
                      and excess
                      water
                      C: In
                      complete
                      dark and
                                                                                                               Characteristics
                      moist soil
                      D: In direct
                      sunlight
                      and moist
                      soil
                                                                                                                   189
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                                                                         Regularly observe the pots for 7-10 days to check
                                                                           the status of germination of the seeds. Record your
                                                                           observations in Table 10.2.
                                                                       Compare your predictions with your observations.
                                                                          Do you think sunlight is necessary for germination of
                                                                      seeds? Do the seeds in all the pots receive air, water and
                                                                      sunlight? Is there any pot in which air is not available to the
                                                                      seeds? If so, why is it not available? What happens to the
                                                                      seeds in the pot where water is provided in excess? Which
                                                                      seeds receive both air and water? Identify the pots where
                                                                      you can notice the germination of seeds.
                                                                          Do your observations match with your predictions?
                                                                      Write possible reasons in favour of your observations in
                                                                      Table 10.2. Based on your observations, state the conditions
                                                                      which favour seed germination.
                                                                          Which of the following are essential for seed germination–
                                                                      air, water and sunlight? Compare the available conditions
                                                                      in each pot. Germination of bean seeds requires the right
                                                                      amount of water and air. Why do seeds require these
                                                                      conditions for germination? Do you think that the absence
                                                                 Seed Coat         of one or more of these conditions will affect
                                                                                   seed germination?
                                                          Embryo                      Let us understand how these conditions help
                                                                                   in seed germination. The effects of the following
                                                                                   conditions have been seen in Activity 10.2.
                                                                                      Water: Seeds require water for germination.
                                                                                   Water enables the seeds to carry out the
                                                                                   processes necessary for their growth. The outer
              Curiosity | Textbook of Science | Grade 6
                                                                                   covering of the seed is called seed coat. Water
                                                                                   softens the seed coat and helps the tiny embryo
                                                           Germinated bean seed
                                                                                   inside it to develop into a plant.
                                                                          Air and Soil: Seeds need air for germination. They use the
                                                                      air available in the spaces between soil particles. Moreover,
                                                                      spaces between the soil particles allow roots to grow easily.
                                                                          Light and/or dark conditions: We have learnt that for
                                                                      the bean seeds, presence of light is not essential for their
                                                                      germination. In general, most seeds do not require light for
                                                                      germination. But after germination, sunlight is required for
                                                                      further growth of the seedling.
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                                     Some seeds of flowering plants, like Coleus and
                                     Petunia, require light to germinate. Covering
                                     these seeds with soil inhibits their sprouting.
                                     Seeds of flowering plants, like Calendula and
                                     Zinnia, need darkness to germinate. These seeds
                           Do you
                                     should be covered with sufficient soil.
                           know?
                         In the Chapter ‘Mindful Eating: A Path to a Healthy Body’,
                      you have learnt that human beings need a balanced diet
                      for good health and proper growth. Similarly, plants too
                      need favourable conditions and nutrients
                      for their proper growth and development.
                      What other conditions do you think would           How would you
                                                                                              ?
                      affect seed germination?                           now categorise a
                         In Activity 10.1, what are the                  seed, as living or
                      characteristics of living beings which             non-living?
                      made you place plants in living beings? Do
                      plants show growth in Activity 10.2? Are
                      there any other characteristics of living
                      beings that these plants show?
                         Let us study another characteristic that can be seen
                      clearly in plants—growth and movement.
                      10.3 Growth and Movement in Plants
                      How do plants respond to sunlight? Does sunlight affect the
                      direction of growth of different parts of plants? In which
                      direction would the root and shoot of a plant grow and
                      move if the plant is placed inverted? How would you design
                      an activity to find answers to these questions?
                                                                                                  Living Creatures: Exploring their
                      Activity 10.3: Let us design
                          Take some bean or gram seeds and allow them to
                            germinate on a moist cloth or a moist tissue paper.
                                                                                                  Characteristics
                          Let them germinate until each of them develop into a
                            seedling having a small root and a small shoot.
                          Now, take three glass beakers or tumblers, and label
                            them as A, B and C.
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                                                                         Take three glass plates and attach a thick blotting paper
                                                                           to one side of each plate using a thick soft cotton thread.
                                                                         Fix one seedling on each plate using a thick soft cotton
                                                                           thread, as shown in Fig. 10.2, ensuring that the plant is
                                                                           not damaged.
                                                                         Now, place one glass plate upright with a seedling
                                                                           attached into each of the beaker A and beaker C, as
                                                                           shown in Fig. 10.2a and Fig. 10.2c.
                                                                         In beaker B, arrange the plate such that the shoot of a
                                                                           seedling is directed downwards and the root is directed
                                                                           upwards, as shown in Fig. 10.2b.
                                                                                                            Hole on the back side of the box
                                                          Upright plant kept
                                                           in sunlight from (a)
                                                             all directions                                                                   Inner view
                                                                                                  (b)                    (c)
                                                                                                                                              of the box
                                                                                Inverted plant kept in             Upright plant kept in
                                                                              sunlight from all directions      sunlight from one direction
                                                                                  Fig. 10.2: Set-up showing plants kept in different conditions
                                                                         Pour water into all the three beakers to ensure that the
                                                                           seedling in each beaker remains above the water level.
              Curiosity | Textbook of Science | Grade 6
                                                                         In each case, let the bottom of the blotting paper get
                                                                           completely wet by soaking in the water. In this way,
                                                                           the seedling will get the moisture from the wet blotting
                                                                           paper.
                                                                         Place beaker A and beaker B in sunlight as shown in
                                                                           Fig. 10.2a and Fig. 10.2b.
                                                                         Position beaker C as shown in Fig. 10.2c. Place a
                                                                           cardboard box in such a way that the seedling gets light
                                                                           from one direction only through a small circular hole.
                                                                         Fill Table 10.3 with your predictions and observations.
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                          Table 10.3: Growth of root and shoot under different conditions
                                                                            Direction of growth of
                                     Direction                                  root and shoot
                                                    Direction
                       Beakers           of
                                                    of plant Shoot/
                                     sunlight                                 Predictions Observations
                                                              Root
                                         All                        Shoot
                           A                          Upright
                                     directions                      Root
                                         All                        Shoot
                           B                         Inverted
                                     directions                      Root
                                        Only                        Shoot
                           C          from one        Upright
                                      direction                      Root
                         What is the direction of growth of root and shoot in
                      beakers A, B and C based on your observations? Do your
                      predictions match your observations? What do you conclude
                      from this activity?
                                                                Hole on the back side of the box
                 Upright plant kept
                in sunlight from all (a)
                                                                                                       Inner view
                     directions
                                                                                                       of the box
                                                                                                                    Living Creatures: Exploring their
                                                      (b)                   (c)
                                           Inverted plant kept in     Upright plant kept in sunlight
                                        sunlight from all directions       from one direction
                         Fig. 10.3: Direction of growth of root and shoot under different conditions
                                                                                                                    Characteristics
                      From the results of this experiment (Table 10.3 and
                      Fig. 10.3), we note that—
                      1. When the plant is kept upright, the root grows downwards
                         and the shoot grows upwards.
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                                                                 2. When the plant is kept inverted, the root bends and grows
                                                                    downwards. Also, the shoot bends and grows upwards.
                                                                 3. When the plant gets sunlight only from one direction,
                                                                    the shoot grows in the direction of light while the root
                                                                    continues to grow downwards.
                                                                 After conducting Activity 10.3, we can conclude that shoots
                                                                 of plants grow upward and exhibit movement towards
                                                                 sunlight but roots of plants grow downwords.
                                                          Know a scientist
                                                             Jagadish Chandra Bose (1858–1937) was an Indian
                                                             scientist who did some fascinating experiments
                                                             with plants. He built a machine called a crescograph
                                                             to record how plants respond to stimuli like light,
                                                             heat, electricity and gravity. With this machine, he
                                                             could measure how fast plants grow. He also showed
                                                             that plants can sense and respond to stimuli.
                                                                  10.4 Life Cycle of a Plant
                                                                  We have learnt about conditions required for germination
                                                                  and how plants grow and exhibit movement. Let us now
                                                                  explore the changes a plant undergoes in its whole life.
                                                                  Activity 10.4: Let us explore
                                                                     Plant a bean seed and provide suitable conditions for
                                                                       its growth. Observe regularly for three months.
              Curiosity | Textbook of Science | Grade 6
                                                                     Record your observations in Table 10.4 as and when
                                                                       changes become visible.
                                                                     Note the date when any change is observed. Record
                                                                       answers for the following questions—
                                                                          How long does it take for any change to occur? Make
                                                                            sketches of various changes that you observe in
                                                                            Table 10.4.
                                                                          After how many days does the first flower appear?
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                             After some parts of the flower have dried, can you
                               see any further growth?
                             Which structure do the remaining parts of flower
                               develop into?
                             Can you notice a pod or a fruit with seeds develop
                               from a flower?
                             What happens to the plant after the fruits containing
                               seeds are formed?
                      Table 10.4: Changes observed during the growth of the plant
                                Date            Observations          Sketches
                                                Seeds are sown
                      Go through the observations you recorded regarding the
                      growth of the bean plant in Table 10.4. What changes do you
                      observe after the fruits are formed? Does the plant become
                      yellow and dry even when you continue watering it? Sow
                      the seeds obtained from your bean plant. Watch how the
                      seeds give rise to a new generation of bean plants. Compare
                      the sketches that you have drawn in Table 10.4 with Fig. 10.4.
                          A seed grows into a young plant and matures to produce
                                                                                       Living Creatures: Exploring their
                      flowers and fruit. The fruit, in this case a pod, contains
                      seeds which give rise to a new generation of bean plants.
                      The entire process from a seed to a plant, and then, to the
                      next generation of seeds is called the life cycle of a plant
                      (Fig. 10.4). When a plant stops growing and all activities of
                                                                                       Characteristics
                      life gradually comes to an end, even after the availability of
                      all the necessary conditions, the plant is considered dead.
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                                                             Stage IV                                                   Death of
                                                           (Appearance                                                   plant
                                                            of flowers)
                                                                              Stage V (Appearance
                                                                                    of fruits)                       Fruit
                                                                                                                  (Pod with
                                                                                                                    seeds)
                                                                                                                      Stage I
                                                                                                                      (Seed)
                                                              Stage III
                                                           (Appearance
                                                             of leaves)
                                                                           Stage II (Seed germination)
                                                                          Fig. 10.4: Life cycle of a bean plant
                                                          10.5 Life Cycle of Animals
                                                          We have learnt about the life cycle of a plant. We have seen
                                                          that a plant goes through many changes in its life cycle.
                                                          Have you ever observed how animals grow over time? Draw
              Curiosity | Textbook of Science | Grade 6
                                                          sketches of their young ones and name them.
                                                          10.5.1 Life cycle of a mosquito
                                                          Mosquitoes buzzing around is a common experience for all of
                                                          us. Female mosquitoes are bloodsucking insects that transmit
                                                          several diseases like malaria, dengue and chikungunya. You
                                                          might have learnt from newspapers, school noticeboards
                                                          or awareness campaigns that mosquito breeding should be
                                                          prevented. We are advised not to allow water to stagnate
                                                          anywhere in our surroundings. Why is it so? Does stagnant
                                                          water have any relation with mosquitoes laying eggs?
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                         Conduct a safety audit in your school, or at your home
                      and surroundings to check for stagnant water (if available,
                      carry a hand lens to observe any small creatures). Some
                      common places where stagnant water is likely to gather
                      are desert coolers, planted pots and any open container.
                      You may find two different types of worm-like creatures
                      (Fig. 10.5). They are larva and pupa, two distinct life stages
                      during the development of mosquito. In case you observe
                      larvae and pupae, report to your teacher. Discuss with the
                      teacher and classmates about the necessary measures one can
                      take to prevent breeding of mosquitoes. What differences do
                      you observe in the shape of larvae and pupae?
                               Pupa
                                                                                        Larva
                        Fig. 10.5: Larvae and pupae of mosquitoes in a stagnant water body
                         Mosquito larvae and pupae observed in water bodies
                      repeatedly come to the water surface. What can be the reason
                      for this? Mosquito larvae and pupae live in water and require
                      air to respire. They move to the surface of the water for air.
                          How can the                        I have seen my mother
                                               ?
                          life cycle of a                     spraying kerosene oil
                                                                                                Living Creatures: Exploring their
                                                             on stagnant water. Why
                          mosquito be
                                                                 does she do so?
                          disrupted?
                                                                                                Characteristics
                                              Kerosene oil forms a thin layer over
                                             the water surface. This layer separates
                                                water from air, and does not allow
                                               larvae and pupae to inhale air. As a                 197
                                                         result, they die.
Chapter 10.indd 197                                                                                        10-07-2024 18:22:24
                                                                      Activity 10.5: Let us analyse
                                                                        Let us solve an interesting puzzle.
                                                                            How will you decide which stage (larva or pupa) comes
                                                                        immediately after the egg stage?
                                                                            Suppose you are given a container with water from a
                                                                        puddle containing larvae and pupae. Design an activity to
                                                                        find out the correct sequence of these stages.
                                                                            You can take help of the following activity designed by
                                                          My design ... Avadhi to create your own activity—
                                                                        Step 1: I have a water container with mosquito larvae and
                                                                                 pupae.
                                                                        Step 2: I will separate 4-5 larvae and pupae into two
                                                                                 separate containers with the same water.
                                                                        Step 3: I will observe them every day until I see them
                                                                                 changing to the next stage.
                                                                        Step 4: If the larvae change into pupae, it would mean that
                                                                                 the larval stage comes before the pupal stage or
                                                                                 vice-versa.
                                                                        Step 5: I will keep watching both the containers to see in
                                                                                 which one a mosquito appears first.
                                                                            These observations will help us to learn the correct
                                                                        sequence of growth.
                                                                            Now, suppose you are given a container filled with water
                                                                        from a puddle which contains larvae and pupae. Without
                                                                        separating them from the container, how would you design
                                                                        an activity to decide which stage, out of the two, gives way
                                                                        to the next?
              Curiosity | Textbook of Science | Grade 6
                                                                         Stage IV (Adult
                                                                           mosquito)
                                                                                                                                 Stage I
                                                                                                                                  (Egg)
                                                                               Stage III
                                                                                (Pupa)
                                                                                                                                 Stage II
                                                                                                                                 (Larva)
                                                                                           Fig. 10.6: Life cycle of a mosquito
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                         Let us learn more about these stages in the life cycle of a
                      mosquito.
                         Mosquitoes pass through four stages in their life cycle—
                      egg, larva, pupa and adult (Fig. 10.6).
                         The adult mosquito that emerges from the pupa rests
                      briefly on the surface of water and then flies away. The adult
                      mosquito may survive for 10 to 15 days.
                         We have seen that a mosquito begins its life as an egg
                      (stage I), the egg develops into a larva (stage II), the larva
                      grows into pupa (stage III), and the pupa transforms into an
                      adult mosquito (stage IV). The adult female mosquito lays
                      eggs directly on or near water, and the cycle continues.
                         Significant changes occur in the appearance, body shape
                      and structure during the various stages in the life cycle of
                      a mosquito. The shape of the egg is quite different from the
                      larva; the larva appears very different from the pupa. The
                      pupa appears very distinct from the adult mosquito. Is it
                      easy to imagine that a mosquito emerges from a pupa?
                       The silk moth also passes through four life stages—egg, larva,
                       pupa and adult. Eggs hatch into larvae, which then grow in
                       size. Larvae secrete thread-like material which they
                       wrap around themselves, before changing to pupae.
                       These are the fibres that are used to make silk fabric.
                       In India, the Khadi and Village Industries Commission
                       (KVIC) has set up several centres for silk production.    Do you
                                                                                 know?
                      10.5.2 Life cycle of a frog
                                                                                          Living Creatures: Exploring their
                      Activity 10.6: Let us analyse
                      Avadhi and Aayush are dressed up in full sleeves shirts and
                      full pants today. It has been raining intermittently for a week.
                                                                                          Characteristics
                      They are going out with their classmates for an activity.
                      After a brief walk led by their science teacher, they reach a
                      shallow pond. It is surrounded by trees and tall grasses. The
                      teacher cautions them to watch everything from a distance
                                                                                              199
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                                                          without causing any disturbance. You may also go to a small
                                                          water body during the rainy season with a facilitator and
                                                          explore it by taking due safety precautions.
                                                             You may notice a white jelly-like substance on the surface
                                                          of water towards the edge of the pond (Fig. 10.7). This may
                                                          also be attached to plants growing in or around the water.
                                                          This jelly-like substance is actually a cluster of eggs of a frog
                                                          and is known as spawn.
                                                             Observe the features of all the stages of a frog shown in
                                                          Fig. 10.7. How will you decide the sequence of the given stages
                                                          (A, B, C, D, E, F)? Some of the stages show distinct changes in
                                                          their initial and final shapes. Record these changes in Table
                                                          10.5.
                                                            A                                    E
                                                                                                                 F
                                                                          B
                                                                                         C
                                                                      Fig 10.7: Different stages of a frog in a pond
              Curiosity | Textbook of Science | Grade 6
                                                              Based on the observations listed in Table 10.5, draw the
                                                          life cycle of a frog. Compare the figure drawn by you with
                                                          Fig. 10.8.
                                                                Table 10.5: Changes in different life stages of a frog
                                                                A         B             C              D               E   F
                                                                                                      It is
                                                                                                  similar to
                                                                                                   ‘C’ but it
                                                                                                   has two
                                                                                                     legs.
             200
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                         Some of the stages have been clubbed together, for
                      example, stages A and F in Fig. 10.7 have been kept under
                      stage I. You will find four stages in the life cycle of a frog—
                      the egg stage, which progresses to the embryo stage; the
                      tadpole stage, consisting of an early stage with a tail and no
                      legs, and a late stage with hind legs; the froglet stage, and
                      the adult frog stage (Fig. 10.8).
                                 Stage IV – Adult frog                                       Stage IA– Spawn
                                           (14 weeks)                                        (Day 1)
                      Stage III – Froglet                                                              Stage IB– Embryo
                             (12 weeks)                                                                (Day 3-4)
                                  Stage IIB – Tadpole with legs                            Stage IIA– Tadpole with tail
                                                  (8-10 weeks)                                      (Day 7-10)
                                                         Fig. 10.8: Life cycle of a frog
                      Discuss in the class along the following points:
                       How are these eggs of a frog different from the other
                          eggs that you may have seen?
                         Which stage has the shortest duration?
                         Is there a change in the habitat during the various
                           stages in the life cycle of a frog?
                                                                                                                          Living Creatures: Exploring their
                         How do the special features support that stage?
                         Observe Fig. 10.8. You will see that tadpoles develop legs
                      but still have tails. Tails help them swim in water. Tadpoles
                      grow gradually and start looking like little frogs called
                                                                                                                          Characteristics
                      froglets. They still live in water but begin to spend some
                      time on land. They continue to grow and lose their tails
                      completely. Their legs become strong to help them jump and
                      land. They become fully developed adult frogs living both in
                      water and on land.                                                                                      201
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                                                                            Do you think that birds also show
                                                                            significant changes in the various
                                                                                 stages of their life cycle?
                                                                                       How
                                                                               does the life cycle of
                                                                            animals differ from that of
                                                                                     plants?
                                                             Plants and animals are a part of the living world. They
                                                          go through various changes during the course of their lives.
                                                          We have learnt that a tiny plant grows and develops into a
                                                          big tree. We have also learnt how animals grow and change
                                                          from young ones to adults. This journey varies for each
                                                          animal, making it unique and special. We have seen pupae
                                                          change into insects, and tadpoles change into frogs. Such
                                                          changes are important for plants and animals to survive
                                                          and to maintain continuity of their kind. We should also take
                                                          care of them and their homes. By nurturing and preserving
                                                          their homes, we contribute to this flourishing living world.
                                                                                          Keywords
                                                                Breathing            Movement                Conclude
                                                            Death                 Non-living              Create
              Curiosity | Textbook of Science | Grade 6
                                                                Excretion            Nutrition               Design
                                                            Froglet                Pupa                   Experiment
                                                                Germination          Reproduction            Explore
                                                            Growth                Respiration             Identify
                                                                Larva                Response                Observation
                                                            Life cycle            Stimulus                Prediction
             202                                                Living                Tadpole
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                                              Summary
                         The objects around us can be categorised into two types
                           living and non-living.
                         The essential features of living beings are that they move,
                           eat, grow, breathe, excrete, respond to stimuli, reproduce
                           and die. Absence of any of these features indicates that they
                           are not living beings.
                         Each living being goes through several stages during its life.
                         Germination of seeds depends upon the availability of
                           water, air and suitable light and/or dark conditions.
                         During germination of seeds, roots generally            grow
                           downwards, while shoots grow upwards.
                         A plant’s life cycle starts with seed germination, followed by
                           several stages of its growth and development. These includes
                           flowering and seed production. Seeds produced during their
                           life cycle would germinate into new plants and the cycle
                           continues.
                         The life cycle of an animal as a result of reproduction, begin
                           with a new born that undergoes various stages of growth and
                           development followed by an adult stage and finally death. The
                           process of reproduction maintains the continuity of its kind.
                         Mosquitoes pass through the stages of egg, larva, pupa
                           and adult. The life stages of a frog include eggs, tadpoles,
                           froglets and adults.
                         In some living beings, such as mosquitoes and frogs,
                           significant changes occur during the various stages of
                           their life cycles. These changes can be seen in body shape,
                           structure and sometimes even in the habitat.
                                                                                            Living Creatures: Exploring their
                              Let us enhance our learning
                                                                                            Characteristics
                      1.   List the similarities and differences in life cycles of plants
                           and animals.
                      2.   The table on the next page shows some data. Study the data
                           and try to find out examples appropriate for the conditions
                           given in the second and third columns. If you think that             203
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                                                                        an example for any of the conditions given below is not
                                                                        possible, explain why.
                                                                      S. no.    Does it grow?         Does it
                                                                                                                 Example Remarks
                                                                                                     respire?
                                                                        1.             No              No
                                                                        2.             No              Yes
                                                                        3.             Yes             No
                                                                        4.             Yes             Yes
                                                                 3.     You have learnt that different conditions are required for
                                                                        seed germination. How can we use this knowledge for
                                                                        proper storage of grains and pulses?
                                                                 4.     You have learnt that a tail is present in a tadpole but it
                                                                        disappears as it grows into a frog. What is the advantage of
                                                                        having a tail in the tadpole stage?
                                                                 5.     Charan says that a wooden log is non-living as it cannot move.
                                                                        Charu counters it by saying that it is living because it is made
                                                                        of wood obtained from trees. Give your arguments in favour
                                                                        or against the two statements given by Charan and Charu.
                                                                                                6.   What are the similarities and
                                                                                                     distinguishing features in the life
                                                                                                     cycles of a mosquito and a frog?
                                                                                                7.   A plant is provided with all the
              Curiosity | Textbook of Science | Grade 6
                                                                                                     conditions suitable for its growth
                                                                                                     (Fig. 10.9). Draw what you expect
                                                                                                     to see in the shoot and the root of
                                                            Fig. 10.9: Pot kept along the            the plant after one week. Write
                                                                       ground                        down the reasons.
                                                                                                8.   Tara and Vijay set up the
                                                                                                     experiment shown in the picture
                                                                                                     (Fig. 10.10). What do you think
                                                                                                     they want to find out? How will
                                                                                                     they know if they are correct?
                                                                                                9.   Design an experiment to check if
                                                          Fig. 10.10: Experimental set-up            temperature has an effect on seed
             204
                                                                                                     germination.
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                                         Learning further
                         Make a field trip to a local garden. Interact with a gardener
                           to learn about various conditions and the time required for
                           the growth of various plants.
                         Can we grow plants without germinating their seeds?
                           Explore and cite some examples.
                         Observe the life cycle of five plants grown at home, school,
                           or in a nearby garden. Create a picture book containing
                           pictures of various stages of their growth. Write the name
                           of each plant and the duration of each of its stage.
                         Try to observe some of the stages in the life cycle of a
                           butterfly or a moth. Are these stages similar to the stages in
                           the life cycle of a mosquito?
                         In your opinion, would the environment affect the life
                           cycles of insects? Explore and list the factors that affect the
                           life cycles of insects.
                                             Let us create
                      Add more lines to the incomplete poem given below. Include
                      information on the different stages in development of a
                      frog. You may also draw and paint each stage as it appears
                      in your poem.
                                                                                             Living Creatures: Exploring their
                                In shaded and grassy bogs,
                                There lived a group of frogs.
                                They happily sang from dusk to dawn,
                                In double bass going on and on.
                                                                                             Characteristics
                                One day sitting beside a reed,
                                Female frogs think it’s time to breed ……..
                                …………………………………………
                                                                                                 205
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                      Notes
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