The chapter “Living Creatures: Exploring their Characteristics” provides an in-depth look at the qualities that define living beings and how they differ from non-living things. It also explores the life cycles of plants and animals, highlighting the processes of growth, reproduction, and adaptation.
What Sets the Living Apart from the Non-living?
Living beings possess several key characteristics that distinguish them from non-living things:
- Movement: Living beings can move, though the type of movement varies. Animals move from place to place, while plants exhibit movement in parts like leaves or flowers (e.g., the opening of flowers or the folding of leaves in touch-me-not plants).
- Nutrition: Living beings require food for energy and growth. Plants make their own food through photosynthesis, while animals do not .
- Growth: Living beings grow in size and complexity over time. For example, a child grows taller, and a plant grows from a seed into a mature plant.
- Respiration: Living beings respire, taking in oxygen and releasing carbon dioxide. Plants loose water through tiny pores called stomata from their leaves.
- Excretion: Living beings remove waste products from their bodies. Humans excrete urine, while plants release excess water and minerals through droplets on leaves.
- Response to Stimuli: Living beings respond to external stimuli. Humans react to pain, and plants like the touch-me-not fold their leaves when touched.
- Reproduction: Living beings reproduce to ensure the continuity of their species. Plants produce seeds, and animals give birth to young ones.
- Death: All living beings eventually die, marking the end of their life cycle.
Non-living things, such as a pencil or a car, do not exhibit these characteristics. For example, a car may move, but it does not grow, respire, or reproduce.
Essential Conditions for Germination of a Seed
Germination is the process by which a seed develops into a plant. For germination to occur, specific conditions must be met:
- Water: Seeds need water to soften the seed coat and activate the embryo inside.
- Air: Seeds require oxygen for respiration, which provides energy for growth.
- Temperature: Seeds need a suitable temperature to germinate. Extreme temperatures can hinder the process.
- Light/Darkness: Some seeds require light to germinate (e.g., Coleus), while others need darkness (e.g., Calendula).
In an experiment, seeds placed in moist soil with access to air and sunlight germinate successfully, while those deprived of water, air, or light fail to sprout.
Growth and Movement in Plants
Plants exhibit growth and movement, though they do not move from place to place like animals. Key observations include:
- Growth Direction: Roots grow downward (towards gravity), and shoots grow upward (towards light).
- Response to Light: Shoots bend towards light sources, a phenomenon known as phototropism.
- Movement in Plants: Some plants, like the touch-me-not, show rapid movement in response to touch. Others, like insectivorous plants, move to trap insects.
An experiment with inverted plants shows that roots and shoots adjust their growth direction to align with gravity and light, demonstrating plants’ ability to respond to environmental stimuli.
Life Cycle of a Plant
The life cycle of a plant involves several stages of growth and development, starting from a seed and progressing to a mature plant that produces seeds for the next generation. Here is a breakdown of the key aspects:
- Seed Germination: The plant’s life cycle begins with a seed. For a seed to germinate, it requires specific conditions such as the right amount of water and air. Water softens the seed coat and allows the embryo to develop, while air provides the necessary resources for growth. Light may not be essential for germination for most seeds, however, sunlight is required for further growth of the seedling after germination.
- Growth and Development: After germination, the plant grows, developing a root and a shoot. The root typically grows downwards, and the shoot grows upwards, often towards sunlight. Plants also exhibit movement, such as the opening of flowers, and movements in response to stimuli such as light and touch.
- Flowering: As the plant matures, it produces flowers. The timing of the appearance of the first flower can vary depending on the plant species.
- Fruit and Seed Production: After the flowers have bloomed, they may develop into fruits, which in turn contain seeds. The fruit protects the seeds and may aid in their dispersal.
- Completion of the Life Cycle: The seeds produced by the plant can give rise to a new generation of plants, continuing the cycle. When a plant stops growing and all of its life activities come to an end, even with all the necessary conditions, the plant is considered dead.
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. This cycle ensures the continuity of plant life.
Life Cycle of Animals
The life cycle of animals involves various stages of growth and development, from young ones to adults. This process varies for each animal, making it unique. The life cycle ensures the continuity of an animal species through reproduction.
Here are some examples of animal life cycles from the sources:
- Mosquitoes: Pass through four stages: egg, larva, pupa, and adult.
- The adult female mosquito lays eggs nearby water.
- The eggs develop into larvae, which live in water and require air to respire, often moving to the water’s surface for air.
- The larvae grow into pupae.
- The pupae transform into adult mosquitoes.
- Significant changes occur in the appearance, body shape and structure during these various stages.
- The adult mosquito can survive upto 15 days.
- The cycle continues as the adult female lays more eggs.
- Frogs: Go through multiple stages in their life cycle:
- The cycle begins with eggs, often laid in a jelly-like substance called spawn.
- The eggs develop into embryos.
- The embryos hatch into tadpoles, which initially have tails and no legs.
- Tadpoles develop legs and gradually transform into froglets, which still have tails.
- Froglets lose their tails completely and become fully developed adult frogs, which live both in water and on land.
- The different stages of a frog’s life cycle also display significant changes in appearance and habitat.
- Silk Moths: Also have a four-stage life cycle: egg, larva, pupa, and adult.
- The eggs hatch into larvae, which grow in size and secrete thread-like material they wrap around themselves.
- The larvae then change into pupae.
- The fibres from pupae are used to make silk fabric.
Key Points about Animal Life Cycles:
- Reproduction: The starting point of the life cycle of an animal.
- Distinct Stages: Animals go through various stages during their life cycle, such as egg, larva, pupa, young and adult.
- Changes: Significant changes in body shape, structure, and sometimes even habitat occur during the different life stages of an animal.
- Continuity: The process of reproduction ensures that a species continues to exist.
- Habitat Changes: Some animals may experience a change in habitat during the various stages of their life cycle. For example, the tadpole lives in the water and then becomes a frog which lives in water and on land.
Life Cycle of a Frog
The life cycle of a frog involves several distinct stages, from egg to adult, with significant changes in appearance and habitat throughout its development.
- Egg Stage (Spawn): The life cycle begins with eggs, which are typically laid in a jelly-like substance called spawn. This spawn is often found on the surface of the water or attached to plants in or around the water.
- Embryo Stage: The eggs develop into embryos within the spawn.
- Tadpole Stage: The embryos hatch into tadpoles, which have a tail and no legs.
- Initially, the tadpole has a tail and no legs (early stage).
- Later, the tadpole develops hind legs (late stage).
- Tadpoles live in water and use their tails to swim.
- Froglet Stage: The tadpoles gradually transform into froglets, which still have tails, but begin to spend some time on land.
- Adult Frog Stage: The froglet continues to grow, losing its tail completely. The legs become stronger, allowing the frog to jump and land.
Key Points about the Life Cycle of a Frog:
- Significant Changes: The frog undergoes significant changes in appearance, body shape, and structure during its life cycle. The shape of the egg is quite different from the tadpole; the tadpole appears very different from the froglet, and the froglet is different from the adult frog.
- Habitat Changes: There is a change in the habitat during the various stages of the life cycle of a frog. Tadpoles live in the water, while adult frogs can live both in water and on land.
- Duration: The stages of the frog’s life cycle vary in duration. For example, the embryo stage is very short, while the tadpole stages last longer.
- Adaptations: The different stages have unique adaptations that support their survival. For example, the tadpole has a tail to swim, while the adult frog has strong legs to jump.
- Continuity: The life cycle ensures the continuity of the frog species. The eggs hatch and develop into the next generation of frogs.
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