Living Creatures: Exploring their Characteristics

Chapter at a Glance

This chapter details the characteristics that distinguish living beings from non-living things (movement, nutrition, growth, respiration, excretion, response to stimuli, reproduction, and death). It investigates the essential conditions required for seed germination (water and air) and explores growth direction in roots and shoots (tropisms). Additionally, it traces the multi-stage life cycles and metamorphosis of plants (bean plant) and animals, specifically focusing on the mosquito (egg, larva, pupa, adult) and the frog (egg/spawn, tadpole, froglet, adult).

Key Definitions & Terminology

Living Beings: Organisms that exhibit all the essential characteristics of life.
Non-living Things: Objects that lack the essential characteristics of life.
Stimulus (plural: Stimuli): Any change or event in the environment that causes a reaction in a living organism.
Response: The reaction of an organism to a stimulus.
Respiration: The biological process by which cells break down food to release energy (of which breathing is the physical intake of oxygen and release of carbon dioxide).
Excretion: The process of removing toxic metabolic waste products (like urine, sweat, and excess salts) from the body.
Reproduction: The process by which living organisms produce offspring of their own kind to ensure the continuity of their species.
Seed Coat: The tough, protective outer covering of a seed.
Embryo: The tiny, undeveloped plant inside a seed that germinates to form a seedling.
Stomata: Microscopic pores on leaf surfaces that enable gas exchange for respiration and photosynthesis.
Metamorphosis: A biological process in which an animal undergoes rapid and distinct structural changes during its life cycle (e.g. mosquito and frog).
Spawn: A jelly-like mass of eggs laid in water by aquatic animals like frogs.
Tadpole: The fish-like larval stage of a frog that lives in water, breathes through gills, and swims using a tail.
Froglet: The transitional stage of a developing frog that has grown legs but still retains a small tail.
Crescograph: An instrument invented by Sir Jagadish Chandra Bose to measure and record the growth rate of plants and their responses to external stimuli.

Formulas, Rules & Properties

The Eight Characteristics of Life:
To be classified as living, a system must display:
Movement (internal or external)
Nutrition (needs food)
Growth (permanent increase in size)
Respiration (energy release and gas exchange)
Excretion (waste elimination)
Response to stimuli (reacting to environmental changes)
Reproduction (producing offspring)
Death (cessation of all life functions)
Seed Germination Rules:
Sprouting requires water (which softens the seed coat and activates the embryo) and air (oxygen present in the spaces between soil particles).
For most seeds (like beans), sunlight is not required to germinate and they can sprout in darkness, though seedlings require light to grow after sprouting.
Plant Growth Direction Rules:
Shoots: Grow upwards (against gravity) and bend toward light sources (positive phototropism).
Roots: Grow downwards (toward gravity) to anchor the plant and absorb water (positive geotropism), even if the seed is sown upside down.

Core Concepts & Topics

Relativity of Movement:
Movement alone does not define life. Cars, clouds, and wind move, but are non-living because they do not grow, respire, excrete, or reproduce.
Sensory and Physical Movements in Plants:
Drosera (Sundew): An insectivorous plant with sticky hair-like projections that fold inward to trap insects for nutrition.
Mimosa pudica (Touch-Me-Not/Chhui-Mui): Folds its leaves instantly when touched.
Amla (Gooseberry): Exhibits "sleeping movements," folding its leaves together after sunset.
Sir J.C. Bose's Research:
Indian scientist who proved experimentally that plants possess sensitivity and respond to stimuli like light, heat, gravity, and electricity.
Life Cycle of a Bean Plant:
Egg/Seed $\rightarrow$ Germination/Sprouting $\rightarrow$ Seedling (leaves) $\rightarrow$ Mature Plant (flowering) $\rightarrow$ Pod/Fruit (with new seeds) $\rightarrow$ Death (the plant dries up naturally even if watered).
Life Cycle of a Mosquito:
Egg $\rightarrow$ Larva $\rightarrow$ Pupa $\rightarrow$ Adult.
Larvae and pupae live in water but breathe air by surfacing.
Disruption: Spraying a layer of kerosene oil on stagnant water cuts off atmospheric air, suffocating the larvae and pupae.
Life Cycle of a Frog:
Spawn (eggs) $\rightarrow$ Embryo $\rightarrow$ Tadpole (swims with a tail, breathes with gills) $\rightarrow$ Tadpole with legs $\rightarrow$ Froglet (transitional tail-shrinking phase) $\rightarrow$ Adult Frog (amphibious, breathes with lungs/skin, hops with strong legs).
Silk Moth Life Cycle:
Egg $\rightarrow$ Larva (silkworm) $\rightarrow$ Pupa (inside a protective cocoon woven of silk fibres) $\rightarrow$ Adult moth. The Khadi and Village Industries Commission (KVIC) supports rural silk production from these cocoons.

Worked Examples

Seed Classification:
Question: Is a dry seed living or non-living?
Solution: A seed is living. It contains a dormant embryo that respires at a very slow rate. When provided with water and air, it germinates and grows, showing active life.
Log of Wood (Living or Non-Living):
Question: Charan says a log of wood is non-living. Charu says it is living because it comes from trees. Who is correct?
Solution: Charan is correct. A log of wood is non-living (dead) because it no longer performs metabolic functions. Charu is correct only about its biological origin.
Growth and Respiration Combinations:
Does not grow, does not respire: Pencil, Rock (Non-living).
Does not grow, respires: Dormant seeds (respire slowly to survive but do not grow until germinated).
Grows, does not respire: Crystals (grow by adding layers of solute but do not breathe).
Grows, respires: Plants, Animals, Humans (Living).
Tadpole Tail Advantage:
Question: What is the advantage of the tail in a tadpole, which disappears in the adult frog?
Solution: The tail serves as a paddle, enabling the aquatic tadpole to swim and maneuver in water. Adult frogs develop strong legs for hopping on land and swimming in water, making the tail unnecessary.
Inverted Plant Growth (Geotropism):
Question: A potted plant is placed horizontally on the ground. Draw and explain what happens to the root and shoot after one week.
Solution: The root will bend and grow downward toward the soil (positive geotropism), while the shoot will bend and grow upward toward the sky (negative geotropism).
Seed Storage Principle:
Question: How does our knowledge of seed germination help in storing grains and pulses safely?
Solution: Germination requires water and air. To prevent grains from sprouting or rotting during storage, they must be kept in dry, airtight, and cool containers.
Temperature Effect Experiment:
Question: Design an experiment to test if temperature affects seed germination.
Solution: Place three pots containing moist soil and bean seeds under different conditions: Pot 1 in a refrigerator ($4^\circ\text{C}$), Pot 2 at room temperature ($25^\circ\text{C}$), and Pot 3 in an incubator ($45^\circ\text{C}$). Only Pot 2 will germinate, proving that a moderate temperature is essential.

Practical Activities & Experiments

Activity 10.1: Living vs. Non-living Sort: Classifying classroom objects and listing the scientific reasons behind the classification.
Activity 10.2: Seed Germination Variables: Growing bean seeds in four pots under varying conditions (dry/sunny, flooded, moist/dark, moist/sunny) to identify water and air as essential variables.
Activity 10.3: Seedling Gravity and Light Assays: Positioning seedlings upright, inverted, and in a boxed chamber with a single light hole to observe root geotropism and shoot phototropism.
Activity 10.5: Mosquito Development Observation: Monitoring puddle water containing larvae and pupae in separate containers to establish the developmental sequence (Larva $\rightarrow$ Pupa $\rightarrow$ Adult).

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