Class 6 Science Chapter 2 Notes Diversity in the Living World
In nature, there is a wide variety of organisms which includes plants like grasses, bushes, and large trees as well as animals such as birds, butterflies, monkeys, etc. These organisms can be classified based on similarities and differences among them. Additionally, the diversity of organisms varies across the regions due to different environmental conditions, which play a crucial role in shaping biodiversity.
Diversity in Plants and Animals Around Us
There is a wide range of living organisms on Earth, including plants and animals. This variety of plants and animals found in a particular region contributes to the biodiversity of that region. Each member of the biodiversity of a region has a different role to play. For example, trees provide food and shelter to some birds and other animals, animals help in spreading seeds after, eating fruits, and so on. This also shows that plants and animals are dependent on each other for their survival. This diversity of plants and animals around us can be easily studied through systematic grouping.
Grouping of Plants and Animals
The diverse range of plants and animals with different features can be grouped based on their similarities and differences. Grouping makes it easier to understand and study plants and animals by considering their common features and variations.
Grouping of Plants
Plants show variation in the features related to stems, flowers, leaves, seeds, and more. The stems of different plants vary in thickness, height, and hardness, flower may show diversity in colour, shape, and scent, while the leaves vary in shape, colour, size, and arrangement. The various criteria on which plants are grouped are discussed in detail below.
Stem
It is the aerial part of the plant which bears branches, flowers, buds, leaves, and fruits. It may be green, hard, or woody. According to the height and nature of the stem, plants are classified into the following three categories.
- Herbs: These are small plants with green, soft and tender stems. They do not have many branches, e.g. mint, tomato plant, etc.
- Shrubs: These are bigger than herbs. Their stem is hard, but not very thick and has branches at the base of the stem, e.g. rose, tulsi, Hibiscus, etc.
- Trees: These are very tall and have hard thick brown and woody stems. The stems have branches on the upper part of the plants, e.g. neem, mango, peepal, etc.
Some plants are different from herbs, shrubs, and trees. These are called creepers and climbers.
- Creepers are plants having thin, long, and weak stems which cannot stand upright, but spread on the ground, e.g. strawberry, pumpkin, watermelon, etc.
- Climbers are plants having soft, green, and weak stems that cannot stand upright just like the creepers, but readily climb up taking support from nearby objects or trees, e.g. bitter gourd, grapevines, bean stalks, etc.
A climber plant has special organs called tendrils for climbing. Some of these have stem tendrils whereas others have leaf tendrils.
Leaf
It is a thin, flat, and green part of the plant that has different shapes and sizes.
Parts of a Leaf
A leaf has the following parts:
- Petiole (leaf stalk): It is a thin stalk by which the leaf is attached to the stem.
- Lamina (leaf blade): It is the broad, green flattened part of the leaf. There are several small, thin lines running across the lamina called veins. The central vein or the main vein of the leaf is called the midrib.
A leaf without a petiole is called a sessile leaf. In such plants, the leaves are attached directly to the plant stem. The pattern of veins on the leaf is called venation. There are two types of venation observed in different plants.
- Reticulate Venation: In this type of venation, veins are arranged in a net-like pattern on both sides of the midrib. This type of venation is found in peas, Hibiscus, neem, sadabahar (Periwinkle), peepal, tulsi, mustard, sunflower, orange, guava, rose, etc.
- Parallel Venation: In this type of venation, veins are arranged parallel to each other and also along the midrib. This type of venation is found in certain plants like wheat, maize, onion, garlic, banana, lily grass, etc.
Root
It is the underground, non-green part of the plant that remains below the ground, i.e. in soil.
Types of Root
There are mainly two types of roots in different plants.
- Tap Root: In some plants, there is one thick main root called tap root from which arises the smaller roots called lateral roots. Tap root grows vertically downwards into the soil and lateral roots spread in various directions. Generally, plants with tap roots have reticulate venation. Taproot is found in plants like chickpeas, radishes, carrots, neem, Hibiscus, mango, tulsi, mustard, and balsam.
- Fibrous Root: In some plants, there is no, main root. All roots are similar in size arising from the base of the stem and make a bushy appearance. This type of root is called fibrous root. Generally, a plant with fibrous roots has parallel venation. The fibrous root is found in plants like onion, lily, lemongrass, wheat, maize, grass, and millet.
Seed
It is an important part of flowering plants that gives rise to a new plant.
Parts of Seed
A seed mainly has the following parts
- Seed Coat: It is the outermost covering of the seed which protects its internal parts.
- Cotyledons: They are present beneath the seed coat and store food for the developing embryo.
- Embryo: It is the small early stage of a plant found inside a seed.
Based on the number of cotyledons, there are mainly two types of plants.
- Dicotyledons (Dicots): These are the group of flowering plants that have two cotyledons, e.g. chickpea, pea, black bean, etc. Generally, dicot plants have reticulate venation and a tap root system.
- Monocotyledons (Monocots): These are the group of flowering plants that have a single thin cotyledon, e.g. wheat, maize, etc. Generally, monocot plants have parallel venation and a fibrous root system.
Grouping of Animals
→ Just like plants, animals also exhibit a wide range of differences. Animals can be grouped on various bases, such as the place where they live, the food they eat, the types of movement they show, and the body parts they use for the movement.
→ For example, ants, goats, and cows can be grouped based on the body parts used for their movement.
→ Similarly, pigeons, bats, and butterflies can be grouped based on the type of their movement. Additionally, many animals differ from each other in shape, structure, colour, and other characteristics which also helps in understanding their diversity.
Janaki Ammal (1897-1984) was an Indian botanist dedicated to environmental work and helped to document and preserve India’s rich plant biodiversity. She played an important role in the ‘Save Silent Valley’ movement. As the head of the botanical survey of India, she pioneered programs to document the plant diversity of India.
Save Silent Valley Movement
The Silent Valley is a moist evergreen forest in the Palakkad district of Kerala, known for its untouched Do you beauty and rich biodiversity. A proposal to construct a hydroelectric dam across the Kunthipuzha River, which flows through a silent valley, initiated the remarkable movement led by people who were not even living near the forest. The movement employed various methods to raise awareness and oppose the dam proposal. They wrote letters to editors, published articles in newspapers, and organized seminars to highlight the issue. Petitions and appeals were filed in the court and after a decade, the movement successfully saved Silent Valley from destruction.’
2.2 Plants and Animals in Different Surrounding
The place where an organism lives and grows is called its habitat. For example, the habitat of sea turtles is the sea or the ocean. The habitat provides the living organisms with food, shelter and favorable climatic conditions to survive, breed and flourish. Several kinds of plants and animals may share the same habitat. It also plays an important role in shaping the biodiversity of a region.
Types of Habitat
Habitat is broadly divided into two types, i.e. terrestrial and aquatic.
- Terrestrial Habitats: The plants and animals that live on land are said to live in terrestrial habitats, e.g. forests, grasslands, deserts, and mountain regions.
- Aquatic Habitats: The habitats of plants and animals that live in water are called aquatic habitats, e.g. points, lakes, rivers, and oceans.
Some animals such as frogs, can live in water as well as on land. These are called amphibians.
Adaptations
The plants and animals living in a particular habitat have special features that make them fit to survive there. These special features are called adaptation. Different plants and animals exhibit various adaptations suited to their habitats. Some of these adaptations are described below.
Adaptations in Cactus
It is generally found in the deserts of Rajasthan, where water is limited and the temperature is extreme. During the day the desert is typically very hot and becomes very cold at night. In order to survive in hot conditions, cactus plants have thick and fleshy stems to store water.
Cacti are not just found in the desert. There are actually around 1,500 different species of cactus and can be found in both arid and semi-arid habitats all over the world.
Adaptations in Deodar Trees
They are found in the Himalayas of Himachal Pradesh, where the temperature is extremely low and snowfall is frequent. To tolerate these conditions, deodar trees are conical in shape and have flexible and sloping branches that allow snow to slide off easily.
Adaptations in Rhododendrons
Sometimes, even similar organisms exhibit different features in different regions to tolerate the specific conditions of those regions. For instance, rhododendrons in the shola forest of Nilgiris are shorter in height and have smaller leaves to withstand the heavy winds on mountain tops. In contrast, rhododendrons in the mountains of Sikkim are taller.
Adaptations in Aquatic Animals
Aquatic animals like whales and fishes are adapted to live in water. The features of a fish that enable it to live in freshwater are listed below.
- They have streamlined shapes. This shape helps them to move inside water.
- They have slippery scales on their bodies. These scales protect the fish and also help in easy movement through water.
- They have flat fins and tails that help them to change directions and keep their body balanced in water.
Adaptations in Camel
Camels are adapted to survive in desert conditions. However, camel from the hot desert of Rajasthan differs from that of the cold desert of Ladakh.
1. In Hot Desert
- Camels in the hot desert have long legs with wide hooves that help them to walk on the sandy desert without sinking into the sand.
- They have a single hump that stores food (fat) and helps them to survive during the scarcity of food.
- They excrete small amounts of urine, their dung is dry and they do not sweat. Since they lose very little water from their bodies, camels can live for many days without water.
2. In Cold Desert
- Camels in cold deserts have short legs that allow them to walk easily in mountainous regions.
- They have two humps that shrink in late winter because there is not much food available in the cold desert and they have to use food (fat) stored in their humps during that time.
- They grow long hair from head to neck, which helps them survive the cold winters of Ladakh.
- Some animals show behavioral adaptation, e.g. cape ground squirrel uses a long bushy tail as a parasol or an umbrella. It provides shade in the scorching heat of the sun.
Loss of Habitat
- In recent times, the habitats of plants and animals have been destroyed due to various human activities.
- The damage to these habitats, results in the loss of their homes, food, and other resources. This leads to the loss of biodiversity. Protecting biodiversity is essential to ensure that the planet remains full of life, allowing plants and animals to survive and thrive.
- For example, the populations of various animals such as the Bengal Tiger, Cheetah, and the Great Indian Bustard have declined in India due to the loss of natural habitats caused by human activities.
To address this decline, the Government of India has initiated several projects to conserve biodiversity, which are as follows.
- ‘Project Tiger’ was initiated in 1973 to protect the declining population of the Bengal Tiger.
- The ‘Cheetah Reintroduction Project’ was initiated in 2022 to restore the population of the Cheetah.
- Habitats of the Great Indian Bustards have been declared as protected areas in the states of Gujarat, Rajasthan, and Maharashtra.
Traditionally Protected Forest: Scared Groves
Sacred groves are undisturbed patches of forest, that vary in size and are found all over India. They are home to different kinds of plants and animals, including numerous medicinal plants.
These are protected by the local community and no one is allowed to harm any animals cut trees in these groves, or disturb the area. This way, sacred groves are a community-protected treasure of biodiversity.
Salim Ali (1896-1987), known as the ‘Birdman of India’, extensively traveled across the country to study the diversity of birds. He prepared a list of birds and documented their travel routes and habitats. He recorded the regions with a high diversity of birds and took measures to conserve these regions. Keoladeo National Park in Bharatpur, Rajasthan, and Ranganathittu Bird Sanctuary in Mandya, Karnataka are examples of regions he preserved. He also wrote a landmark series of 10 books on birds of the Indian subcontinent. For his work, he was awarded with Padma Vibhushan in 1976.
→ Adaptation: It refers to the special features that enable plants and animals to survive in a particular region.
→ Amphibians: The animals that can live in water as well as on land.
→ Aquatic: It refers to anything related to or occurring in water.
→ Biodiversity: The variety of plants and animals found in a particular region.
→ Cotyledon: It is a part of a seed that is crucial for the growth and development of seedlings.
→ Dicot Plants: These are plants having seeds with two cotyledons.
→ Fibrous Roots: Network of numerous thin, similarly sized roots that arise from the base of the stem and spread out widely.
→ Habitat: The place where an organism lives.
→ Herbs: These are small plants having soft and green stems.
→ Monocot Plants: These are plants having single thin cotyledon.
→ Parallel Venation: In this, the veins in the leaf lamina are arranged parallel to each other.
→ Reticulate Venation: In this, the veins in the leaf lamina are arranged in a net-like pattern.
→ Sacred Groves: These are undisturbed patches of forests that are protected by the local community.
→ Shrubs: These plants have a hard and woody stem that is not very thick.
→ Tap Root: This type of root contains one main root which grows vertically downwards.
→ Terrestrial: It refers to anything related to or occurring on land.
→ Trees: They are very tall plants with hard, thick, and brown stems.
→ Venation: The arrangement of veins in a leaf.