Diversity in the Living World

Why This Matters

Step outside for a minute. Look around you.

You will see grass on the ground. A tall tree giving shade. A small plant in a pot. Maybe a crow on a wire. An ant on the wall. A dog walking by.

Now think about this. Not one of them is exactly the same as another. The grass is soft and short. The tree is hard and tall. The crow flies. The ant crawls. The dog runs.

This is diversity. Diversity just means variety — many different kinds. The living world is full of variety. There are millions of different plants and animals on Earth. No two kinds are exactly alike.

But here is the problem. When there are so many different living things, how do we even study them? You cannot learn about each one, one by one. It would take forever.

So we do something clever. We put them into groups. Things that are alike go together. Once they are in groups, they become easy to understand.

In this chapter, you will learn to see the variety around you. Then you will learn how to group it. By the end, you will look at any plant and say what kind it is — and you will know why it lives where it lives.

The Big Idea

The living world has a huge variety of plants and animals. To study this variety, we group living things by the features they share. Plants can be grouped by their size and stem (herbs, shrubs, trees, climbers, creepers), by their leaves, and by their roots. Animals can be grouped by where they live and how they move. And each living thing has special features that help it survive in its own home. Grouping turns a confusing crowd into a few neat, easy-to-study sets.

Let’s Break It Down

The variety of living things

Imagine you go for a walk in a park. You take a notebook with you.

You start writing down everything living that you see. Plants first. There is soft grass. There is a holy basil (tulsi) plant. There is a hibiscus (gudhal) bush. There is a big neem tree.

Even these few plants are very different. Look:

• Some have soft stems. Some have hard stems.
• Some are short. Some are tall.
• Their leaves are different shapes.
• Their flowers are different colours and smells.

Now the animals. A crow sits on a tree. An ant carries a tiny twig. A cow eats grass. A fish swims in a pond. A frog sits on a rock.

These are different too:

• They live in different places — tree, soil, water.
• They eat different food — insects, leaves, seeds.
• They move in different ways — fly, walk, crawl, swim.

This variety of all the living things found in one area is called the biodiversity of that area. (“Bio” means life. So biodiversity means the variety of life.)

And here is something beautiful. All these living things need each other. A tree gives food and a home to birds. A bird eats a fruit, then drops the seed far away, and a new plant grows. So plants and animals depend on one another. Nothing in nature lives all alone.

Grouping plants — herbs, shrubs, trees, climbers and creepers

There are far too many plants to study one by one. So let us group them.

One easy way is to look at the height of a plant and the kind of stem it has. (The stem is the main part that holds the plant up — like the body of the plant.)

Using this idea, we get five groups. Figure 2.1 below shows all five together, drawn at the correct sizes so you can compare them at a glance.

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Let us meet each one slowly.

Herbs are small plants. They have a soft, green stem. You can bend the stem easily without breaking much. Most herbs also live for only a short time. A tomato plant is a herb. So is grass and a wheat plant.

Shrubs are bigger than herbs but not as big as trees. They have many hard, woody, brown stems. The stems start branching out close to the ground. This makes a shrub look bushy. A rose plant is a shrub.

Trees are the giants. They are very tall. They have one thick, hard, woody, brown stem. This single main stem is called the trunk. The branches start high up, away from the ground. A mango tree and a neem tree are trees.

Some plants have a stem that is too weak to stand up by itself. These plants need help.

Climbers have a weak stem that takes support and climbs up. It may wind around a stick, a wall, or another plant to go higher. A money plant and a grapevine are climbers.

Creepers also have a weak stem. But a creeper does not climb up. It creeps along the ground, spreading flat. A pumpkin plant and a watermelon plant are creepers.

The first three — herbs, shrubs, and trees — are the most common groups. Let us put them next to each other so the difference is crystal clear.

Let us use these rules on a real plant.

Parts of a plant, leaf venation, and root types

We grouped plants by their size and stem. But there are other ways too. We can look at their leaves and their roots. First, let us be sure of the main parts of a plant.

Most plants have four main parts. Figure 2.2 shows them on one plant.

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So the four parts are the roots, the stem, the leaves, and the flower. Now let us look closely at two of them — the leaves and the roots — because they help us group plants.

Leaf venation. Pick up a fallen leaf and hold it up to the light. You will see thin lines all over it. These lines are called veins. The pattern that these veins make on the leaf is called venation. (Think of “veins” plus “-ation”, which means the pattern of the veins.)

There are two main kinds of venation. Figure 2.3 shows both, side by side.

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In reticulate venation, the veins make a net-like web. There is a thick middle vein, and smaller veins branch off it and join up like a net. A hibiscus leaf has reticulate venation.

In parallel venation, the veins run side by side, like the lines on a ruled notebook. They do not cross to make a net. A banana leaf and a grass leaf have parallel venation.

Root types. Now gently pull up a small plant with its roots and wash off the soil. The roots will look one of two ways. Figure 2.4 shows both.

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A taproot has one thick main root growing straight down. Small side roots come off this main root. A mustard plant has a taproot.

A fibrous root has many thin roots of similar size. They all grow out together from the bottom of the stem, like a bunch of threads. There is no single main root. A grass plant has fibrous roots.

Let us put these two roots side by side.

Now here comes the surprising part. The leaf and the root of a plant are linked.

Plants with reticulate venation (net-like leaves) usually have a taproot.

Plants with parallel venation (side-by-side leaves) usually have fibrous roots.

This is not a coincidence. Why does this link exist? Because of how the plant is built from its very first day. When a seed sprouts, some plants have a baby plant with two cotyledons — the first tiny leaves packed inside the seed, which often carry a store of food. Other plants have only one. Plants built the first way grow up with net-like leaves and a taproot. Plants built the second way grow up with parallel-veined leaves and fibrous roots. The leaf pattern and the root type are decided together, right from the seed. That is why one always comes with the other.

So if you ever see a leaf with net-like veins, you can already guess what its roots look like — a taproot — even before you dig it up. That is the power of grouping. One clue tells you about another.

Some of this idea — drinking water and making food — comes from earlier classes. Let us quickly refresh it so nothing feels new.

Animals and their habitats

We grouped plants. Now let us think about animals.

Animals are different from each other in many ways. They live in different places. They eat different food. They move in different ways. We can group them using any of these.

The simplest grouping is by where they live. Some animals live on land. Some live in water.

The place where a plant or an animal lives is called its habitat. A habitat is simply the natural home of a living thing. It gives the animal everything it needs — food, water, air, and shelter.

Figure 2.5 below shows two different habitats and an animal in each.

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Animals that live on land live in a terrestrial habitat. (“Terra” means land.) Forests, deserts, grasslands, and mountains are all terrestrial habitats. A goat, a lion, and a camel live on land.

Animals that live in water live in an aquatic habitat. (“Aqua” means water.) Ponds, rivers, and oceans are aquatic habitats. A fish lives in water.

Some animals do not fit neatly into just one of these. A frog can live both on land and in water. It swims in the pond and it also sits and hops on the land nearby. Animals that live both on land and in water like this are called amphibious animals. And a few animals spend much of their time in the air, flying high in the sky. A place in the air or high on treetops where flying animals like birds live is called an aerial habitat.

Now look again at how each animal moves. The goat walks on legs. The fish swims with fins. This is not random. The body of each animal is matched to its home.

This matching has a name. The special features that help a living thing survive in its home are called adaptations. (“Adapt” means to fit in.)

Here comes the “why”. Why does a fish have fins and a smooth body, but a goat has legs? Because their homes are different, and each body is built to suit its home.

Water is thick and pushes back as you move through it. A smooth, slim body slides through water easily, and fins push the water to swim. Legs would be almost useless under water. On land, there is firm ground to step on. Legs are perfect for walking and running on it, but fins would just flop around uselessly. So each animal has the body that works best where it lives.

Think of the desert too. A desert is very hot in the day and there is little water. A camel that lives there has special features to cope: it can go many days without drinking water. A cactus plant in the desert stores water in its thick, fleshy stem. These are adaptations as well.

Why we group living things

We have grouped plants and animals in several ways now. Let us stop and ask the big question. Why do we bother grouping at all?

Think about your school bag. If you throw all your books, pens, and lunch box in together, it is a mess. You waste time hunting for things. But if you keep books in one part, pens in a pocket, and the lunch box in another part, everything is easy to find.

Grouping living things works the same way. There are millions of different plants and animals. That is far too many to study one by one. But when we put the similar ones together in groups, the huge crowd becomes a few neat sets. Each set is easy to understand and study. Putting similar things into groups like this is also called classification.

Figure 2.6 below shows this idea as a simple chart.

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There is one more important point. There is no single right way to group. It depends on the feature you choose.

If you group plants by height, you get herbs, shrubs, and trees. If instead you group them by whether they have flowers or not, you get different groups. Both are correct. They just use different features.

So grouping is a tool. We pick the feature that helps us answer the question we care about.

Common Mistakes

Here are the slip-ups students make most often. Read them once and you will avoid them.

Quick Check

Try these. Each one checks an idea from the chapter.

Practice Problems

Try each one yourself first. Only then tap to see the full answer.

Easy

Medium

Challenge

Summary

• The living world has huge diversity — a great variety of plants and animals. The variety of living things in one area is its biodiversity.
• To study so many living things, we group them by the features they share. There is no single correct way to group; it depends on the feature you pick.
• Plants can be grouped by size and stem into herbs (small, soft stem), shrubs (medium, woody, bushy), trees (tall, one thick trunk), climbers (weak stem, climbs up with support), and creepers (weak stem, spreads flat on the ground).
• A plant’s main parts are the roots, stem, leaves, and flower. Roots hold the plant and drink water; leaves make food.
• The vein pattern on a leaf is its venation: reticulate (net-like) or parallel (side by side). Roots are either a taproot (one thick main root) or fibrous (many thin equal roots).
• Reticulate venation usually goes with a taproot, and parallel venation with fibrous roots, because the leaf and root type are decided together when the seed sprouts.
• The natural home of a living thing is its habitat (terrestrial = land, aquatic = water). Features that help a living thing survive in its habitat are called adaptations, like a fish’s fins for water and a camel’s water-saving body for the desert.

What’s Next

You now know how to see and group the variety of life around you. Next, we turn to something every living thing needs every single day — food.

In Chapter 3, Mindful Eating: A Path to a Healthy Body, you will learn what is in the food you eat, why your body needs different kinds of food, and how to make healthy food choices. Just as different plants and animals have different needs, your own body has needs too — and food is how you meet them.