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Lakhmir Singh’s Science Class 4

Learning Objectives:

• Parts of a leaf

• Functions of a leaf

• How green leaves produce food

• Interdependence of plants and animals

Plants, animals and humans need energy to live. They get this energy from the food and nutrients they consume.

Green plants can make their own food through a process known as photosynthesis. The green leaf is the site where this process of producing food occurs in plants. Humans and animals depend on plants for food, either directly or indirectly. So, plants are known as producers.

GREEN LEAF – A PLANT’S KITCHEN The green colour of leaves comes from a substance called chlorophyll. This substance is essential for the process of producing food or photosynthesis to occur.

Parts of a LeafLeaves are of different shapes and sizes and have different parts. However, there are some basic parts that are common in most leaves. These are:

GREEN PLANTS

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Petiole

Blade

Midrib

Apex

Side veins

Parts of a leaf

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41. Blade: The broad flat part of the

leaf

2. Apex: The tip of the leaf

3. Midrib or main vein: Veins are framework of hollow tubes that carry water and minerals; the midrib runs along the centre

4. Side veins: Veins that branch out from the midrib

5. Petiole: The part that joins the leaf to the main stem

Stomata are tiny openings or pores mostly found on the under-surface of leaves. Air enters and leaves the plant through these openings. Stoma helps the plant to breathe. A stoma is very tiny and can be seen only under a microscope.

Stoma

Stomata in leaf

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The outer surface of the leaf has a waxy coating called cuticle which protects the leaf.

Functions of a LeafLeaves are very useful for the plants. The main functions of a leaf are: • to produce food • exchange of gases through stomata • food storage • transpiration or evaporation of water • reproduction or vegetative propagation In this chapter we will learn about the role of leaves in photosynthesis or food production.

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How Green Leaves Produce FoodPlants need three basic things to live: water, sunlight and carbon dioxide. Photosynthesis is the process by which a plant produces its food using energy from sunlight, carbon dioxide from the air and water from the soil. The word photosynthesis can be separated to make two smaller words: ‘photo’ which means light

‘synthesis’ which means putting together

In this process, light energy from the Sun is absorbed by the green substance, called chlorophyll, present in leaves. This energy allows the production of glucose (food) by the reaction between carbon dioxide and water. Oxygen is also produced as a by-product.

Carbon dioxide + Water Light energy → Glucose + Oxygen

Photosynthesis

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Photosynthesis is unique to green plants. This process supplies food for the plant and oxygen for other forms of life. A green plant helps make the oxygen we are breathing today. So, green plants are often referred as green lungs.

ACTIVITYObjective: To find out if a plant has carried out photosynthesis by testing for starch. Presence of starch implies that photosynthesis has occurred. Important fact: Iodine solution is a special solution that is normally a brown liquid. When iodine solution is dropped on starch, the iodine and starch combine and produce a blue colour. Materials needed: A piece of potato, small amount of cooked rice, ink dropper, iodine solution, two dishesSteps:

1. Fill some iodine in the ink dropper. 2. Add a few drops of iodine directly to the piece of potato and the cooked rice.

Dish 1 Dish 2Iodine test for starch

Observations:

Dish 1: Potato Dish 2: Cooked rice

The iodine turned blue-black The iodine turned blue-black

Conclusion: Both potato and cooked rice contain starch as iodine turns blue-black in the presence of starch. Thus we can say that photosynthesis has occurred.

PHOTOSYNTHESIS GIVES FOOD AND OXYGEN

FoodSome of the glucose is used to provide energy for the growth and development of plants while the rest is stored as starch in leaves, roots, fruits, flowers and seeds for later use by plants. These are food sources for humans and some animals too.

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ACTIVITYObjective: To show that sunlight is necessary for photosynthesis.Materials needed: A leafy potted plant, black paper, scissors, iodine solution, ink dropper and paper clipsSteps:

1. Cover a leaf partly with black paper as shown below.

Paper clip

Exposed to sunlight Black paper clipped to both sides of a leaf

Potted plant

Demonstration of necessity of sunlight for photosynthesis

2. Leave the potted plant in sunlight for 2-6 hours.3. Remove the paper and test the leaf for starch by doing the iodine starch test.Conclusion and explanation: Only the uncovered parts turn blue-black when iodine solution is dropped on the leaf. The part that had been covered does not change colour.

Blue or BlackBrown

The uncovered part turns blue-black

Starch is produced only in the areas that received sunlight, showing that sunlight is necessary for photosynthesis.

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Some food we get from plants are

carrot, beet, turnip onion, celery lettuce, spinach, cabbage

ROOTS STEMS LEAVES

peas, green beans, corn tomato, apple, watermelon broccoli, cauliflower

SEEDS FRUITS FLOWERS

Oxygen Oxygen produced during photosynthesis is released into the atmosphere. This oxygen is what we breathe to stay alive.

INTERDEPENDENCE OF PLANTS AND ANIMALSPlants and animals depend on each other for many things.

For Food Animals depend on plants and other animals for food. Animals can be divided into the following groups, according to what they eat: • Herbivores eat plants. • Carnivores eat other animals. • Omnivores eat both plants and animals. • Scavengers feed on dead animals. • Decomposers eat and break down the remains of dead animals. The elements

that are released during this process are put back in the soil and become food for plants.

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Grass Deer (Herbivore) Lion (Carnivore) Vulture (Scavenger)Food chain

For Pollination Plants depend on animals for pollination or transfer of pollen grains from one flower to another. Pollination helps in the growth of new plants. Bees, butterflies and wasps are some pollinators. They visit flowers to get nectar, which is food for them.Plants attract pollinators through • sweet nectar • nice smell or fragrance • colourful flowers

Seed Dispersal Plants need to have their seeds spread over a wide area. If all the seeds fall in one area, the plants that grow will not have enough water, soil or sunlight to grow properly. Animals eat fruits. At times seeds get stuck to their fur and are carried away and dispersed at a distance. This is called seed dispersal. It helps in the growth of new plants. So, while animals get food from plants, they in turn, help in the growth of new plants.

SUMMARY• Green plants or producers can make their own food through a process known as

photosynthesis.• The green colour of leaves comes from a substance called chlorophyll.• Photosynthesis is the process by which a plant produces its food using energy from

sunlight, carbon dioxide from the air and water from the soil.• Photosynthesis is unique to green plants. This process supplies food for the plant

and oxygen for other forms of life.• Plants and animals are dependent on each other.

Pollination by bee

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GLOSSARY• Apex: the tip of the leaf• Blade: the broad flat part of the leaf• Chlorophyll: the substance that gives leaves their green colour• Petiole: the part that joins the leaf to the main stem • Photosynthesis: process through which green plants can make their own food• Stomata: tiny openings or pores mostly found on the under-surface of leaves• Veins: framework of hollow tubes that carry water and minerals

Objective Type Questions 1.Underlinethecorrectwordstofillintheblanks.

(a) Stomata are tiny openings or pores mostly found on the .................... (upper-surface/under-surface) of leaves.

(b) The ............................ (green/brown) colour of leaves comes from a substance called chlorophyll.

(c) Air enters and leaves the plant through ........................... (roots/stomata).

(d) Photosynthesis is unique to ........................ (green plants/all living things).

(e) ............................. (Oxygen/Carbon dioxide) produced during photosynthesis is released into the atmosphere.

2. Draw and label the following:

(a) Parts of a leaf

(b) Photosynthesis

(c) Stomata

3. Which part of the plant do we eat when we eat the following?

(a) (b) (c)

..................................... ..................................... .....................................

(d) (e) (f)

..................................... ..................................... ......................................

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4. Write true or false.

(a) All living things can produce their own food. ……………….

(b) Chlorophyll is essential for photosynthesis. …………………

(c) Plants consume all the food they produce. ……………………..

(d) Animals depend directly or indirectly on plants. …………………..

(e) Pores called stomata help in the movement of air in plants. …………………

(f) Carbon dioxide is released during photosynthesis. ………………………

Subjective Type Questions 5. Answer the following.

(a) Why plants are called producers?

(b) What is the role played by green leaves in the production of food?

(c) What are the different parts of a leaf?

(d) What is photosynthesis? Describe how it occurs.

(e) How are plants and animals dependent on each other? Explain through two examples.

Multiple Choice Questions (MCQs) 6. Tick (3) the correct options.

(a) Which of these is a necessary ingredient for photosynthesis?

(i) water (ii) carbon dioxide

(iii) sunlight and chlorophyll (iv) all of these

(b) The tip of the leaf is

(i) blade (ii) midrib (iii) apex (iv) petiole

(c) Framework of hollow tubes that carry water and minerals

(i) leaves (ii) veins (iii) blades (iv) stomata

(d) Which of the following correctly shows the process of photosynthesis?

(i) Oxygen + Water Sunlight → Glucose + Carbon dioxide

(ii) Carbon dioxide + Water Sunlight → Glucose + Oxygen

(iii) Carbon dioxide + Air Sunlight → Glucose + water

(iv) Carbon dioxide + Oxygen Sunlight → Glucose + Starch

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(e) Which of these is not a function of leaves?

(i) to produce food

(ii) exchange of gases through stomata

(iii) food storage

(iv) absorption of water and nutrients from the soil

Questions Based on Higher Order Thinking Skills (HOTS) 7. Tara wants to find out whether cooked pasta contains starch. How can she find out?

8. Mohit kept a potted plant in the dark storeroom. Later, he found that its leaves had turned yellow and the plant had withered. Why did this happen?

ANSWERS 1. (a) under-surface (b) green (c) stomata (d) green plants (e) oxygen 3. (a) leaves (b) fruit

(c) seed (d) fruit (e) stem (f) flower 4. (a) F; (b) T; (c) F; (d) T; (e) T; (f) F 6. (a)(iv); (b)(iii); (c)(ii); (d)(ii); (e)(iv)

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Learning Objectives:

• Habitat

• Adaptation

• Plants on land

• Plants in water

• Other plants

Plants grow in different places. They can be found in dry and sandy deserts, damp and wet plains, hilly areas, valleys, snow-covered high mountains and even

under water. The local environment of a plant is known as its habitat. A habitat can be as small as a patch of a garden or as big as a forest. Plants often have to adapt, or change in order to survive in their habitat. Adaptations are special features that help a plant survive in its habitat. Plant habitats can be divided into two major groups: • land or terrestrial habitats • water or aquatic habitats

WHERE PLANTS LIVE – ADAPTATIONS

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LAND OR TERRESTRIAL PLANTSLand habitat can be subdivided into many areas. Plants growing in each of these areas need to adjust to the kind of weather, amount of rainfall, type of soil, and other such factors found in that place.

Plants in the PlainsPlants growing in flat plains have more space to spread out. Usually, they grow several branches and have flat leaves. These help water vapour to evaporate and keep the tree cool when the climate gets hot. Flat leaves also help to trap a lot of sunlight. Mango, banyan, neem, peepal, mulberry, poplar and sheesham are some trees that grow in plains.

Some of these trees lose all their leaves at once in autumn. As spring approaches, new leaves start growing.

Plants in Deserts Hot deserts are sandy, dry and very hot places. There is scarcity of rainfall and a lot of direct sunlight falls on the plants.

The soil in desert is sandy and unable to hold much water. Strong, dry winds and extreme temperatures make survival tough. However, all these difficulties cannot stop plants from growing in deserts. Some adaptations in desert plants are • Plants called succulents, store water in their

stems or leaves. • Long root systems in desert plants spread and

go deep into the ground to absorb the available water.

• Some plants have very small seasonal leaves that only grow after it rains. The lack of leaves helps reduce water loss.

Plants grow several branches in plains

Plants spread out in plains

Succulent desert plants

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• Some plants are leafless, and conduct photosynthesis in their green stems.

• Leaves covered with hair provide shade for the plant and thus reduce water loss.

• Prickly spines discourage animals from eating plants for water.

• Waxy coating on stems and leaves help reduce water loss.

Plants in Mountains In the mountains most plants are tall and straight. They are cone-shaped. Most plants growing in hills and high mountains have needle-like leaves. The needle-shape prevents too much water loss and helps shed snow more easily than flat, broad leaves. Waxy coatings on the needles prevent evaporation and loss of water. The dark colour of the needles allows more solar heat to be absorbed. Many trees have branches that droop downward to help shed excess snow to keep the branches from breaking.

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The Tundra region is cold year-round. It has a permanently frozen sub layer of soil called permafrost. Some Tundra plants grow in clumps to protect one another from the wind and cold. Some plants have dish-like flowers that follow the Sun helping the plant stay warm.

Plants in Heavy-rainfall Areas In areas with heavy rainfall the plants are evergreen, which means they do not lose their leaves. Rice, lychee, cashew, pineapple, sugarcane, cotton, rubber and teak grow well in these areas.

Cone-shaped mountain plants

Prickly spines in desert plants

Cotton is an evergreen plant

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Plants along the Sea CoastCoconut trees grow well in these areas. They are adapted to grow in salty water and high rainfall. The seeds of plants growing in coastal regions are carried from place to place or dispersed by water.

Plants in Marshy or Swampy AreasThese areas have clayey soil that is very sticky. It is difficult for plants to grow in such areas as air cannot reach the roots. Mangroves with their breathing roots are well-adapted to grow in swampy areas.

WATER OR AQUATIC PLANTSPlants that grow in water have special adaptations too. Aquatic plants can be floating, fixed or submerged. Floating plants like duckweed and water hyacinth are light, spongy and can float on the surface of the water. Chlorophyll is restricted to the upper surface of leaves that receives sunlight. The upper surface is waxy to repel water.Fixed plants have roots fixed to the bottom of the water body such as a pond. They have long stems to reach the surface of water. They have broad leaves with waxy coating that helps the leaves to stay dry and prevents rotting. Lotus and water lily are examples of fixed plants.

Plants in coastal area

Mangroves

Duckweed Water hyacinth

Lotus Water lily

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Underwater plants such as pond weed and tape grass have narrow leaves without stomata. They breathe through the surface and keep the water clean. In submerged plants water, nutrients and dissolved gases are absorbed through the leaves directly from the water.

Non-green PlantsAs the name suggests, non-green plants do not have chlorophyll. The Indian pipe and coral root plants are examples. Such plants cannot produce their own food and are called saprophytes. They depend on dead plants and animals to fulfil nutritional needs.

CARNIVOROUS OR INSECTIVOROUS PLANTSCarnivorous plants grow in places with poor soil that doesn’t offer many nutrients. These amazing plants have developed insect traps to get their nutritional needs met.Venus flytrap, pitcher plant, cobra lily and sundews are some carnivorous plants. The leaves of the Venus flytrap consist of two lobe-like leaves joined in the middle. Tiny hairs grow near the hinge. When an insect walks across the hairs, the lobes snap shut and trap the insect inside. Digestive juices secreted by glands on the surface of the leaf help in absorbing the nutrients. Sundew plants have long tentacles topped with a sweet, sticky substance. Once an insect gets stuck, more tentacles move in the direction of the insect to make a tighter trap.Pitcher plants are shaped like a pitcher. The top and inside of the pitcher is covered with a slippery, sweet-smelling nectar. When insects come to take a sip, they slip and fall into the pitcher.

Tape grass

Indian pipe

Pitcherplant Venusflytrap

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SUMMARY• Adaptations are special features that help a plant survive in its habitat. • Plants growing in flat plains have more space to spread out.• Long root systems in desert plants go deep into the ground to absorb the available

water.• The needle-shaped leaves prevent too much water loss and help shed snow more

easily than flat, broad leaves. • Evergreen plants grow in areas with heavy rainfall. • Plants that grow along the sea coast are adapted to salty water. • Mangroves with their breathing roots are well-adapted to grow in swampy areas.• Aquatic plants can be floating, fixed or underwater. • Non-green plants do not have chlorophyll.• Carnivorous plants have developed insect traps to get their nutritional needs

met.

GLOSSARY• Habitat: the local environment of a plant• Adaptations: special features that help a plant survive in its habitat• Terrestrial plants: plants that grow on land • Succulents: desert plants that store water in their stems or leaves• Aquatic plants: plants that grow in water • Swampy areas: areas with clayey soil that is very sticky• Non-green plants: plants without chlorophyll• Saprophytes: plants that survive on dead plants and animals • Carnivorous or insectivorous plants: plants that eat insects

Objective Type Questions 1.Tick(3) the odd one.

(a)

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(b)

(c)

(d)

2. Complete the table.

(a) adapted to grow in salty water and high rainfall

(b) long tentacles topped with a sweet, sticky substance

(c) the Indian Pipe

(d) lotus and water lily

(e) the needle-shaped leaves prevent too much water loss and help shed snow

3.Fillintheblanks.

(a) ....................................., ..................................... and ..................................... are some trees that grow in plains.

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(b) .............................. in some desert plants discourage animals from eating plants for water.

(c) Underwater plants such as pond weed and tape grass have narrow leaves without ..................................... .

(d) In a pitcher plant the top and inside of the ..................................... is covered with a slippery, sweet-smelling nectar.

(e) Sundew plants have long ..................................... topped with a sweet, sticky substance.

(f) ..................................... plants breathe through the surface and keep the water clean.

(g) Long ..................................... in desert plants go deep into the ground to absorb the available water.

4. Name the following.

(a) Two floating plants: ....................................., .....................................

(b) Two fixed plants: ....................................., .....................................

(c) Two submerged plants: ....................................., .....................................

(d) Two non-green plants: ....................................., .....................................

(e) Two carnivorous plants: ....................................., .....................................

Subjective Type Questions 5. Answer the following.

(a) What is adaptation?

(b) How are adaptations useful for desert plants?

(c) What are the three different kinds of aquatic plants? Give examples for each.

(d) Why carnivorous plants are called so?

(e) How does a pitcher plant trap food?

(f) What are saprophytes?

Multiple Choice Questions (MCQs) 6.Tick(3) the correct options.

(a) Light, spongy and ........................... can float on the surface of the water.

(i) Venus flytrap and pitcher plant (ii) duckweed and water hyacinth

(iii) lotus and water lily (iv) cactus

(b) The seeds of plants growing in ..................................... regions are carried from place to place or dispersed by water.

(i) desert (ii) swampy

(iii) coastal (iv) hilly

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(c) ........................ have narrow leaves without stomata.

(i) underwater plants (ii) fixed plants

(iii) floating plants (iv) none of these

(d) They depend on dead plants and animals to fulfil their nutritional needs.

(i) carnivorous plants (ii) saprophytes

(iii) saguaro (iv) fig and neem

(e) Plants in heavy rainfall areas are

(i) rice, cotton, sugarcane (ii) sundew, pitcher plant

(iii) Indian pipe, coral root (iv) cactus, saguaro

Questions Based on Higher Order Thinking Skills (HOTS) 7. In her essay on non-green plants, Megha wrote about how non-green plants carry out

photosynthesis. Was Megha right? Give reasons.

8. “Plants need to modify one or more body parts to adapt to their local environment.” Give three examples (from the lesson) to support this fact.

9. In a tropical rainforest, where it is hot and it rains a lot, which of these would be helpful adaptation for plants. Also say why.

(a) Waxy leaves

(b) Tips

(c) Both of these

ANSWERS 2. (a) coconut tree (b) Sundew plant (c) non-green plant without chlorophyll (d) long stems

to reach the surface of water (e) mountain plants 3. (a) banyan; neem; mulberry (b) prickly spines (c) stomata (d) pitcher (e) tentacles (f) Underwater (g) root 4. (a) duckweed, water hyacinth (b) lotus, water lily (c) pond weed, tape grass (d) Indian pipe, coral root (e) venus flytrap, cobra lily 6. (a)(ii); (b)(iii); (c)(i); (d)(ii); (e)(i) © S C

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