Plant Life Chapter Notes | Preparation for EmSAT Grade 6 PDF Download

Introduction

There are various types of plants around us. Some are small- or medium-sized whereas others are big. They also show variations in structure, shape, size and colour of their leaves, flowers, roots and stems. However, the overall structure of all these plants consist of two parts. 

• The root system 
• The shoot system 

The part of a plant that grows below the ground is called the root system. It consists of roots.
The part of the plant which grows above the ground is called the shoot system. It consists of stem, leaves, buds, flowers and fruits.

Leaf

Parts of a Leaf

• Leaf blade or lamina: The broad, flat, green part of the leaf.
• Petiole: The short, narrow stalk that connects the lamina to the stem.
• Sessile leaf: A leaf without a petiole, directly attached to the stem (e.g., zinnia).
• Midrib: A thick central vein in the lamina, extending from the petiole to the leaf tip.
• Veins and veinlets: Smaller branches from the midrib that transport water and food and support the leaf.
• Leaf base: The slightly swollen part where the petiole attaches to the stem.

Types of Leaves

• Simple leaf: Has a single lamina; cuts, if present, do not reach the midrib (e.g., mango, guava, banana, banyan).
• Compound leaf: Lamina is divided into smaller leaflets without axillary buds (e.g., neem, acacia, rose).

Classification of Leaves on the Basis of Shape and Margin
On the Basis of Shape

• Needle-shaped (e.g., pine, onion).
• Oval or elliptical (e.g., guava, apple).
• Heart-shaped (e.g., betel, Tinospora).
• Oblong (e.g., banana).
• Circular (e.g., lily, lotus).

On the Basis of Margin

• Complete or entire margin (e.g., banyan, mango).
• Toothed or serrate margin (e.g., rose, China rose).
• Wavy margin (e.g., ashoka, Polyalthia).
• Spinose margin (e.g., prickly poppy).

Arrangement of Leaves

• Phyllotaxy: The pattern of leaf arrangement on a stem.
• Alternate: One leaf per node, with successive leaves in opposite directions, forming a spiral (e.g., China rose, mustard, sunflower).
• Opposite: Two leaves arise from the same node, opposite each other (e.g., basil, guava, jasmine).
• Whorled: More than two leaves arise from the same node, forming a circle or whorl (e.g., oleander).

Venation of Leaves

• Venation: The pattern of veins and veinlets on the leaf’s lamina.
• Reticulate venation: Veins and veinlets form an irregular network across the lamina (e.g., peepal, guava, mango).
• Parallel venation: Veins run parallel to each other from the midrib (e.g., banana, grass, wheat).
• Monocot plants usually have parallel venation, while dicot plants have reticulate venation.

Functions of a Leaf

• Manufacturingof food: The primary function of a leaf is to manufacture food (sugar and starch) in the presence of sunlight. The food is prepared by green leaves containing chlorophyll. The process by which green leaves prepare their own food in the presence of sunlight using carbon dioxide and water is called photosynthesis. Oxygen is released in this process which supports life on earth. 
• Exchange of gases: Many minute pores called stomata are present on the lower surface of leaves. The exchange of carbon dioxide and oxygen takes place through these pores. During the day, plants take in carbon dioxide and give out oxygen, while at night they take in oxygen and release carbon dioxide. 
• Transpiration: Plants give out extra water in the form of vapour through stomata of leaves. This process of loss of water through leaves is called transpiration. This helps in keeping the plants cool. 

Modifications of Leaves

• Leaf tendrils: Thin, coiled structures for climbing and support, sensitive to touch (e.g., grapevine, pea).
• Leaf spines: Sharp, pointed structures for protection from animals and reducing water loss in deserts (e.g., cactus, prickly pear).
• Scale leaves: Thick and fleshy for storing food and water (e.g., onion) or thin and dry to protect buds (e.g., ginger).

Modification of Leaves in Insectivorous Plants

• Insectivorous plants grow in nutrient-poor soil and trap insects for food using modified leaves.
• Pitcher plant: Leaf forms a pitcher with a lid; insects enter, the lid closes, and digestive juices break down the insect.
• Venus flytrap: Leaf has pointed hairs and a hinged lamina; it closes when an insect is trapped and digests it.
• Bladderwort: Leaf segments form bladders with a trap door; small flies enter and are digested.

Vegetative Propagation in Leaves

• Some plants, like Bryophyllum and Begonia, reproduce through leaves.
• In Bryophyllum, buds in leaf margin notches develop into plantlets, which detach and grow into new plants, even if the leaf falls on moist soil.

Flower

• Flowers are the reproductive parts of plants, developing from floral buds, and vary in shape, size, and color.
• They produce fruits and seeds.

Parts of a Flower

• Flowers have four whorls: calyx, corolla, androecium, and gynoecium.
• Calyx: Outermost whorl with green sepals that protect the bud.
• Corolla: Second whorl with colorful, scented petals that protect reproductive parts and attract insects.
• Androecium: Male reproductive part with stamens, each having a filament and an anther containing pollen grains with male gametes.
• Gynoecium: Female reproductive part with carpels (pistils), each having an ovary (with ovules containing female gametes), style, and stigma.
• Flowers are attached to the stem by a pedicel; those without are called sessile.
• Thalamus: The enlarged, flattened tip of the pedicel where whorls arise.

Types of Flowers

• Bisexual flowers: Have both male and female reproductive parts (e.g., lily, rose, Hibiscus).
• Unisexual flowers: Have either male or female reproductive parts (e.g., oak, hazel, walnut).

On the Basis of Number of Whorls

• Complete flowers: Have all four whorls (e.g., pea, tulips, Hibiscus).
• Incomplete flowers: Lack one or more whorls (e.g., oaks, begonia, elms).

Functions of a Flower

Reproduction in Plants

Pollination

• Pollination is the transfer of pollen grains from an anther to a stigma of the same or another flower of the same species.
• Self-pollination: Pollen transfers within the same flower or to another flower on the same plant.
• Cross-pollination: Pollen transfers to a flower on another plant of the same species.

Agents of Pollination

• Agents like wind, water, insects, and animals transfer pollen grains.

Pollination by Wind

• Occurs in plants like dandelion, rice, maize, and grass.
• Flowers are small, not colorful, lack nectar or smell.
• Anthers produce many light, smooth, dry pollen grains.
• Stigma is large and feathery to catch wind-blown pollen.

Pollination by Water

• Occurs in aquatic plants like Hydrilla and Vallisneria.
• In Vallisneria, male flowers float to the surface when mature, contact female flowers with long stalks, and transfer pollen.

Pollination by Insects

• Common in plants like rose and marigold, pollinated by bees, flies, wasps, moths, and beetles.
• Flowers are brightly colored, have a sweet smell, produce nectar, and have sticky pollen and stigma.

Pollination by Animals

• Occurs in plants like silk-cotton tree, pollinated by birds, squirrels, bats, and snails.

Fertilization

• Fertilization is the fusion of male and female gametes.
• Pollen grains germinate on the stigma, forming a pollen tube that carries male gametes through the style to the ovule in the ovary.
• The male gamete unites with the egg in the ovule, forming a zygote.
• After fertilization, the ovule becomes a seed, the ovary becomes a fruit, and sepals/petals fall off.

Fruit

Parts of a Fruit

• Pericarp: The fruit wall, developed from the ovary wall, has three parts:
• Epicarp: The outermost thin layer.
• Mesocarp: The fleshy middle part.
• Endocarp: The innermost hard part containing seeds.
• Seed: Developed from ovules.
• False fruits: Fruits where parts other than the ovary (e.g., thalamus in apple) form the edible part.

Types of Fruits

• Dry fruits: Have a thin, hard pericarp enclosing the seed (e.g., walnut, pea, maize, sunflower).
• Fleshy fruits: Have a thick, fleshy pericarp with epicarp, mesocarp, and endocarp (e.g., mango, orange, cherry, plum).

Functions of a Fruit

• Protects seeds from animals and harsh conditions.
• Attracts animals for seed dispersal.
• Stores food material.

Seed

• Seeds develop from ovules after fertilization and vary in shape, size, and appearance.
• Some fruits have one seed (e.g., mango, plum), others have many (e.g., orange, papaya, tomato).

Structure of a Seed

• Seed coat: The outer protective covering.
• Embryo: The baby plant inside, with three parts:
• Plumule: Develops into the shoot.
• Radicle: Develops into the root.
• Cotyledons: Store food and become the first leaves.

Types of Seeds

• Monocot seeds: Have one cotyledon (e.g., wheat, rice, corn).
• Dicot seeds: Have two cotyledons (e.g., gram, bean, pea).

Germination of Seeds

• Germination is the process where a dormant embryo in a seed becomes active and grows into a new plant under suitable conditions.
• Steps: The seed absorbs water, swells, and the seed coat bursts; the radicle grows downward to form the root; the plumule grows upward to form the shoot; cotyledons form the first leaves.

Conditions Required for Germination

• Water: Needed to swell the seed, burst the seed coat, and dissolve stored food for the embryo.
• Air: Oxygen is required for respiration to provide energy for embryo growth.
• Temperature: Ideal range is 35°C to 40°C for enzyme activity; extreme temperatures prevent germination.

Keywords

• Root system: Part of the plant below the soil.
• Shoot system: Part of the plant above the soil, including stem, leaves, flowers, and fruits.
• Sessile leaf: Leaf attached directly to the stem without a petiole.
• Simple leaf: Leaf with a single lamina.
• Compound leaf: Leaf with lamina divided into leaflets.
• Venation: Arrangement of veins and veinlets on the leaf lamina.
• Photosynthesis: Process where green plants make food using sunlight, carbon dioxide, and water.
• Transpiration: Loss of water vapor through leaf stomata.
• Androecium: Male reproductive part of a flower, consisting of stamens.
• Gynoecium: Female reproductive part of a flower, consisting of carpels.
• Sessile flowers: Flowers without a pedicel.
• Pollination: Transfer of pollen from anther to stigma.
• Fertilization: Fusion of male and female gametes to form a zygote.
• Germination: Process where a seed’s embryo becomes active and grows into a new plant.