Chapter 7 — Getting To Know Plants

What are plants? Plants are living organisms that make their own food using sunlight. Most plants are multicellular, have cell walls, and contain chlorophyll (a green pigment) that captures light energy.

Key features of plants

• Autotrophic: They prepare their own food by photosynthesis.
• Cell structure: Plant cells have a rigid cell wall and chloroplasts (where photosynthesis happens).
• Growth: Plants grow throughout their life by producing new cells.
• Reproduction: They reproduce by seeds, spores, or vegetatively (e.g., cutting, runners).

Main parts of a typical flowering plant and functions

• Root — anchors the plant, absorbs water and minerals from soil, and sometimes stores food.
• Stem — supports leaves and flowers; transports water, minerals and food between roots and leaves.
• Leaves — main sites of photosynthesis and transpiration (loss of water vapour).
• Flower — reproductive organ that helps in making seeds; may develop into fruit.
• Fruit and seed — protect and disperse seeds; seeds grow into new plants.

How do plants make food? Through photosynthesis — leaves use sunlight, carbon dioxide (CO2) from air and water (H2O) from soil to make glucose (food) and oxygen (O2). The basic equation is:

6CO2 + 6H2O —> C6H12O6 + 6O2 (in presence of sunlight and chlorophyll)

Other processes: Plant cells also respire to release energy from food. Simplified respiration equation:

C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy

Types of plants (simple categories)

• By size/form: herbs (small, soft-stemmed), shrubs (medium, woody stems), trees (large, woody stem).
• By habitat: terrestrial (land), aquatic (water), epiphytes (grow on other plants).
• By reproduction: flowering (angiosperms) and non-flowering (gymnosperms, ferns, mosses).

Adaptations — Plants show special features to survive in different environments. Examples: cactus has thick stem and spines to save water (desert), lotus has broad leaves and air spaces (aquatic).

Importance of plants

• Produce oxygen and food (directly or indirectly for animals and humans).
• Provide raw materials (wood, fibres, medicines).
• Prevent soil erosion, provide habitats and maintain ecological balance.

Simple observation activities

• Grow a bean seed in a transparent cup to watch root and shoot development.
• Place 2 potted plants in different light conditions and note differences in leaf colour and growth.

Plant body and its main parts

Plants have a body made of different parts that perform specific functions needed for survival, growth and reproduction. The main parts are root, stem, leaf, flower, fruit and seed. Each part has a structure suited to its job.

Roots

• Functions: anchor the plant, absorb water and minerals from soil, store food.
• Types: taproot (one main root, e.g., carrot), fibrous roots (many similar roots, e.g., grass), adventitious roots (from stem, e.g., banyan prop roots).
• Modifications: storage roots (sweet potato), breathing roots (mangrove pneumatophores), prop roots (maize buttress-like support).

Stems

• Functions: hold leaves and flowers, transport water/minerals (upwards) and food (downwards), store food, sometimes do photosynthesis.
• Structure: nodes (where leaves attach) and internodes (between nodes). Vascular bundles contain xylem and phloem for transport.
• Modifications: tubers (potato) for storage, stolons/runners (strawberry) for vegetative propagation, rhizomes (ginger), thorns (defence).

Leaves

• Functions: main site of photosynthesis (making food), transpiration (water loss), and gas exchange (CO2 in, O2 out).
• External parts: lamina (blade), petiole (stalk), veins.
• Internal structure: upper and lower epidermis (with cuticle), stomata (pores for gas exchange), mesophyll with palisade cells (many chloroplasts) and spongy cells (air spaces), vascular bundles (veins).
• Modifications: tendrils (climbing plants), spines (cactus for protection), storage leaves (onion), insect-catching leaves (Venus flytrap).

Flower, fruit and seed (Reproductive parts)

• Flower: the reproductive structure; main parts are sepals, petals, stamens (male: anther and filament) and pistil/carpel (female: stigma, style, ovary).
• Pollination and fertilization: pollination transfers pollen to stigma; fertilization is fusion of male and female cells to form zygote.
• Fruit: develops from ovary and protects seeds; helps in seed dispersal.
• Seed: contains embryo and stored food; germinates to form a new plant under suitable conditions.

Basic tissues and transport

• Xylem: conducts water and dissolved minerals from roots to aerial parts.
• Phloem: conducts food (sugars) produced in leaves to other parts.
• These tissues form continuous transport paths through stem, roots and leaves to support life processes like growth and photosynthesis.

Important life processes related to plant parts

• Photosynthesis: occurs mainly in leaves; chlorophyll captures light to make food.
• Transpiration: loss of water vapour from leaves mainly through stomata; helps in upward movement of water.
• Respiration: breakdown of food to release energy; happens in all living cells.

Understanding how the plant body is organised helps explain how plants obtain water and minerals, make their food, grow, and reproduce.

What are roots?

Roots are the underground part of a plant that grow away from the stem into the soil. They anchor the plant, absorb water and dissolved minerals, store food, and sometimes help in breathing and vegetative reproduction.

Main functions

• Anchorage: hold the plant firmly in the soil.
• Absorption: take up water and mineral salts from the soil through root hairs.
• Conduction: transport water and minerals to the stem via xylem and transport food downwards via phloem.
• Storage: store food and water in modified roots (e.g., carrot, sweet potato).
• Special functions: support (prop roots), breathing in waterlogged soils (pneumatophores), vegetative propagation (stolons, suckers).

Basic structure of a typical root (from tip upwards)

• Root cap: protects the growing tip as it pushes through soil.
• Meristematic zone: region of cell division behind root cap where growth occurs.
• Elongation zone: cells lengthen and root gets longer.
• Maturation zone: cells differentiate; root hairs form here to increase surface area.
• Internal tissues: epidermis (outer layer), cortex (stores food), endodermis (selective barrier), vascular tissue (xylem and phloem) for transport.

Types of root systems

• Tap root system: one main primary root with smaller lateral roots (common in dicots). Example: carrot, radish.
• Fibrous root system: many roots of similar size arise from the stem base (common in monocots). Example: grass, wheat, maize.
• Adventitious roots: roots that arise from parts other than the radicle (stem or leaves). Example: banyan prop roots, ivy climbing roots.

Modified roots (with examples)

• Storage roots: swollen to store food — carrot, sweet potato, beet.
• Prop roots: provide extra support — banyan, maize (sometimes).
• Pneumatophores: breathing roots in mangroves that stick above water to take in oxygen.
• Contractile roots: pull bulbs deeper into the soil (seen in some bulbous plants).

How roots absorb water and minerals

Fine root hairs increase surface area and take up water and dissolved minerals from the soil. Water moves into roots by osmosis (from higher water potential in soil to lower water potential in root cells) and then moves through the cortex into the xylem vessels to be transported to other parts of the plant.

Simple classroom observation

• Germinate a bean seed on a moist paper towel and observe the radicle (first root) emerge. Monitor root growth and root hair formation under a magnifier.
• Compare root systems of a dicot seed (pea) and a monocot seed (maize) by germinating both and observing differences.

What is a stem?
A stem is the plant body part that grows above (and sometimes below) the ground and bears leaves, buds, flowers and fruits. It connects roots to leaves and acts as a pipeline for materials and as a support structure.

Basic features

• Nodes – points on a stem where leaves, branches or buds arise.
• Internodes – stem regions between two nodes.
• Buds – undeveloped shoots. Apical (terminal) bud causes lengthwise growth; axillary (lateral) buds form branches or flowers.

Structure (external and internal)

• External: stem surface is covered by epidermis; young stems may be green and soft, older stems become woody and hard.
• Internal (typical dicot young stem cross-section): epidermis, cortex, vascular bundles (containing xylem and phloem), and central pith. Xylem conducts water and dissolved minerals upward; phloem transports food (sugars) both up and down.

Functions of stems

• Support – hold leaves and reproductive structures in positions to receive sunlight and pollinators.
• Transport – xylem moves water/minerals from roots to leaves; phloem moves food from leaves to other parts.
• Storage – some stems store food or water (e.g., potato tubers, cactus stems).
• Photosynthesis – green stems (e.g., cacti, some succulents) perform photosynthesis.
• Reproduction and propagation – many stems help vegetative propagation (runners, suckers, cuttings).

Types of stems and common modifications

• Herbaceous vs woody – herbaceous stems are soft and green (e.g., sunflower), woody stems form bark and wood (e.g., mango tree).
• Modified stems (with examples):
  • Rhizome – underground horizontal stem (ginger).
  • Runner (stolon) – above-ground horizontal stem for propagation (strawberry).
  • Tuber – swollen underground storage stem (potato).
  • Corm – short, thick underground stem (crocus).
  • Bulb – short stem with fleshy leaf bases for storage (onion; the basal plate is the stem).
  • Tendril – slender coiling stem for climbing (grape tendrils).
  • Thorns – modified stems for protection (bougainvillea thorns).
  • Sucker – shoots from base used for propagation (mint).

Why stems are important in everyday life
Stems give us food (sugarcane, potato), timber and fuel (trees), medicines, spices (ginger), and garden propagation methods (cuttings, runners).

How students can observe stems
Look for nodes and internodes on common plants, cut a young stem cross-section with safe tools or observe prepared slides to see vascular bundles, and note modified stems (potato as a tuber, ginger as a rhizome, cactus stems storing water).

What is a leaf? A leaf is a green, flat plant organ attached to the stem. Leaves are the main sites for making food in most plants.

External structure (easy to see):

• Lamina (leaf blade): the broad, flat part of the leaf.
• Petiole: the stalk that joins the leaf to the stem (absent in sessile leaves).
• Midrib and veins: the midrib is the main central vein; veins form a network that carries water, minerals and food.
• Apex and base: the tip and the part nearest the petiole.
• Margin: the edge of the leaf (entire, toothed, lobed, etc.).

Internal structure (cross-section):

• Epidermis: thin outer layers on upper and lower surfaces; may have a waxy cuticle to reduce water loss.
• Palisade mesophyll: column-like cells just below the upper epidermis; rich in chloroplasts and the main site of photosynthesis.
• Spongy mesophyll: loosely packed cells with air spaces for gas exchange.
• Vascular bundles (veins): contain xylem (carries water) and phloem (carries food).
• Stomata and guard cells: tiny openings mostly on the lower surface that allow gas exchange and transpiration; each stomatal pore is flanked by two guard cells.

Functions of leaves:

• Photosynthesis: produce food (glucose) using sunlight, water and carbon dioxide.
• Transpiration: loss of water vapour helps cool the plant and creates a suction for water uptake.
• Gas exchange and respiration: intake of CO2 and release of O2 (during day); respiration occurs day and night.
• Storage: some leaves store food or water (e.g., onion, succulents).
• Protection, support and reproduction: leaves may form spines (cactus), tendrils (peas) or showy parts in some plants.

Types and venation: Leaves may be simple (single blade) or compound (blade divided into leaflets). Venation can be parallel (typical in monocots like grass) or reticulate (net-like, typical in dicots like neem). Reticulate venation includes pinnate (one main vein with branches) and palmate (several main veins from one point).

Leaf adaptations (modifications): Tendrils for climbing (pea), spines for protection and reduced water loss (cactus), fleshy leaves for water storage (aloe), storage leaves (onion scales), insect-catching leaves (pitcher plants, Venus flytrap), floating leaves (lotus).

Important points to remember: Leaves contain chlorophyll in chloroplasts which captures sunlight. Stomata control the exchange of gases and water loss. Leaves come in many shapes and sizes adapted to the plant's habitat and lifestyle.

A flower is the reproductive structure of flowering plants (angiosperms). Its main function is to produce seeds so the plant can reproduce. Flowers vary greatly in size, shape, colour and scent according to their role in attracting pollinators or in enabling wind/water pollination.

Main parts of a typical flower and their functions:

• Pedicel (flower stalk): supports the flower.
• Receptacle: swollen tip of the pedicel where flower parts are attached.
• Sepals (calyx): usually green; protect the bud before it opens.
• Petals (corolla): often colourful; attract pollinators.
• Stamen (male organ): consists of anther (produces pollen) and filament (holds the anther).
• Pistil / Carpel (female organ): consists of stigma (receives pollen), style (pollen tube grows through it) and ovary (contains ovules which develop into seeds after fertilization).

Types of flowers (basic categories):

• Complete flower: has all four main whorls — sepals, petals, stamens and pistils (e.g., hibiscus).
• Incomplete flower: missing one or more of the whorls (many grasses).
• Bisexual (perfect) flower: has both stamens and pistils (e.g., rose, mustard).
• Unisexual (imperfect) flower: has either stamens or pistils only; may be on the same plant (monoecious, e.g., maize, cucumber) or on separate plants (dioecious, e.g., papaya).
• Inflorescence: a cluster of many small flowers arranged together (e.g., sunflower head is made of many small florets).

Pollination and fertilization (simple sequence):

• Pollination: transfer of pollen from anther to stigma. Types: self-pollination (same flower or same plant) and cross-pollination (between different plants).
• Pollination agents: insects (bees, butterflies), birds, wind, water, and animals. Flower features often reflect the agent (e.g., bright scented flowers for insects; small pale, pollen-rich flowers for wind).
• Fertilization: after pollination, a pollen grain germinates on the stigma, the pollen tube grows down the style to the ovule, and a male gamete fuses with the female gamete to form a zygote. The zygote becomes the embryo (seed) and the ovary develops into a fruit.

Adaptations: flowers show adaptations to help pollination — bright colours, nectar, scented oils, tubular shapes for certain pollinators, or reduced petals and lots of pollen for wind pollination.

Importance of flowers: they are essential for producing fruits and seeds (food crops such as mango, apple, cereals), provide nectar and pollen for insects and birds, have medicinal and aromatic uses, and are important in ecosystems and horticulture.

Definition: Pollination is the transfer of pollen grains from the anther (male part) of a flower to the stigma (female part) of the same or another flower. It is the first essential step that may lead to fertilization and seed formation.

Parts involved: Pollen (male gamete carrier), anther (producer of pollen), stigma (pollen-receptive surface), style and ovary (inside which ovules are fertilized).

How pollination happens (simple sequence):

• Pollen is released from the anther.
• Pollen is carried to the stigma by an agent (wind, water or animals such as insects, birds, bats).
• On a compatible stigma, pollen grains germinate and form a pollen tube that grows down the style to reach an ovule.
• Sperm cells travel through the pollen tube and fuse with egg cells (fertilization) to form seeds; ovary develops into fruit.

Types of pollination:

• Self-pollination: Pollen from the anther of a flower lands on the stigma of the same flower or another flower on the same plant (example: many pea varieties). Advantages: ensures seed production even when pollinators are scarce. Disadvantage: less genetic variation.
• Cross-pollination: Pollen from the anther of one plant is transferred to the stigma of a flower on another plant of the same species (example: hibiscus, many fruit trees). Advantage: increases genetic variation.

Agents of pollination:

• Abiotic agents: Wind (anemophily) and water (hydrophily). Example: wheat and maize are mainly wind-pollinated; some aquatic plants like Vallisneria use water.
• Biotic agents: Animals — insects (entomophily: bees, butterflies, beetles), birds (ornithophily: sunbirds, hummingbirds), bats (chiropterophily). Example: bees pollinate mustard and many fruit trees; birds pollinate some tropical flowers.

Flower adaptations for different pollinators:

• Wind-pollinated flowers: small or no petals, exposed stamens and stigmas, large amounts of light, dry pollen grains.
• Insect-pollinated flowers: bright colors, scent, nectar, sticky or spiky pollen, petals providing landing platforms.

Importance of pollination: It leads to fertilization and seed/fruit formation, ensures plant reproduction, increases genetic diversity (in cross-pollination), and supports food chains and agriculture (many crops depend on animal pollinators).

Pollination vs Fertilization: Pollination is the transfer of pollen to the stigma. Fertilization is the fusion of male and female gametes inside the ovule that follows successful pollination.

Fertilisation is the process in flowering plants when the male gamete (from the pollen) fuses with the female gamete (egg cell) present in the ovule. Fertilisation occurs after pollination — when pollen grains are transferred from the anther to the stigma.

Step-by-step sequence

1. Pollination: Pollen grains reach the stigma (by wind, insects, water, animals, or self).
2. Pollen germination: A pollen grain absorbs moisture and forms a pollen tube on the stigma.
3. Pollen tube growth: The tube grows through the style toward the ovary carrying male gametes.
4. Fertilisation: A male gamete moves down the pollen tube and fuses with the egg cell in the ovule to form a zygote.
5. Seed formation: The zygote develops into an embryo; the ovule becomes the seed (seed coat from integuments; stored food in cotyledons or endosperm).
6. Fruit formation: The ovary surrounding the ovule develops into a fruit that helps protect and disperse the seeds.

Parts of a seed (basic)

• Embryo: young plant inside the seed (radicle = root tip, plumule = shoot tip).
• Cotyledons: seed leaves that store food (1 in monocots, 2 in dicots).
• Seed coat: outer protective layer.
• Endosperm (in some seeds): extra food reserve.

Self-pollination vs Cross-pollination

• Self-pollination: Pollen from the same flower or same plant reaches its stigma (e.g., pea). Gives uniform offspring.
• Cross-pollination: Pollen from one plant reaches the stigma of a flower on a different plant of the same species (e.g., maize, many fruit trees). Increases variation.

Agents of pollination: insects (bees, butterflies), wind, water, birds, bats, and humans (by hand).

Importance: Fertilisation leads to seed and fruit formation — essential for reproduction, survival of plant species, and food for humans and animals.

What is a fruit? A fruit is the mature ovary of a flower. After fertilization, the ovary develops into a fruit that surrounds and protects the seed(s). Fruits help in protecting seeds and in their dispersal to new places.

Why fruits form and why seed dispersal is important

• Fruits develop after fertilization and contain seeds that can grow into new plants.
• Seed dispersal reduces competition between the seedling and the parent plant for water, light and nutrients.
• Dispersal helps plants colonize new areas and maintain genetic diversity.

Types of fruits (simple overview for Class 6)

• Fleshy fruits: Soft and juicy when ripe (examples: mango, banana, tomato, orange). Often eaten by animals.
• Dry fruits: Not juicy. Some split open to release seeds (dehiscent) and some do not (indehiscent). Examples: pea pods (dehiscent), coconut and nuts (indehiscent).

Modes of seed dispersal and plant adaptations

• Wind dispersal: Seeds are light or have structures like wings or hairs to catch wind. Examples: coconut (light endosperm helps float too), maple (winged samara), dandelion (hairy parachute).
• Water dispersal: Seeds or fruits can float and travel by water. Example: coconut can float long distances across the sea.
• Animal dispersal: Seeds are carried externally by hooks or embedded in fur (burrs like Xanthium) or are eaten and later excreted at a new site (fruits like mango, apple). Seeds that pass through the gut are often helped by the animal to be deposited with natural fertilizer.
• Mechanical (explosive) dispersal: Some plants forcibly eject seeds when their fruit bursts open. Example: balsam or touch-me-not (Impatiens).
• Gravity (falling): Seeds simply fall to the ground near the parent plant. Example: mangoes, coconuts falling from trees.
• Human dispersal: People carry seeds intentionally (farming) or unintentionally (on clothing, in transported soil).

Seed adaptations — what helps dispersal

• Light weight, wings or hairs for wind dispersal.
• Buoyant or waterproof coverings for water dispersal.
• Edible, colorful fruits to attract animals for ingestion.
• Hooks, spines or sticky surfaces to attach to animal fur.
• Dry pods with built-in tension for explosive dispersal.

From seed to seedling

After dispersal, seeds may remain dormant until conditions (water, temperature, oxygen, light) are suitable for germination. Successful establishment depends on both dispersal and suitable habitat.

Simple classroom activities: Observe and sort seeds by dispersal type, blow models to test wind dispersal, germinate bean seeds to study requirements for growth.

What is germination? Germination is the process by which a seed begins to grow into a new plant. A seed contains an embryo (young plant), stored food (endosperm or cotyledons) and a protective coat (testa). When conditions are favourable the embryo becomes active and grows out of the seed.

Seed structure (short):

• Embryo: radicle (future root) + plumule (future shoot)
• Cotyledon(s): store food for the young plant
• Testa: seed coat that protects the seed

Conditions required for germination (sometimes remembered as W.O.T.):

• Water: Seeds absorb water (imbibition) which swells them and activates enzymes.
• Oxygen: Needed for cellular respiration and energy release.
• Suitable temperature: Each species has an optimal temperature range.
• Light or dark: Some seeds need light to germinate (light-loving), others need darkness.

Stages of germination (simple sequence):

1. Imbibition: seed takes up water and swells.
2. Activation of enzymes: stored food is broken down into usable energy.
3. Respiration increases: energy released to fuel growth.
4. Radicle emerges first: becomes the primary root.
5. Plumule emerges: grows into the shoot and first leaves.
6. Seedling develops leaves and begins photosynthesis, using sunlight to make food.

Types of germination (brief): Epigeal — cotyledons pushed above the soil (e.g., bean). Hypogeal — cotyledons stay below ground (e.g., pea).

Seedling growth after germination: After the radicle and shoot appear, growth continues: roots elongate and branch to absorb water and minerals, the shoot produces leaves, and photosynthesis starts. Healthy growth depends on soil nutrients, water, light, temperature and space.

Importance: Germination is the beginning of a plant’s life cycle and is essential for agriculture, gardening and natural vegetation regeneration.

Overview
Plants reproduce to produce new plants. There are two main modes: sexual reproduction (involving seeds formed by fusion of male and female gametes) and asexual (vegetative) reproduction (new plants arise from parts of the parent without fusion of gametes).

1. Sexual Reproduction

• Where it happens: Mostly in flowering plants (angiosperms) and gymnosperms.
• Key steps:
  • Flower structure: stamens (male: anther + filament) produce pollen; pistil (female: stigma + style + ovary) contains ovules.
  • Pollination: transfer of pollen from anther to stigma. Agents: wind, water, insects, birds, animals.
  • Fertilization: pollen grain forms a pollen tube and male gamete fuses with female gamete (ovule) to form a zygote.
  • Seed and fruit formation: zygote develops into an embryo inside the seed; ovary becomes the fruit (in angiosperms).
  • Germination: under suitable conditions (water, oxygen, right temperature) the seed sprouts into a new plant.
• Importance: Produces seeds that help dispersal and provide genetic variation among offspring.

2. Asexual (Vegetative) Reproduction

• Where it happens: Many flowering plants, ferns (some reproduce by spores), and non-flowering plants.
• Methods and examples:
  • Runners (stolons): horizontal stems on the ground produce new plants (e.g., strawberry, grasses).
  • Rhizomes: underground horizontal stems (e.g., ginger, turmeric).
  • Tubers: swollen underground stems store food and give rise to new plants (e.g., potato).
  • Bulbs: short stems with fleshy leaves used for storage (e.g., onion, tulip, garlic).
  • Cutting: a piece of stem or leaf develops roots and grows into a new plant (e.g., rose, sugarcane cuttings).
  • Layering: a branch is bent to the ground and rooted while still attached (e.g., jasmine, grapes).
  • Grafting and budding: parts of two plants are joined so they grow as one (used in fruit trees like apple, mango rootstock & scion).
  • Spore formation: non-flowering plants like ferns and mosses produce spores that grow into a new plant.
• Importance: Quick, does not require pollinators, produces offspring identical to parent (useful for maintaining desirable traits).

Advantages and disadvantages (summary)

• Sexual: Advantage — genetic variation, adaptation; Disadvantage — requires pollination, slower.
• Asexual: Advantage — fast, reliable, preserves good traits; Disadvantage — no genetic variation, vulnerable to disease.

Practical points for students

• Identify flower parts and label them: anther, filament, stigma, style, ovary, ovule.
• Observe common examples: potato tuber, onion bulb, rose cutting, strawberry runner, germinating seed.
• Remember conditions for germination: water, oxygen, suitable temperature.

Overview
Plants can be classified two useful ways: by their habit (growth form) and by their habitat (where they grow). Habit describes the plant's shape, size and structural features (herb, shrub, tree, climber, creeper). Habitat describes the natural place or environment in which a plant lives (aquatic, terrestrial, epiphytic, parasitic, xerophytic, marshy, etc.).

Classification by Habit — key groups and features

• Herbs: Small, soft (non‑woody) stems that live for a short time (one season or a few years). Examples: spinach, coriander, basil (tulsi). Leaves are usually green and tender; stems are flexible.
• Shrubs: Woody plants with several stems arising near the ground and a lower height than trees (usually under 3–5 m). Examples: rose, hibiscus.
• Trees: Tall, woody plants with a single main stem (trunk) and branches forming a crown. They live many years. Examples: mango, banyan, neem.
• Climbers: Plants with weak stems that climb up supports using tendrils, hooks, twining stems or adventitious roots. Examples: pea, money plant (Pothos), grape.
• Creepers: Plants whose stems spread on the ground and root at nodes; they do not climb upward on supports. Examples: pumpkin, watermelon.

Classification by Habitat — common types and adaptations

• Aquatic plants: Live in water (fresh or saline). Leaves and stems are adapted to float or to allow gas exchange under water. Examples: water lily, lotus, Hydrilla, duckweed.
• Terrestrial plants: Grow on land in soil. Most common crops, garden and forest plants are terrestrial (mango, wheat, rose).
• Epiphytes: Grow on other plants (usually on branches) but are not parasitic; they get moisture and nutrients from air, rain and debris. Examples: many orchids, some ferns). Adaptations include aerial roots and specialized leaves.
• Parasitic plants: Obtain water and nutrients from a host plant by connecting to the host's vascular tissues. Examples: Cuscuta (dodder), mistletoe.
• Xerophytes (dry‑habitat plants): Adapted to very dry conditions (thick cuticle, reduced leaves, fleshy stems). Examples: cactus, Euphorbia.
• Marsh/wetland plants: Grow in marshy or swampy soils, often with special roots for breathing (aerenchyma or pneumatophores). Examples: Typha (cattail), mangrove species (with pneumatophores).

How habit and habitat relate
Habit is about how a plant grows; habitat is about where it grows. The two are linked because habitat often drives adaptive features of habit — e.g., many climbers in dense forests use trees for support; xerophytes are often shrubs or succulents.

Why this classification matters
It helps identify plants quickly in the field, understand their adaptations, choose suitable plants for gardening or agriculture, and conserve ecosystems by knowing species roles in their habitats.

What are adaptations and modifications?
Plants live in very different environments (deserts, swamps, forests). To survive, they show adaptations — traits that help them live and reproduce in their habitat. Many of these adaptations are visible as structural modifications of roots, stems or leaves. In Class 6, 'modifications' means special changes in plant parts that perform functions different from the usual ones.

Types of adaptations (short):

• Structural — changes in shape or structure (thick leaves, deep roots, spines).
• Physiological — internal processes (ability to store water, dormancy, photosynthesis).
• Behavioral — movements or activity patterns (opening/closing stomata, leaf folding).

Common modifications of roots, stems and leaves

• Root modifications: Roots may become specialised for storage, support or breathing. Examples: storage roots like carrot and turnip (store food), prop roots in banyan and maize (support), aerial roots in orchids (absorb moisture), pneumatophores in some mangroves (for gas exchange).
• Stem modifications: Stems can store food/water, help in vegetative propagation, or climb/support other plants. Examples: tubers (potato) store food; bulbs (onion) are short stems with fleshy leaves; rhizomes (ginger) grow horizontally underground; stolons or runners (strawberry) help spread; tendrils (in ivy) may be modified stems or branches for climbing; thorns in some plants are modified stems for protection; succulent stems (cactus) store water.
• Leaf modifications: Leaves can adapt for protection, climbing, storage or catching insects. Examples: spines of cacti (modified leaves) reduce water loss and protect; tendrils in peas (modified leaves) help climbing; fleshy leaves in succulents (aloe) store water; insectivorous leaves (pitcher plant, Venus flytrap) trap and digest insects to obtain nutrients in poor soils; phylloclades (flattened stems that look like leaves) in some plants like Opuntia.

Why these modifications help
- In deserts (xerophytes) plants reduce leaf area, develop thick cuticles, store water and protect themselves (spines) to reduce water loss.
- In water-rich places (hydrophytes) plants have thin or absent cuticle, large air spaces and thin leaves to float and exchange gases easily.
- For climbing plants, tendrils or twining stems help reach sunlight without investing in thick trunks.
- Storage organs (tubers, bulbs, roots) let plants survive unfavorable seasons and help humans as food sources.

Link to everyday life
Many foods and useful plants are examples of modifications: potatoes (tubers), carrots (storage roots), ginger (rhizome), onions (bulbs), sugarcane (stem), aloe (succulent leaves). Understanding these helps explain how plants are suited to their habitats and how humans use them.

What it means
Green plants make their own food using sunlight. This process is called photosynthesis. Because plants produce food, they are called primary producers — they are the base of all food chains.

Where it happens
Photosynthesis happens mainly in the leaves, in cell structures called chloroplasts that contain the green pigment chlorophyll. Water is absorbed by roots and transported through xylem; carbon dioxide (CO2) enters leaves through tiny pores called stomata.

What plants need

• Sunlight — provides energy.
• Carbon dioxide (from air).
• Water (from soil).
• Chlorophyll (in leaves).

Simple steps of photosynthesis

1. Leaves absorb sunlight using chlorophyll.
2. Light energy splits water into hydrogen and oxygen; oxygen is released into air.
3. Carbon dioxide combines with hydrogen to form sugars (like glucose).
4. Sugars are used for growth, respiration, or stored as starch, oil or other forms.

Importance and uses of the food made by plants

• Food for humans and animals (grain, fruits, vegetables, leaves, seeds, tubers).
• Oxygen release maintains atmospheric oxygen for respiration.
• Raw materials: timber, fibres (cotton, jute), oils, rubber.
• Fuels: wood, biofuel sources (e.g., dried plant matter).
• Medicines and chemicals (e.g., neem, tulsi, aloe).
• Ecological benefits: prevent soil erosion, maintain water cycle, provide habitat and shade.

How plant food is stored and used
Plants convert glucose into complex forms: starch in roots and tubers (potato), sucrose in sugarcane, oils in seeds (mustard), and proteins in legumes (beans). When animals eat plants, stored plant energy moves up the food chain.

Role in food chains
Example: Grass (producer) → Goat (primary consumer) → Human (secondary consumer). Without producers, consumers cannot survive.

Key structures to remember

• Leaf blade — large surface for light capture.
• Veins — xylem (water) and phloem (food transport).
• Stomata and guard cells — gas exchange and transpiration control.

What this topic covers
Practical Activities and Observations teach students to observe plant structure and functions by simple hands‑on experiments. They develop skills: careful observation, drawing and labeling, recording data, making inferences and drawing conclusions.

Typical classroom activities (what to do and what you will observe)

1. Observe and record whole plants (herb, shrub, tree)
   • Steps: Go outdoors, select examples of an herb (e.g. coriander), shrub (rose) and tree (mango). Note height, stem type, leaf arrangement, and whether it is climber/creeper.
   • Observe: size, woody or soft stem, presence of tendrils (climbers), and shape of leaves.
   • Conclusion: Classify plants into herb, shrub, tree, climber, creeper.
2. Dissect a flower and identify parts
   • Steps: Take a simple flower (hibiscus or mustard), carefully remove sepals and petals, cut open to see stamen (anther + filament) and pistil (stigma, style, ovary).
   • Observe: number and arrangement of petals, stamens and position of ovary.
   • Conclusion: Relate parts to their functions (stamen – male, pistil – female, petals – attract pollinators).
3. Seed germination experiment
   • Steps: Place equal numbers of soaked seeds (mung/gram) on wet cotton in Petri dish or transparent cup. Keep sets under different conditions: (A) water + light, (B) no water, (C) water + dark. Record daily germination and seedling length for 5–7 days.
   • Observe: Seeds with water germinate; without water do not. Light affects stem elongation but not initial germination much.
   • Conclusion: Water is essential for germination; light influences growth direction and elongation.
4. Observe root and stem modifications
   • Steps: Look at and touch potato, sweet potato, ginger, onion, grass runners, and stolons (strawberry). Note where food is stored.
   • Observe: Potato = tuber (stem modification storing starch), carrot = root modification storing food, onion = modified leaf bases.
   • Conclusion: Plants store food in roots, stems and leaves as adaptations.
5. Leaf venation and arrangement
   • Steps: Collect different leaves. Note if venation is parallel (grass) or reticulate/pinnate (neem). Note arrangement: alternate, opposite, whorled.
   • Observe: Monocots show parallel venation; dicots show netted venation.
6. Observe stomata using nail‑varnish/peel method (simple epidermal view)
   • Steps: Apply a thin layer of clear nail varnish on the lower surface of a leaf; let dry; peel off carefully with tape and view under a magnifying lens or microscope.
   • Observe: Stomata appear as tiny openings with guard cells—usually more on the lower surface of many leaves. Note shape and approximate number per unit area.
   • Conclusion: Stomata regulate gas exchange and transpiration.
7. Transpiration demonstration (plastic bag method)
   • Steps: Cover a healthy leafy branch with a transparent plastic bag and seal it. Observe after several hours.
   • Observe: Water droplets collect inside bag or bag becomes moist; if weighed pots are used, mass decreases over time.
   • Conclusion: Plants lose water through leaves (transpiration); varies with humidity, temperature and wind.

How to record observations

• Use a table for daily records (date, condition, number germinated, seedling length).
• Draw labelled diagrams (whole plant sketch, dissected flower, leaf venation) and note magnification if using a microscope.
• Make simple calculations (percent germination, rate of growth) to support conclusions.

Safety and precautions

• Handle sharp scissors and blades only under teacher supervision (for dissection).
• Use clean hands/tools to avoid contamination in germination experiments.
• Do not pull on plant roots in the field; dig carefully to avoid damage.

Learning outcomes Students will be able to: identify plant parts, perform simple experiments to test seed germination and transpiration, recognise modifications for storage or support, and present results as labelled drawings, tables and graphs.