Chapter 7 — Getting to Know Plants

Plants are living organisms that carry out life processes such as growth, nutrition and reproduction. They are very common on land and in water. Unlike many animals, plants are usually fixed in one place. They grow from seeds or other parts, respond to light and water, and have life cycles that include growth, maturation and reproduction. Plants are essential to life on Earth because they provide food, oxygen and habitats for many animals and microorganisms. They also help hold soil, maintain the water cycle and influence the climate around us.

Plants have specialised cells and tissues that perform different functions. Many parts that we see — roots, stems, leaves, flowers, fruits and seeds — each have important roles. Some plants are green because they contain chlorophyll, which helps them make food using sunlight. Other plants such as fungi are not green and get food differently. In this chapter we focus on green plants, particularly flowering plants, because they are familiar and easy to observe in gardens, fields and homes.

Plants can be small or large, live for a short time or many years. There are flowering plants, non-flowering plants (like ferns and mosses), trees, shrubs, herbs and climbers. We can study them by observing, drawing and doing simple experiments. For example, you can watch a seed sprout in a pot or note how a plant leans toward light. Doing such activities helps you understand how plants grow and how they fulfil their needs for water, minerals, air and sunlight. Caring for plants also teaches responsibility and connects classroom learning to daily life.

A typical flowering plant is made of vegetative parts and reproductive parts. Vegetative parts include roots, stems and leaves which help the plant obtain water, minerals and sunlight, grow and store food. Reproductive parts include flowers, fruits and seeds which allow the plant to produce the next generation. Each part has a special structure and function that helps the whole plant survive.

Roots usually grow into the soil to hold the plant and take in water and dissolved minerals. Some roots are modified to store food as in carrots. Stems support the plant, carry water and nutrients between roots and leaves, and produce leaves and flowers from buds. Stems can be soft and green in herbaceous plants or hard and woody in trees. Leaves are generally flat and green; they capture sunlight, exchange gases and make food. The main parts of a leaf such as blade, midrib and veins help in transport and support.

Flowers are often colourful and scented to attract pollinators. They contain male and female reproductive structures that produce pollen and ovules. After pollination and fertilisation, the ovary develops into fruit which encloses seeds. Seeds contain the embryo plant and stored food, and they begin a new plant when conditions are favourable. Fruit types vary widely: fleshy fruits like mango and dry fruits like pods play different roles in protecting and dispersing seeds.

Understanding these parts helps you recognise plants and know their roles in gardens and nature. You can dissect a simple flower or cut open a fruit to observe the seed arrangements. Noting how each part supports the plant’s life gives a clear picture of plant form and function.

Roots are vital for anchorage, absorption and sometimes storage in plants. They hold the plant firmly in the soil and help it resist being blown or washed away. Roots absorb water and mineral salts from the soil which are necessary for the plant’s growth. The nutrients absorbed are carried to other parts of the plant through conducting tissues.

Roots show different types and modifications. The two broad types are taproot systems and fibrous root systems. In taproot systems, a single main root grows downwards with smaller side roots; examples include carrot and mango. In fibrous systems, many thin roots spread out close to the soil surface, as seen in grasses. Each system suits the plant's needs—taproots often reach deeper water while fibrous roots cover more soil area to quickly absorb surface water.

Root structures include root hairs which are tiny extensions that increase surface area for absorption, and the root cap which protects the growing tip as it moves through soil. Many roots are modified: storage roots (like beet and sweet potato) store food, aerial roots (as in banyan) help in support and breathing, and adventitious roots can grow from stem parts to help propagation. Some roots form associations with microorganisms: root nodules in legumes host nitrogen-fixing bacteria that convert atmospheric nitrogen into usable forms for the plant.

Practical activities like carefully washing soil from a young plant’s roots show the root pattern and root hairs. Observing different crops and wild plants will help you identify root types and recognise how roots adapt to soil and water conditions. Healthy roots are essential for healthy plants, and soil conditions such as aeration, moisture and nutrients strongly affect root growth.

Stems are above-ground structures that support leaves and flowers and connect roots to the rest of the plant. They keep leaves in position to receive light and arrange flowers so pollinators can reach them. Stems also act as conduits, containing tissues that move water, minerals and food between roots and leaves. Many stems also store food and water, and some are modified for special functions.

Inside a stem are vascular tissues: xylem and phloem. Xylem carries water and dissolved minerals from roots up to leaves and other parts. Phloem transports the food produced in leaves to growing areas and storage organs. The arrangement of these tissues varies in herbaceous and woody stems; in woody plants xylem builds up each year forming growth rings.

Stems may be herbaceous (soft and green) or woody (hard and rigid). They have nodes where leaves and buds are attached and internodes between nodes. Many stems are modified: tubers like potato store food, rhizomes like ginger grow horizontally underground, and runners like in strawberry produce new plants. Tendrils help climbers attach to supports; thorns protect plants from animals. Aerial stems may help breathing in swamp plants, and succulent stems in cacti store water for dry spells.

Studying stems includes cutting a young stem to see the position of leaf scars and buds or examining a cross section under a microscope to view xylem and phloem. Understanding stem structure helps in pruning, grafting and supporting plants in gardens, and explains why different plants have different stem shapes and strengths suited to their environment.

Leaves are the main sites of photosynthesis and gas exchange in most plants. Their flat, broad surfaces provide a large area to capture sunlight. A leaf typically has a blade or lamina and often a petiole that attaches it to the stem. The arrangement of leaves on a stem affects how much light each leaf receives. Leaf veins contain vascular tissues that transport water to the leaf and carry food away to other parts of the plant.

Leaf structure is adapted to its functions. The upper surface may have a waxy cuticle that reduces water loss while the internal tissues contain chloroplast-rich cells where photosynthesis takes place. The lower surface often has more stomata — tiny pores controlled by guard cells. Through stomata, carbon dioxide enters the leaf for photosynthesis and oxygen and water vapour leave. Guard cells open and close the stomata to balance gas exchange with water conservation depending on environmental conditions.

Leaves come in many shapes and sizes: simple or compound, needle-like or broad, and may have special modifications. Some leaves store water (succulents), some wrap around stems and form protective sheaths (grasses), and some become tendrils to support climbing plants. Venation patterns — parallel in many monocots and reticulate in many dicots — help identify plant groups. Seasonal changes may bring leaf fall (deciduous plants) as an adaptation to cold or dry periods, allowing plants to conserve resources.

Studying leaves involves observing shape, arrangement, and texture, and performing simple tests like checking for starch after keeping a plant in sunlight. Recording differences helps you recognise plants and understand how leaf structures are matched to their roles in capturing light, exchanging gases and conserving water.

Flowers are the specialised reproductive structures of many plants that produce seeds and fruits. A complete flower commonly has sepals, petals, stamens (male part) and pistil/carpel (female part). Sepals form the outer protective layer around a bud. Petals are often showy and attract pollinators with colour and scent. Stamens produce pollen grains which contain male reproductive cells, and the pistil contains the ovary with ovules that become seeds after fertilisation.

Pollination is the transfer of pollen from an anther to a stigma. It can occur by abiotic means such as wind and water, or by biotic agents like insects, birds and bats. Flowers adapted to insect pollination are typically bright and produce nectar. Wind-pollinated flowers are usually small and produce large amounts of light pollen. Successful pollination followed by fertilisation leads to the development of seeds inside the ovary, which later becomes a fruit that helps protect and disperse seeds.

Flowers vary widely: some are bisexual with both stamens and pistils, while others are unisexual. Inflorescences are groups of flowers arranged on the stem, as seen in sunflower heads which have many small flowers forming one showy head. Flower structures also adapt to pollinators — tubular flowers fit long-beaked birds, and night-blooming flowers with strong scents attract bats or moths.

Classroom dissection of a common flower such as hibiscus helps students identify each part and understand their roles. Observing pollinators in a garden shows the link between plant reproduction and animal behaviour. Learning flower parts and pollination explains how fruits and seeds are formed and why biodiversity of pollinators is important for food crops.

Fruits form from the ovary of a flower after fertilisation and protect the developing seeds. Inside each ovary are one or more ovules. When a pollen grain reaches the stigma and fertilisation occurs, the ovule develops into a seed containing an embryo and stored food. The ovary wall develops into the fruit which can be fleshy (like mango, banana) or dry (like pods, nuts). Fruits have many roles: they protect seeds, aid in dispersal and sometimes provide food for animals which helps spread the seeds.

Seeds are the unit of reproduction for many plants and contain an embryo, a protective seed coat and stored food either in endosperm or in cotyledons. The embryo has the radicle (future root) and plumule (future shoot). Seed size and structure vary widely depending on the plant’s strategy for survival and dispersal. Some seeds are built to survive harsh conditions and remain dormant until suitable conditions return.

Seeds and fruits show many adaptations for dispersal. Wind-dispersed seeds often have wings or hairs (e.g., maple samara, cotton). Water dispersal requires buoyant seeds or fruits like coconut. Animal dispersal relies on fleshy fruits that are eaten and later excreted at new locations, or on seeds with hooks that cling to fur. Mechanical dispersal occurs when dry fruits burst open and scatter seeds, such as in balsam. Dispersal reduces competition between parent and offspring and increases the chance of colonising new habitats.

Practical activities include cutting open fruits to see seed arrangement, testing seed viability by germination experiments, and comparing types of fruits and seeds collected from the locality. Such observations show the link between structure and function and help understand how plants reproduce and spread in nature.

Photosynthesis is the chemical process by which green plants make their food using sunlight, water and carbon dioxide. Chlorophyll in chloroplasts absorbs light energy. In the presence of light this energy drives reactions that combine carbon dioxide from air and water from soil to form glucose, a simple sugar. Oxygen is released as a by-product. Photosynthesis mainly occurs in leaf cells where chloroplasts are abundant.

The process has two broad stages: light-dependent reactions and light-independent reactions. Light reactions use sunlight to produce energy-rich molecules (ATP and NADPH) and split water to release oxygen. The dark reactions (also called Calvin cycle) use the energy to fix carbon dioxide into sugars. While the detailed chemistry is studied later, at this class level the important idea is that light, chlorophyll, water and carbon dioxide are necessary components and oxygen is produced.

Photosynthesis provides the food and energy that sustains the plant and, indirectly, the animals and humans that eat plants. It also removes carbon dioxide from the atmosphere and releases oxygen which is essential for respiration of other organisms. Factors affecting the rate of photosynthesis include amount of light, availability of carbon dioxide, water supply and temperature.

Simple experiments help demonstrate photosynthesis: a starch test shows that starch forms in leaves where photosynthesis occurs; covering part of a leaf with foil prevents starch formation in the covered area, proving the role of light. Observing how plants kept in darkness become pale also shows the need for light. Understanding photosynthesis explains why green plants are called producers and why they are the base of food chains.

Plants need mineral elements from the soil in addition to water and sunlight for healthy growth and development. These mineral elements include macronutrients like nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and micronutrients such as iron, zinc and manganese. Each plays specific roles: nitrogen is important for building proteins and chlorophyll; phosphorus is key for energy transfer and root development; potassium helps in enzyme activation and overall vigour.

Roots absorb mineral salts dissolved in soil water. Soil type, pH and organic matter content affect the availability of nutrients. Deficiencies in particular minerals show as visible symptoms; for example, nitrogen deficiency often causes yellowing of older leaves, while phosphorus deficiency may lead to poor root growth and delayed maturity. Understanding these signs helps gardeners and farmers make timely corrections.

To maintain soil fertility, people use organic matter like compost and manure, which release nutrients slowly, and chemical fertilisers to provide specific nutrients quickly. Overuse of chemical fertilisers can harm soil health and pollute water, so balanced use and soil testing are important. Crop rotation, green manures and planting legumes that fix nitrogen are sustainable practices that enhance soil fertility. Legume roots have nodules with bacteria that convert atmospheric nitrogen into forms plants can use, benefiting subsequent crops.

Practical lessons include comparing plant growth with and without added fertiliser, observing root nodules in legumes, and testing soil with simple kits. These activities show how plant nutrition affects growth and yield, and why proper soil management is important for agriculture and gardens. Learning basic plant nutrition prepares students to make informed decisions about plant care and farming practices.

Water taken up by roots moves through the plant and is lost mainly from leaves by transpiration. Water enters root hairs from the soil by osmosis and travels through root tissues into xylem vessels. From the xylem, water moves upward through stem vessels to leaves where it reaches cells and eventually evaporates into leaf air spaces and exits via open stomata as water vapour. This continuous movement is often called the transpiration stream.

The driving forces for upward water movement include root pressure, capillary action in narrow xylem tubes and the pulling force created by transpiration. When water evaporates from leaves, it creates a negative pressure that pulls more water up the xylem in a continuous column. This process also helps transport dissolved minerals from the soil to leaves and other parts where they are used for growth.

Transpiration has benefits and costs. It cools the plant and maintains nutrient flow, but excessive transpiration can lead to dehydration and wilting. Plants regulate water loss by opening and closing stomata using guard cells. Many plants adapt to dry conditions with features like thick cuticles, reduced leaf size, hairy surfaces, sunken stomata or CAM metabolism in succulents to reduce daytime water loss.

Class experiments to demonstrate transpiration include covering leaves with polythene to collect water vapour or measuring loss of water from a potted plant kept in sun versus shade. Observing how stomata open and close in response to light and humidity and noting leaf wilting under water stress illustrate the balance plants maintain between gas exchange for photosynthesis and conserving water.

Seed germination is the series of events by which an embryo inside a seed grows into a young plant. For germination to begin, a seed usually requires water, oxygen and a suitable temperature; some seeds also require light or special conditions to break dormancy. When water is available, seeds swell as they imbibe water. This activates enzymes that use the stored food to provide energy for growth.

The main stages are imbibition (water uptake), breaking of the seed coat, emergence of the radicle (young root), and then growth of the plumule (young shoot) which reaches upward toward light. The radicle anchors the plant and starts absorbing water and minerals, while the plumule develops leaves and begins photosynthesis, after which the seedling depends less on stored food.

Seeds contain stored food in endosperm or cotyledons. These reserves provide energy and building materials for early growth until the seedling can make its own food. Some seeds may remain dormant for long periods to survive unfavourable seasons and germinate only when conditions improve. Germination rates depend on seed viability, temperature, moisture and oxygen supply.

Students can test germination by placing seeds on moist filter paper or soil and keeping them in different conditions to observe effects on speed and success. Recording time for root and shoot emergence, comparing different seed types and noting temperature effects are useful activities. Understanding germination helps farmers choose the right sowing time and helps gardeners raise healthy seedlings for transplanting.

Seed dispersal spreads offspring away from the parent plant so they face less competition and can colonise new areas. Dispersal increases the chance that at least some seeds will find suitable conditions for growth. Plants have evolved many clever ways to move their seeds using wind, water, animals and mechanical forces.

Wind dispersal suits seeds that are light and have structures to catch the air, such as hairs, plumes or wing-like extensions. Examples include cotton fibres and the samaras of maple trees. Water dispersal requires buoyant seeds or fruit that can float, like coconuts that travel long distances across the sea. Animal dispersal occurs when animals eat fruits and release seeds elsewhere, or when seeds cling to fur or feathers with hooks or sticky coatings. Some plants rely on ants or other small animals to carry seeds to their nests where they may germinate.

Mechanical dispersal uses built-in tension in dry fruits; when they dry, pods may split and actively fling seeds away, as seen in balsam and some legumes. Each dispersal method influences seed size, protection and the fruit structure. Human activities have also become a dispersal agent, sometimes spreading invasive species unintentionally.

Learning about dispersal includes collecting local seeds and noting their structures, observing how far seeds travel from parent plants, and understanding why plants choose particular strategies. This knowledge helps in agriculture, forestry and conservation by guiding seed collection, sowing methods and control of unwanted species. Teachers can set simple experiments to test how far wind or animals might carry certain seed types.

Plants can be grouped by growth form, life span and habitat; each group shows features suited to its environment. Based on structure, common groups include herbs (soft-stemmed plants that live a short time), shrubs (medium-sized woody plants with multiple stems), trees (large woody plants with a single main stem) and climbers or creepers (plants that rely on supports to spread or climb). These basic categories help us identify and study plants in the field and garden.

Adaptations are special features that enable plants to survive in particular conditions. Xerophytes are plants adapted to dry environments; they may have thick cuticles, sunken stomata, reduced leaves or spines, deep roots and water-storing tissues to reduce water loss and store water. Hydrophytes live in water or very wet soils and often have thin leaves, large air spaces for buoyancy and reduced cuticles; they may have stomata only on the upper leaf surface. Mesophytes are plants of moderate conditions and have typical leaf and root structures.

Climbers and epiphytes adapt to grow on other plants or structures to reach light: climbers use tendrils or hooks while epiphytes grow on branches and absorb moisture from the air. Some plants show seasonal adaptations such as deciduous trees that shed leaves in dry or cold seasons to conserve water and energy. Others have modifications like bulb, tuber or rhizome for storing food and surviving unfavourable periods.

Studying these types and adaptations involves observing local plants, noting leaf and root forms, stem features and habitats. Understanding adaptations explains why certain crops grow well in particular regions and how wild plants survive. It also helps in conservation by showing which plants might be vulnerable to climate change or habitat loss.

Basic plant care and hands-on experiments help students understand plant needs and practise scientific skills. Caring for plants includes providing suitable water, light, soil and nutrients. Water should be regular and appropriate to the plant type; some need frequent watering while others must be kept drier. Light governs photosynthesis, so placing plants where they receive enough sunlight is important. Good soil with air spaces, organic matter and proper drainage supports root health. Adding compost or balanced fertiliser supplies essential minerals.

Simple experiments show how factors affect plant growth. For example, growing two identical plants under different light conditions reveals the role of light. Testing plants with and without fertiliser demonstrates the need for minerals. Germinating seeds on moist paper shows the stages of growth and importance of water. A starch test on leaves demonstrates photosynthesis: after exposing leaves to light, boiling and treating them with iodine reveals starch presence in exposed parts but not in dark-covered parts.

Record keeping is important in experiments: measure plant height, count leaves, and note the time taken for events like germination. Use a control plant for fair comparisons. Safety is essential: wash hands after handling soil, use tools carefully and avoid harmful chemicals. By maintaining a school garden or pot plants, students learn responsibility, observe seasonal changes and build skills in observation, measurement and drawing conclusions from data.

These activities connect classroom theory to everyday life, showing how proper care produces healthy plants and why plants are valuable for food, shade and the environment. They also encourage curiosity and can inspire careers in agriculture, horticulture and environmental science.