Chapter 3 — Plant Life

What is a plant?
Plants are living organisms that make their own food by photosynthesis and are generally rooted in soil. They vary from tiny mosses to giant trees. Plants show features such as green colour from chlorophyll, cell walls made of cellulose, and growth by adding new cells. They form the base of food chains and provide oxygen and materials humans use.

Why study plants?
Studying plants helps us understand how ecosystems work, how food is produced and how medicines and raw materials come from nature. Observations of plants build skills like careful measurement, drawing, and recording results.

Basic plant organisation
A typical flowering plant has root, stem, leaves, flowers, fruit and seeds. Each part has specialised roles: roots anchor and take up water, stems support and transport, leaves manufacture food, flowers enable reproduction. Even simple non-flowering plants like ferns and mosses show organised parts though differently arranged.

Human uses and environment
Plants give us food, timber, fibre, medicines and shade. They improve air quality and prevent soil erosion. Understanding plant needs such as light, water and minerals encourages better gardening and conservation.

How we will study plants
In this unit you will observe, dissect, draw, and carry out simple experiments. You will learn correct botanical terms and how to record observations carefully. This prepares you for higher study and for making decisions about plants in everyday life.

Purpose of classification
Classification helps us group plants with similar features so identification, study and communication are easier. By using visible characters such as presence of flowers, type of seeds, presence of vascular tissues and general habit (how the plant grows), we can place a plant in a suitable group and learn its typical life processes.

Major groups studied
For Class 7 we learn four broad groups. Bryophytes (mosses and liverworts) are small, non-vascular plants that need moist environments and reproduce by spores. Pteridophytes (ferns and horsetails) are vascular but reproduce by spores, and have true roots, stems and leaves. Gymnosperms (like pines) produce naked seeds usually on cones and lack flowers. Angiosperms are flowering plants that produce seeds enclosed in fruits.

Angiosperms in more detail
Angiosperms are the most diverse and are divided into monocots and dicots using several visible features. Monocots have one seed leaf (cotyledon), parallel leaf venation, scattered vascular bundles in stems and flower parts in threes. Dicots have two cotyledons, net-like venation, vascular bundles arranged in a ring and flower parts commonly in fours or fives. These differences are practical when identifying garden plants, crops and trees.

Using identification keys
Simple dichotomous keys ask a series of yes/no questions about observable traits (for example: does the plant have flowers? Are the veins parallel?) Students learn to use these keys to identify common local plants. This trains observation, comparison and logical choice-making.

Local examples and field work
Collecting a few local specimens—moss on stones, a fern in shaded places, a conifer if available and several flowering plants—helps connect theory with real plants. Note habitat, life form (tree, shrub, herb), and reproductive features. Field observation encourages curiosity and care in handling living things.

Plant cells: special features
Plant cells have features that give plants their shape and functions. A typical plant cell has a rigid cell wall made of cellulose surrounding the cell membrane; inside are the cytoplasm, nucleus (which controls cell activity), large central vacuole for storage and turgor, mitochondria for energy release, and chloroplasts which carry out photosynthesis. Chloroplasts contain chlorophyll pigments that capture light energy. Observing onion epidermis or a peeled leaf under a microscope shows many of these structures.

Tissue level organisation
Similar cells join to form tissues. There are two main groups: meristematic tissues where cells actively divide, and permanent tissues where cells have matured and specialise. Meristem is found at root tips and shoot tips and is responsible for growth in length and new organs.

Simple permanent tissues
Parenchyma consists of living cells with thin walls used for photosynthesis, storage and secretion. Collenchyma cells have unevenly thickened walls and provide flexible support in young stems and leafstalks. Sclerenchyma cells have very thick, lignified walls and often are dead at maturity; they provide rigid support and form fibres.

Complex tissues — xylem and phloem
Xylem and phloem are conducting tissues made of different cell types that work together. Xylem conducts water and mineral salts upward and contains tracheids, vessels, xylem parenchyma and fibres. Many xylem elements are dead at maturity, forming hollow tubes. Phloem transports organic products (mainly sugars) from leaves to growing and storage parts; it includes sieve tube elements, companion cells and phloem parenchyma. Sieve tubes are living but lack nuclei and depend on companion cells.

Arrangement and function
Groups of xylem and phloem form vascular bundles in stems and roots. Their arrangement differs in monocots and dicots and explains how water, minerals and food are transported efficiently. Understanding tissues helps explain plant support, repair and transport, and links microscopic structure to whole-plant function.

Functions of roots
Roots perform several vital roles: they anchor the plant in the soil, absorb water and dissolved minerals, store food reserves, and sometimes help in vegetative reproduction. Roots also interact with soil organisms, such as nitrogen-fixing bacteria and beneficial fungi (mycorrhiza), improving nutrient availability. Some roots are modified for special tasks like storage or breathing.

Types of root systems
There are two main patterns: a tap root system, where one main root grows large with lateral branches (common in dicots like carrot and mango), and a fibrous root system, where many roots of similar size spread from the base of the stem (common in monocots like grasses). Each system suits the plant's habitat and life strategy.

External and internal structure
The tip of a root has a root cap that protects the delicate meristematic tissue as it pushes through soil. Behind the cap lie regions of cell division, elongation and maturity where root hairs form. Root hairs are tiny extensions of epidermal cells that greatly increase surface area for absorption. Internally, a young root has an epidermis, cortex (for storage and transport), an endodermis which acts as a selective barrier with the Casparian strip, and a central vascular cylinder containing xylem and phloem for long-distance transport.

Absorption and movement of water
Water enters root hairs by osmosis due to a higher solute concentration inside root cells. Mineral ions enter by diffusion or active transport. Water moves across the cortex via cell-to-cell, apoplast and symplast routes until it reaches the endodermis; the Casparian strip forces water into cytoplasm for selective entry into the vascular tissue. From xylem, water is drawn upward by transpiration pull and capillary action.

Root adaptations
Many roots are modified: storage roots (carrot, beet), aerial roots (banyan) for support, pneumatophores (mangrove) for gas exchange in waterlogged soils, and nodulated roots in legumes that host nitrogen-fixing bacteria. Observing these forms helps connect structure with function and environment.

Main roles of stems
Stems support leaves, flowers and fruits, hold them in positions for light capture and pollination, and act as conduits for water, minerals and food between roots and leaves. Stems also store food in some plants and produce new shoots and roots. Their structure adapts to different functions and habitats.

External features and modifications
Externally, stems show nodes where leaves attach and internodes between them. Buds at nodes can be terminal or axillary and can develop into branches or flowers. Some stems are modified: tubers (potato) store starch and bear buds; rhizomes (ginger) are horizontal underground stems for perennation and spread; stolons or runners (strawberry) help vegetative propagation; tendrils may be modified stems that support climbers; thorns can be modified stems for protection.

Internal structure and vascular tissue
Internally, stems show an outer epidermis with a protective cuticle, a cortex that may store food, vascular bundles containing xylem and phloem, and a central pith in many species. The arrangement of vascular bundles differs between plant groups: in dicot stems they are arranged in a ring allowing secondary growth, while in monocot stems they are scattered. The arrangement is important for transport efficiency and mechanical strength.

Secondary growth and wood formation
In many dicots and gymnosperms a lateral meristem called the vascular cambium produces secondary xylem (wood) toward the inside and secondary phloem toward the outside, causing the stem to thicken. Annual activity of cambium produces growth rings in trees which can indicate age and past environmental conditions.

Transport role
Xylem vessels in the stem form long pathways that move water and dissolved minerals upward; phloem transports dissolved sugars from leaves to roots and storage organs. The stem’s mechanical tissues—collenchyma, sclerenchyma and xylem—help plants remain erect and resist bending forces from wind and rain.

Primary functions
Leaves are the main site for photosynthesis in most plants; they capture light energy, exchange gases and regulate water loss. Leaves may also store food or water in some species, and can be modified for climbing, protection or catching insects.

External features and variation
A typical leaf has a broad lamina (blade) for light capture and a petiole that connects it to the stem. Leaves can be simple (single blade) or compound (several leaflets). The arrangement of leaves on a stem—phyllotaxy—may be alternate, opposite or whorled. Venation patterns vary: monocots usually show parallel venation, while dicots show reticulate or netted venation. Leaf shape, margin, apex and base vary widely and are useful for identifying species.

Internal structure for function
In cross-section a dicot leaf shows an upper epidermis with a waxy cuticle to reduce water loss, a layer of densely packed palisade mesophyll cells rich in chloroplasts where most photosynthesis occurs, and a spongy mesophyll with air spaces facilitating gas exchange. The lower epidermis often has more stomata than the upper surface; each stoma is flanked by two guard cells that open or close to regulate gas exchange and transpiration. Veins containing xylem and phloem transport water into the leaf and carry away manufactured sugars.

Stomatal function and water balance
Stomata open in response to light and water status, allowing carbon dioxide in for photosynthesis and releasing oxygen and water vapour. Guard cells change shape by taking up or losing water, and control stomatal aperture. Leaves have various adaptations to reduce water loss in dry climates: thick cuticles, sunken stomata, reduced surface area (needles), or hairy surfaces to trap humid air.

Adaptations and examples
Succulent leaves (aloe) store water; tendrils in peas are modified leaves for climbing; insectivorous plants have modified leaves to capture prey. Observing these variations helps relate form to habitat and function.

Parts of a flower
Flowers are reproductive structures of angiosperms. A typical flower has four whorls: calyx (sepals), corolla (petals), androecium (male part made of stamens with anther and filament) and gynoecium (female part made of carpels; each carpel has stigma, style and ovary). Flowers may be complete (all whorls present) or incomplete, and bisexual (both sexes) or unisexual.

Pollination
Pollination is the transfer of pollen grains from an anther to a stigma. Self-pollination occurs within the same flower or plant; cross-pollination occurs between different plants. Pollination agents include wind, water, insects, birds and bats. Flower structure often reflects the pollination agent: showy fragrant flowers with nectar attract insects and birds; lightweight pollen and exposed stamens suit wind pollination.

Fertilisation
After pollen lands on a compatible stigma, it germinates to form a pollen tube that grows down the style to the ovary carrying male nuclei. These fuse with female nuclei in the ovule to form a zygote (fertilisation), leading to seed development. Double fertilisation, unique to angiosperms, produces a zygote and endosperm which nourishes the embryo.

Flower types and symmetry
Flowers can be actinomorphic (radially symmetrical) or zygomorphic (bilaterally symmetrical). Inflorescences arrange multiple flowers on a stem in specific patterns such as raceme, spike or head.

Practical work
Students will dissect flowers to identify parts, observe pollen under a microscope and study pollination adaptations. Linking structure with function shows how plants ensure successful reproduction under different environmental conditions.

Formation of fruit and seeds
After fertilisation in flowering plants, the ovary of the flower develops into a fruit while the fertilised ovules become seeds. The ovary wall may thicken into a pericarp that surrounds and protects the seeds. Fruit development protects the developing seeds and often helps in their dispersal to favourable places for germination.

Types of fruits
Fruits can be classified by how they form and their structure. Simple fruits develop from a single ovary of one flower (e.g., mango, peas). Aggregate fruits form from many ovaries of one flower (e.g., strawberry). Multiple fruits form from ovaries of many flowers growing close together (e.g., pineapple). Other distinctions include fleshy fruits, which are soft and edible at maturity, and dry fruits, which may split open to release seeds or remain closed.

Seed structure and variation
A seed contains three basic parts: the embryo (young plant), stored food reserves (endosperm or cotyledons) and a protective seed coat. Monocot seeds have one cotyledon and often large endosperm (e.g., maize); dicot seeds have two cotyledons that may store food (e.g., bean). Seed size, shape and the amount of stored food relate to the seedling's needs and the plant’s life strategy.

Germination requirements
Seeds need suitable water, oxygen, temperature and sometimes light to germinate. Water softens the seed coat and activates enzymes that break down stored food into usable forms for the growing embryo. Some seeds have dormancy mechanisms and need treatments—scarification (breaking the coat), stratification (cold treatment) or exposure to fire or smoke—to break dormancy and allow germination under the right conditions.

Dispersal methods and importance
Dispersal reduces competition with the parent plant and allows colonisation of new habitats. Seeds and fruits are dispersed by wind (winged or hairy seeds), water (buoyant seeds like coconut), animals (fleshy fruits eaten and seeds later deposited in dung; hooks that cling to fur), and mechanical methods (explosive pods). Understanding dispersal informs agriculture, forestry and conservation practices such as seed collection and planting strategies.

Definition and overview
Photosynthesis is the process by which green plants, algae and certain bacteria convert carbon dioxide and water into carbohydrates using light energy captured by chlorophyll. This process not only builds the plant’s food but also supplies oxygen to the atmosphere. It is the primary source of energy entering most ecosystems.

Where and how it happens
Photosynthesis takes place mainly in the chloroplasts of leaf mesophyll cells, especially in the palisade layer where chloroplasts are densely packed. Light is absorbed by chlorophyll and accessory pigments; this energy drives reactions that split water molecules releasing oxygen and produce energy-rich compounds like ATP and NADPH. These are used in the carbon-fixation steps to assemble simple sugars from carbon dioxide.

General equation and significance
The simplified overall equation states that carbon dioxide and water, in presence of light and chlorophyll, yield glucose and oxygen. The sugars produced provide energy and building blocks for growth, storage (starch) and production of cellulose for cell walls. Photosynthesis is essential for food production, biomass accumulation and maintaining atmospheric oxygen levels.

Factors affecting the rate
The rate of photosynthesis is influenced by light intensity, carbon dioxide concentration, temperature and the amount of chlorophyll. At low light or CO2 levels the rate is limited; increasing these factors raises the rate until another factor becomes limiting. Extremely high temperatures can damage enzymes and reduce the rate. Leaf structure, water availability and stomatal opening also affect CO2 uptake.

Practical demonstrations
Students can test leaves for starch to show carbohydrate production: a leaf exposed to light will give a positive iodine test after decolourisation. Variegated leaves or covered sections demonstrate the need for chlorophyll and light. Aquatic plant experiments collecting oxygen bubbles can show variation of photosynthesis with light intensity.

What is transpiration?
Transpiration is the loss of water vapour from plant parts, mainly through stomata in leaves. It creates a pull that draws water up through the xylem from the roots to the leaves, aiding transport of water and minerals and helping cool the plant.

Pathway of water
Water moves from soil into root hairs by osmosis, passes through root cortex to xylem, travels up the stem in xylem vessels and reaches leaves where it evaporates into air spaces and exits through stomata. Cohesion (water sticking to water) and adhesion (water sticking to xylem walls) help form a continuous water column enabling transpiration pull.

Factors affecting transpiration
Light, temperature, humidity, wind and the number and opening of stomata influence transpiration. Higher light and temperature, low humidity and wind increase transpiration. Plants reduce water loss by closing stomata, having waxy cuticles, hairy leaves or reduced leaf area.

Experimental demonstration
Students may measure transpiration by weighing potted plants over time or by collecting water loss from leaves using a potometer. Such activities show relative rates under different conditions and teach careful measurement and control of variables.

Balance of water
Plants must balance water uptake and loss. Excessive transpiration in dry weather can lead to wilting; conservation strategies and stomatal control are vital for survival. Understanding water relations is important for agriculture and irrigation practices.

Essential nutrients and categories
Plants need water, carbon, hydrogen and oxygen (from soil and air) and a range of mineral elements from soil. Mineral elements are classified by the amounts required: macronutrients needed in large amounts (nitrogen, phosphorus, potassium, calcium, magnesium, sulphur) and micronutrients needed in trace amounts (iron, manganese, zinc, copper, boron, molybdenum). Each has specific roles in metabolism and structure.

Roles and deficiency symptoms
Nitrogen is crucial for amino acids, proteins and chlorophyll; its deficiency causes stunted growth and yellow leaves (chlorosis). Phosphorus is important for energy transfer (ATP), root development and flowering; deficiency causes poor root growth and purplish leaves. Potassium helps in enzyme activation, water balance and disease resistance; deficiency results in leaf scorching and poor fruit quality. Calcium is important for cell wall stability and root development; magnesium is central to chlorophyll; iron is needed for chlorophyll synthesis though required in small amounts.

Soil properties and uptake
Soil type (sand, silt, clay), organic matter, pH and aeration affect nutrient availability. Roots absorb nutrients in ionic form dissolved in soil water by diffusion or active transport. The endodermis and Casparian strip regulate selective uptake into the vascular system. Mycorrhizal fungi associate with roots to extend effective absorptive surface area and improve uptake of phosphorus and other elements.

Fertilizers and sustainable practices
Agricultural fertilizers supply missing nutrients; balanced NPK fertilizers are widely used. Overapplication leads to nutrient runoff polluting water bodies and harming organisms. Organic manures and compost release nutrients slowly and improve soil structure. Crop rotation, intercropping with legumes (which fix atmospheric nitrogen via root nodules) and soil testing help maintain soil fertility sustainably.

Practical classroom work
Students learn to recognise deficiency symptoms, perform simple experiments showing nutrient limits (e.g., growing seedlings with and without nitrogen), and understand basic soil testing and composting. Linking plant nutrition to food production helps students appreciate responsible fertilizer use and conservation of soil resources.

Growth and development
Growth is a permanent increase in size and mass due to cell division and enlargement. Development includes growth plus differentiation—where cells specialise into tissues and organs—and maturation to reproductive stages. Primary growth in length occurs at apical meristems in root and shoot tips, while secondary growth in thickness occurs from lateral meristems such as vascular cambium in woody plants, forming wood and bark.

Meristems and differentiation
Meristematic cells are small, thin-walled and capable of active division. As new cells are produced they elongate and differentiate into specialised tissues: epidermis for protection, vascular tissues for transport, and ground tissues for storage and support. Patterns of differentiation determine organ shape and function, for example a leaf vs a root.

Plant hormones and control
Plant growth regulators shape many processes. Auxins promote cell elongation and root formation and influence apical dominance. Gibberellins stimulate stem elongation and breaking of seed dormancy. Cytokinins promote cell division and delay senescence. Abscisic acid often induces dormancy and closes stomata under stress, while ethylene affects fruit ripening and leaf drop. Hormones work in small quantities and interact to produce coordinated responses.

Responses to environment
Plants respond to light (phototropism), gravity (gravitropism), water (hydrotropism) and touch (thigmotropism). Photoperiod and temperature control flowering in many species: some plants flower in long days, others in short days, and some require vernalization (cold) to flower. These responses link growth and reproduction to seasonal cues.

Reproduction and life cycles
Plants reproduce sexually by forming gametes and seeds, and asexually by vegetative propagation (runners, bulbs, tubers, cuttings). Sexual reproduction in flowering plants involves pollination, fertilisation (including double fertilisation), seed and fruit formation, and germination of the seed into a new plant. Some plants show alternation of generations: a multicellular diploid sporophyte producing spores and a multicellular haploid gametophyte producing gametes; the prominence of each phase varies among groups (mosses vs ferns vs seed plants).

Practical and applied aspects
Students will observe germination, measure seedling growth, perform simple hormone experiments (e.g., apical bud removal and effect on lateral buds), and practise vegetative propagation techniques. Understanding growth and reproduction is central to agriculture, horticulture and forestry, helping improve crop yields and manage plant resources.