Biology Class 11th

Last Updated : 27 Mar, 2026

Class 11 Biology introduces the fundamental concepts of life sciences and the diversity of living organisms. It builds the foundation for understanding the structure and functions of living systems, from molecules and cells to tissues and whole organisms. The syllabus includes topics such as biological classification, plant and animal physiology, cell biology, biomolecules, and structural organization in plants and animals.

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The Living World

The living world is rich in variety. Millions of plants and animals have been identified and described, but a large number remains unknown. The very range of organisms in terms of size, color, habitat, physiological, and morphological features makes us seek the defining characteristics of living organisms.

Biological Classification

Biological classification of plants and animals was first proposed by Aristotle on the basis of simple morphological characters. Linnaeus later classified all living organisms into two kingdoms—Plantae and Animalia. Whittaker proposed an elaborate five-kingdom classification—Monera, Protista, Fungi, Plantae, and Animalia.

The Plant Kingdom

The plant kingdom includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms. Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic organisms. Depending on the type of pigment possessed and the type of stored food, algae are classified into three classes, namely Chlorophyceae, Phaeophyceae, and Rhodophyceae.

The Animal Kingdom

The basic fundamental features, such as level of organization, symmetry, cell organization, coelom, segmentation, notochord, etc., have enabled us to broadly classify the animal kingdom. Besides the fundamental features, there are many other distinctive characters that are specific to each phylum or class.

Morphology of Flowering Plants

Flowering plants exhibit enormous variation in shape, size, structure, mode of nutrition, life span, habit, and habitat. They have a well-developed root and shoot system.

Anatomy of Flowering Plants

Anatomically, a plant is made of different kinds of tissues. The plant tissues are broadly classified into meristematic (apical, lateral, and intercalary) and permanent (simple and complex). Assimilation of food and its storage, transportation of water, minerals, and photosynthates, and mechanical support are the main functions of tissues.

Structural Organisation in Animals

Cells, tissues, organs, and organ systems split up the work in a way that ensures the survival of the body as a whole and exhibits division of labor. A tissue is defined as a group of cells along with intercellular substances performing one or more functions in the body.

Cell: the unit of life

All organisms are made of cells or aggregates of cells. Cells vary in their shape, size, and activities/functions. Based on the presence or absence of a membrane-bound nucleus and other organelles, cells and, hence, organisms can be named as eukaryotic or prokaryotic.

Biomolecules

Although there is a bewildering diversity of living organisms, their chemical composition and metabolic reactions appear to be remarkably similar. The elemental composition of living tissues and non-living matter also seems to be similar when analyzed qualitatively. This chapter explains the structure and functions of carbohydrates, proteins, lipids, nucleic acids, and enzymes.

Cell Cycle and Cell Division

According to the cell theory, cells arise from pre-existing cells. The process by which this occurs is called cell division. Any sexually reproducing organism starts its life cycle from a single-celled zygote. Cell division does not stop with the formation of the mature organism but continues throughout its life cycle.

Photosynthesis in Higher Plants

Green plants make their own food by photosynthesis. During this process, carbon dioxide from the atmosphere is taken in by leaves through stomata and used for making carbohydrates, principally glucose and starch. Photosynthesis takes place only in the green parts of the plants, mainly the leaves.

Respiration in Plants

Plants, unlike animals, have no special systems for breathing or gaseous exchange. Stomata and lenticels allow gaseous exchange by diffusion. Almost all living cells in a plant have their surfaces exposed to air.

Plant Growth and Development

Growth is one of the most conspicuous events in any living organism. It is an irreversible increase expressed in parameters such as size, area, length, height, volume, cell number, etc. It conspicuously involves increased protoplasmic material.

Breathing and Exchange of Gases

Cells utilize oxygen for metabolism and produce energy along with substances like carbon dioxide, which is harmful. Animals have evolved different mechanisms for the transport of oxygen to the cells and for the removal of carbon dioxide from there. We have a well-developed respiratory system comprising two lungs and associated air passages to perform this function.

Body Fluids and Circulation

Vertebrates circulate blood, a fluid connective tissue, in their bodies to transport essential substances to the cells and to carry waste substances from there. Another fluid, lymph (tissue fluid), is also used for the transport of certain substances.

Excretory Products and Their Elimination

Many nitrogen-containing substances, ions, CO₂, water, etc., that accumulate in the body have to be eliminated. Nature of nitrogenous wastes formed and their excretion vary among animals, mainly depending on the habitat (availability of water). Ammonia, urea, and uric acid are the major nitrogenous wastes excreted. This chapter explains the structure and function of the human excretory system.

Locomotion and Movement

Movement is an essential feature of all living beings. Protoplasmic streaming, ciliary movements, movements of fins, limbs, wings, etc., are some forms exhibited by animals. A voluntary movement that causes the animal to change its place is called locomotion. Animals move generally in search of food, shelter, a mate, a breeding ground, a better climate, or to protect themselves.

Neural Control and Coordination

The neural system coordinates and integrates functions as well as metabolic and homeostatic activities of all the organs. Neurons, the functional units of the neural system, are excitable cells due to a differential concentration gradient of ions across the membrane.

Chemical Coordination and Integration

There are special chemicals that act as hormones and provide chemical coordination, integration, and regulation in the human body. These hormones regulate metabolism, growth, and development of our organs, the endocrine glands, or certain cells. The endocrine system is composed of the hypothalamus, pituitary and pineal glands, thyroid, adrenals, pancreas, parathyroid, thymus, and gonads (testes and ovaries). In addition to these, some other organs, e.g., gastrointestinal tract, kidney, heart, etc., also produce hormones

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