A typical flower has four whorls: (1) Calyx (sepals) - the outermost green whorl that protects the flower in the bud stage; (2) Corolla (petals) - usually coloured, it attracts pollinators; (3) Androecium (stamens) - the male reproductive whorl producing pollen; and (4) Gynoecium (carpels/pistil) - the female reproductive whorl containing ovules that develop into seeds after fertilisation.

An inflorescence is the arrangement of flowers on the floral axis. In a racemose inflorescence, the main axis continues to grow (it has unlimited growth) and the flowers are borne laterally in an acropetal order (older flowers at the base, younger towards the tip), e.g. radish. In a cymose inflorescence, the main axis ends in a flower and so has limited growth, and the flowers are borne in a basipetal order (older flowers at the top or centre), e.g. Jasmine.

Venation is the arrangement of veins and veinlets in the lamina of a leaf. In reticulate venation the veinlets form a network, typical of dicot leaves (e.g. mango); in parallel venation the veins run parallel to one another, typical of monocot leaves (e.g. grass). Phyllotaxy is the pattern of arrangement of leaves on the stem or branch; it may be alternate, opposite or whorled.

Meristematic tissue consists of actively dividing cells that are responsible for the growth of the plant. The cells are small, thin-walled, with dense cytoplasm and prominent nuclei, and little or no vacuole. Based on position the three types are: apical meristem (at the tips of root and shoot, causing increase in length), intercalary meristem (at the base of internodes or leaves) and lateral meristem (along the sides, e.g. cambium, causing increase in girth).

Simple permanent tissues are made of one type of cell. (1) Parenchyma - thin-walled living cells with intercellular spaces; they perform storage, photosynthesis and secretion. (2) Collenchyma - living cells with corners thickened by cellulose and pectin; they provide mechanical support and flexibility to young stems and leaves. (3) Sclerenchyma - dead cells with thick, lignified walls (fibres and sclereids); they provide mechanical strength and rigidity.

Xylem conducts water and dissolved minerals from the roots upward to other parts of the plant and gives mechanical support. Its components are tracheids, vessels, xylem fibres and xylem parenchyma. Phloem transports food (mainly sucrose) prepared in the leaves to the rest of the plant (translocation). Its components are sieve tube elements, companion cells, phloem fibres and phloem parenchyma. Both are complex (conducting) tissues.

(1) In a dicot root the number of xylem bundles (vascular bundles) is few, usually two to four (tetrarch or less), whereas in a monocot root they are many (polyarch, often more than six). (2) A dicot root has secondary growth due to the presence of cambium, whereas a monocot root usually lacks secondary growth as cambium is absent. Also, the pith is small or absent in dicot roots but large and well developed in monocot roots.

Stomata are tiny pores present mainly in the epidermis of leaves. Each stoma is bounded by two bean-shaped (kidney-shaped) guard cells that contain chloroplasts; in monocots the guard cells are dumb-bell shaped. Functions: stomata allow the exchange of gases (carbon dioxide and oxygen) between the plant and the atmosphere and control transpiration (loss of water vapour). The opening and closing of the stoma is regulated by the turgidity of the guard cells.

Epithelial tissue is a covering or protective tissue that lines the free surfaces of the body and its organs; it rests on a basement membrane and has little intercellular material. Simple epithelium is a single layer of cells and its types are: (1) squamous epithelium - flat cells, found in the walls of alveoli and blood vessels, involved in diffusion; (2) cuboidal epithelium - cube-shaped cells, found in kidney tubules and glandular ducts, for secretion and absorption; and (3) columnar epithelium - tall cells, found in the lining of the stomach and intestine, for secretion and absorption.

Connective tissue links, supports and binds together other tissues and organs of the body; its cells are loosely spaced in an abundant matrix. Main types: (1) loose connective tissue, e.g. areolar tissue and adipose (fat-storing) tissue; (2) dense connective tissue, e.g. tendons (connect muscle to bone) and ligaments (connect bone to bone); and (3) specialised connective tissue, e.g. cartilage, bone and blood (a fluid connective tissue that transports materials).

The three types of muscular tissue are: (1) striated (skeletal) muscle - cylindrical, unbranched, multinucleate and voluntary, attached to bones for movement; (2) smooth (unstriated) muscle - spindle-shaped, uninucleate and involuntary, found in the walls of internal organs such as the stomach, intestine and blood vessels; and (3) cardiac muscle - branched, striated and involuntary, found only in the wall of the heart.

A neuron is the structural and functional unit of nervous tissue. It has three main parts: (1) the cell body (cyton), which contains the nucleus and cytoplasm with Nissl granules; (2) dendrites, which are short branched processes arising from the cell body that receive impulses and carry them towards the cell body; and (3) the axon, a single long process that carries impulses away from the cell body to the next neuron or effector. The axon may be covered by an insulating myelin sheath.

The cell theory was proposed by M. Schleiden (a botanist) and T. Schwann (a zoologist) in 1838-39. Its postulates are: (1) all living organisms are composed of cells and products of cells; (2) the cell is the basic structural and functional unit of life. Later Rudolf Virchow (1855) added that all cells arise from pre-existing cells (omnis cellula-e-cellula).

(1) Prokaryotic cells lack a true membrane-bound nucleus (the genetic material lies free in the cytoplasm as a nucleoid), whereas eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane. (2) Prokaryotes lack membrane-bound organelles such as mitochondria, endoplasmic reticulum and Golgi bodies, while eukaryotes possess them. (3) The ribosomes are 70S in prokaryotes and 80S in the cytoplasm of eukaryotes. Examples: bacteria are prokaryotic; plant and animal cells are eukaryotic.

A mitochondrion is a double-membrane organelle. The outer membrane is smooth, while the inner membrane is folded inward to form finger-like cristae that increase the surface area; the inner space is filled with a matrix. It contains its own DNA and 70S ribosomes. Function: it is the site of aerobic respiration, where the Krebs cycle (in the matrix) and the electron transport chain (on the inner membrane) produce ATP, the energy currency of the cell. Because it produces most of the cell's ATP, it is called the powerhouse of the cell.

A chloroplast is a double-membrane organelle found in green plant cells. Its inner space, the stroma, contains stacks of disc-shaped membranes called thylakoids; a stack of thylakoids is a granum (plural grana), and grana are connected by stroma lamellae. The thylakoid membranes contain the green pigment chlorophyll. It has its own DNA and 70S ribosomes. Function: it is the site of photosynthesis - the light reactions occur on the thylakoid membranes and the dark reactions (Calvin cycle) occur in the stroma.

The endoplasmic reticulum (ER) is a network of membranous tubules and sacs in the cytoplasm. Rough ER (RER) has ribosomes attached to its surface and is mainly involved in the synthesis and transport of proteins. Smooth ER (SER) lacks ribosomes and is involved in the synthesis of lipids and steroids and in detoxification. Both help in intracellular transport of materials.

The Golgi apparatus consists of a stack of flattened membrane-bound sacs called cisternae arranged parallel to one another, along with associated vesicles. Functions: it packages, modifies and sorts materials (such as proteins and lipids) received from the endoplasmic reticulum and secretes them in vesicles. It is also the site of formation of lysosomes and the synthesis of certain complex carbohydrates and cell wall materials.

Ribosomes are non-membrane-bound organelles made of RNA and protein; they are the site of protein synthesis. Lysosomes are single-membrane-bound vesicles containing powerful digestive (hydrolytic) enzymes that digest worn-out organelles, food and foreign material. They are called suicidal bags because on rupture their enzymes can digest the cell's own contents, causing the cell to die (autolysis).

The nucleus is a spherical, membrane-bound organelle that controls the activities of the cell. It is bounded by a double membrane called the nuclear envelope, which has nuclear pores for exchange of materials. Inside is the nucleoplasm containing chromatin (DNA plus proteins) and one or more nucleoli. Functions: it stores the genetic material (DNA), controls cell metabolism and heredity, and the nucleolus is the site of ribosome (rRNA) synthesis. During cell division the chromatin condenses into chromosomes.