Ch 5Cell: The Unit of Life — Class 11 Botany, concept-first.

Look around you and it is easy to sort objects into two groups: things that are alive and things that are not.

The cell is the basic building block of every living organism — both the smallest unit that has structure and the smallest unit that can actually carry out the work of being alive.

The cell theory is the central generalisation of biology that describes what every living body is made of and where every cell comes from.

A quick tour of cell structure shows both how much cells have in common and how greatly they differ. The familiar examples from earlier observation — an onion peel and human cheek cells — make a good…

Living things are all made of cells: some are unicellular, existing as a single cell, while others — such as human beings — are multicellular, made of many cells.

Most prokaryotic cells, and bacterial cells in particular, are wrapped in a chemically complex cell envelope.

This section covers two internal features of prokaryotic cells: the ribosomes, where proteins are built, and the inclusion bodies, where reserve materials are stored.

Eukaryotic cells are the more complex of the two great cell types, marked above all by internal compartments and a properly organised nucleus.

The cell membrane, or plasma membrane, is the boundary that separates the inside of the cell from its surroundings.

The cell wall is a non-living, rigid layer that surrounds the plasma membrane and forms the outermost covering of the cells of fungi and plants.

Several of the membrane-bound organelles inside a eukaryotic cell each have their own particular structure and job.

When eukaryotic cells are examined under the electron microscope, they reveal a network, or reticulum, of very small tube-like structures spread throughout the cytoplasm.

The Golgi apparatus was first noticed in 1898 by Camillo Golgi, who observed densely stained, net-like structures lying close to the nucleus.

Lysosomes are tiny, membrane-bound vesicular structures. They are produced through the packaging activity that takes place in the Golgi apparatus, so they originate as vesicles pinched off from that o…

A vacuole is a membrane-bound space present within the cytoplasm of a cell. Rather than being solid, it is an enclosed pocket that holds a variety of contents, including water, sap, excretory products…

Mitochondria (a single one is called a mitochondrion) are usually hard to see under an ordinary microscope unless they have been specially stained.

Plastids are organelles found in all plant cells and also in euglenoids. They are large enough to be seen easily under the microscope, and they carry particular pigments that give plants their charact…

Ribosomes are small, dense particles built from ribosomal RNA together with protein — because of this combination they are called ribonucleoproteins — and unlike most other organelles they carry no su…

The cytoskeleton is an extensive internal framework of protein filaments that runs throughout the cytoplasm, giving the cell an organised internal architecture.

Cilia and flagella are hair-like projections that extend outward from the surface of the cell, and both are involved in movement.

The centrosome is an organelle that organises the microtubule structures of an animal cell, and it is built around a pair of small cylinders called centrioles.

The nucleus is the control centre of the eukaryotic cell — it directs the activities of the other organelles and carries the hereditary material.

Besides the large, familiar organelles, the cytoplasm of both plant and animal cells contains many extremely tiny, membrane-bound sacs called microbodies.

The cell is the fundamental structural and functional unit of every living organism. All organisms are built either from a single cell or from aggregates of many cells, and cells themselves vary widel…

Higher-order thinking / exemplar-style practice problems.