Everything Life Sciences Grade 10

3 The basic units of life

3.1 Overview

Introduction DUMMY

”In the year of 1657 I discovered very small living creatures in rain water.” — Antonie

van Leeuwenhoek, the Father of Microbiology on discovering cells. Together with Robert

Hooke’s discoveries, van Leeuwenhoek’s findings laid the foundations of microbiology.

Key concepts

• The invention of microscopes allowed us to see life at the microscopic level.


• Cell walls are present in plants, bacteria and fungi and provide a rigid support structure.


• Cell membranes are semi-permeable and have a fluid rather than a fixed structure.
  Substances move across them by diffusion, osmosis, facilitated transport and active
  transport.


• Cells contain organelles with structures adapted to perform specific functions within
  the cell.


• Cells differ in size, shape and structure in order to carry out specialised functions.
  Cells with similar structures and functions associate to form tissues.


• Plant and animal cells differ in many crucial ways.

The previous chapter discussed the various organic molecules that make up living organisms.

In this chapter we will look at the cellular level of organisation of living things.

atom→molecule→cell→tissue→organ→system→organism→ecosystem

3.2 Molecular make up of cells

Cells are the basic structural and functional units of all living organisms. Cells are made up

of the compounds you learnt about in the previous chapter: carbohydrates, fats, proteins,

nucleic acids and water. The word ’cell’ was first used by the 17th century scientist Robert

Hooke to describe the small pores in a cork that he observed under a microscope. Cells are

very small structures. The human body is made up of 10^13 cells. Each of these is too small

to see with the human eye and it is through the development of microscopic techniques that

we have been better able to visualise and understand them.

Microscopy DUMMY

Early attempts to magnify images of objects through grinding of glass lenses eventually gave

rise to the earliest microscope. In 1600, Anton van Leeuwenhoek, a Dutch microbiologist

62 3.1. Overview