Study Combined Science notes for O-Level. Useful for revision, homework, and exam preparation in Zimbabwe.
A free account is needed to download. Sign in or create one
This is the ZIMSEC O-Level Combined Science notes from 2019. It is a free notes for revision.
COMPILED BY Mr Muchenje @ I.C.T ACADEMY (2019) +263 785094369 call/text/WhatsApp I.C.T ACADEMY ORDINARY LEVEL COMBINED SCIENCE Compiled by the One on One Tutor M.R. Muchenje (+263 785094 369) SECTION A: BIOLOGY TOPIC 1: STRUCTURE AND FUNCTION OF A CELL INTRODUCTION - All living organisms are made up of single units which are known as cells. - These cells are the basic units of the structure and function of all living organisms. - Cells have the ability to reproduce, as a result all existing cells come from other pre-existing cells through the process of cell reproduction. - Cells are microscopic therefore one would need a microscope in order to view cells. IDENTIFYING PARTS OF A CELL AND THEIR FUNCTIONS - When it comes to living organisms there are two main types of cells, there are animal cells and plant cells. - These cells have some similarities and at the same time they have some differences between them, these can be observed when we compare and contrast the features of both cells. - The following are the common features of a cell, these can be found in both plant and animal cells. Cytoplasm. - The cytoplasm looks like a thick liquid full of tiny particles, in plant cells it may be seen to be moving around inside the cell. - The particles inside the cytoplasm include food droplets or granules of starch. - A lot of chemical reactions take place inside the cytoplasm keeping the cell alive by providing it with energy as well as other substances that the cell needs. - Liquid part of cytoplasm is $90 \%$ water, inside this liquid part molecules of salts and sugars can be found as well as dissolved nutrients like fats (lipids) and proteins which are used to build cell structures. - Some of the proteins inside the cytoplasm are enzymes, these control the rate and type of chemical reactions happening inside the cell. Cell Membrane - This is a thin membrane around the cytoplasm, it stops contents of the cell from escaping or leaving the cell, it also controls substances which are allowed to enter the cell or leave it depending on the situation. - Generally, oxygen, food and water are allowed to enter the cell by the membrane whilst waste material like carbon dioxide and other harmful substances are allowed to leave the cell or kept out. - Basically the cell membrane maintains the structure and chemical reactions of the cytoplasm