iGCSE Biology CAIE

Cell Structure and Functions

Cell Structure

• All living organisms are composed of cells which can be classified as either prokaryotic (bacteria) or eukaryotic (plants, animals).

• Main components of a typical cell include: cell membrane, nucleus, cytoplasm, mitochondria, and ribosomes.

• Cell membrane, a delicate semi-permeable layer, encases the cell and regulates the movement of substances in and out of the cell.

• The nucleus controls cell activities including growth and reproduction. It contains chromosomes, which are made up of DNA coding for the cell's genetic information.

• The cytoplasm is a jelly-like substance where the cell's metabolic reactions occur, controlled by enzymes.

• Mitochondria, often termed the 'powerhouse' of the cell, generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of energy.

• Ribosomes are minute particles involved in protein synthesis.

Prokaryotic and Eukaryotic cells

• Prokaryotic cells like bacteria are simpler and smaller than eukaryotic cells. They lack a true nucleus and membrane-bound organelles.

• Eukaryotic cells have a defined nucleus enclosed in a nuclear membrane, and feature numerous organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

Plant vs Animal Cells

• Plant cells are distinguished by extra components: a cell wall for added support, chloroplasts for photosynthesis, and a large central vacuole storing water and nutrients.

• Animal cells do not have a cell wall or chloroplasts, and instead of one large central vacuole, there are smaller vacuoles scattered throughout the cell.

Cell Functions

• Cells are the building blocks of life and carry out all vital biological processes.

• Functions include growth, replication, energy production, protein synthesis, and waste elimination.

• Every function depends on the cell's ability to take in nutrients, excrete waste, reproduce, and respond to its environment.