A Level Life and Health Science CCEA

Cell Structure and Function

Cell Structure and Function

• All living organisms are composed of cells that display a range of structures and functions.

Cell Theory

• The cell theory states that all living things are composed of cells, the cell is the fundamental unit of life, and all cells are produced from pre-existing cells.

Common Cellular Components

• Cells have several common components including cell membrane, cytoplasm, nucleus, and mitochondria.
• The cell membrane is the outer covering of the cell that controls the movement of substances in and out of the cell.
• The cytoplasm is the jelly-like substance wherein cell organelles are located and metabolic reactions take place.
• The nucleus contains genetic information in the form of DNA.
• Mitochondria are the sites of aerobic respiration, producing energy for the cell.

Differences between Prokaryotes and Eukaryotes

• Prokaryotes, such as bacteria, are unicellular organisms with no nucleus or membrane-bound organelles.
• Eukaryotes comprise all plant and animal cells which have a true nucleus and membrane-bound organelles.

Plant Cell and Animal Cell

• Plant cells and animal cells are eukaryotic, however, plant cells have additional structures: cell wall, chloroplasts and a larger vacuole.
• The cell wall provides structure and support to the plant cell.
• Chloroplasts are found in plant cells only and are where photosynthesis takes place.
• The vacuole is larger in plant cells and stores water and nutrients.

Cell Specialisation and Differentiation

• Cells may undergo specialisation and differentiation to carry out specific functions, such as nerve cells for transmitting signals, red blood cells for carrying oxygen, and root hair cells for absorbing water in plants.

DNA and Protein Synthesis

• The nucleus is the control centre housing DNA, which is transcribed into mRNA, and subsequently, translated into proteins.
• Proteins perform a variety of functions within a cell, including structural supports, enzymes to catalyse reactions, and signals that communicate with other cells.

The Role of Ribosomes

• Ribosomes are small structures either floating freely or attached to the endoplasmic reticulum, which are responsible for protein synthesis.

Cell Division

Mitosis

• Mitosis is the process where a single cell divides into two identical daughter cells, necessary for growth and tissue repair.
• During mitosis, the number of chromosomes remains constant.

Meiosis

• Meiosis is a type of cell division that halves the chromosome number and gives rise to four genetically different haploid gametes, which are used in sexual reproduction.