GCSE Biology A (Triple) OCR

Cells and Microscopy

Cells: The Basic Units of Life

• All living organisms are made up of cells, they are the basic unit of life.
• There are two main types of cells: prokaryotic and eukaryotic.
• Prokaryotic cells, found in bacteria and archaea, do not have a nucleus. Their DNA resides in a region called the nucleoid.
• Eukaryotic cells, found in animals, plants, fungi, and protists, have a nucleus which houses their DNA.
• All cells contain cytoplasm, a cell membrane, and ribosomes.

Eukaryotic Cell Structure

• The nucleus controls the cell's activities by controlling the production of proteins. It also contains the cell's DNA.
• The cytoplasm is a gel-like substance where the cell's metabolic reactions occur.
• The cell membrane controls what enters and leaves the cell.
• The mitochondria are responsible for respiration and providing energy.
• Ribosomes are sites of protein synthesis.
• In plant cells, you will also find a cell wall, chloroplasts and a central vacuole.

Prokaryotic Cell Structure

• Prokaryotic cells, compared to eukaryotic cells, are smaller and have fewer structures.
• They have a cell membrane and cell wall and also have a further protective layer, the capsule.
• They have plasmids, small rings of DNA.
• They do not have a true nucleus, but they have a nucleoid where DNA resides.

Specialised Cells

• Some cells in multicellular organisms become specialised, meaning they take on a specific role.
• Specialised cells include sperm cells, nerve cells, and root hair cells in plants.
• Each type has its own unique structure, relevant to its function.

Microscopy

• Microscopes are crucial tools in biology to study cells.
• There are multiple types of microscopes. The most common are the light microscope and the electron microscope.
• The light microscope uses light and lenses to magnify an object and works well for viewing live organisms.
• The electron microscope uses an electron beam, and can view much smaller structures, like the structures within a cell, with a higher resolution.
• However, electron microscopes are more expensive and require more preparation of the sample.

Cell Cultures

• Cell culture involves the distribution of cells in a lab, usually onto a flat surface in a dish.
• It's valuable for studying cell growth, response to drugs or the behaviour of cancer cells.
• Sterile techniques are used to prevent contamination of the cultures.