Level 3 Applied Science AQA

Biology: Cell Structure

Basics of Cell Structure

• Each living organism is made up of cells, the basic building blocks of life.
• Cells can be broadly classified into two categories: prokaryotic cells (like bacteria, which are simple and do not have a nucleus or other membrane-bound organelles), and eukaryotic cells (like plant and animal cells, which are more complex and contain a nucleus and other membrane-bound organelles).
• The cell is filled with a substance called cytoplasm, where cellular activities occur.
• A cell membrane encloses the cell, protecting the cell’s contents and controlling what enters and leaves the cell.

Cell Organelles

• The nucleus is an organelle found in eukaryotic cells. It contains the majority of the cell’s genetic material and controls the cell’s activities by regulating gene expression.
• Mitochondria are known as the powerhouses of the cell. They generate a cell's energy by producing adenosine triphosphate (ATP) through the process of cellular respiration.
• Ribosomes are the sites of protein synthesis. They convert genetic material in the form of RNA into protein.
• The endoplasmic reticulum (ER) is involved in protein and lipid synthesis. It can be smooth (for lipid synthesis) or rough (dotted with ribosomes for protein synthesis).

Cell Specialisation

• Cells differentiate (become specialised) to carry out specific functions, a process called cell specialisation.
• For instance, red blood cells are specialised for carrying oxygen, nerve cells (or neurons) are specialised for carrying electrical signals, and muscle cells are specialised for contraction and movement.
• In plants, root hair cells are specialised for absorbing water and nutrients, and photosynthetic cells in the leaves are specialised for capturing light energy.

Plant Cells vs Animal Cells

• Both plant and animal cells are eukaryotic, meaning they contain a nucleus and other membrane-bound organelles.
• Unlike animal cells, plant cells have a rigid cell wall outside the cell membrane, which provides structure and support.
• Plant cells also contain chloroplasts, which are necessary for photosynthesis, and a large central vacuole that stores water and helps maintain cell turgor pressure.

Microscopy

• Light microscopes are used to observe cells and cellular structures. They can magnify objects up to 2000 times, but have a lower resolution than electron microscopes.
• Electron microscopes use beams of electrons to achieve higher magnification and resolution, allowing the intricate details of cell structures to be seen. However, they are more complex and costly to use. Remember, the magnification of a microscope is different from its resolution; the former is about enlarging an image while the latter relates to the level of detail that can be observed.