Cell Structure

All cells have structures inside them - these are called sub-cellular structures. 

In an animal cell, the sub-cellular structures include: 

• a nucleus, which controls the activites of the cell and contains the genetic material 
• cytoplasm, in which most of the chemical reactions take place 
• a cell membrane, which controls the passage of substance into and out of the cell 
  
• mitochondria, where aerobic resperation takes place 
• ribosomes, where protiens are synthesised (made)

Plant cells and algal cells contain all the sub-cellular structures found in animal cells

They also have: 

• a cell wall made of cellulose, whihc strengthens the cell 
• a permenant vacuole filled with cell sap, whihc supports the plant 

Plants need to make their own food, so some of their cells contain chloroplasts

Chloroplasts absorb light to make food (glucose) by photosynthesis 

There are two main types of cell: 

• prokaryotic 
• eukaryotic 

Plant, animal and fungal cells are all eukaryotic 

Bacteria cells are prokaryotic 

There are a number of differences between the two types of cell

Prokaryotic cells are much smaller in size and: 

• the genetic material is not enclosed in a nucleus 
• the genetic material is a single DNA loop and there may be one or more small rings of DNA, called plasmids
• plasmids are present, which are circles of DNA that can be transferred from one cell to another 

Bacteria cells have many different shapes - some are round, some are rod-shaped and some are spiral - but they are all prokaryotic cells

In bacterial cells, the roles of the mitochondria and chloroplasts are taken over by the cytoplasm 

Plasmids are presentsm which are circles of DNA that can be transferred from one cell to another

Plasmids allow bacterial cells to move genes from one cell to another.

• Plasmid DNA - a small, commonly circular, section of DNA that can replicate independently of chromosonal DNA 
• Chromosonal DNA - the DNA of bacteria is not found within a nucleus and is usually found as one circular chromosome
• Flagella - tail-like structures that rotate to help some bacteria move 
• Cell Wall - provides structural support to the bacteria (it is not made of cellulose) 
• Cytoplasm 

Key Points 

• Not all plant cells have chloroplasts. For example, they are not present in root cells because they do not recive any light
• Prokaryotic cells are much simpler in structure than eukaryotic cells. That is why scientists think that they developed before eukaryotic cells
• Plasmids have become very useful to scientists. They allow genes to be insterted into bacteria in genetic engineering.

• Sub-cellular Sructures
• Nucleus 
• Cytoplasm
• Cell Membrane
• Mitochondria
• Ribosomes 
• Cell Wall 
• Cellulose 
• Vacuole 
• Chloroplast 
• Prokaryotic 
• Eukaryotic 
• Plasmid  

Cells are the basic building blocks og all living organisms 

As an organism develops, cells differentiate to form different types of cells. They become specialised

Most types of animal cell can differentiate at an early but many types of plant cell can differentiate throughout their life

As a cell differentiates: 

• it may change shape 
• different sub-cellular structures develop to let it carry out a specific function 

Specialised animal cells include sperm, nerve and muscle cells. 

Specialised plant cells include root hair, xylem and pholem cellls.