Biology

Structure:

• The nucleus is the largest organelle, when this is stained, it shows darkerned patches known as chromatin.
• It is surronded by a nuclear envelope. This is a structure made up of two membranes with fluid between them.
• A lot of holes, called nuclear pores, go right through the envelope. The holes are already large enough for relatively large molecules to pass through.
• This is a dense, spherical structure, called the nucleolus, inside the nucleus.

Function:

• The nucleus houses nearly all the cells genetic material.
• The chromotonin consists of DNA and proteins
• It has instructions for making protein, some of these proteins regulate the cells activitiy.
• When the cell divides, chromotonin condenses into visible chromosomes. 
• The nucleolus makes the RNA and ribosomes.
• Theses pass into the cytoplasm and proteins assembled at them.

Structure

• ER consists of a senses of flattened, membrane bound sacs called cisternae
• They are continuous with the outer nuclear membrane
• Rough endoplasmic reticulum is studded with ribosomes
• Smooth endoplasmic do not have ribosomes

Function:

• Rough ER transports proteins that were made on the attached ribosomes
• Some of the seperate proteins may have been secreted from the cell.
• Some will be placed on the surface membrane
• Smooth ER is involved in making the lipids that the cell needs

Stucture:

A stack of membrane bound, flattened sacs.             (looks like a bread pile.)

Function:

• Golgi apparatus recieves proteins from the ER and modifies them.
• It may add sugar molecules to them. The golgi apparatus then packages the modified proteins into vesicles that can be transported.
• Some modified proteins may go to the surface of the cell so they may be secreted.

Structure:

• These may be spherical or sausage shaped.
• They have two membranes seperated by a fluid filled space.
• The inner membrane is highly folded to form cristae
• The central part of the mitochondrion is called the matrix

Function:

• Mitochondria produce most of the adneosine trophosphate ( ATP) during respiration.
  
• ATP is sometimes called the universal energy carrier because almost all activities that need energy in the cell are driven by the enerhy released from ATP.

Structure:

• These are found only in plant cells and the cells of some protoctists.
  
• Chloroplasts also have two membranes seperated by a fluid- filled space.
• The inner membrane is continuos, with an elobarate network of flattened membrane sacs called thylakoids.
• These look like piles of plates. A stack of thylakoids is called a granum or the plural grana.
• Chlorophyll molecules are present pn the thylakoid membranes and in intergranal membranes.

Function:

• Chloroplasts are the site of photosynthesis in plant cells. Light energy is used to drive the reactions of photosynthesis, in which carbohydrate molecules are made from carbon dioxide and water.

Structure:

• These are spherical sacs surronded by a single membrane

Function:

• Lysosomes contain powerful digestive enzymes.
• Their role is to break down materials. For example, white blood cell lysosomes help break down invading microorganisms; the specialised lysosome ( acrnosome ) in the head of a sperm cell helps it penetrate the egg by breaking down the material surronding the egg

Structure:

• These are tiny organelles. Some are free in the cytoplasm and some are bound to ER.
• Each ribosome consists of two subunits

Function:

• Ribsomes are the site of protein sythesis in the cell ( where new proteins are made )
• They act as an assembly line where coded information (mRNA ) from the nucleus is used to assemble proteins from amino acids.

Structure:

• These are small tubes of proteins fibres ( microtubels)
• There is a pair of them next to the nucleus in animal cells and in the cells of some protocists.

Function:

• Centrioles take part in cell division.
• They form fibres, known as the spindle, which move chromosomes during nuclear division.