Mitochondria A Cell Organelle example essay topic

The diagram below shows a picture of an electron microscope. This is a type of microscope that makes use of a beam of electrons rather than visible light. Because the wavelength of electrons is much smaller than the wavelength of visible light, an electron microscope not only gives a high magnification but it also has high resolution. This means that details can be seen clearly.

An electron microscope is very similar to a light microscope in the ways in which it works but, instead of using glass lenses to focus a beam of light, it uses magnets to focus a beam of electrons. Electrons are very small so they are scattered if they hit molecules in the air. Because of this they must travel through a vacuum. Specimens that are to be examined must be cut into very thin sections, and these must be treated so that they can be examined in these conditions. The variety of chemical processes that are carried out in this preparation may change the appearance considerably. Features which have been introduced in this way are known as artefacts and care needs to be taken in interpreting electron micrographs because of the possible presence of artefacts.

The main differences between a light microscope and an electron microscope are shown in the table below. FEATURE LIGHT MICROSCOPE ELECTRON MICROSCOPE Source of illumination Visible light Beam of electrons Method of focusing Glass lenses Magnets Specimens which can Live or dead Dead Be examined Magnification Student microscopes magnify up Up to 500000 times To about 400 times but the Maximum magnification that can Be achieved with a light Microscope is about 1500 times Resolution About 0.2 About 1 or 0.001. (B) Outline the structure and functions of the following organelles endoplasmic reticulum. A network of membranes found in the cytoplasm of a cell.

It consists of a complex system of pairs of membranes arranged parallel to each other enclosing flattened, fluid-filled spaces. These membranes may be covered with ribosomes, in which case they form rough endoplasmic reticulum. The ribosomes produce proteins which are transported through the spaces between the membranes. Smooth endoplasmic reticulum does not have ribosomes on its surface. Its main function is the production and transport of lipids.

Golgi apparatus An organelle which is responsible for the processing and packaging of substances produced by a cell. The golgi apparatus consists of a series of flattened sacs, each one enclosed by a membrane. These sacs are continually being formed on one side and pinched of to form small vesicles at the other. Mitochondria A cell organelle in which the biochemical reactions associated with aerobic respiration take place. Each mitochondrion is surrounded by an envelope consisting of two membranes. The inner one is folded to form structures crista e.

Numbers of mitochondria vary considerably from cell to cell. Cells which contain particularly large amounts of these organelles usually require large amounts of ATP. Ribosomes A very small organelle which plays an important part in making proteins. It is made of a mixture of protein and a special sort of RNA called ribosomal RNA. During protein synthesis a molecule of messenger RNA (mRNA) carries the genetic code for a particular protein from the nucleus into the cytoplasm of the cell. Ribosomes now move along this mRNA molecule.

This results in amino acids being assembled in the correct order to form a molecule of the protein concerned. There are two basic types of ribosome. Those found in the cytoplasm of eukaryotic cells are slight larger than those found in the prokaryotic cells. Lysosomes An organelle containing digestive enzymes.

These enzymes are seperated from the rest of the cell contents by the membrane which surrounds the lysosomes. This is essential otherwise these enzymes would digest the proteins and lipids normally found in the cell and destroy them. Lysosomes are usually associated with animal cells where they have a number of different functions. Chloroplasts A chlorophyll containing organelle found in the cells of plants and algae. It is where photosynthesis takes place. The chloroplasts found in plant cells are small, flattened discs, each about five micrometers in diameter.

They are found in the cytoplasm but can change their position in response to differences in light intensity. Chloroplasts are surrounded by an outer envelope consisting of two cell membranes. Plasma membrane A highly selective filter and a protective boundary. A new permeable membrane of ~5 nm in thickness termed the plasma membrane surrounds the cell, similar membranes surround each organelle. Nuclear envelope The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum. The nuclear envelope is conspicuously perforated by the nuclear pores.

Centriole Structures found in the animal cells which are associated with the separation of chromosomes during mitosis. They are small, hollow cylinders each containing a ring of microtubules. Nucleus The nucleus is the largest cell organelle. It is surrounded by two membranes known as the nuclear envelope. These allow exchange between the nucleus and the cytoplasm. Nucleolus A dark staining body found in the nucleus of a cell.

It contains the DNA with the copies of the genes that code for the special sort of RNA found in ribosomes, ribosomal RNA. It is in the nucleolus that ribosomal RNA is produced and the early stages of ribosomes formation take place. Cilia Tiny, hair-like organelles found on the cell surface membranes of certain cells. They have a distinctive internal structure.

Each has a ring on nine pairs of tubules towards the outside and a single pair in the centre, the so-called 9+2 structure. (C) Compare and contrast the structure of prokaryotic and eukaryotic cells. Eukaryotic cells found in members Prokaryotic cells found in of the kingdoms Protoctista, members of the kingdom Fungi, Animalia and Plantae Prokaryote Large cells up to 50 m in diameter Cells small with a mean diameter Under 5 m DNA linear and associated with proteins Circular strands of DNA not to form a true chromosome. Chromosomes associated with proteins and found found within a nucleus. In the cytoplasm. No nucleus present Many membrane-surrounded organelles Few organelles present and none are such as mitochondria present.

Surrounded by a plasma membrane Flagella (correctly known as undulipodia) Flagella lack system of microtubules have an internal arrangement of microtubules.