Golgi Apparatus

 

Structure

·         Similar to smooth ER, more compact

 

Function

·         Collect, process and sort molecules.

The stack of flattened sacs (cisternae) are constantly being formed by vesicles budding off at the end of smooth ER and being broken down at the other end to form Golgi vesicles.

 

Ribosome

 

Structure

·         One large and one smaller subunit

·         Comprise of RNA (ribosomal) and protein

·         20nm size

 

Function

·         Protein synthesis

 

 

 

Lysosome

 

Structure

·         Around 0.1-1.0µm in diameter

·         Membrane surrounding digestive enzymes known as hydrolases

 

Functions

·         Digesting worn out organelles, or bacterium taken in during phagocytosis

·         Bind to the cell membrane and release their enzymes   outside of it in a process known as exocytosis like exocism

 

Cilia and flagella

 

These two organelles are almost identical except that cilia are shorter and more numerous. Their structure is a two central micro tubules, surrounded by nine pairs of micro tubules on the outside, wrapped in a plasma membrane, in a long elongated shape similar to a hair. Their function can either be to move an entire organism or to move material within an organism. An example of the latter is the cilia in the trachea moving mucus along the throat.

 

Centriole

A centriole is a hollow cylinder formed from a ring of microtubules and used to grow the spindle fibres used in nuclear division.

 

Plasma Membrane

This is a very thin phospholipid bi-layer. It controls the movement of substances in and out of the cell; further explanation can be found later in this book.

 

Plants Only

 

Chloroplast

 

These are relatively large organelles, found only in photosynthesising cells, are green in colour due to the presence of the pigment chlorophyll, and at high magnifications grana can be seen in them. Grana are used in photosynthesis which will be discussed more later.

 

Vacuole

 

The vacuole is a fluid filled sac bound by a single membrane - it contains a solution of sugars, amino acids, waste products and mineral salts. It can serve as a temporary store, for waste or food, and can also contain hydrolytic enzymes. They also support some plants by providing an osmotic system which creates a pressure potential.

 

Cell Wall

 

Functions of the cell wall in plant cells include preventing the cell bursting when osmosis allows water to enter and provides the cell with structure and a definite shape.

 

Plasmodesmata

 

These fine strands of cytoplasm are linked through the cell wall, connecting neighbouring cells.

 

TABLE 1: SIMILARITIES BETWEEN ANIMAL AND PLANT CELL

 

ANIMAL CELL	PLANT CELL
Has Nucleus	Has Nucleus
Has Rough Endoplasmic Reticulum	Has Rough Endoplasmic Reticulum
Has Smooth Endoplasmic Reticulum	Has Smooth Endoplasmic Reticulum
Has Ribosome	Has Ribosome
Has Golgi Apparatus	Has Golgi Apparatus
Has Plasma Membrane	Has Plasma Membrane
Has Mitochondria	Has Mitochondria
*Has vesicles	*Has vesicles
Has Cytoplasm	Has Cytoplasm

 

TABLE 2: DIFFERENCES BETWEEN ANIMAL AND PLANT CELL

 

ANIMAL CELL	PLANT CELL
Has Cytoskeleton	Has no cytoskeleton
Has Lysosome	Has no Lysosome
Has Centriole	Has no Centriole
Has, Small, Temporary Vacuole	Has Large, Central, Permanent Vacuole
Has no Cell Wall	Has Cell Wall
Has no Plasmodesmata	Has Plasmodesmata

 

 

Prokaryotes and Eukaryotes

Karyote means 'nucleus' and thus prokaryote means 'before nucleus' which is an easy way to remember that these are the less complex cell type. They are also 1,000 to 10,000 times smaller than eukaryotes. Eukaryotes have a membrane bound nucleus, whereas prokaryotes have no membrane bound nucleus or no nucleus at all.

 

 

 

TABLE 3: DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES

	PROKARYOTES	EUKARYOTES
Typical organisms	bacteria, archaea	fungi, plants, animals
Typical size	~ 1-10 µm	~ 10-100 µm (sperm cells, apart from the tail, are smaller)
Type of nucleus	No membrane bound nucleus or no nucleus at all	nucleus with double membrane
DNA	circular (usually)	linear molecules (chromosomes)
RNA-/protein-synthesis	coupled in cytoplasm	RNA-synthesis inside the nucleus protein synthesis in cytoplasm
Ribosomes	Smaller (18nm)	Larger (22nm)
Cytoplasmatic structure	very few structures	highly structured by endomembranes and a cytoskeleton
Mitochondria	none	one to several thousand (though some lack mitochondria)
Chloroplasts	none	in algae and plants
Organization	usually single cells	single cells, colonies, higher multicellular organisms with specialized cells
Cell division	Binary fission (simple division)	Mitosis (fission or budding), Meiosis

 

 

Tissues and Organs

 

·         Tissue: A collection of cells specialised to perform one or more functions, and the cells do not have to be of the same type - merely collectively perform the same functions.

·         Organ: Composed of more than one type of tissue which forms a structural and functional unit. Leaves, the brain, the heart are all examples of organs.

·         System: Collection of organs with the same function, such as the digestive system.

 

Epithelium

 

Epithelial tissue is tissue that forms sheets covering surfaces and both the types you are required to learn about are said to be simple epithelia as they are one cell thick. They rest on a basement membrane, which is NOT a cell membrane, but rather a network of collagen and glycoproteins and holds the epithelium cells in place.

 

Squamous Epithelium

 

Squamous Epithelium is very smooth, flat and thin - they fit together like floor tiles providing a smooth almost frictionless surface over which fluids can move easily. The thickness (or lack thereof) in epithelium aids in processes like diffusion. This type of epithelium cell covers many surfaces in the body, for example the inner surfaces of atria and blood vessels. It also forms alveoli walls.

 

Ciliated Epithelium

 

This is epithelium with cilia and is found for example in the trachea, where it is tall and narrow and the cilia is used to waft mucus along the trachea.

 

Glandular Epithelium

 

This is epithelium with cells that excrete some substance in the body. Some substances it secretes include hormones, mucous, and lubricating fluid.