Cell organelles

Cell Organelles
Nucleus

Its function is to control the cell's activities and retain the chromosomes.
The nucleus is bound by a double membrane, the nuclear envelope. The nuclear envelope has pores in it to allow the transport of mRNA. The cytoplasm like material is called nucleoplasm which contains chromatin (coils of DNA and histone proteins), it is chromatin that condenses to form chromosomes during cell division.

Within the nucleus is a small spherical body called the nucleolus which manufactures RNA to from ribosomes.
Ribosomes

Are very small organelles but are present in large numbers.
They are made up of two subunits, the large subunit and the small subunit.
70s ribosomes are found in prokaryotes whilst 80s ribosomes are found in eukaryotes. They are involved in protein synthesis.
They can either be found free in the cytoplasm or on the outer surface of the rough endoplasmic reticulum.

Mitochondria

Aerobic respiration occurs here producing ATP (the energy currency of the cell). They have a highly folded inner membrane which provides a large surface area for the respiration reactions.
Some reactions also take place in the matrix (Kreb's cycle) as well as the cystol of the cytoplasm.
The amount of mitochondria varied from cell to cell. More are found in cells with greater ATP requirements these are; cells that move a lot (sperm, muscle), cells with a high metabolic rate (liver) and cells that carry out active transport (small intestine).
Endoplasmic reticulum
Is an elaborate system of membrane bound sacs (cisternae) that are often continuous with the Golgi body and the nuclear envelope. There are two types of endoplasmic reticulum (ER)
Rough ER (rER) - has ribosomes lining it and is involved in protein synthesis as a transport system

Smooth ER (sER) - lacks ribosomes and is involved in the synthesis and transport oflipids

Golgi Apparatus
Is a collection of flattened membrane bound sacs that are constantly forming on one side and budding off as vesicles on the other.
Its functions are: to package proteins for secretion to secrete carbohydrates to produce glycoproteins to transport and store lipids to form lysosomes

Lysosomes

They are membrane bound vesicles which contain digestive enzymes. They are especially abundant in secretory cells and phagocytic blood cells.
Its functions are to: digest material from the environment. Useful chemicals are absorbed into cytoplasm and waste is egested by exocytosis e.g white blood cells and bacteria digest damaged or worn out organelles (autophagy). After cell death they completely breakdown the cell (autolysis) release their enzymes outside the cell (exocytosis) in order to breakdown other cells.

Other organelles
Peroxisomes - protect the cell from it's own production of hydrogen peroxide (which is produced by white blood cells). It makes oxidative enzymes that break hydrogen peroxide into water and hydrogen
Secretory Vesicles - neurotransmitters are packaged in secretory vesicles at the Golgi apparatus. The vesicles are then transported to the cell surface from release
Microtubules - move vesicles, granules and organelles via special attachment proteins. They may work alone or join with proteins to form more complex structures e.g cilia, flagella or centrioles.
Centrioles - during cell division they migrate to opposite poles of the cell where they synthesis the microtubules of the spindle.
Plant cell organelles
Chloroplasts

Photosynthesis takes place here. It involves the production of sugars and other substances from carbon dioxide and water using light energy trapped by chloroplasts. They are bound by a double membrane called the chloroplast envelope. Inside is a colourless matrix called the stroma, floating in the stroma are thylakoids which are stacked to form a granum. Granum are interconnected by tubular extensions called intergranlar lamellea.
Starch grains are present and they act as a temporary store for starch that is produced during photosynthesis.
Vacuole
They are a fluid filled sac bound by a single membrane called the tonoplast In plants the vacuole is large and permanent. The vacuole is filled with cell sap, a concentrated solution which acts as a storage site fro chemicals, mineral salts, dissolved gasses, wastes and pigments.
Their function is to provide support ,especially in young tissues, and to store soluble food.

Cell walls

Adjacent plant cells are connected as their cell walls are fused together. The middle lamella connects adjacent cell walls. The adjacent cells are connected by aplasmodesmata (strands of cytoplasm).
The cell wall is made up to cellulose microfibriles embedded in a polysaccharide background matrix. The cellulose fibres have a high tensile strength and the background matrix transfer stress to the microfibrils making it very strong. ( example is reinforced concrete)
The functions of a cell wall are: to provide strength and support to permit the movement of water from cell to cell
Tissues
A tissues is a group of cells and their inter-cellular substances which are linked together and perform a particular function. Some tissues may be made up of a single type of cell whilst others have more than one type of cell included.
An organ is composed of different tissues that are co-ordinated to perform a function
Organs work together as a single unit or organ system
Organisms are made up of a number of different systems working together.
In animals there are four main groups of tissues:
Epithelia - covers body surface and forms the lining of internal cavities. Major functions include protection, secretion, absorption and filtration.
Connective - supports and protects. The main proteins in connective tissues are collagen and elastin
Muscle - provides stability to skeleton and organs as well as allowing movement. 3 types of muscle; cardiac, skeletal and smooth
Nervous - receives stimuli and conducts impulses to and from all parts of the body
In plants the types of tissue is split up into simple and compound
Simple
Parenchyma - wound healing and regeneration. Forms the most edible part of the plant
Collenchyma - provides structural support and flexible support for organs, leaves and flowers
Sclerenchyma - offers support and makes the seed coats, the shell of nuts and the stone of fruit
Compound
Xylem - carries water and dissolved substances
Phloem - carries dissolved food substances