CELL ORGANELLES- Levels of Organisation

Unicellular: Single-celled organisms which carry out all life functions within the cell.

Multicellular: Organisms consisting of multiple cells which are specialised, forming tissues and organs.

Organism: All the systems of the body working together make an organism, which is a discrete individual.

Differentiation: A process by which a stem cell becomes specialised into a specific type of cell.

Divisions of Labour: The adaptation of different parts of an organism that carry out different functions. The more advanced the organism, the greater the division of labour.

Tissues: A group of specialised cells with the same structure, working together to perform a specific function. E.g. Epithelial (Squamous, Cuboidal & Columnar), connective, and muscle (Smooth, Skeletal & Cardiac.)

Organ: An aggregation of several tissues that carry out a specific function of the whole organism.

Organ system: Composed of two or more different organs that work together to provide a common function. E.g. Skeletal, muscular, circulatory, reproductive, endocrine, excretory, digestive, nervous, respiratory & immune.

Atom < Molecule < Macro-molecule < Organelle < Cell < Tissue < Organ < Organ system

In plants-

Xylem: Transports water and minerals.

Phloem: Produced sugars and transports them.

Palisade mesophyll: Photosynthesis mainly occurs here.

Spongy mesophyll: Provides air space for diffusion of gases in/out of the leaf.

Upper epidermis: Contains cells found at the top of the surface of the leaf coated by a waterproof waxy cuticle.

THE CELL- Cell strucuture

The membrane:
-Provides a large surface area for the attachment of enzymes involved in metabolic processes.
-They separate areas from the rest of the cytoplasm so that harmful chemicals/enzymes cannot harm the cells, e.g. lysosome.
-Defines he shape of discrete structures inside eukaryotic cells called organelles.

The nucleus:
-Its function is to retain chromosomes.
-Each strand of DNA is a genetic code carrying information to make new proteins.
-It is bounded by a double membrane (nuclear envelope).
-Pores in the nuclear envelope allow the transport of mRNA out of the nucleus and allow nucleotides into the nucleus.

The mitochondrion:
-Its function is to release chemical energy in the form of ATP.
-Acts as the site for aerobic respiration.
-The inner membrane is folded to form cristae, which in turn increase surface area on which respiration takes place.
-They are found in metabolically active cells, e.g. liver cells.
-They contain circular DNA and 80S ribosomes so they are able to carry out DNA replication.

Endoplasmic reticulum:
It is a system of membranes forming flattened sacks, these sacks are interconnected which allows the transport of materials throughout the cell. Fluid-filled spaces within the membranes are called cisternae.

Rough ER-                                                                 

The ribosomes on the outside bind with mRNA to make polypeptide chains that are transported to the Golgi body. RER is more common in cells that secrete enzymes.                    

Smooth ER-
The SER is in charge of synthesising lipids and transporting then. They don't have any ribosomes.

Ribosomes:

They are made in the nucleus from ribosomal RNA and protein. They move out through the nuclear pore and are free in the cytoplasm, however, some will attach onto the endoplasmic reticulum. 

Golgi Body:

This is formed by the RER being pinched off at the end to form small vesicles, many vesicles will fuse together to form a body. Proteins (polypeptide chains) are transported to the Golgi body and are then packaged and modified into proteins or glycoproteins. 

Functions-

>Produce secretory proteins, e.g. insulin.

>Produce glycoproteins.

>Form Lysosomes.

>Secrete carbohydrates, e.g. cellulose.

>Store and transport lipids.

Lysosomes:

These are small vacuoles that contain and isolate digestive enzymes from the remainder of the cell. They digest worn-out organelles and bacteria but release useful contents back into the cell.

Centrioles:

They are found in animal cells and protoctists. The centrioles divide during cell division and move to opposite poles of the cell where they synthesise the microtubules of the spindle. They are found at right angles from one another.

Additional organelles found in PLANTS ONLY:

Chloroplast:

They are found in the cells of photosynthesising tissue. 

The arrangement in thylakoids produces a large surface area for trapping light energy.

Vacuole:

Permanent vacuole consists of a fluid-filled sac bound by a single membrane (tonoplast). 

The cell sap is a storage site for chemicals like glucose and they provide an osmotic system.

Cellulose cell wall:

The cellulose cell wall is made from cellulose microfibrils embedded in a polysaccharide matrix.

They provide strength and support and permit the movement of water from cell-to-cell as they are permeable to water.

BIOLOGICAL MOLECULES- Inorganic ions & Water

Macronutrients:
Magnesium (Mg)2+ ---> is a constituent of chlorophyll.
Iron (Fe)2+ ---> is a consituent of haemoglobin.
Phosphate (PO4)3- ---> constituent of DNA/RNA and phospholipids in the cell membrane.
Calcium (Ca)2+ ---> used by animals to form healthy bones and teeth.


WATER:

Water is a polar molecule and has no overall charge. The slightly -/+ regions are attracted to charged regions of other molecules, forming hydrogen bonds.

High specific heat capacity-
A lot of energy is needed to raise the temperature of water because the H-bonds restrict movement.

• The temperature of aquatic habitats is stable so the organisms don't experience extreme conditions.
• This also allows enzymes within the cell to work efficiently.

Density-
As the temperature of water decreases, the H-bonds are less able to break so they form a semi-crystalline structure of the molecules. This holds the molecules apart, which makes ice less dense than water.

• Ice insulates water beneath, allowing organisms to survive.

Cohesion-
Water has a high cohesion because of hydrogen bonding. Cohesion also gives water a high surface tension.

• Cohesion allows water to travel up the xylem.
• It also allows small organisms to walk on water, e.g. the pond skater.

Universal solvent-
Water is a good solvent because it is a polar molecule and will attract other charged particles. It also acts as a transport medium for dissolved substances.

• In animals, blood transports many dissolved substances.
• In plants, water transports dissolved mineral ions inside the xylem and dissolves sucrose/amino acids inside the phloem. 

Water is metabolite-
It is used in biochemical reactions as a reactant.

• In photosynthesis water reacts with carbon dioxide to produce glucose.
• Hydrolysis reactions in the body. (maltose + water ---> glucose + galactose)

Transparency-
Water is transparent which allows light to pass through it.

• This allows aquatic plants to photosynthesise.

BIOLOGICAL MOLECULES- Proteins

Role of Proteins:
-Biological activities; hormones, enzymes, antibodies, transport/carrier proteins in the cell membrane.
-Globular proteins; functional proteins e.g. enzymes, and have a spherical shape.
-Fibrous proteins; perform structural functions e.g. keratin in hair and nails, and have a long and narrow shape.

General formula of Amino Acids: NH2CHRCOOH (R is the variable group)
There are 20 types of amino acids, and when two amino acids join they form a dipeptide.

STRUCTURE
Primary:
A number and sequence of amino acids in a polypeptide chain. Molecules are held together by peptide bonds.

Secondary:
The polypeptide chain will either coil into an alpha helix or fold into a beta pleated sheet. Hydrogen bonds form between amino acids.

Tertiary:
This is the final 3D structure for a single polypeptide chain, the secondary structure is coiled/folded further into a globular shape. The molecule is held by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulphide bridges.

Quaternary:
Two or more polypeptide chains in tertiary structure join together and are held by interactions.

BIOLOGICAL MOLECULES- Lipids

Functions:
>Store twice as much energy per gram than carbohydrates.
>Energy storage in plant seeds.
>Form adipose tissue of animals.
>Protection of delicate internal organs.
>Produce metabolic water when oxidised.

Properties:
>Insoluble but dissolve in organic solvents, e.g.ethanol.
>Oils are liquid at room temperature while fats are solid.


Triglycerides:
General formula of glycerol- C3H8O3
Components of a fatty acid- Carboxyl group, hydrocarbon chain, and a methyl group.

They are formed by the condensation reaction between ONE glycerol molecule and THREE fatty acid molecules. A molecule of water is removed and an ester bond is formed. Remember that glycerol never loses the oxygen and the fatty acid always loses its OH group.


Phospholipids:
Similar to triglycerides but with one of the FA groups replaced by a phosphate group.


Waxes:
Similar to fats and oils but also contain alcohol.
They are insoluble and reduce water loss in plants as they make up the waxy cuticle. This stops the osmotic effect and effectively reduces transpiration.


There are two types of fatty acids; Saturated and Unsaturated.

Saturated-
>Carbon atoms are joined by single covalent bonds.
>Hydrocarbon chain has maximum number of hydrogen atoms bonded to carbon.
>Found in animals.
>Contribute to heart diseases because they are solid at physiological temperatures and can block vital   blood vessles.

Unsaturated-
>Carbon atoms are joined by 1/1+ double bonds.
>Hydrocarbon chain has less than maximum number of hydrogen atoms bonded to carbon.
>Found in plants.
>Higher level of HDL (high-density lipoproteins) means harmful fats are disposed so there is a lower   risk of heart disease.