A level Biology Core Concepts (Eduqas)

EDUQAS A LEVEL BIOLOGY:

CORE CONCEPTS:

BIOLOGICAL MOLECULES; CELL STRUCTURES AND ORGANISATIONS; CELL MEMBRANES AND TRANSPORT; ENZYMES; STRUCTURE OF NUCLEOTIDES.

BIOLOGICAL COMPOUNDS

Inorganic Ions

-Magnesium (Mg2+): Constituent/component of *chlorophyll* and so is essential for photosynthesis

-Iron (Fe2+): Constituent of *haemoglobin* which transports oxygen in red blood cells

-Phosphate (PO4): Constituent of *phospholipids* and used to *make nucleic acids* like DNA,RNA and ATP

-Calcium (Ca2+): *Structural component of teeth and bones* as well as plant cell walls

Polymers

-Polymers are made up of smaller molecules linked together called monomers during a polymerisation reaction.

-Condensation reaction: the *linking together* of two or more monomers to form a polymer and *water* is *eliminated*

-Hydrolysis reaction is the *breaking down* of polymers into monomers with the *chemical insertion* of *water*

-Examples of Large polymers include carbohydrates and proteins

Carbohydrates

-Contain the elements: Carbon, Hydrogen and Oxygen

-Main functions: *storage and release energy*; *cellular structures* e.g cellulose cell walls

-Three classes of carbohydrates, this includes Monosaccharides, Disaccharides and Polysaccharides.

Carbohydrates:

Monosaccharide

-Monosaccharides: Monomers *(single units)*. They form building blocks for larger carbohydrates.

-General Formula of Monosaccharides: Cn(H20)n

-Glucose is the most abundant monosaccharide and comes in two forms- alpha glucose and beta glucose.

-Alpha and Beta glucose are isomers (*ABBA*- *A*lpha *B*elow carbon 1, *B*eta *A*bove on carbon 1).

-Isomers are molecules with the same chemical formula but different arrangements of their atoms.

Properties: *soluble* - can easily dissolve inside the cell and transported in bloodstream.

-Name is determined by n.o carbons in molecules

Carbohydrates:

Disaccharides

-Disaccharides: *Two monosaccharides*/ hexose sugars join together by a 1-4 *glycosidic bond* during condensation reaction

-General Formula of Disaccharides: C12H22O11 (H20 is removed in a condensation reaction)

- Examples of Disaccharides:

1. a-glucose + a-glucose = *Maltose* (used in seeds as a sources if energy for germination.)

2. glucose + fructose = *Sucrose* (transported through phloem of all plants)

3. glucose + galactose = *Lactose* (found in mammalian milk and important source of energy for their young).

-Resulting link between two sugars is a glycosidic bond which occurs between the carbon of one sugar and fourth of the other hence a *1-4 glycosidic bond*

- Can be broken down to a monosaccharide via a hydrolysis reaction

Carbohydrates:

Polysaccharides

-Polysaccharide: *3 or more monosaccharides* joined together by a glycosidic bond in a series condensation reaction

- They either have a *energy storage or structural function.*

-Properties of Polysaccharides include: insoluble compact, easily hydrolysed and contain lots of energy,

-Examples include starch, glycogen, cellulose and chitin

Carbohydrates:

Polysaccharides-Starch

-Starch is an *energy storage* polysaccharide in *plant* cells

-Made up of thousands of *alpha* glucose monomers

-Starch is made up of 2 different molecules: *Amylose* and *Amylopectin*

-Amylose: Straight chained, helical polymer and contains *alpha 1-4 glycosidic bonds*

-Amylopectin: Branched polymer, contains *alpha 1-4 and 1-6 glycosidic bonds*

*TEST for Starch: iodine- colour change from orange/red to purple/black

Carbohydrates:

Polysaccharides-Glycogen

-Glycogen is an *animal storage polysaccharide* found inside liver and muscle cells

-Made up of many *Alpha* glucose molecules

-Highly branched- allows *quick release* of glucose from ends of branches (due to 1-6 bond)

-Has *alpha 1-4 and 1-6 glycosidic bonds*

Carbohydrates:

Polysaccharides-Cellulose

-Cellulose is a *structural* carbohydrate and is the most important component of the *plant* cells

-Made up of *Beta* glucose monomers

-Gives the plant cell ridigity as the cellulose cell wall is inelastic and has a high tensile strength preventing it from bursting

-Beta glucose monomers joined by glycosidic bonds, each adjacent beta glucose rotated 180, forming straight chains

-Hydrogen bonds form between OH groups of straight chains

-Many straight chains join to form a *strong microfibril* which intern form a strong cellulose bundle

Carbohydrates:

Polysaccharides-Chitin

-Chitin is similar in structure to cellulose, but differs as some of the OH groups are replaced by *Nitrogen*, containing acetylamine groups- makes chitin a *muco-polysaccharide.*

-Lightweight, waterproof, and very strong.

-Forms exoskeleton of insects and cell wall of fungi.

Lipids

-Lipids include triglycerides and phospholipids.

-Made from same elements as carbohydrates but contain less oxygen: carbon , hydrogen and oxygen.

-Non polar: no charge

-Polar: charged

Lipids:

Triglycerides

-Triglycerides are made up of two main components: *glycerol and fatty acids.*

-They are not polymers as they are made up of two different sub-units (fatty acids and glycerol), which have different structures.

-Triglycerides are *not made from identical monomers.*

-Glycerol: an alcohol with the formula C3H8O3 and is the constant in triglycerides and phospholipids.

-Fatty Acids: made up of 3 parts: a methyl group (CH3); long hydrocarbon (CH2); & a carboxyl group (COOH)

-Many different types of fatty acids and they vary by the length of they hydrocarbon chain.

Lipids:

Triglycerides-Saturated or Unsaturated

-Two types of fatty acids: saturated and unsaturated.

-*Saturated *Triglycerides: contain saturated fatty acid, which contain *no carbon carbon double bonds* and contain the max n.o hydrogens. They have a *straight chain structure* and are solid at room temp, and come from animal sources e.g lard

-*Unsaturated* Triglycerides: contain unsaturated fatty acids which contain *one or more double carbon carbon bonds* and doesn't contain the. max n.o hydrogens. They have *bends/ kinks in the chain* and are liquids at room temperature and come from plant sources e.g sunflower oil

Lipids:

Triglycerides Formation

-To form a triglyceride *one glycerol* molecules combines with *three fatty acids* and is linked by an *ester bond.*

-One triglyceride with have a total of three ester bonds which are formed by a condensation reaction- removal of water

-If a lipid is broke down to fatty acids and glycerol then a hydrolysis reaction has take place - chemical insertion of water.

Lipids

Triglyceride extra content :)

-A *high intake* of fats especially *saturated fat*, damages the heart and coronary arteries by *restricting blood* from and so contribute to heart disease.

-*L*ow *d*ensity *l*ipoproteins: Contain and transport *saturated* fats and cause harm. Fatty materials can *block major arteries* and cause a myocardial infarction (heart attack).

-*H*igh *d*ensity *l*ipoproteins: Contain and transport *unsaturated fats* and carry harmful fats away to the liver for disposal and a higher proportion of HDL in the blood lowers the risk of heart disease.

-Properties of Lipids: *insoluble* in water but soluble in organic solvents, fats are solid at room temp, oils are liquid at room temp

Lipids:

Functions of Lipids:

-Lipids have several functions within living organisms:

-*Energy Storage*: used in seeds and animals as they release a lot *more energy* then carbohydrates when used as an alternative respiratory substrate.

-*Protection Of Vital Organs*: Act as *shock absorbers by preventing physical damage to internal organs.

-*Thermal Insulation*: To reduce heat loss.

-*Buoyancy*: Lipids are *less dense* than water so they float and are key in maintaining buoyancy in organisms e.g fish.

-*Metabolic Water*: Production of metabolic water when lipids are oxidised by *respiration*. Important for desert animals like camels, whose humps are made of fat.

-*Waterproofing*: Waxes are *hydrophobic* and cover exoskeletons of insects and cuticles of plants and so reduce water loss.

Lipids:

Phospholipids

-They differ in their structure to triglycerides as they have a glycerol, two fatty acids and *phosphate group.*

-The fatty acids tails are *hydrophobic* (repel water).

-The polar, phosphate heads are *hydrophilic* ( attracted to water).

-Phospholipids are an important component of cell membranes.

Amino Acids and Proteins:

-Amino acids are made up of Carbon, Hydrogen and Oxygen but also contain the element Nitrogen. (sulphur is also found in some amino acids such as cysteine)

-Amino Acids contain: the amino group (NH2); central carbon (C) ; carboxyl group (COOH); hydrogen group (H); R group ( different for each amino acid)

-The R group is called the *variable group* and represents the rest of the molecule. 20 different variable groups

Amino Acids and Proteins:

Dipeptide

-Two amino acids can be joined together to form a *dipeptide* during a condensation reaction which involves the amino (NH2) group of one amino acid the the carboxyl (COOH) group of another

-The resulting link is called a *peptide bond.*

-Dipeptides can be broken back down to amino acids by hydrolysis reaction.

Amino Acids and Proteins:

Polypeptides

-Polypeptides are formed by *many amino acids* joined together by peptide bonds. (Polypeptides are polymers and amino acids are monomers)

-Amino acids form polypeptides which form proteins (functioning)

-All proteins have:-

-Primary Structure: *n.o and sequence* of amino acids in a polypeptide chain

-Secondary Structure

-Sometimes proteins have a Tertiary Structure

-Occasionally proteins have a Quaternary Structure

Amino Acids and Proteins:

Polypeptides-Secondary Structure

-The primary structure of a polypeptides can *coil* to form either an *alpha-helix* or a *beta pleated sheet*.

-The most common type of secondary structure is the alpha helix which is held in a spiral shape by *hydrogen bonds*.

-Some *fibrous* proteins have alpha helices linked into *rope*-like strands:e.g:

-*keratin*: found in hair and nails

-*collagen*: found in connective tissue and the skin

-A less common secondary structure also stabilised by hydrogen bonds is the *beta-pleated sheet* - *flat zig-zag* structure e.g protein silk.

Amino Acids and Proteins:

Polypeptides- Tertiary Structure

-The secondary structure *folds* to give *complex 3D-shapes*

-These are *globular* proteins e.g enzymes, hormones, plasma and cell membrane proteins.

-The secondary structure is folded and held in a specific 3D shape by bonds or interactions that form such as:

-*Hydrogen bonds* between OH and O

-*Ionic bonds* between oppositely charged R groups

-*Disulphide bridges* between S atoms e.g in cysteine

-Hydrophobic R groups on inside the protein

-Hydrophilic R groups on the outside of the protein

Amino Acids and Proteins:

Polypeptides- Quaternary Structure

-They occur when *more than one* polypeptide chain, each with a *tertiary structure* combines to form a *larger protein complex.*

-Are joined by similar bonds as those in tertiary structures (hydrogen, ionic, disulphide bridges, and hydrophobic interactions)

-Quaternary Structures are often *associated with non-protein groups* called prosthetic groups e.g haemoglobin which has the non-protein component haem group which contains iron.

Amino Acids and Proteins:

Polypeptides- Classification of Proteins

-Proteins can be classified according to their structure.

-*Fibrous proteins* e.g keratin and collagen which carry out *structural* functions. Collagen is made up of 3 alpha helix polypeptide chains twisted into rope like strands and are held by hydrogen bonds.

-Fibrous Proteins are: *Tough*; *Non-Specific* ;*Insoluble*

-*Globular* Proteins: can be tertiary structures e.g enzymes and plasma proteins or quaternary structures e.g haemoglobin and antibodies

-Globular protiens are: *compact* and folded into spherical molecules; have *specific* shape; *soluble* in water

Biochemical Food Tests:

Reducing Sugars e.g Glucose

-To your test tube add *Benedicts* reagent and test sample

-Boil/Heat in a water bath

-*POSITIVE *result: colour change from *Light blue* to *Brick red*

-Negative result: *no colour change*; non-reducing sugars maybe be present

-Samples of reducing sugars may give a gradual colour change from green to brick red depending on the concentration of reducing sugars in the sample (*SEMI-QUANTITATIVE*).

Biochemical Food Tests:

Non-Reducing Sugars e.g Sucrose

-If a negative samples was found initially with the Benedicts+boil test:

-Add *Hydrochloric Acid* to sample and boil (Will hydrolyse any glycosidic bonds)

-Add *hydrogen carbonate* powder (alkali) to neutralise

-Add benedicts reagent and boil.

-POSITIVE results: Colour change from *light blue* to *brick red* - sucrose was present in OG sample

Negative result- No colour change

Biochemical Food Tests:

Starch

-Iodine solution is used

-Positive result: Colour change from *orange-brown* to a *blue-black* colour in the presence of starch

-Qualitative test- accurate concentration cannot be determined.

Biochemical Food Tests:

Proteins

-Biuret Test:

-Add a few drops of biuret reagent to protein solution and gently shake.

-Positive result: Colour Change from *light blue* to *purple*

-Negative result: No colour change

Biochemical Food Tests:

Lipids

-Lipids are hydrophobic and only dissolve in *organic solvents* sugar as ethanol.

-Mix the test sample with absolute ethanol to dissolve any lipids.

-Add an equal volume of water and gently shake

-Positive result: Lipids will form small droplets and appear as a *white and cloudy emulsion*

Water

-Water consists on 2 hydrogen *covalently bonded* to 1 oxygen.

-Water is a *polar* molecule as the oxygen ends have a slight negative charge and the hydrogen ends have a slight positive charge making water a dipole.

-When 2 water molecules are in close conact their opposite charges attract each other forming a weak hydrogen bond.

-Individually hydrogen bonds are weak but many of them form a strong lattice

-Water molecules tend to *stick together* as a result of then formation of hydrogen bonds-COHESION!!

Properties of Water:

Surface Tension

-Water molecules form hydrogen bonds with other nearby water molecules but not with molecules in the air.

-This cohesion produces an *uneven distribution* of force called surface tension.

-This forms a skin which can *support* aquatic plants and insects.

Properties of Water:

Universal Solvent

-Water is a solvent as it is a *polar* molecule which *attracts* and dissolves other charged particles such as ions and other polar molecules e.g. glucose

-Water acts as an excellent *transport medium.*

-In animals, blood transports dissolved substances around the body

-In plants, xylem vessels transport water and dissolved mineral ions

-Examples of substances soluble in water include: glucose, sodium chloride, maltose, and globular proteins.

Properties of Water:

High Specific Heat Capacity

-Water has a HSPC as lots of energy is required to break the hydrogen bonds and *increase the temperature* of the water

-This provides a more *stable* environment for aquatic organisms as it prevents their habitats evaporating.

-This also allows enzymes to *efficiently catalyse* important chemical reactions inside the body without being denatured.

Properties of Water:

High Latent Heat Capacity

-Water has a HLHC as lots of energy is required to break the hydrogen bonds and change water from a *liquid to a vapour*.

-This means lots of energy is required for water to evaporate from the surface of an organisms, and so provides a significant *cooling effect* as heat is removed from the body (e.g transpiration in plants and sweating in animals)

Properties of Water:

Density

-Water is *less dense* in it's solid state, as ice, compared to liquid state, water, so floats on the surface of water.

-It forms an *insulating layer* which allows organisms to survive in water underneath the ice as well as providing a habitat for organisms like polar bears

Properties of Water:

Metabolite and Transparency

Metabolite:

-Water is a *reactant* in photosynthesis and hydrolysis.

-It is also *produced* during aerobic respiration and condensation reactions.

Transparency:

-Water is a *transparent* substance that allows light to pass through to underwater aquatic plants and enables them to *photosynthesise effectively.*

CELL STRUCTURES AND ORGANISATIONS:

:))))

Eukaryotic Cells

-All living organisms are composed of one or more living cells

-The cell is the *fundamental unit* of structure, function and organisation in all living organisms,

-Cells can only arise from *pre-existing cells*

-*Organelle:A specialised structure inside a cell with a specific function.*

Unit of Measurement

Measurement ---> Symbol ---> N.o Meters ---> object

-Kilometre ---> km ---> 10^3 ---> ecosystem

-Metre ---> m ---> 1 ---> large organism

-Millimetre ---> mm ---> 10^-3 --->tissues

-Micrometre ---> ym ---> 10^-6 ---> cells

-Nanometer ---> nm ---> 10^-9 ---> molecules

Microscopy

-The purpose of a microscope is to magnify small objects, such as biological specimens mounted on glass slides.

LIGHT MICROSCOPE DIGRAM

-Total Magnification= eyepiece x objective

-*Magnification=Image size/Actual size *

(always measure in mm)

Structure And Function Of Organelles:

Nucleus

-This is the largest organelle in the cell. Its function is to retain the *genetic information* (DNA) which codes for protein synthesis.

-Nuclear Envelope: A double membrane with pores to allow the *transport* of mRNA and ribosomes out of the nucleus to the cytoplasm.

-Nucleoplasm: Cytoplasm-like material which contain *chromatin*

-Chromatin: Made up of coils of DNA bound to a histone protein. During cell division, it condenses to form visible *chromosomes*

-Nucleolus: One of more spherical bodies, which *synthesise ribosomal RNA* (rRNA)

Structure And Function Of Organelles:

Mitochondria (Singular: Mitochondrion)

-The function of the mitochondrion is to *release energy in the form of ATP* during aerobic respiration

-Mitochondria have a double membrane with a marrow, free-fluid filled intermembrane space.

-The inner membrane is folded inwards to form extensions called cristae. The cristae *increase* the *surface area* for ATP synthesis to occur.

-Inside the mitochondrion is an organic matrix which contains chemical compounds including lipids, protein, small (70s) ribosomes and a small circle of DNA to allow for *self replication* to occur in response to the energy needs of the cell

-Stages of aerobic respiration occur in the matrix and on the inner membrane

-Large number of mitochondria are found in the liver and muscle cells.

Structure And Function Of Organelles:

Ribosomes

-The small sub-unit and large sub-unit of a ribosomes are made of rRNA and protein

-*Protein synthesis* (translation) occurs at the ribosomes as it provides the code for a sequence of amino acids

-Ribosomes are found free in the cytoplasm or are associated with the rough endoplasmic reticulum.

Structure And Function Of Organelles:

Endoplasmic Reticulum's (RER+SER)

Rough Endoplasmic Reticulum:

-RER is an internal system of flattened membranous sacs, or cisternae which are continuous with the nuclear membrane

-The RER is covered in *ribosomes* and its function is *protein synthesis and transport of proteins*

Smooth Endoplasmic Reticulum:

-SER is similar in its structure to the RER, but has *no ribosomes*

-It is involved in the *synthesis and transport of lipids*

-Cells that store large quantities of carbohydrates, proteins or fat have extensive ER's like liver and secretory cells.

Structure And Function Of Organelles:

Golgi Body

-The Golgi body is made up of interconnected flattened membranous sac.

-Vesicles containing polypeptides, pinch off from the RER and fuse with the Golgi body.

-The main function of the Golgi body are:

-*Modifying* and *packaging proteins* into *secretory vesicles*

-*Secreting carb*ohydrates

-*Producing glycoprotein*

-*Transporting* and *storing lipids*

-*Forming lysosomes*

Structure And Function Of Organelles:

Lysosomes

-Lysosomes are single membrane bound vesicles which contain *digestives enzymes.*

-They are produced by the Golgi body, and *isolate* the potentially *harmful digestive enzymes* from the remainder of the cell

-Functions of lysosomes include:

-Releasing enzymes to *break down worn out organelle*s

-*Digest materials* that have been taken into the cell e.g lysosomes fuse with. the vesicle made when a white blood cell engulfs a bacteria by phagocytosis, and their enzymes digest the bacteria.

Structure And Function Of Organelles:

Cell Membrane

-All cells are surrounded by a cell membrane or a plasma membrane

-The principle biochemical component are phospholipid and protein molecules.

-Phospholipids are arranged as a *BILAYER*, with one sheet of phospholipid molecules opposite each other

-Width of the cell membrane in *7-8nm.*

Structure And Function Of Organelles:

Structural Components of the membrane

1.Phospholipids:

-Phospholipids form *bilayers* with *hydrophilic heads* pointing *outwards* interacting with the tissue/blood plasma that surrounds the cell and cytoplasm.The *hydrophobic tails* of both layers point towards the *inside* of the membrane.

2.Proteins

-All proteins in the membrane are *globular* and can either be found on the surface of the bilayer, partially embedded (*EXTRINSIC*) or extending completely across both phospholipid bilayers (*INTRINSIC/transmembrane*).

3.Carbohydrates

-They are found pointing *outside* the cell attached to either proteins *(glycoproteins)* or attached to the phospholipids *(glycolipids)*. They are formed through *glycosylation* and are collectively know as the glycocalyx.

4.Cholesterol is present *between* the phospholipids in animal cell membranes

Structure And Function Of Organelles:

Cell Membrane (Fluid Mosaic Model)

-The model is called fluid mosaic as the individual phospholipid molecules can *move around relative to one another* and the *proteins* embedded in the bilayer *vary in size and shape* and are arranged in a random pattern.

-The main function of the cell membrane is to *aid the transport* of certain substances into/out of cells e.g to obtain oxygen and remove carbon dioxide.

Structure And Function Of Organelles:

Centrioles

-They are found in the cells of all animals and most protoctists, but not in the cells of higher plants.

-They are located just *outside* the *nucleus* and are two rings of microtubules arranged in hollow cylindrical positions at right angles.

-During cell division, they migrate to opposite poles of the cell and *form* the *spindle.*

Structure And Function Of Organelles:

Vacuole

Plant Cells:

-Most *plant* cells have a *large permanent vacuole* which consists of a fluid filled sac bound to a single membrane, the *tonoplasts*.

-Vacuoles contain cell sap, a solution which store major chemicals such as glucose, amino acids, minerals and vitamins. They have a major role in *supporting soft plant tissues*.

Animal Cells:

-Vacuoles are *small, temporary vesicles* and may occur in large numbers.

-They can be formed by phagocytosis.

Structure And Function Of Organelles:

Cell Wall & Plasmodesma

Cell Wall:

-The plant cell wall is made up of *cellulose microfibrils* embedded in a polysaccharide matrix called pectin. It confers rigidity (strength) on plant cells

Plasmodesma:

-Cell Wall contains *narrow pores* called plasmodesma.

-Fine strands of cytoplasm pass through, connecting one cell to the next and allows substances to pass between them.

Structure And Function Of Organelles:

Chloroplasts

-Chloroplasts. are found only in plant cells. Each has a *double membrane*

-Within chloroplasts is a colourless gelatinous matrix called stroma, which contains small (70s) ribosomes, circular DNA (*self replication*), lipids and starch grains.

-In the stroma are flattened sacs known as thylakoids, which are stacked to form grana, and are connected to each other by lamellae.

-Chloroplasts are the *site of photosynthesis* (conversation of light energy to chemical energy) in plants. Photosynthesis pigments such as chlorophyll are found within each thylakoid.

Structure And Function Of Organelles:

Endosymbiotic Theory

-States that organelles such as chloroplasts and mitochondria were originally free-living *prokaryotic cells*

-A hypothesis states that these prokaryotic cells were *engulfed* by a cell through *endocytosis* and gained an additional membrane.

-For the prokaryotic cells that formed *mitochondria*, it would have *gained protection* and *glucose* from the cell, and the *cell gained ATP* energy from the prokaryote- eventually this prokaryote formed the mitochondrion in every cells

(This eventually led to the evolution of eukaryote cells.)

-Mitochondria and Chloroplasts do contain their own DNA.

Prokaryotic Cells

-Prokaryotes: Single-celled organisms *lacking membrane-bound* organelles, such as a nucleus, with DNA free in the cytoplasm.

-They are: small 1-10ym; unicellular; have no nucleus; circular DNA found free in the cytoplasm; cell division via binary fission; no membrane bound organelles; cell wall made from murien; capsule provides addition protection; plasmids may be present; site of respiration: mesasomes

Eurkaryotic Cells

-Eukaryotes: Organisms made of cells that *have membrane-bound* organelles, with DNA within the nucleus in the form of chromosomes.

-They are: large 10-100ym; multicellular; have a nucleus; large (80s) ribosomes free in cytoplasm or attached to ER; linear DNA bound to a histone protein; cell division via mitosis or meiosis; has membrane bound organelles; cellulose cell wall in plants and chitin in fungi; site of respiration:mitochondria

Viruses

-They are not made up of cells and are '*acellular*'. They are so small they can't be seen through a light microscope.

-They have no organelles, no chromosomes, no metabolism, and no cytoplasm.

-When they invade a cell they *hijack* the *host's metabolism* and multiply inside the host cell.

-Each Virus is made up of nucleic acid surrounded by a protein coat (capsid). Some viruses have DNA whilst others contain RNA.

-Bacteriophages are viruses that attack bacteria.

-Viruses can be transmitted by aerosol; insect vectors; exchange of bodily fluids; bites.

Exampes of viruses are HIV, measles, flu in humans; tobacco mosaic and cauliflower mosaic virus in plants; swine flue, cow pox and feline leukaemia in other mamals.

Levels of Organisation In The Body:

-Organism: All the systems of the body working together making a discreet individual.

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

-Multicellular: Organisms consisting of many *specialised cells* which form tissues and organs, which have various structures and roles.

-Differentiation: The process by which a stem cell becomes *specialised* into a specific type of cell.

-Division of Labour: The adaptation of different parts of an organism to carry out different functions. The more advanced the organism the greater the division of labour.

Levels of Organisation In The Body:

Cells

-Cells undergo differentiation where they are adapted to carry out specialised functions

-Examples include: red blood cell; egg cell/ovum; intestinal epithelial cell; nerve cell; sperm cell

Levels of Organisation In The Body:

Tissues

-Tissues: An *aggregation of specialised cells carrying out a specific function.*

-4 primary tissue types:

-Epithelial tissue: forms a *continuous layer*, covering or lining the internal and external surfaces of the body

-Connective tissue: *connects* and *anchors structure* and gives strength and support to the body and it organs

-Muscle tissue

-Nerve tissue

Levels of Organisation In The Body:

Tissues-Epithelial Tissue

-Four types of Epithelial Tissue:

-*Squamous* Epithelial Tissue: Flattened cells found *lining body cavities* such as the mouth and alveoli. (thin barrier to allow for quick diffusion)

-*Cuboidal* Epithelial Tissue: Cube-shaped cells found *lining the kidney tubules* and ducts of glands (secretion)

-*Columnar* Epithelial Tissue: Elongated column shaped cells that are found *lining the stomach and intestines*

-*Ciliated* Epithelial Tissue: Columnar-shaped cells that have fine hair-like projections (Cilla) on the surface. Found in the *oviduct, trachea*

Levels of Organisation In The Body:

Tissues- Connective Tissue

-Connective Tissue connects and anchors structures and gives *strength and support* to the body and its organs

-Collagen protein forms extracellular fibres that give strength to dense connective tissues like tendons and ligaments.

-Collagen is also found on the tough outer layer of large blood vessels.

Levels of Organisation In The Body:

Tissues-Muscle Tissue

-Nerve Impulses bring about *muscle contractions*, causing the muscle to shorten.

-As the contraction of the muscle ends, normal muscle length is once again attained.

Levels of Organisation In The Body:

Organs

-Organs: An *aggregation of several tissue that carry our a specific function for the whole organism*.

E.g liver, skin, heart, kidneys, lungs ect

Levels of Organisation In The Body:

Organ Systems

-*Organ Systems: Two or more different organs working together to provide a common function* e.g stomach, kidney and liver ect. make up the digestive system

Levels of Organisation In Plants:

Cells,Tissues and Organs

Cells

-Specialised plant cells include palisade cell, guard cells and root hair cell.

Tissues:

-Xylem: Transport water and dissolved minerals

-Phloem: Transports sucrose and amino acids (photosynthates)

-Palisade Mesophyll: Photosynthesis

-Spongey Mesophyll: Some photosynthesis, and provides air space for diffusion of gases in/out of the leaf

-Organs

-Flowers/Petals: Sexual Reproduction

-Leaves: Photosynthesis

-Stem: Transport+Support

-Roots: Water and mineral uptake and acts as an anchor.

Cell Membranes And Transport:

-The cell membrane is *selectively permeable* to water and some solutes.

-Lipid soluble substance move through the cell membrane *more easily* than water soluble substances

Transport Across the Membrane:

Lipid Soluble Substances:

-*Small uncharge* molecules e.g CO2 and O2, dissolve in the hydrophobic tails of the phospholipid tails and *diffuse* across the membrane

-*Non-polar* substances e.g Vitamin A can also dissolve in phospholipids and diffuse across the cell membrane

*Water soluble* substances:

-Polar molecules e.g glucose and amino acids, as well as charged ions like Na+ *can't easily diffuse* through phospholipids.

-They pass through *intrinsic protein molecules*

Factors Affecting Membrane Permeability:

Temperature:

-At *high temperatures* phospholipids gain *more kinetic energy* in the membrane and so move around more.

-This creates *gaps* in the membrane and *increases the permeability* of the membrane. The proteins in the membrane may also denature, creating large gaps.

Organic solvents

-All lipids including phospholipids *dissolve* in solvents like ethanol, which may also *denature* the protein and create large *gaps* in the protein.

Methods Of Transport Across A Membrane:

Diffusion

-*Passive movement of a molecule or ion down a concentration gradient*. (high conc to low conc).

-Passive so does not require ATP

Factors affecting rate of diffusion include:

-Concentration gradient: The *steeper* the concentration gradient the *more* molecules that will diffuse in a give time.

-Thickness of Surface: The *shorter* the diffusion pathways the *more* molecules that will diffuse in a given time.

-Surface Area of the Membrane: The *larger* the surface area the *higher* n.o molecules that will diffuse in given time

-Size of Diffusing Molecule: *Smaller* molecules *diffuse faster* than larger molecules

-Nature of Diffusing Molecule: Molecules that are soluble in phospholipids *(non-polar)* diffuse *faster* than water soluble *(polar)* molecules.

-Temperature: As the temperature *increase* so does the rate of diffusion as the molecules/ions have *more kinetic energy*

Methods Of Transport Across A Membrane:

Facilitated Diffusion

-*Passive transfer of polar molecules or charged ions down a concentration gradient by a channel or carrier protein*

-Used to *transport ions and large polar* molecules e.g Na+, glucose and amino acids which are insoluble in phospholipids

-Does not require ATP

-It is *faster* than simple diffusion as going through a protein is easier than directly through the bilayer.

-Factors Affecting Rate of Facilitated Diffusion:

1. *N.o channel/carrier proteins* present- once full, rate will plateau.

2. *Steepness of concentration gradient*.

-*Channel* Proteins: Protein molecules with hydrophilic *pores*; ions are water soluble and so pass through; each channel is specific for one type of ion; they open and close depending on the the cells needs.

-*Carrier* Proteins: Allows diffusion of larger polar molecules e.g glucose and amino acids; polar molecule attaches to *binding site* on the carrier protein; causes protein to change shape and releases the molecule on the other side of the membrane.

Methods Of Transport Across A Membrane:

Co-Transoport

-Type of *Facilitated Diffusion* that bring molecules and ions into cells together on the same protein transport molecules.g sodium-glucose co-transport.

-Passive Process - ATP not required

1. Concentration gradient for sodium ions to move into the cell

2. Sodium ions and glucose *bind* to carrier protein

3. Carrier protein changes shape, sodium and glucose are transported to the other side of the membrane.

4. This process can move glucose against its concentration gradient without the use of ATP- known as secondary active transport.

Methods Of Transport Across A Membrane:

Active Transport

-Transport of ions and molecules *against* the concentration gradient

-Active process- *requires ATP* (Released by cell in respiration.

-If respiration is *inhibited* e.g by cyanide poisoning, active transport is too.

-Requires an *intrinsic carrier protein, like facilitated diffusion, which acts as a *pump* as transport is against the concentration gradient.

-Only charged particles e.g ions and polar molecules like glucose, that are insoluble in lipids, can be actively transported.

1. Molecule/ion binds to carrier protein on the outside of the cell membrane

2. ATP transfers a phosphate group to the carrier protein

3. Carrier protein changes the shape and carries ion/molecule across the membrane

4. Molecule or ion is released into the cytoplasm

5. Carrier protein returns to original shape

Methods Of Transport Across A Membrane:

Application Graph Answers

-Active Transport: As it uses energy from they hydrolysis of ATP made from respiration; When respiratory inhibitors are added the rate of uptake in the cell membrane fall as ATP production is inhibited.

-Diffusion: As the concentration difference across the membrane increases, the rate of uptake increases; Respiratory inhibitors have no effect on diffusion as it is a passive process-ATP not required

-Facilitated Diffusion: As the concentration difference across the membrane increase, the rate of uptake slowly levels outs the carrier/channel proteins are full; Respiratory inhibitors have no effect as it is a passive process-ATP not required.

Methods Of Transport Across A Membrane:

Bulk Transport (Exocytosis and Endocytosis)

-Endocytosis and Exocytosis are the processes where the cell transports material in *bulk* into or out of the cell.

-Active Process - *ATP required*

*Exocytosis (Secretion)*:

-Process by which substances may *leave* the cell having been transported through the cytoplasm in a *vesicle*, which fuse with the cell membrane

-A vesicle is produced in the cytoplasm (budding off at one end of the Golgi body)

-Vesicle migrates to the plasma membrane, fuses with it and secretes its contents outside the cell e.g secretion of the hormone insulin or digestive enzymes.

*Endocytosis (Uptake)*:

-Cell membrane *folds* around the particle and the folding closes off the link to the outside of the cell

-Particle is fully *trapped* inside the cell in a vesicle or vacuole

-Two Types of endocytosis

-*Phagocytosis*: Uptake of *solids* e.g white blood cells engulfing bacteria

-*Pinocytosis*: Uptake of *liquids* e.g lipid droplets

Methods Of Transport Across A Membrane:

Osmosis

-Osmosis is the *diffusion of water from an area of higher water potential to an area of lower water* potential across a *selectively permeable membrane*.

-Passive Process- ATP not required

Methods Of Transport Across A Membrane:

Osmosis-Water Potential

-*Water Potential: Tendency for water to leave a solution or cell by osmosis.* Measured in kPa. ( The greater the n.o free water molecules in a solution the higher the water potential)

-Pure water has the *greatest* potential energy to move so has the highest value of *0kPa*

-As you add more solute to water, the n.o free water molecules decreases and the potential energy of water decreases. (Water potential becomes more negative)

-*Hypotonic* Solution: Solution has a *high* water potential than the cell (weak solution). ~The solution has a low concentration of solute. Water *enters* cell via osmosis

-*Hypertonic* Solution: Solution has a *low* water potential than inside the cell. (strong solution). The solution has a high concentration of solute. Water moves *out* of cell into the solution by osmosis

-*Isotonic Solution*: The cell has the *same* water potential as the surrounding solution. *No net movement*

Methods Of Transport Across A Membrane:

Osmosis And Plant Cells

-Water moves from an area of *higher* water potential to an area of *lower* or more negative water potential.

-In plant cells the following equation is used to describe the relationship between the forces involved in water potential:

*Water potential = Solute potential + Pressure potential*

-*Solute Potential*: The concentration of dissolved substances inside the plant cells vacuole and cytoplasm. Solute potential is always a *negative value.*

-*Pressure Potential*: When water enters a plant cell by osmosis the cytoplasm and vacuole swell and push against eh cell wall. This increases the pressure potential of the plant cell. Always a *positive value.*

1. Water enters a plant cell causes the vacuole and cytoplasm to swell-turgid

2. Cell wall is inelastic and so outward pressure builds up as the cytoplasm pushes against the cell wall

INCIPIENT PLASMOLYSIS:

-*Theoretically* defined as the point at which the *cell membrane* is just *about to come away from the cell*

-*Experimentally* it is the point where *50% of the cells in the sample are plasmolysed.*

-Water Potential=Solute Potential as Pressure Potential is equal to 0kPa

Methods Of Transport Across A Membrane:

Osmosis In Animal Cells:

-In a *hypotonic*, the solution there is a *high* water potential in the solution (weak solution) and so water moves *into* the cell via osmosis. This causes the cell to *swell and burst*.

-In a *hypertonic* solution, there is a higher water potential in the cell (strong solution) and so water moves *out* of the cell via osmosis. This causes the cell to *shrivel and crenate.*

Enzymes

Enzymes:

Structure and Function

-To stay alive cells must perform many biochemical reactions to break down large molecules into smaller molecules and vise versa. These biochemical reaction are collectively known as metabolism.

-Enzymes are *globular* proteins with specific tertiary structure, held by hydrogen and ionic bonds, disulphide bridges and hydrophobic interactions

-They acts as *biological catalysts*, they speed up the rate of reaction by lowering the activation energy.

-Enzymes can work inside (*intracellular*) or outside (*extracellular*) our cells.

-They can catalyse metabolic reactions in two ways:

-*Anabolic Reactions*: Substrates *join* e.g a-glucose + a-glucose--> maltose

-*Catabolic Reactions*: Substrates *break down* e.g Dipeptide--> amino acid + amino acid

-Only a small region of an enzyme is functional- the active site.

-The substrate comes into contact with the active sire and an enzyme, forming an enzyme substrate complex; The reaction takes place and then the products are released from the active and so the enzyme is free to catalyse another reaction.

Enzyme:

Lock and Key + Induced Fit

Two Main Models for Enzyme Action:

- LOCK AND KEY MODEL

- Substrate molecule fits into the active site of the enzyme molecules like a 'key fitting into a lock' as they are *complimentary shapes*. Forms enzyme substrate complexes.

- The product is then formed and no longer fits into the active site and so is released.

- This model explains why enzymes are *very specific* i.e each enzyme only catalyses one reaction

-INDUCED FIT MODEL:

- Substrate and active site of the enzyme are *not complimentary shapes* and so when a substrate binds to the active site, it changes shape to fit around the substrate.

- This places a strain on the substrate molecule and distorts a particular bond, lowering the activation energy required to break the bond.

- The products are formed and leave the active site which then return to the original shape.

- Example includes lysozomes which help to kill bacteria by catalysing the hydrolysis of sugars in the cell walls- they are weakened and so the bacteria absorbs water by osmosis and burst. Lysozomes are present in many secretions e.g tears, saliva, human milk and in lysosomes.

Enzymes:

Properties

- Specific: Due to the sequence of amino acids that make up the active site

- Fast acting: with a high turnover number- can convert many molecules of substrate per unit time.

- Soluble: Hydrophilic R groups are found on the outside of the molecule

Enzymes:

The Course Of An Enzyme Controlled Reaction:

1. The curve is steepest initially as there is a *high concentration of substrate* molecules, so they are more likely to successfully collide with an active site and form the product. Initially the enzyme concentration is the limiting factor

2. As the reaction proceeds there is a decreasing concentration of substrate so *less chance* of successful collision; now substrate concentrations is the limit factor

3. The graph eventually levels off as all of the substrate has been converted to product and so no further product is formed

Enzymes:

The Course Of An Enzyme Controlled Reaction

1. Substrate concentration is at a *maximum* level at the start of the reaction.

2. There is a *rapid fall* in the concentration of substrate. Substrate molecules bind to the enzymes active site and are converted into product.

3. Substrate concentration is very low. All the substrate has been converted into product.

Enzymes:

Factors Affecting Enzyme Action

-Enzymes are *synthesised inside* living cells but may catalyse reactions:

- Inside the cell (intracellular) e.g in solution, membrane-bound

-Outside the cell (extracellular) i.e they're secreted.

-There are a n.o environmental conditions and factors that can affect the rate of an enzyme-controlled reaction:

-Temperature

-pH

-Substrate Concentration

-Enzyme Concentration

-Inhibitors (Competitive or Non-Competitive)

Enzymes:

Temperature

- At low temperatures the rate of reaction is low. As there are a less successful n.o collisions and the molecules have *less* kinetic energy.

- At increasing temperatures up to the optimum, increases the rate of reaction. As the kinetic energy of the enzyme and substrate molecules *increase*, increasing the chance of successful collisions. *More enzyme-substrate complexes form*.

- At the optimum temperature the rate of reaction is at its highest.

- Above the optimum temperature the rate of reaction falls. As the molecules have more kinetic energy . The increasing vibrations begin to break the hydrogen bonds, changing the tertiary structure of the enzyme. This *alters* the shape of the *active site* so it is *no longer complimentary* to the substrate. This lowers the rate of reaction as the enzyme substrate complexes cannot form.

- At very high temperatures the rate of the reaction falls to zero. As the enzymes have *denatures*. This is where the active site is *permanently distorted* (changes shape) by irreversibly breaking the bonds. Prevents the substrate from binding to the active site as it is no longer complimentary to the active site

Enzyme:

pH

- Most enzymes have an optimum pH at which the rate of reaction is at is maximum.

- Enzymes only work within a *narrow* range of pH values and small deviation can cause reversible changes in the enzyme structure resulting in inactivation.

-Extremes of pH can permanently denature an enzyme.

-An extreme change of pH may alter the *electrostatic charges* on the sides of the chains of amino acids.

-If an active site has too many H+ ions (acidic) or OH- ions (alkali) the active site may have the same charge and so the enzyme will repel the substrate.

-*Buffers* can be added to the reaction to *maintain a constant pH*.

Enzyme:

Effect of Substrate Concentration

-At a fixed enzyme concentration the rate of reaction will increase as the substrate concentration increases.

-At low substrate concentrations, the substrate concentration is the limiting factor as the enzyme molecules have only a few substrate molecules to collide with.

-As more substrate is added there are *more successful collisions* and more occupied enzyme active sites, until the maximum rate of reaction is reached and the substrate becomes in excess and the enzyme concentration becomes the limiting factor

Enzyme:

Effect of Enzyme Concentration

- As the enzyme concentration increases there are *more active sites* available and therefore the rate of reaction increases.

Enzyme:

Enzyme Inhibition (Competitive and Non-Competitive)

-Enzyme inhibition is the *decrease* in the rate of an enzyme controlled reaction by another molecule. The inhibitor combines with the enzyme either directly or indirectly to prevent it from forming enzyme substrate complexes.

COMPETITIVE INHIBITORS

- Competitive inhibitors are *similar* in shape to the substrate and bind to it, *blocking* the actual substrate from entering the active site- less enzyme substrate complexes form.

- Rate of reaction decreases due to less product being produced

- If the concentration of substrate increases, the effect of the inhibitor is reduced.

- Example of competitive inhibitor is *malonic acid* which inhibits the respiration reaction between the enzyme succinic dehydrogenase and succinic acid (the substrate) malonic acid has a similar shape to the substrate and the active site of the enzyme.

NON-COMPETITIVE INHIBITOR:

- A non-competitive inhibitor is *not similar* in its shape to the substrate and bind to the enzyme at another point - the *allosteric site*.

This changes the shape of the enzymes actives site so it is *no longer complimentary* to the substrate. The enzyme may be permanently damaged.

-Example of a non-competitive inhibitor is cyanide.

Enzyme:

Enzyme Inhibition (Competitive and Non-Competitive) And Its Effect In On The Rate Of Enzyme-Controlled Reaction

- The competitive inhibitor rate of reaction peaks at the same rate as the original reaction, as the substrate 'outcompetes' the inhibitor.

- The non-competitive inhibitors rate of reaction peaks at a lower rate, as the active sites are knocked out/occupied.

- For both inhibitors there is a *slower increase* in the rate of reaction as the inhibitors reduce the n.o active sites available for the substrate.

Enzymes:

Immobilised Enzymes

- Immobilised Enzymes are enzymes that are *fixed, trapped or bound on an inert matrix*

- Examples of how enzymes are immobilised are: absorption onto an insoluble matrix; covalently binding to a solid support; trapped within a gel; encapsulated behind a selectively permeable membrane.

- They have a lowered rate of reaction as some of the enzymes are trapped within beads and so it takes time for the substrate to diffuse into them, whereas enzymes of the surface have active sites that are more readily available to the substrate, hence an initial higher rate of reaction.

- Advantages of immobilised enzymes: *Easily recovered* for reuse; Product *not contaminated *with enzyme; *Increased stability* over a wide range of pH values and temperatures; Several enzymes with different pH and temperature optima can be used in one process; Can be *easily added or removed* - greater control over the rate of reaction.

-Trapping an enzyme stabilises it and prevents its active site from denaturing and changing shape, so it can be used over a wide range of conditions.

Enzymes:

Uses Of Immobilised Enzymes

Lactose Free Milk:

-Milk contains the sugar lactose which some people are intolerant to as they do not possess the enzyme lactase.

-Lactose free milk can be produced using immobilised enzymes trapped in an *aliginate bead* in a column to hydrolyse lactose into its monosaccharides glucose and galactose.

Biosensors:

-The device converts chemical signals into an electrical signal by rapidly detecting and measuring low concentration of a specific substrate in a complex mixture.

-e.g Glucose concentration in blood samples as the enzyme glucose oxidase in immobilised on a *selectively permeable* membrane. When placed in the sample binds to the glucose where a small electric current is produced and detected by an electrode. The concentration of glucose can then be read on a screen.

High Fructose Corn Syrup (HFCS):

HFCS is a sweetener manufactured in a multi-step process from starch and involves several immobilised enzymes which required different conditions:

-Starch (a-amylose @90)---> Oligosacchairdes (glucoamylase @60)---> Glucose (Glucose isomerase @60 max)--->Fructose

STRUCTURE OF NUCLEOTIDES

Nucleotides:

-Nucleic Acids are polymers made from *monomers* called nucleotides.

-All nucleotides are made up of three parts, combined by a condensation reaction: a phosphate group: pentose group; organic nitrogenous base

-There are two groups of organic nitrogenous bases;

-Pyrimidine (Single Ring): *T*hymine; *C*ytosine; *U*racil

-Purine (Double Ring): *A*denine; *G*uanine

Nucleic Acids:

DNA

-*DNA*: *D*eoxyribose *N*ucleic *A*cid

-It is a very *large* and *stable* molecule found as chromatin in nucleus of eukaryotic cells and small amounts are found in mitochondria and chloroplasts

-Functions of DNA: Carries *genetic code for protein synthesis*; Replicates in dividing cells

-DNA consists of two polynucleotide strands twisted in a *double helix*, and the two strands run in opposite directions and are said to be *anti-parallel*

-DNA nucleotides contain a pentose sugar (deoxyribose) and one of four organic bases: *Adenine: Guanine; Cytosine; Thymine.*

-Nucleotides are held together by bonds between the phosphate group attached at the 5th carbon on one pentose sugar and the 3rd carbon of another. This means that one end of the stand finishes on carbon 5, so its called a 5 prime end and the other finished on a C3 so is called a 3 prime end.

-Two sugar phosphate 'backbone' protect genetic information stored within the sequence of bases which face each other in the double helix, according to the complimentary base pair rule. They are held together by hydrogen bonds.

-*G*uanine pairs with *C*ytosine and has *3* hydrogen bonds (*C*ar in *G*arage).

-*A*denine pairs with *T*hymine and has *2* hydrogen bonds (*A*pple in *T*ree)

Nucleic Acids:

RNA

-*RNA*: *R*ibo*n*ucleic *A*cid

-RNA is *short-lived* molecule, found mainly in the cytoplasm and in the nucleus.

-RNA is a *single stranded* polynucleotide and contains a different pentose sugar (ribose) and one of four organic nitrogenous bases: *Adenine; Guanine; Cytosine; Uracil.*

Function of RNA:

-RNA is involved in *protein synthesis*. There are 3 types of RNA involved:

1. *mRNA* :*M*essenger : single stranded molecule that *carries the genetic code for a specific protein* from DNA in the nucleus to ribosomes in the cytoplasm.

2. *tRNA*: *T*ransfer: *transfer specific amino acid*s to the ribosomes and a single strand of RNA forms a clover leave shape held by hydrogen bonds between certain base- pairs

3. *rRNA*: *R*ibosomal: forms a large protein complex molecule: a ribosome, which *translate* the *genetic code* and joins amino acids together to *form polypeptides.*