BIOLOGY PAPER 1 MOCK

describe the function of the nucleus

• contains coded genetic info- in the form of DNA molecules

• directs the synthesis of all proteins required by the cell

• controls metabolic activities

• DNA associations with histones to form chromatin→ coils and condenses to form chromasomes

describe the structure of the nucleus

• DNA contained within the nuclear envelope (double membrane)

• nuclear envelope contains nuclear pores- allows molecules in and out

• DNA is too big to leave through nuclear pores for protein synthesis- so it is transcribe into smaller RNA molecules

what is the function of the nucleolus

• responsible for producing ribosomes

• composed of protein and RNA 

• RNA is used to produced ribosomal RNA (rRNA) then combines with proteins to form ribosomes

describe the function of mitocondria

• site for final stages of respiration

• energy stored in bonds of organic molecules is made available for cell to use to produce ATP 

• no. mitocondria in a cell is a reflection of how much energy it uses

describe the structure of mitocondria

• double membrane

• fluid interior= matrix

• membranes forming cristae contains enzymes used for aerobic respiration

• contains a small amount of DNA (mtDNA)

• can produce own enzymes and reproduce themselves

what is the function and structure of vesicles

• membranous sacs- single membrane with fluid inside

• storage and transport roles- used to transport materials inside of cells

what is the function and structure of lysosomes

• speciallised forms of vesicles that contain hydrolytic enzymes

• responsible for breaking down waste materials in cells 

• important role in the immune system→ breaks down pathogens ingested by phagocytic cells 

• role in apoptosis (cell death) 

what is the cytoskeleton?

• present in cytoplasm of all Eukaryotic cells

• network of fibres- needed for shape and stability of cells 

• organelles held in place by cytoskeleton 

• composed of microfilaments, microtubules, and intermediate fibres

describe microfilaments

• contractile fibres- form from protein actin

• responsible for cell movement + cell contraction in cytokinesis

describe intermediate fibres

gives mechanical strength to cells and helps them maintain integrity 

describe microtubules

• globular tubulin proteins polymerise to form tubes used to determine shape of cell 

• act as tracks for movement of organelles 

• spindle fibres are composed of microtubules

describe centrioles

• composed of microtubules

• plays a role in positioning flagella+ cilia

describe the endoplasmic rectillium

• network of cisternae

• connected to outer membrane of the nucleus 

describe the smooth ER

responsible for lipid and carbohydrate synthesis and storage

describe the rough ER

has ribosomes bound to the surface, responsible for synthesis and transport of protein

describe ribosomes

• can be free floating in cytoplasm or attached to the rough ER

• constructed of RNA molecules

• site of protein synthesis

describe the golgi apparatus 

• similar to structure of smooth ER 

• formed of cisternae- doesnt contain ribosomes

• modifyes proteins and packs them into vesicles

• secretory vesicles or lysosomes

describe cellulose cell walls 

• freely permeable 

• gives the cell shape- contents of cell press up against wall

• cell wall acts as defense mechanism against invading pathogens

describe vacuoles

• membrane lines sacs

• plant cells have permenant vacuoles

• membrane of vacuole= tonoplast 

• selectively permeable 

describe chloroplasts

• responsible for photosynthesis 

• double membrane structure 

• fluid enclosed= stroma 

• light dependant reactions take place in photosynthesis 

• able to make own proteins 

what are the functions of the cytoskeleton?

• establishes cell shape

• provides mechanical strength 

• movement

• chromosome separation in mitosis and meiosis 

describe microtubules

• 25nm in diameter

• globular tubulin proteins polymerise to form tubes 

• involved in the transport of organelles

describe microfilaments

• 7nm in diameter

• contractible fibres formed from the protein actin 

• responsible for cell movement and cell contraction in cytokinesis 

describe the structure of undulipodia and cilia

• cylinder of 9 pairs of microtubules in a circle and 2 in the middle 

• 9+2 arrangement

what is the function of undulipodia and cilia

• move liquid past the surface of the cell 

• enables them to swim 

describe flagella

• only present in bacterial cells 

• structurally different to undulipodia

• made of a spiral of flagellin protein attached by a hook to a protein disk that can rotate

describe division of labour 

• each organelle in a cell is speciallised to carry out a specific role

what is the first step of protein synthesis

• nucleolus produces ribosomes and mRNA 

what is the second step of protein synthesis

• mRNA and ribosomes leave through nuclear pores

what is the third step of protein synthesis

• ribosomes bind to ER

• mRNA travels to the roughER 

• ribosomes that synthesis the proteins mRNA codes for 

what is the fourth step of protein synthesis

• proteins passed into cisternae and packaged into transport vesicles

• vesicles then move towards the golgi apparatus 

what is the fifth step of protein synthesis

• vesicles fuse with cis face of golgi apparatus- modification of proteins occur 

• vesciles leave from trans face

cells

cells

describe prokaryotic cells

• no membrane bound organelles 

• 1-10 micrometers

• divide by binary fission 

• unicellular 

• genetic material= single looped chromosome

what happened in 1600-1800 with microscopes

• lenses were developed

• light microscopes became available

what did Robert Hooke do

• used microscope to observe a cork

• saw that the cork was made of cells

What did schleiden do

suggested all plants are made of cells

what did Schwann do

• proposed all animals are made of cells

what is the cell theory

• all living things consist of cells 

• new cells are formed only by the division of pre existing cells 

• cells contain DNA that acts as instructions for growth

what is a temporary mount

a specimen that will only last a few hours to be seen under a microscope

what is a permenant specimen

• prepared by dehydrating the specimen

• fixed in wax→ then thinly sliced

what is a dry mount

• solid specimens are viewed whole or cut into very thin slices

• placed on slide+ covered with a coverslip

what is a wet mount

• specimens suspended in liquid 

• coverslip placed on an angle to avoid airbubbles

what is a squash slide

• wet mount prepared and coverslip pressed on 

• or sample squashed between 2 slides

what is a smear slide

• edge of slide used to smear a sample along another 

• coverslip placed on top

how do you make a biological drawing from a microscope slide

• pencil 

• continuous lines

• rules label lines

• add a title

• add magnification and scale

why are stains used

• stains increase the contrast of the different components within a cell 

• contrast allows different components to be visable and identified

describe crystal violent and methalene blue

• positively charged and so it is attracted to negatively charged materials in cytoplasm 

• leads to staining of cell components

describe nigrosin and congo red

• negatively charged- repelled by cytosol

• dyes stay outside of cell leaving cells unstained 

• negative stain technique 

what is differential staining

• can distinguish between 2 types of organisms 

• can also differentiate between different organelles of a single organism

what is the Gram stain technique

• separates bacteria into 2 groups (gram+ and gram-) 

• crystal violet applied and then iodine

• slide washed w. alcohol

• gram+ retains stain (blue/purple) 

• gram- lose stain 

what is the acid fast technique

• differentiate mycobacterium from other bacteria 

• lipid solvent carry dye into cells 

• cells washed with dilute acid alcohol solution

• mycobacterium not affected (bright red)

• other bacteria loses stain (blue)

describe the fixing stage of slide preparation

chemicals used to preserve specimens in a near natural state

describe the sectioning stage of slide prep

• specimens dehydrated with alcohols and placed in a mould with wax or resin

• then thinly sliced

describe the mounting stage of slide prep

specimens secured to a microscope slide and coverslip placed on top

what is magnification

number of times larger the image is compared to the real size

what is resolution

ability to distinguish between two separate points

what are the different types of electron microscopes

• transmission electron microscope (TEM)

• scanning electron microscope (SEM)

describe TEM’s 

• beam of electrons pass through the specimen and are focused

• 2D images produced

describe SEM’s

• scans the surface and electrons are reflected to make up an image 

• 3D images

what are the disadvantages of electron microscopes

• black and white images

• specimen must be in a vacuum

• specimen must be dehydrated and therefore dead

• very expensive and large 

what is a squash slide

• wet mount prepared and a coverslip pressed on or squashed between 2 slides

what is an eyepiece graticule

• a small ruler that can be inserted into the eyepiece of a microscope

• the scale is arbitrary and therefore one unit represents different lengths depending on the objected lense used 

• must be calibrated

how do you calibrate an eyepiece graticule

• superimpose the two scales

• match up two points 

• count the number of epg divisions

• count the number of micrometer divisions

• division the micrometer divisions by the EPGU’s to find the conversion number 

describe the relationship between polar and hydrophobic/hydrophilic

• polar phosphate heads= hydrophilic

• non-polar fatty acid tails= hydrophobic

describe the discovery that the Davson-Danelli model was incorrect

• it was found that proteins are distributed throughout the membrane in a mosaic pattern

• found that the membrane is fluid

describe the fluid mosaic model for plasma membranes

• proteins can move freely through the lipid bilayer

what is the movement of proteins dependant on in the membrane

the number of phospholipids with unsaturated fatty acids in the bilayer

what can diffuse through the phospholipid bilayer

• fat- soluble organic molecules

• polar molecules- (require proteins)

describe intrinsic proteins

• completely span the phospholipid bilayer

• main transport system of the membrane

• can form channels, carrier proteins or active pumps

describe extrinsic proteins

• on surface of bilayer or partially embedded in it

• provide mechanical support

• act as cell receptors

what are channel proteins

pores in the membrane that let ions diffuse through

describe carrier proteins

• change shape to let specific molecules through

describe glycoproteins

• carbohydrate molecules attached to membrane proteins

• can allow cell adhesion

• act as receptors for hormones and neurotransmitters

describe glycolipids

• carbohydrates attached to phospholipid molecules

• act as cell markers or antigens

describe cholesterol

stabilises the membrane and regulates its fluidity

describe membrane structure and permeability at 0 degrees

• permeability increases due to proteins unfolding and becoming deformed

• lower energy→ cannot move around as much

• if temperatures are low enough for ice crystals to form, they can puncture the membrane

• rigid → phospholipids are tightly packed together

describe membrane permeability and structure at 0-45 degrees

• partially permeable

• as temperature increases, components gain kinetic energy

• more fluid the membranes are, more substances it will allow through it

describe membrane structure and permeability above 45 degrees

• permeability rapidly increases

• proteins in membrane become denatured and begin to unravel

• water inside cytoplasm starts to expand, puts pressure on the cell membrane, creates gaps within the bilayer

describe membrane permeability with small hydrophobic molecules

permeable

describe membrane permability with small uncharged polar molecules

mostly permeable 

describe membrane permeability with large uncharged polar molecules

mostly impermeable, requires transport molecules

describe membrane permeability with ions

completely impermeable, requires transport proteins

what is passive transport

• movement of molecules or ions across membranes down the concentration gradient

• no energy requires

what is active transport

• movement of molecules or ions against the concentration gradient

• requires ATP

what is diffusion

net movement of particles down a concentration gradient; from a region of high concentration to a region of low concentration

what factors effect the rate of diffusion

• temperature

• concentration

what molecules can easily diffuse

• small molecules

• non-polar molecules

• lipid-based molecules (e.g. hormones)

• molecules in high concentrations

What is ficks law

rate of diffusion is proportional to: SA x difference in concentration/ length of diffusion path (membrane thickness)

what happens in diffusion if there is a small SA: vol ration

cell cannot get enough raw materials fast enough

what is facilitated diffusion

• passive process

• carrier proteins or protein channels allow molecules through

• specific molecules can fit into carrier

• carrier flips to allow the molecule to pass through the membrane

how do slightly polar molecules travel through membranes

diffuse through hydrophilic channels in channel proteins

describe channel proteins

• pores in the membrane

• can be specific to one molecule and/or gates

• channel is water filled with allows polar molecules through

• use for diffusion of sodium, calcium and potassium ions into/out of neurones

what does it mean for channel proteins to be gated

can be open or closed under certain condition

describe carrier proteins

• specific to particular molecules

• when a molecule binds to a protein, the protein changes shape to allow the molecule through it

• used for glucose and amino acids

• can also be used for active transport

what are the differences of carrier proteins in active transport to those used in facilitated diffusion

• they only work one way

• they use ATP

• they are specific to certain molecules/ions

• they carry molecules against the concentration gradient

give some examples of active transport

• uptake of glucose and amino acids in the small intestines

• absorbtion of mineral ions by plant roots

• excretion of hydrogen ions and urea by the kidneys

• exchange of sodium and potassium ions in the neurones and muscle cells

describe how carrier proteins move molecules across membranes

1. carrier proteins takes in molecules from outside plasma membrane

2. glucose molecules bind to carrier proteins- ATP attaches to plasma membrane on the inside of the cell

3. protein changes shape- other side opens and allows molecules to exit into the inside of the cell

what are the two types of bulk transport

• endocytosis

• exocytosis

describe endocytosis

• bulk transport of materials into the cell

• split into phagocytosis (solids) and pinocytosis (liquids)