Markscheme specific

Created by

Niamh Mumby

Cards (137)

What are the differences between the structure of tRNA and mRNA?
tRNA is clover leaf shape, mRNA is linear
tRNA has hydrogen bonds, mRNA doesn't
tRNA has an amino acid binding site, mRNA doesn't
tRNA has anticodon, mRNA has codon
Describe how HIV is replicated
Attachment proteins attach to receptors on helper T cell
RNA enters the cell
Reverse transcriptase converts RNA to DNA
Viral protein is produced
Virus is assembled and released
Describe how a gene is a code for the production of a polypeptide without mentioning transcription or translation
Base sequence in triplets determines the sequence of amino acids
Describe how the structure of glycogen is related to its function
It is helical so compact
A polymer of glucose so is easily hydrolysed
Branched so more ends for faster hydrolysis
Glucose provides a respiratory substrate for energy
Insoluble so does not affect water potential
Give the pathway a red blood cell takes when travelling from a kidney to the lungs
Renal vein
Vena Cava to right atrium
Right ventricle to pulmonary artery
Explain how water from tissue fluid is returned to the circulatory system
Plasma proteins remove which creates a water potential gradient so water moves to the blood by osmosis
And is returned to the blood by the lymphatic system
Define species
A group of organisms that can reproduce to produce fertile offspring
Define organ
A structure made up of a group of tissues, working to perform a specific function
How does bacteria differ from other organisms?
Cell wall made of murein
No nucleus
Loop of DNA
No mitochondria
No chloroplast
No vacuole
Have a capsule
Smaller
What are features that all prokaryotes have?
Cytoplasm
Cell membrane
Unicellular
No nucleus
A loop of DNA
No membrane-bound organelles
Cell wall made of murein
State the function of the nucleus
Stores genetic information that controls the activities of the cells
Controls how cells reproduces
Codes for a protein
Stores instructions for protein synthesis
State the function of a cell membrane
Forms a barrier between the cell and the surroundings
Keeps the contents of the cell inside
Controls movement of substances across the membrane
Define tissue
A group of cells with similar structures working together to perform a shared function
Outline the roles of DNA in a cell
Stores genetic information
DNA base sequence codes for proteins
Sequence of DNA bases codes for amino acid sequence
Transfers information to daughter cells in mitosis
DNA is copied as mRNA
State features of diffusion that don't apply to active transport?
Passive - doesn't require energy
Substances move down a concentration gradient
No need for protein
Doesn't have to occur across a membrane
Why is the shape of an enzyme important?
Substrate binds to active site of enzyme
The enzyme must have a complementary shape to the substrate
To make an enzyme - enzyme-substrate complex must form
Only fits one substrate
Describe in detail how enzymes function
Enzymes are proteins
Enzymes can be reused
They are specific
They are catalysts so lower the activation energy needed for the reaction
Create successful collisions between the active site and substrate to form a complementary enzyme-substrate complex
Temperature above the optimum results in the enzyme denaturing
Below or above the optimum pH results in the enzyme denaturing
Define the term catalyst
A substance that increases the rate of reaction by lowering the activation energy and is not changed by the reaction
Describe the use of carbohydrates in plants
Cellulose for cell walls
Starch for energy and respiration
To attract insects
Describe the use of amino acids in plants
To make proteins for enzymes for growth
Why does increasing the temperature increase the rate of photosynthesis?
Temperature is a limiting factor
Kinetic energy is increased so there are more collisions between substrate and enzymes which speed up reactions
The stomata open wider
So there is increased carbon dioxide entering the leaf
Describe the role of bile
Emulsification
Increased surface area of fat globules
For lipase
Speeds up digestion of fats to fatty acids and glycerol
Neutralises stomach acid
How are the villi adapted for absorption?
One cell thick
Good blood supply
Lots of microvilli so large surface area
Mitochondria for active transport
Explain how transpiration occurs in leaves
Water evaporates
From the surface of mesophyll cells
Water diffuses through the stomata out of the leaf by osmosis
Explain cohesion-tension
Evaporation from mesophyll cells
Water moves through stomata by osmosis
Creates a lower water potential inside of the mesophyll cells
This creates negative pressure and tension so water moves upwards in the xylem
Cohesion due to hydrogen bonds between water molecules results in water moving in a continuous column
Adhesion between water molecules and xylem walls
Explain the role of phloem in plant transport
Translocation
Movement of food from source to sink
Sucrose is produced at the source
Growth occurs at the sink
Describe differences between cellulose and glycogen
Cellulose is made up of beta glucose monomers and glycogen is made of alpha glucose monomers
Cellulose has straight chains and glycogen is branched
Cellulose has straight chains and glyocgen is helical
Gylogen has 1,4 and 1,6 glycosidic bonds and cellulose only has 1,4 glycosidic bonds
Describe and explain why starch is a good storage molecule
It is insoluble in water so doesn't affect the water potential
It is helical so compact
Polymer of alpha glucose so provides glucose for respiration
Branched for hydrolysis
Large molecule so can't cross the cell membrane
Describe how glycogen acts as a source of energy
Hydrolysed to glucose
Glucose is used in respiration
Explain how cellulose are adapted for their function in plant cells
Long and straight chains
Linked together by hydrogen bonds to form microfibrils
Provide strength and rigidity to cell walls
How would you test for the presence of lipid in a liquid sample of food?
Add ethanol
Then add water
Then shake
A white emulsion forms in a positive test
Describe how a triglyceride molecule is formed
One glycerol and three fatty acids
Condensation reaction and removal of three molecules of water
Ester bonds formed
Describe how an ester bond is formed in a phospholipid molecule
Condensation reaction
Between glycerol and fatty acid
Describe the induced fit model and how an enzyme acts as a catalyst
Substrate binds to the active site
The active site changes shape so it is complementary to the substrate
Acts as a catalyst by reducing the activation energy
How does a competitive inhibitor reduce the rate of reaction?
The inhibitor is a similar shape to the substrate
Binds to active site
Reduces enzyme-substrate complexes forming
How does the structure of a protein depend on amino acids?
Structure is determined by the position of amino acids
The primary structure is the sequence of amino acids
The secondary structure is alpha helices or beta pleated sheets
Tertiary structure is hydrogen, ionic bonds and disulphide bridges forming in specific places
This creates the active site in enzymes
The quaternary structure is more than one polypeptide chain linked together
Describe how a non-competitive inhibitor reduces the rate of reaction
Attaches to allosteric site
Changes the shape of the active site
So the substrate is no longer complementary so no more enzyme-substrate complexes form
Describe how a peptide bond is formed between two amino acids to form a dipeptide 
Condensation reaction
Between amine and carboxyl
Describe the structure of DNA
It is a polynucleotide
Formed from deoxyribose, a phosphate group and a nitrogenous base
Phosphodiester bonds
Double helix held by hydrogen bonds
Pairing between adenine, thymine and cytosine, guanine
Explain why new nucleotides can only be added in a 5' to 3' direction
DNA polymerase
Is specific
Only complementary to 5' end
Not the 3' end