EXAM QUESTION Flashcards
How to use an eyepiece graticule to find mean size of stomata (3)
measure each stomata using eyepiece graticule
calibrate eyepiece graticule using stage micrometer
take many measurements to calculate a mean
Explain why antibodies only attack specific cells (4)
- specific tertiary structure
- binding site is complementary to one antigen
- antigen to this antibody is only found in specific cells
- so antibody binds to form an antibody complex with these cells
describe cohesion tension theory in the xylem (5)
- water leaves the leaf by transpiration-water in spongy mesophyll evaporates out the stoma
- lowers the water potential of mesophyll cells
- water moves by osmosis from xylem into spongy mesophyll
- water is pulled up the xylem
- water molecules cohere
- continuously forms a water column
- water molecules adhere the walls of xylem
How is mRNA produced in a plant cell?(5)
- DNA helicase unwinds DNA by breaking hydrogen bonds between complementary base pairs
- only one strand acts as a template
- free nucleotides bind to exposed nucleotides by hydrogen bonding- complementary base pairing
- RNA polymerase reforms the sugar phosphate backbone by catalysing the formation of phosphodiester bonds between nucleotides
- pre-mrna formed
- splicing occurs, removes introns
Describe the process of crossing over and explain how it increases genetic variation(4)
- homologous chromosomes pair to form bivalents
- chiasmata form
- exchange of lengths of chromatids/ sections of chromatids break and re-join on homologous chromosome
- new combination of alleles
how would you use cell fractionation to isolate chloroplasts?
homogenate leaf to split cells open
filter and centrifuge
separate supernatant and pellet
re spin at higher speeds until separating the chloroplasts
How does a vaccine lead to the production of antibodies? (4)
- vaccine is dead or inactive pathogen
- dead or inactive pathogen has foreign antigen that in recognised and presented by antigen presenting cells on their surface
- helper t cells bind to antigen-undergoes mitosis and stimulates specific b cells to undergo mitosis
- b cells produce plasma cells which produce antibodies to destroy the pathogen
how do mutations lead to the formation of a non-functional protein?(4)
- mutation- change in the nucleotide base sequence of dna
- codes for different amino acids
- change in primary structure
- different position of hydrogen bonds
- change in tertiary structure of protein
describe how structures of starch and cellulose are related to their functions
-Starch
- helical/spiral shape so compact for storage
-large/insoluble so doesnt effect water potential of cells
-branched, so glucose is easily released for respiration
-large, so cannot cross cell membrane
Cellulose
-long, straight, unbranched chains of b glucose
-parallel chains joined by hydrogen bonding
-form microfibrils which for macro fibrils
-provides rigidity and strength
describe the processes involved in the transport of sugars in plant stems (5)
- sucrose facilitated transport to companion cells
- sucrose actively transported into the phloem from companion cells
- decrease water potential, water enters from the xylem by osmosis
- produces high hydrostatic pressure
- causes mass flow to tissues
- sugars unloaded at sink
describe direction of blood flow of deoxygenated blood leaving the kidney to return to the kidney (6)
- blood leaves the kidney via renal vein to the vena cava
- vena cava into the right atrium
- from heart to lungs via the pulmonary artery
- from lungs to heart via pulmonary vein
- pulmonary vein into left atrium
- blood leaves heart via aorta to the renal artery where it returns to the kidnrys
explain how water travels from the soil to the xylem to the leaves
water enters root hair cells by osmosis
water moves from one cell to another apoplast or symplast route
symplast: moves into cytoplasm from cell membrane and travels from one cell to another through plasmodesmata
apoplast: water moves through cell wall-carries mineral ions
reaches casparian strip-blocks apoplast route, only symplast route
active transport by endodermis
transpiration from leaves
creates cohesion between water molecules
adhesion
creates continuous water column
how does the heart coordinate regular muscle contraction of ventricles?
SAN to AVN to bundle of His impulse over atria non conducting tissue delay at AVN ensures atria empty before ventricles contract ventricles contract from apex upwards
how is tissue fluid made?
contraction of ventricles to produce high blood pressure
forces out water and dissolved substances out of blood capillaries
describe types of gene transmission and why they make it harder to treat disease
resistant bacteria
vertical gene transfer
resistant bacteria reproduce
increase in frequency of resistant bacteria
horizontal gene transfer
plasmids
conjugation
can occur between different species of bacteria.
