Mistakes that haunt me

membrane fluidity

ability of lipids/proteins to diffuse laterally

why does cholesterol reduce membrane fluidity

it fits between the fatty acid tails of the phospholipids which restricts movement of the membrane components

why do red blood cells have more cholesterol than gut epithelial cells

• cholesterol provides strength to the cell membrane

• red blood cells need more of this strength and support as they are free in blood and don’t have cells around them to support them like gut epithelia do

• red blood cells need the extra support as they have to squeeze through capillaries, whereas gut epithelia experience less physical force

latent heat of vapourisation

the heat energy absorbed by a liquid/water to evaporate without changing temperature

where are antigens displayed by APCs

on the cell membrane

How do antibodies help

they bind to their complementary antigen (to form an antigen-antibody complex), which results in the destruction of the pathogen, e.g. by causing agglutination of bacteria which makes phagocytosis easier

why are antibodies specific

they have a variable region with a specific tertiary that is only complementary to the antigen, so they bind to their antigen to form an antigen-antibody complex

process of vaccine working

• Vaccine contains antigens

• Macrophage presents antigens on surface (on the cell membrane)

• T cell with complementary receptor binds to the displayed antigen

• T cell stimulates B cell with complementary antigen on surface

• B cell clones itself to produce plasma and memory cells

• Plasma cells secrete large quantities of antibodies

• Memory cells remain in body and cause a secondary immune response in case of infection by pathogen in the future, and they produce antibodies in a greater quantity and faster

diploid cells to diploid spores process

mitosis

Genetic variation is caused by independent segregation…

of homologous chromosomes

Genetic variation is caused by crossing over…

between homologous chromosomes

why take samples from many places

• to calculate a reliable mean

• to ensure the sample is representative

• because the distribution may not be uniform

Why might rate of water uptake by plant in potometer be the same as rate of transpiration

• Water used in photosynthesis

• Used for hydrolysis

• Produced in respiration

• Enters cells to maintain turgor

why does removal of hedges cause a decrease in diversity of birds

• Fewer habitats/niches

• Removes species of plant/insect

• So fewer food sources

Why does a different primary structure affect protein function

changes THE POSITION OF the hydrogen/ionic/disulfide bonds in the tertiary structure, so the protein has a different 3D shape

how to test for the presence of a lipid

add ethanol to the sample, then water - if lipids are present, a WHITE, MILKY emulsion will form

induced fit explanation

• Before binding active site is not complementary to the substrate

• Shape of active site changes as substrate binds and e/s complex forms

• Binding stresses bonds in the substrate leading to the reaction

After Benedict’s test, how could you measure quantity of reducing sugar

• Colorimetry

• Filter out precipitate, dry it, weigh it

When calculating percentage uncertainty, what happens when you have two different types of measuring equipment

ADD the individual percentage errors for both

beta glucose monomers in a chain

position of the hydrogen and hydroxyl groups inverted for every other beta glucose monomer

how does secondary structure of proteins form

hydrogen bonds form between the NH group on one amino acid and the C=O bond on another, to form an alpha helix or a beta pleated sheet

why is resolution lower in light microscopes

wavelength of light longer

why does a stained cell membrane appear as two lines

phospholipid bilayer structure, stain binds to phosphate on inside and outside of membrane

how can you tell if an image has been made by a TEM

you can observe the internal structure of organelles (as TEMs have the highest resolution)

advantage of membrane-bound digestive enzymes

enzymes not lost through egestion with other contents of the gut

how does a macrophage stimulate a B lymphocyte

it presents antigens on its cell-surface membrane to lymphocytes

Why might children fail to respond to a vaccine given too early

• Immune system has not yet developed, so they do not have the right T and B lymphocytes

• Malnutrition - lack of protein to make antibodies

Emulsification of lipids: higher surface area for?

FASTER hydrolysis of triglycerides by lipase

Golgi role in lipid digestion

• Modifies/processes triglycerides

• Combines triglycerides with proteins

• Packaged for release

How does a carrier protein work for active transport

• Uses hydrolysis of atp

• Molecule/ion binds to the protein

• Protein changes shape to move molecule/ion across the membrane

Why does high temperature denature proteins

Breaks hydrogen/ionic bonds between the R groups, so changes the tertiary structure and therefore 3D shape

action of membrane bound dipeptidases and their importance

hydrolyse peptide bonds between dipeptides to release amino acids - these can cross the cell membrane into the epithelial cells, whereas dipeptides cannot

Adaptations of insect ventilation system for efficient gas exchange

• Tracheoles have thin walls so short diffusion distance to cells

• Highly branched so short diffusion distance to cells, and large surface area for efficient gas exchange

• Tracheae provide tubes full of air so fast diffusion into cells

• Fluid in the ends that moves out during exercise so faster diffusion of oxygen into cells

• Body can be moved by muscles to move air so maintains steep concentration gradient for oxygen

Describe how ATP is formed from its component molecules

ATP is made up from a molecule of adenine (a nitrogenous base), bonded to ribose sugar, which is bonded to three phosphate groups. The enzyme ATP synthase catalyses the formation of a bond between a molecule of ADP and a phosphate group.

Describe the process of crossing over

• homologous pairs of chromosomes associate with each other

• To form bivalents

• Chiasmata form

• Alleles between the non-sister chromatids on the chromosomes swap

Why might certain structures not be visible using a light microscope

the resolution is too low as the wavelength of light is too long

Role of the golgi apparatus in lipid digestion

• Modifies and processes triglycerides

• Combines triglycerides with proteins

• Packages them into chylomicrons for release

In RT-PCR (which detects the presence of mRNA), why are enzymes added that hydrolylse DNA?

to remove any DNA present, which would be amplified

Why might a log scale be used

as there are large increases in numbers

How to do quadrats

• divide area into a grid and use a random number generator to generate pairs of coordinates

• Place quadrats at these coordinates and measure % cover inside the quadrat

• Repeat at least 20 times at different random coordinates

• Calculate the average % cover - total % cover / no. Quadrats

Receptors on the postsynaptic…

membrane

Why do rod cells have low visual acuity

multiple rod cells are connected to one bipolar cell, so only one impulse is sent to the brain from these multiple cells

Why does colour blindness affect more men than woman

the gene is on the X chromosome, and is recessive, which means that females require 2 recessive alleles to be affected, but males only require one

How would you find a median

list the values in order from smallest to largest, then find the middle value

how can a faulty receptor protein result in the damaged cell being destroyed

• Faulty protein recognised as antigen

• T cells will bind

• T cells stimulate clonal selection

• Resulting in plasma cells being formed which release antibodies complementary to the faulty protein

DNA/RNA bases align along the template strand due by complementary base pairing?

DNA/RNA NUCLEOTIDES.

Describe how hydrolysis reactions are used in the digestion of lipids

ester bonds are broken by the addition of water molecules