TOPIC 2 BIO PMT CORRECTIONS (22 - 24)

CELL STRUCTURE AND MICROSCOPY (2016 - 2021) Accident

CELL STRUCTURE AND MICROSCOPY (2016 - 2021) Accident

Cell A injests bacteria and digests them in the cytoplasm. Describe the role of one named organelle in digesting bacteria (3)

Lysosomes

Fuse with vesicle (Phagosome)

Release hydrolytic enzymes

Contrast the cells visible (Advice)

Determine which cells is which (plant, animal etc)

Use magnification to determine which ones bigger

What must you remember to include in biological drawing (4)

A SCALE

Label

No shading

Must look similar

What is a drawback of TEMS compared to optical

Requires thinner samples

Much more complex preparation

Why are no orgnalles visible in the cytoplasm of red blood cells (1)

Cytoplasm of red blood cills is filled with haemoglobin

Stained cell caused cell surface mebrane to appear as two dark lines. Explain why (3)

Membrane has phospholipid bi layer

Stain binds to phosphate

On inside and outside of membrane

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in cells with light microscope (3)

Add drop of water to slide

Obtain thin section of plant tissue and place on slide

Add iodine stain

Lower coverslip using mounted needle at angle

How do you know when an image was made using a transmission electrom microscope (TEM) (2)

Higher resolution

You can see the internal structure of organelles

THE CELL CYCLE INCLUDING MITOSIS

THE CELL CYCLE INCLUDING MITOSIS

Describe the behaviour and appearance of chromosomes during prophase (2)

Chromsomes condense / continue to condense

Chromosomes attach to spindle fibres

What is the formula for mitotic index (1)

Number of cells in mitosis / number of cells in field of view

DO NOT ADD x100 AS THIS MAKES IT A PERCENTAGE

What must you do when given graph and told to use info from graph of mitosis

State what you can see on graph and assumptions you can make using graph and your own knowlege of mitosis

Why are plant tissues put into hydrocholric acid before observing it (2)

To separate the cells/cell walls

So that the stain used diffuses into the cells

State two precautions when handling HCL (2)

Wear eye protection

Wear gloves

What are two considerations to make when comparing mitotic index between two different plant species (2)

Make sure you measure same distance from root tip

Make sure both roots had same growing conditions

At what point of interphase is the abitral mass of DNA in cells between 1 and 2 (1)

During the S phase of interphase

What happens to no. of cells with DNA mass between 1 and 2 with tumour cells (2)

Increases

Because cell division is faster and uncontrolled

Answer to MITAB question

19.7

70 and 2000 are the readings from the graph

Define a tumour (2)

A mass of cells/tissues

Undergoing uncontrolled cell division

How would you determine a reliable mitotic index from tissue observed using optical microscope (3)

Count cells in mitosis IN FIELD OF VIEW

Divide this by total number of cells IN FIELD OF VIEW

Repeat many times

Why would you press down on a coverlislip of a slide in a optical microscope (2)

To create a layer of cells one cell thick

So that light can pass through

Why might two students calculate two different mitotic indexes when using the same method (2)

The single field of view may not be representative of the whole root tip

The roots are a different age

2.3 TRANSPORT ACROSS CELL MEMBRANES

2.3 TRANSPORT ACROSS CELL MEMBRANES

Describe how sodium ions are transported out of the cells and into the cells (2)

Out of cells via active transport against conc gradient

Into cells via facillitated diffusion down conc gradient

Describe the process of active transport (1)

Movement against conc gradient VIA CARRIER protein using constant supply of ATP

What are microvilli (1)

Highly folded extensions of cell surface membrane

What do micelles do for non polar molecules (1)

Makes them soluble in watery intestine whilst containing the non polar molecules in a watery medium

Why does membrane fluidity increase after rats consume a fish oil diet high in unsaturated fatty acids (3)

Fatty acid B is unsaturated

Increase in fuilidity due to increase in unsaturated fatty acids

Carbon double bonds in unsaturated fatty acids called kinks in fatty acid tail

Give two features that all prokaryotic cells that eukaroytic cells DO NOT HAVE (1)

No membrane bound organelles

Circular DNA loop

Why do antimicrobial polypeptides produced by multicellular organisms not damage eukayotic cells (2)

Eukaryotic cells have cholesterol in cell membrane which acts as fluidity buffer and makes it more rigid

So APs cannot disrupt the eukaryotic membrane

How does using a monoclonal antibody with gold attached to it allow us to see APs using a TEM (3)

Antibody binds to AP

Gold present where the AP is located which can be picked up on TEM

Gold interacts with electrons in TEM

How does ileum epithelial cells losing their microvilli reduce absorption of water (3)

Reduced surface area

Decreases water potential in the ielum

So water moves out of cells into ileum by osmosis

For the (c - difficile) question, which patients should be offered the anti - toxin antibody and how this passive immunity would work (3)

Anti toxin antibodies given which will cause phagocytosis of toxin

Anti toxin antibody reduced the chance of diarrhoea

It should be offered to C difficile patients with diarrohoea

Describe how the anti toxin antibody would be digested (4)

Peptide bonds hydrolysed

Endopeptidases hydrolyse bonds in middle of polypeptide chain

Exopeptidases hydrolyse bonds at the end of the polypeptide chain

Membrane bound dipeptidases break dipeptides into amino acids

What is on the line at T in an Elisa test and why does a line form (2)

Antigen

Enzyme substrate complex forms

Why does a line at C show the test has worked (1)

The sample has diffused above the T test

How do cancer cells fused with B cells continuously produce monoclonal antibodies (2)

The cancer cells divide uncontrollably

The B cells produce monoclonal antibodies

How does blood proteins moving out of the capillaries affect the return of tissue fluid to capillaries (2)

Increases water potential of capillary

Less water returns returns to capillaries via osmosis

(WHEN TISSUE FLUID IS REABSORBED ONLY WATER IS TAKEN BACK)

Give two types of cells that can stimulate immune response (2)

An APC

A cell from different organism of same species

Pathogen

How to plot data with SDs

Plot the mean and do bar chart

Put SDs as lines correctly plotted above AND below the peak of each bar

When given data about cellular vs humoral response with SD, how do you compare

Look for which categories are ‘significant’ (If SD do not overlap)

Dismiss changes that overlap with eachothers SD as not ‘significant’ changes

How is the composition of blood in the pulmonary artery of a fetus different to the artery of the mother (2)

The fetal blood has more oxygen

Because gas exchange does not occur in fetal lungs

How is a fetus protected from the pathogens that infect its mother during pregnancy (3)

Antibodies from mother bind specifically

To pathogens crossing placenta

Giving passive immunity to fetus

Protection against tetanus (For that one weird question)

No herd immunity

Why does giving children more than one tetanus shot help to develop good immunity against tetanus (2)

Vaccination stimulates the production of more memory B cells

So more rapid production of antibodies upon reinfection