Transport And Cells

Question 1

Oxygen and chloride ions can diffuse across cell- surface membranes The diffusion of chloride ions involves o membrane protein. The diffusion of oxygen does not involve a membrane protein . Explain why the diffusion

Answer 1

1. Chloride ions water soluble/charged/polar;
2. Cannot cross lipid bilayer ;
3. Chloride ions transported by facilitated diffusion using channel/carrier protein;
4. Oxygen not charged/ non-polar ;
5. Oxygen soluble in / can diffuse across lipid bilayer;

Question 2

The movement of substances across cell membranes is affected by membrane structure . Describe how.

Answer 2

1. Phospholipid (bilayer ) allows movement /diffusion of non-polar/lipid- soluble substances ;
2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/-insoluble substances OR (Membrane ) proteins allow polar /charged substances to cross the nbrane /bilayer;
3. Carrier proteins allow active transport ;
4. Channel / carrier proteins allow facilitated diffusion / co- transport ;
5. Shape /charge of channel carrier determines which substances move ;
6. Number of channels / carriers determines how much movement ;
7. Membrane surface area determines how much diffusion /movement ;
8. Cholesterol affects fluidity /rigidity /permeability ;

Question 3

Describe and explain how cell fractionation and ultracentrifugation be used to mitochondria

Answer 3

1. Cell homogenisation to break open cells
2. Filter to remove large debris / whole cells;
3. Use isotonic solution to prevent damage to mitochondrialorganelles
4. Keep cold to reduce damage by enzymes use buffer to prevent enzyme denaturation
5. Centrifuge at lower speed to separate nuclei cell fragments heavy organelles
6. Re-spin (supernatant / after nuclei / pellet removed ) at higher speed to get mitochondria at bottom

Question 4

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure

Answer 4

Principles
1 Electrons pass through thin specimen 2 Denser parts absorb more electrons
3 So denser parts appear darker;
4 Electrons have short wavelength so high resolutions

Limitations
5 Cannot look at living material / Must be in a vacuum
6 . Specimen must be very thin;
7 Artefacts present;
8 Complex staining method / complex / long preparation time ;
9 Image not in 3D / only 2D images produced

Question 5

Describe how you could make a temporary mount of piece of plant to the in the cells when using an optical ( light ) microscope

Answer 5

1. Add drop of water to pass slide ,
   2 Obtain thin section of plant and place on slide
2. Stain with iodine in potassium iodide .
3. Lower cover slip using mounted needle