AS Human Biology Unit 1: Cells and Cell Structure

Text questions

P8/Q1	a) b)	Cell wall present in both plant and bacterial cell, but not in the animal cell. Capsule present in a prokaryotic cell but absent in plant and animal cells. Nucleus present in a plant and an animal cell but absent in a prokaryotic cell.
P10/Q2		10 x 40 = 400
P10/Q3		Magnification tells you how many times the image is larger than the real object (Magnification = size of image/size of the object). Resolution (resolving power) is the ability of an optical device (e.g. a microscope) to separate out two objects (points), which are close together. Resolution is measured in units of length. It is a distance between two points, which still can be defined (seen), as two separate points, not a blurred single shape.
P11/Q4		All air must be removed/vacuum created, because scattering of electrons by air molecules interferes with image production.
P12/Q5		Magnification too low.
P16/Q6	a) b) c)	If the water potential is the same then the cells will not lose or acquire water by osmosis which could lead to plasmolysis or excessive turgidity (→ cell bursting). { osmotic shock } Changes in pH affect the enzymes (denaturation) and hence metabolism (life processes) in the cells. Changes in the metabolism of a cell could affect the structure of the cell. Low temperature slows down the reaction rate (on an average drop in temperature by 10 C will half the reaction rate).
P16/Q7		Mitochondria, lysosomes, rough ER, ribosomes. Rough ER and lysosomes could be separated from the rest by centrifugation at 100 000g for 60 min., and then removing the sediment (pellet) containing mitochondria and lysosomes.

Assignment

P18/Q1

They are lighter colour in the middle. Thinner → more light is transmitted through this part of the cell.

P18/Q2

9mm/1000 = 0.009mm = 9 micrometers

P18/Q3

The slide waved backwards & forwards→ water molecules present around the cells evaporate rapidly, but water molecules in the cytoplasm enclosed by the cell membrane (CM) evaporate very slowly. CM is mainly made of phospholipid, which is impermeable to water. Water molecules will evaporate through the protein molecules which penetrate the phospholipid bilayer. (These protein molecules are the only gateways available to diffusing/evaporating water molecules → more time is needed before the results of the loss of water molecules can be seen, i.e. the cells being smaller & crinkled).

P18/Q4

The membrane is subjected to the action of the detergent, the lipid component will be removed from the membrane → the membrane will be decomposed (will "collapse").

P19/Q5

Your drawing here...

The sections show the cells of various shapes because the cells were cut across over different planes.

P19/Q6

Although red blood cells are very small (ca 9 micrometers), the image has been magnified many times more than the image in fig. 1.10 (where optical microscope was used), without any loss of the resolution.

P19/Q7

Conclusion	Evidence
The plasma membrane allows water molecules to pass through	The red blood cells in a smear that is left to dry slowly appear smaller and crinkled around the edges
Many of the molecules in the cytoplasm are of the same type	The red blood cells in Fig 1.11 are a uniform dark colour
Red blood cells do not use oxygen and cannot respire aerobically	There are no mitochondria present
Red blood cells are biconcave in shape	The appearance of the cells when seen with a Scanning E.M.
Red blood cells don't contain DNA, so they can't make proteins	There is no nucleus present

Examinations

P20/Q1

Feature	Epithelial cell from small intestine	Prokaryotic cell
Golgi	V	X
Mitochondrion	V	X
Nuclear envelope	V	X
Plasmid	X	V
Ribosome	V	V

P20/Q1

(i) Electron microscope in comparison with an optical one allows for a much higher magnification and a better resolution to be obtained easily. This allows a much better definition of all fine details in the structure in a cell under observation

(ii) Preparation of cell material for the electron microscopy involves use of formalin (fixation/"killing"), ethanol (dehydration), resins or plastics (embedding), salts of heavy metals (staining). These substances may leave traces in the cell material which normally would not be found in living cells.

P20/Q2

Nuclear pore

Ribosomes are involved in the synthesis of polypeptides and protein

The Golgi apparatus (GA) collects substances (proteins and lipids) made in the endoplasmic reticulum (ER) by the fusion of the vesicles pinched off from the ER with its own fattened sacks. In the GA additional substances are added, the products are repackaged into fresh vesicles, which are then cut off and moved to other parts of the cell, where the secretions discharged.

Calculation: 20mm/30 000 = 0.0007mm = 0.7 micrometre